Five inhibitory transmitters coexist in pelvic autonomic vasodilator neurons

Here we describe the localization of a potent vasodilator, calcitonin gene-related peptide (CGRP), in pelvic autonomic neurons containing four other inhibitory transmitters: vasoactive intestinal peptide (VIP), neuropeptide Y, nitric oxide and acetylcholine. These neurons mediate endothelium-independent vasodilation by releasing nitric oxide and one or more neuropeptides. Sixty percent of nerve cell bodies in guinea-pig paracervical ganglia with immunoreactivity (IR) for VIP, choline acetyltransferase (ChAT) and nitric oxide synthase (NOS), also contained IR for CGRP. Furthermore, many VIP-IR varicose nerve terminals at the adventitia-medial junction of the guinea-pig uterine artery contained IR for CGRP, ChAT and NOS. Both alpha-hCGRP and beta-hCGRP were potent dilators of the uterine artery (pD2 values 8.1, 8.3, respectively), but 1 microM hCGRP(8-37) did not antagonize dilations produced by either agonist. Dilations produced by alpha-hCGRP were unaffected by removal of the endothelium. Taken together with results of our previous studies, we propose that CGRP can contribute directly to autonomic vasodilation, possibly via CGRP2 receptors on smooth muscle cells, and that CGRP is the fifth inhibitory transmitter co-existing in pelvic vasodilator neurons.     

Autonomic control of bronchial circulation in awake sheep during rest and behaviour

1. We tested the hypothesis that the pattern and the intensity of autonomic mechanisms causing vasoconstriction in the resting bronchial circulation of awake dogs also exists in awake sheep. It was also postulated that sighing behaviour and the associated bronchovascular dilatation induced by non-adrenergic, non-cholinergic (NANC) mechanisms observed in the dog exist in sheep. 2. Bronchial arterial blood flow to lower airways of both lungs of awake sheep was measured continuously using pulsed Doppler flow probes mounted on the bronchial artery at prior thoracotomy. 3. Cumulative and factorial analysis of responses to randomized combinations of autonomic alpha 1-, alpha 2-, beta 1- and beta 2-adrenoceptors and cholinoceptor autonomic blockade suggests that resting vasoconstrictor activity is less in sheep than in dogs. At normal aortic pressure, the autonomic activity of these receptor groups in the sheep lowers bronchial blood flow and conductance by 30%, whereas in the awake dog, the corresponding autonomic effect is 50%. 4. Tonic autonomic control of bronchial conductance can be partitioned in sheep to show significant and separate alpha- and beta-adrenoceptor vasoconstrictor activity at a ratio of 1.8:1, an effect normally offset by a weaker vasodilator alpha-/beta-adrenoceptor interaction. In contrast to the situation in awake dogs, cholinoceptors do not play a role in awake sheep. 5. Nitric oxide (NO) synthase inhibition in sheep using NG-nitro-L-arginine following blockade of alpha- and beta-adrenoceptors and cholinoceptors causes hypertension, but minor changes, if any, in pulmonary pressures or heart rate. Bronchial flow and conductance, however, fall from a higher resting conductance by approximately 50%, suggesting that, normally, resting bronchial flow conductance is dominated by strong tonic NO vasodilator effects that interact with weaker tonic autonomic vasoconstrictor effects. 6. Superimposed (respiratory) behaviours of sighing, sneezing and coughing, which involve negative swings in intrathoracic pressure and the movement of inspired air, evoke large active bronchovascular dilator effects. These appear to be largely NANC in origin and appear to be dependent, in part, on mechanisms associated with NO release. It is postulated that the C-fibre axon reflex using substance P, calcitonin gene-related peptide and neurokinin A may be involved. Vocalization and eructation do not evoke bronchovascular effects.     

