A1 adenosine receptor modulation of electrically-evoked contractions in the bisected vas deferens and cauda epididymis of the guinea-pig

1. The effects of adenosine receptor agonists upon both electrically-evoked and phenylephrine-induced contractile responses were investigated in the bisected vas deferens and the cauda epididymis of the guinea-pig. Electrical field-stimulation (10 s trains of pulses at 9 Hz, 0.1 ms duration, supramaximal voltage) elicited biphasic and monophasic contractile responses from preparations of bisected vas deferens and cauda epididymis, respectively; these responses were abolished by tetrodotoxin (300 nM). 2. In the prostatic half of the vas deferens the A1 selective adenosine receptor agonists, N6-cyclopentyladenosine (CPA) and (2S)-N6-[2-endo-norbornyl]adenosine ((S)-ENBA) and the non-selective A1/A2 adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) inhibited electrically-evoked contractions (pIC50+/-s.e.mean values 6.15+/-0.24, 5.99+/-0.26 and 5.51+/-0.24, respectively). The responses to CPA were blocked by the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine, DPCPX (100 nM). 3. In the epididymal half of the vas deferens NECA potentiated (at < or = 100 nM) and inhibited (at > or = 1 microM) electrically-evoked contractions. In the presence of the non-selective alpha-adrenoceptor antagonist phentolamine (3 microM), the alpha1-adrenoceptor antagonist, prazosin (100 nM), or at a reduced train length (3 s) NECA inhibited electrically-evoked contractions (pIC50 values 6.05+/-0.25, 5.97+/-0.29 and 5.71 +/-0.27, respectively). CPA (at 10 microM) also inhibited electrically-evoked contractions in this half of the vas deferens. In the presence of prazosin (100 nM), CPA also inhibited electrically-evoked contractions (pIC50 6.14+/-0.67); this effect was antagonized by DPCPX (30 nM, apparent pK(B) 8.26+/-0.88). In the presence of the P2 purinoceptor antagonist, suramin (300 microM), CPA (up to 1 microM) potentiated electrically-evoked contractions. 4. NECA, CPA and APNEA potentiated electrically-evoked contractions in preparations of cauda epididymis (pEC50 values 7.49+/-0.62, 7.65+/-0.74 and 5.84+/-0.86, respectively), the response to CPA was competitively antagonized by DPCPX (100 nM) with an apparent pK(B) value of 7.64+/-0.64. 5. The alpha1-adrenoceptor agonist phenylephrine elicited concentration-dependent contractile responses from preparations of bisected vas deferens and cauda epididymis. NECA (1 microM) potentiated responses to phenylephrine (< or = 1 microM) in the epididymal, but not in the prostatic half of the vas deferens. In preparations of epididymis NECA (1 microM) shifted phenylephrine concentration response curves to the left (4.6 fold). In the presence of a fixed concentration of phenylephrine (1 microM), NECA elicited concentration-dependent contractions of preparations of the epididymal half of the vas deferens and of the epididymis (pEC50 values 7.57+/-0.54 and 8.08+/-0.18, respectively). NECA did not potentiate responses to ATP in either the epididymal half of the vas deferens or the epididymis. 6. These studies are consistent with the action of stable adenosine analogues at prejunctional A1 and postjunctional A1-like adenosine receptors. The prejunctional A1 adenosine receptors only inhibit the electrically-evoked contractions of purinergic origin (an effect predominant in the prostatic half of the vas deferens). At the epididymis, where electrically-evoked contractions are entirely adrenergic, the predominant adenosine receptor agonist effect is a potentiation of alpha1-adrenoceptor-, but not of ATP-induced contractility.     

Correct blue-light regulation of pea Lhcb genes in an Arabidopsis background

The phasic contraction of the isolated guinea pig vas deferens induced by adenosine 5'-triphosphate (ATP) 1mM was significantly augmented by acidification of bathing solution induced by administration of hydrochloric acid (HCL) 10mM (pH = 6.87 +/- 0.015 (n = 5); mean +/- S.E.), while the tonic contraction induced by norepinephrine (NE) 10microM was significantly depressed by HCl 10mM. The contractile response to ATP 1mM was markedly potentiated in the presence of NE 10 microM. The potentiated contractile response to ATP 1mM in the presence of NE 10microM was significantly augmented by HCl 1mM or 10mM. The potentiating ratio of the contraction induced by ATP 1mM in the presence of NE 10microM to that induced by ATP 1mM alone was almost unaffected by the administration