Vascular 5-HT1-like receptors mediating vasoconstriction and vasodilatation: their characterization and distribution in the intact canine cardiovascular system

1. In anaesthetized dogs, intra-left atrial administration of 5-hydroxytryptamine (5-HT) and selected tryptamine analogues (5-carboxamidotryptamine, 5-CT; 5-methyl tryptamine, 5-MT; alpha-methyl 5-hydroxytryptamine, alpha-HT; sumatriptan, Sum) in the presence of ketanserin and MDL72222 (5-HT2 and 5-HT3 receptor antagonists, respectively), produced dose-related changes in carotid, coronary and renal vascular conductance mediated by vascular 5-HT1-like receptors. 2. In the carotid vascular bed, 5-HT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-HT = Sum > 5-MT > alpha-HT. By contrast in this vascular bed, 5-CT was a potent vasodilator. 3. In the coronary vascular bed, 5-HT, 5-CT, 5-MT and alpha-HT were vasodilators with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > 5-MT > alpha-HT. In this vascular bed, Sum was without effect. 4. In the renal vascular bed, 5-HT, 5-CT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > Sum > 5-MT > alpha-HT. 5. The coronary (and carotid) vasodilator responses to 5-CT were antagonized by the 5-HT1-like receptor antagonists, spiperone (1 mg kg-1) and methiothepin (0.1 mg kg-1), whereas the renal vasoconstrictor responses to this tryptamine analogue were antagonized only by methiothepin. 6. It is concluded from these studies that agonist finger-printing in vivo, using tryptamine analogues,identifies and confirms the functional presence of at least two pharmacologically distinct subtypes of the 5-HT1-like receptor in the intact canine cardiovascular system. These two subtypes are located on the vascular smooth muscle and mediate direct vasoconstriction and vasodilatation responses in vivo.7. In addition, these studies confirm that the distribution of these subtypes within the major vascular beds, shows a marked heterogeneity. The carotid vascular responses to the tryptamine analogue sindicate the presence of both the vasodilator and the vasoconstrictor subtypes. The coronary vascular responses to these analogues are, however, consistent with presence of the vasodilator subtype, only. By contrast, the renal vascular responses to these analogues indicates only the presence of the vasoconstrictor subtype.     

An association study between a transcriptional polymorphism in the serotonin transporter gene and panic disorder in a Japanese population

1. To determine the effects of an acute oral dose of glibenclamide on blood pressure (BP), basal forearm vascular resistance (FVR) and FVR responses to the K+ATP channel activating vasodilator diazoxide, a placebo-controlled, double-blind cross-over study was performed in eight male volunteers with non-insulin-dependent diabetes mellitus. 2. Changes in vascular responses to progressively increasing concentrations of diazoxide (3.75-30 mg/kg per min) and noradrenaline (25-100 ng/kg per min) were measured by venous occlusion plethysmography. 3. Glibenclamide significantly lowered plasma glucose levels compared with placebo (P < 0.02) and attenuated the decrease in FVR (P < 0.05) and the decrease in systolic BP (P < 0.05) that followed a meal. However, vasodilator responses to diazoxide were potentiated by the administration of oral glibenclamide (P < 0.01). 4. Acute administration of oral glibenclamide attenuates the normal decrease in FVR and systolic BP that follows a meal and potentiates rather than inhibits forearm vasodilator responses to intra-arterial diazoxide, probably via indirect humoral effects. These results suggest that glibenclamide has direct or indirect vasoconstrictor effects that antagonize the normal increase in forearm blood flow that follows a meal and that the inhibition of vascular K+ATP channels following acute oral glibenclamide administration is clinically insignificant compared with other indirect vascular effects of the drug.     

Neurochemistry of the nodose ganglion

Placode-derived general visceral afferent neurons of the nodose ganglion transmit visceral sensory information from specialized sensory endings of the vagus nerve and its branches to the nucleus of the solitary tract. These neurons are critical in relaying information such as elevations in blood pressure, changes in blood oxygenation, passage of contents through the esophagus and intestines, and distention of the heart, stomach, and lungs to the CNS for reflex maintenance of visceral functions. Multiple neurotransmitters, neuropeptides, calcium binding proteins, and other neuroactive substances are associated with neurons of the nodose ganglion. Many neurons colocalize 2 or more neuroactive substances creating the potential for complex interactions of neurochemical signals in the NTS. Neurons of the nodose ganglion also contain a variety of receptors which respond to transmitters, inflammatory mediators, and neurotrophic factors. The contents of these neurochemicals and receptors are not static as alterations in their expression are noted in response to epigenetic influences. Although not yet well understood, potential factors and mechanisms regulating neurochemical events in the nodose ganglion neurons are discussed.     

Glaucoma, capillaries and pericytes. 3. Peptide hormone binding and influence on pericytes

To test the potential for vasoactive neuropeptide receptors to affect capillary resistance, we have begun to study the plausibility that pericytes might be equipped to respond to a representative peptide vasoconstrictor and a representative peptide vasodilator. Pericytes cultured from the bovine retinal vasculature specifically bind the angiotensin II (Ang II) antagonist saralasin (1 nM125I-saralasin bound at 2.2 +/- 0.41 fmol/mg protein) and 125I-vasoactive intestinal peptide (VIP; Kd of 0.5 nM with a population of 30 fmol/mg protein). Incubation with 100 microM Ang II induced minimal cAMP synthesis, while VIP (1 microM, 10 microM) did not induce any change in cAMP concentration. Ang II (10 microM and 100 microM) caused contraction of pericytes cultured on an elastic silicone surface. Circulating or locally produced vasoactive neuropeptides might affect pericyte contractile tone via several intracellular pathways, moderated by indirect effects of these peptides through endothelial stimulation, with the net effect on local blood flow resulting from the effects on arteries and veins as well as capillaries.     

Synergy between T cell Receptor and Fas (CD95/APO-1) signaling in mouse thymocyte death

Both extracellular and intracellular calcium (Ca2+) play important roles in hypoxic pulmonary vasoconstriction (HPV) and the vasoconstrictor responses to endogenous pulmonary vasoconstrictor substances, as evidenced by the effect of calcium-channel blockers on these vasoconstrictor responses and the measurement of changes in Ca2+ flux or intracellular Ca2+ concentrations in isolated cells. The more vasoselective the calcium-channel blocker, the greater its effect on pulmonary vasoconstriction. However, these drugs are not selective for the pulmonary vascular bed and are not as potent as pulmonary vasodilators when compared with other vasodilator drugs, including prostaglandin E1, isoproterenol, prostacyclin, or nitroglycerin. Moreover, the primary effect of vasoselective calcium-channel blockers on pulmonary vascular resistance is secondary to the effects of these agents on systemic vascular resistance and cardiac output. Although there is improvement in oxygen delivery, exercise tolerance, and survival in patients with primary pulmonary hypertension who respond to calcium-channel blockers, the response of individual patients to these drugs is difficult to predict because the extent of reversible versus irreversible changes in the pulmonary vasculature is not known. The use of these drugs in patients with chronic hypoxia-induced pulmonary vasoconstriction may be associated with a worsening of ventilation-perfusion mismatching secondary to inhibition of HPV.     

Angiotensin II regulates choroid plexus blood flow by interacting with the sympathetic nervous system and nitric oxide

Blood flow to the rat choroid plexus has minimal variability when plasma angiotensin II (AII) concentration is changed within a broad range of levels. We tested the hypothesis that a complex interplay of the vasoconstrictor and vasodilator AII actions in choroidal tissue results in small net changes in choroidal blood flow. Blood flow was measured with 123I- or 125I-N-isopropyl-p-iodoamphetamine. AII was infused intravenously (i.v.) at 30 (moderate dose) and 300 ng kg-1 min-1 (high dose), which respectively decreased (15%) and did not change choroidal blood flow. To determine whether AII regulates choroidal blood flow by interacting with the sympathetic nervous system, rats were given phentolamine (1 mg kg-1, i.v.). This alpha-adrenoceptor antagonist by itself did not alter blood flow; however, it attenuated the blood flow-lowering effect of moderate AII dose. Phentolamine also unmasked the vasodilator AII actions at high peptide concentration. beta-Adrenoceptor blockade, with propranolol (1 mg kg-1, i.v.), reduced blood flow (18-20%) and increased vascular resistance (23-26%). During beta-adrenoceptor blockade, a further decrease in blood flow (15-21%) and increase in vascular resistance (23%) was noted when high AII dose was administered. The direct vasoconstrictor effect of AII at moderate dose on choroidal vasculature was examined in rats subjected to chronic bilateral superior cervical ganglionectomy. In these animals, AII decreased blood flow (24%) and increased vascular resistance (24%). To find out whether the hemodynamic AII actions in choroidal tissue are mediated by nitric oxide (NO), Nomega-nitro-l-arginine methyl ester (l-NAME) was used. l-NAME (0.1 mg kg-1, i.v.) by itself did not alter blood flow; however, in l-NAME-treated rats high AII dose lowered blood flow (25-32%) and increased vascular resistance (30-43%). We conclude that the vasoconstrictor AII actions involve a direct peptide effect on the choroidal vascular bed, and the AII-mediated potentiation of sympathetic activity, which results in the activation of alpha-adrenoceptors. The AII-mediated stimulation of sympathetic nerves also results in the beta-adrenoceptor-dependent relaxation of choroidal blood vessels. In addition, choroidal vasodilatory actions of AII are NO-mediated.     

UTP induces vascular responses in the isolated and perfused canine epicardial coronary artery via UTP-preferring P2Y receptors

1. Vasoconstrictor responses of the isolated and perfused canine epicardial coronary artery to uridine 5'-triphosphate (UTP) were analysed pharmacologically. 2. At basal perfusion pressure, UTP induced vasoconstriction in a dose-related manner and the vasoconstriction was sometimes followed by a slight vasodilatation at large doses (more than 10 nmol). The rank order of potency for vasoconstriction was UTP = UDP > ATP > TTP > or = ITP > UMP. At raised perfusion pressure by 20 mM KCl, the vasoconstriction was not changed and a small vasodilatation was induced at large doses. The rank order of potency for vasodilatation was induced at large doses. The rank order of potency for vasodilatation was ATP > ITP > or = UDP > UTP > or = TTP. The maximal vasodilator response to UTP was much less than that to ATP. UMP did not induce vasodilatation. 3. The P2X receptor agonist and desensitizing agent alpha, beta-methylene ATP (1 microM) and the P2 receptor antagonist suramin (100 microM) inhibited the vasoconstrictor responses to ATP but not those to UTP and UDP. The P2 receptor antagonist reactive blue 2 (30 microM) did not inhibit the vascular responses to UTP. 4. UTP (200 microM) desensitized the vasoconstrictor responses to UTP, but not either the vasodilator responses to UTP or the vasoconstrictor responses to ATP and UDP. UDP (200 microM) did not desensitize the vascular responses to UTP. 5. Preincubating the UDP stock solution and arterial preparation with hexokinase (10 and 1 uml-1, respectively) did not change the vasoconstrictor responses to UDP. 6. The Ca channel blocker diltiazem (1 microM) inhibited the vasoconstrictor responses to UTP but not those to ATP and UDP. Incubation in a Ca(2+)-free solution containing 1 mM EGTA inhibited the vascular responses to ATP, UTP and UDP. 7. Removal of the endothelium by an intraluminal injection of saponin (1 mg) inhibited the vasodilator responses to UTP. Indomethacin, a cyclo-oxygenase inhibitor (1 microM), inhibited the vasodilator responses to UTP, but NG-nitro-L-arginine, a nitric oxide synthase inhibitor (300 microM), did not have an inhibitory effect. 8. The results suggest that (1) UTP induces vasoconstriction via UTP-preferring P2Y receptors on the smooth muscle and vasodilatation via receptors different from those mediating the vasoconstriction induced by UTP and mediating the vasodilatation by ATP on the endothelium, through mainly the release of prostacyclin in the canine epicardial coronary artery; (2) UDP induces vasoconstriction via UDP-preferring P2Y receptors; and (3) L-type Ca ion channels are involved in the vasoconstriction induced by UTP, but not in that induced by UDP.     

Vascular actions of purines in the foetal circulation of the human placenta

1. The vasoactive effects of adenosine triphosphate (ATP), adenosine and other purines in the foetal circulation of the human placenta were examined. Single lobules of the placenta were bilaterally perfused in vitro with Krebs buffer (maternal and foetal sides 5 ml min-1 each, 95% O2:5% CO2, 37 degrees C). Changes in foetal vascular tone were assessed by recording perfusion pressure during constant infusion of each purine. To allow recording of the vasodilator effects, submaximal vasoconstriction was induced by concomitant infusion of prostaglandin F2 alpha (0.7-2.0 mumol l-1). 2. ATP (1.0-100 mumol l-1) usually caused concentration-dependent reductions in perfusion pressure. However, biphasic with initial transient increases, or only increases in pressure were sometimes observed. Falls in pressure caused by ATP were significantly reduced by addition to the perfusate of NG-nitro-L-arginine (L-NOARG) (100 mumol l-1) but not NG-nitro-D-arginine (D-NOARG) (100 mumol l-1). They were not influenced by addition of indomethacin (10 mumol l-1) or L-arginine (100 mumol l-1). 3. Adenosine (0.01-1.0 mmol l-1) consistently caused concentration-dependent reductions in perfusion pressure, this effect not being influenced by indomethacin. L-NOARG, but not D-NOARG, reduced the potency of adenosine approximately three fold. L-Arginine, but not D-arginine enhanced its potency by a similar amount. 4. 2-Methylthio-ATP, a selective P2 gamma agonist was approximately 50 times more potent than ATP as a vasodilator agent, always causing decreases in perfusion pressure. 5. Beta-gamma-Methylene ATP, a selective P20 agonist, was approximately 100 times more potent than ATP as a vasoconstrictor, but only caused transient increases in perfusion pressure.6. The rank order of vasodilator potencies of a selection of adenosine receptor agonists was, 2-chloroadenosine>5-(N-cyclopropyl)-carboxamidoadenosine, >5-N-ethylcarboxamidoadenosine, >2-chloro-N6-cyclopentyladenosine, >CGS-21680 > N6-cyclohexyladenosine = adenosine. Vasodilatation due to adenosine was inhibited by the PI-A2 receptor antagonist 3,7-dimethyl-l-propargylxanthine(DMPX).7. These results suggest that ATP may cause an endothelium-dependent vasodilatation in the foetal vessels of the human placenta via activation of a P2y receptor linked to the formation of nitric oxide(NO). Vasodilatation caused by ATP may mask an accompanying vasoconstrictor effect mediated, via a P2X receptor, in the villous vascular smooth muscle. Adenosine acting on P1-A2 receptors, which are also present in the foetal vasculature, may require synergistic interaction with NO to achieve a maximal vasodilator response.     

Operational characteristics of the 5-HT1-like receptors mediating external carotid vasoconstriction in vagosympathectomized dogs. Close resemblance to the 5-HT1D receptor subtype

It has recently been shown that the external carotid vasoconstrictor response to 5-HT in the dog is primarily mediated by sumatriptan-sensitive 5-HT1-like receptors; however, the fact that these receptors are not blocked by metergoline, a 5-HT1D ligand, raises questions about their possible correlation with the 5-HT1D receptor subtype. Since a number of drugs display high affinity for the 5-HT1D (GR127935) and 5-HT1F (e.g. methysergide and oxymetazoline) receptor subtypes, in this study we have used these drugs to determine whether the above vasoconstrictor 5-HT1-like receptors correlate with the 5-HT1D and/or 5-HT1F receptor subtypes. One-minute intracarotid infusions of 5-HT (0.3-30 micrograms/min), sumatriptan (1-30 micrograms/min), oxymetazoline (0.03-3 micrograms/min) and noradrenaline (0.3-3 micrograms/min) resulted in dose-dependent decreases in external carotid blood flow without changes in arterial blood pressure or heart rate. These vasoconstrictor responses remained unaltered after i.v. administration of physiological saline (0.015, 0.05 and 0.15 ml/kg; n = 4) or ritanserin (1 mg/kg; n = 5). In contrast, GR127935 (1, 3 and 10 micrograms/kg, n = 6) potently blocked the responses to 5-HT (unmasking a dose-dependent vasodilator component) and sumatriptan without affecting those to oxymetazoline or noradrenaline. Interestingly, methysergide (10, 30 and 100 micrograms/kg, n = 5) also blocked the vasoconstrictor responses to 5-HT and sumatriptan, but unlike GR127935, did not revert the vasoconstrictor response to 5-HT; the responses to oxymetazoline remained unaffected, but those to noradrenaline were apparently attenuated by the highest dose. Taken together, the above findings suggest that the sumatriptan-sensitive 5-HT1-like receptors mediating canine external carotid vasoconstriction resemble 5-HT1D receptors, probably of the 5-HT1D beta subtype on the basis of the resistance to blockade by ritanserin. The pharmacological profile of these receptors could be similar (bovine and human cerebral arteries, porcine carotid arteriovenous anastomoses and human coronary arteries) to other putative 5-HT1D receptors mediating vascular responses.     

Multi-messenger innervation of the male sexual system of Lymnaea stagnalis

The male copulation behaviour of the hermaphrodite pond snail Lymnaea stagnalis is under the control of five groups of central neurons that produce a variety of neuropeptides and a classical transmitter, 5-hydroxy tryptamine (5HT). In this article, we describe how the male sexual organs of this snail are innervated by axons from these central neurons. We carried out immunocytochemistry with antisera against the tetra peptide Ala-Pro-Gly-TRP-NH2 (APGWamide), the Lymnaea form of neuropeptide tyrosine (LNPY), conopressin, pedal peptide, the FRMFamide copeptide SEEPLY, the GDPFLRFamide co-peptide DEILSR, myomodulin, Lymnaea inhibitory peptide, and 5HT on tissue sections of the following male sexual organs that receive input from the penis nerve: the prostate gland, vas deferens, preputium, and penis. The results demonstrate that the axons of the separate muscle systems contain particular combinations of transmitters. In addition, two networks of peripheral neurons were revealed. In the tip of the everted preputium lies what appears to be a network of conopressin-containing sensory neurons, which is possibly involved in probing; probing is the part of copulation behaviour in which the male searches for the female genital pore. The other network of peripheral neurons surrounds the most proximal part of the vas deferens and is most likely involved in the pacemaker control of vas deferens motility. On the basis of the data obtained, we hypothesize how the preputium and penis are everted during copulation and which transmitters and central neurons might be involved.     

Complete degradation of xenobiotic surfactants by consortia of aerobic microorganisms

The ubiquitous nature of neuropeptides and their respective receptors in the central and peripheral nervous systems suggests that peptides play a key role in controlling physiological processes. Investigations on a cellular level have demonstrated that neuropeptides exert powerful modulatory effects on neurons and neuronal circuits; however, despite these compelling considerations, investigators have rarely been able to assign discrete functional roles to individual neuropeptides. Numerous studies have addressed the influence of neuropeptides on learning and memory processes. Workers have primarily utilized peripheral or central injection of neuropeptides to suggest a facilitatory, or less commonly inhibitory, role in acquisition, retention, or retrieval of memories. Although highly suggestive, critical concerns regarding the specificity of the observed effects have often remained. Recently, the neurogenetic approach has demonstrated the role of a novel neuropeptide in a specific memory phase, high affinity antagonists have confirmed the importance of some endogenous neuropeptides, and evidence of neuropeptide dysfunction in disease states, particularly Alzheimer's disease, has emerged. Continued refinement of traditional techniques, combined with information from alternative approaches, promises to consolidate the role of neuropeptides in learning and memory.     

Composite autonomic scoring scale for laboratory quantification of generalized autonomic failure

An autonomic reflex screen, which consisted of a quantitative sudomotor axon reflex test, orthostatic blood pressure and heart rate response to tilt, heart rate response to deep breathing, the Valsalva ratio, and beat-to-beat blood pressure measurements during phases II and IV of the Valsalva maneuver, tilt, and deep breathing, was used to develop a 10-point composite autonomic scoring scale of autonomic function. The scheme allots 4 points for adrenergic and 3 points each for sudomotor and cardiovagal failure. Each score is normalized for the compounding effects of age and sex. Patients with a score of 3 or less on the composite autonomic scoring scale have only mild autonomic failure, those with scores of 7 to 10 have severe failure, and those with scores between these two ranges have moderate autonomic failure. The sensitivity and specificity of the method were assessed by evaluating the composite autonomic scoring scale in four groups of patients with known degrees of autonomic failure: 18 with multisystem atrophy, 20 with autonomic neuropathy, 20 with Parkinson's disease, and 20 with peripheral neuropathy but no autonomic symptoms. The composite scores (means +/- SD) for these four groups, respectively, were as follows: 8.5 +/- 1.3, 8.6 +/- 1.2, 1.5 +/- 1.1, and 1.7 +/- 1.3. Patients with symptomatic autonomic failure had scores of 5 or more, those without symptomatic autonomic failure had scores of 4 or less, and no overlap existed in these groups. Thus, autonomic laboratory tests should be useful in grading the degree of autonomic failure.     

Hemodynamic actions of systemically injected pituitary adenylate cyclase activating polypeptide-27 in the rat

The aims of this study were (1) to characterize the hemodynamic mechanisms underlying the hypotensive effects of pituitary adenylate cyclase activating polypeptide-27 (PACAP-27 0.1-2.0 nmol/kg, i.v.) in pentobarbital-anesthetized rats, and (2) to determine the roles of the autonomic nervous system, adrenal catecholamines and endothelium-derived nitric oxide (NO) in the expression of PACAP-27-mediated effects on hemodynamic function. PACAP-27 produced dose-dependent decreases in mean arterial blood pressure and hindquarter and mesenteric vascular resistances in saline-treated rats. PACAP-27 also produced pronounced falls in mean arterial blood pressure in rats treated with the ganglion blocker, chlorisondamine (5 mg/kg, i.v.). The hypotensive and vasodilator actions of PACAP-27 were not attenuated by the beta-adrenoceptor antagonist, propranolol (1 mg/kg, i.v.), or the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME 50 micromol/kg, i.v.). PACAP-27 produced dose-dependent increases in heart rate whereas the hypotensive response produced by the nitrovasodilator, sodium nitroprusside (10 microg/kg, i.v.), was associated with a minimal tachycardia. The PACAP-27-induced tachycardia was unaffected by chlorisondamine, but was virtually abolished by propranolol. These results suggest that the vasodilator effects of PACAP-27 are due to actions in the microcirculation rather than to the release of adrenal catecholamines and that this vasodilation may not involve the release of endothelium-derived NO. These results also suggest that PACAP-27 produces tachycardia by directly releasing norepinephrine from cardiac sympathetic nerve terminals rather than by direct or baroreceptor reflex-mediated increases in sympathetic nerve activity.     

Effect of prostaglandins on vascular resistance and adrenergic vasoconstrictor responses in the canine uterus

Prostaglandins appear to play an important role in a number of reproductive processes. The effect of prostaglandins on numerous vascular beds has been extensively studied, but the effects on uterine hemodynamics have not. The present study was designed to determine the effects of prostaglandins of the A and E series on uterine vascular resistance and responses to adrenergic nerve stimulation in the canine uterus. PGE1, PGE2 and PGA1 were found to be potent uterine vasodilators. In addition, these agents were able to modify adrenergic vasoconstrictor responses. These effects on uterine vascular resistance and adrenergic vasoconstrictor responses were separable. The results of these studies suggest that prostaglandins of the A and E series may play an important role in regulating uterine blood flow in the nonpregnant animal.     

Optimisation of a heterogeneous non-competitive flow immunoassay comparing fluorescein, peroxidase and alkaline phosphatase as labels

GABA, somatostatin and enkephalin are neurotransmitters of enteric interneurons and comprise part of the intrinsic neural circuits regulating peristalsis. Within the relaxation phase of reflex peristalsis, nitric oxide (NO) is released by inhibitory motor neurons and perhaps enteric interneurons as well. Previously, we identified by GABA transaminase (GABA-T) immunohistochemistry, a subpopulation of GABAergic interneurons in the human colon which also contain NO synthase activity and hence produce NO. In this study, we have examined further the capacity for cotransmission within the GABAergic innervation in human colon. The expression of two important neuropeptides within GABAergic neurons was determined by combined double-labelled immunocytochemistry using antibodies for GABA-T, enkephalin and somatostatin, together with the demonstration of NO synthase-related NADPH diaphorase staining in cryosectioned colon. Both neuropeptides were found in GABAergic neurons of the colon. The evidence presented herein confirms the colocalization of NO synthase activity and GABA-T immunoreactivity in subpopulations of enteric neurons and further allows the neurochemical classification of GABAergic neurons of the human colon into three subsets: (i) neurons colocalizing somatostatin-like immunoreactivity representing about 40% of the GABAergic neurons, (ii) neurons colocalizing enkephalin-like immunoreactivity, about 9% of the GABAergic neurons and (iii) neurons colocalizing NO synthase activity, about 23% of the GABAergic neurons. This division of GABAergic interneurons into distinct subpopulations of neuropeptide or NO synthase containing cells is consistent with and provides an anatomical correlate for the pharmacology of these transmitters and the pattern of transmitter release during reflex peristalsis.     

A comparison of the effects of bradykinin, 5-hydroxytryptamine and histamine on the hepatic arterial and portal venous vascular beds of the dog: histamine H1 and H2-receptor populations

1 The hepatic arterial and hepatic portal venous vascular beds of anaesthetized dogs were separately perfused in different experiments.2 From measurements of perfusion pressures and blood flows in the two series of experiments, hepatic arterial vascular resistance (HAVR) and hepatic portal venous vascular resistance (HPVR) respectively were calculated.3 Bradykinin, 5-hydroxytryptamine (5-HT) and histamine were injected intra-arterially and intra-portally and dose-response curves constructed from these data.4 Bradykinin injected intra-arterially caused dose-dependent hepatic arterial vasodilatation, and with an ED(50) of 2.66 x 10(-13) mol was more potent than any other vasodilator agent yet examined on this vascular bed.5 Bradykinin injected intraportally at doses up to 10 times those which were maximal on the arterial circuit did not alter the calculated HPVR.6 5-HT injected intra-arterially caused weak and variable rises in HAVR, indicating vasoconstriction. The maximum rise in HAVR was much less than that attained with noradrenaline in the same preparations.7 5-HT injected intraportally caused dose-dependent rises in HPVR indicating portal constriction at doses above 15-100 mug: in some experiments small doses of 5-HT resulted in reductions in calculated HPVR.8 Histamine has previously been shown to cause hepatic arterial vasodilatation: by intraportal injection, it caused dose-dependent rises in HPVR.9 In order to examine the receptors responsible for the effects of histamine, dose-response curves were constructed before and after mepyramine and metiamide.10 On the hepatic arterial vascular bed, metiamide did not antagonize the vasodilator effects of intra-arterial histamine, but these effects were antagonized by mepyramine.11 Similarly on the hepatic portal bed, the rises in HPVR due to histamine were antagonized by mepyramine but not by metiamide.12 The effects of histamine on both the hepatic arterial and portal venous vascular beds of the dog are therefore mediated predominantly by histamine H(1)-receptors.     

Inhibitory effects of Hoe 140 on vasodilator responses to bradykinin in the mesenteric vascular bed of the cat

The effect of Hoe 140, a bradykinin B2 receptor antagonist, on vasodilator responses to bradykinin was investigated in the mesenteric vascular bed of the cat under constant flow conditions. Injections of bradykinin into the mesenteric vascular bed induced dose-related decreases in perfusion pressure which were reduced significantly following administration of Hoe 140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin) (100 micrograms/kg i.v.). The inhibitory effects of Hoe 140 were longer than 3 h in duration and vasodilator response to acetylcholine and S-nitroso-N-acetylpenicillamine and vasoconstrictor responses to norepinephrine, angiotensin II, and the thromboxane mimic, U46619 (9,11-dideoxy-11 alpha,9 alpha-epoxymethano-prostaglandin F2 alpha) were unchanged by the B2 receptor antagonist. Hoe 140 had little effect on baseline systemic arterial and mesenteric arterial perfusion pressures. These results suggest that Hoe 140 is a potent, highly selective, long-acting bradykinin B2 receptor antagonist with little agonistic activity in the mesenteric vascular bed of the cat.     

Neuropeptides in the skin: interactions between the neuroendocrine and the skin immune systems

The interaction between components of the nervous system and multiple target cells in the cutaneous immune system has been receiving increasing attention. It has been observed that certain skin diseases such as psoriasis and atopic dermatitis have a neurogenic component. Neuropeptides released by sensory nerves that innervate the skin and often contact epidermal and dermal cells can directly modulate functions of keratinocytes, Langerhans cells (LC), mast cells, dermal microvascular endothelial cells and infiltrating immune cells. Among these neuropeptides the tachykinins substance P (SP) and neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and somatostatin (SOM) have been reported to effectively modulate skin and immune cell functions such as cell proliferation, cytokine production or antigen presentation under physiological or pathophysiological conditions. Expression and regulation of their corresponding receptors that are expressed on a variety of skin cells as well as the presence of neuropeptide-specific peptidases such as neutral endopeptidase (NEP) or angiotensin-converting enzyme (ACE) determine the final biological response mediated by these peptides on the target cell or tissue. Likewise, skin cells like keratinocytes or fibroblasts are a source for neurotrophins such as nerve growth factor that are required not only for survival and regeneration of sensory neurons but also to control responsiveness of these neurons to external stimuli. Therefore, neuropeptides, neuropeptide receptors, neuropeptide-degrading enzymes and neurotrophins participate in a complex, interdependent network of mediators that modulate skin inflammation, wound healing and the skin immune system. This review will focus on recent studies demonstrating the role of tachykinins, CGRP, SOM and VIP and their receptors and neuropeptide-degrading enzymes in mediating neurogenic inflammation in the skin.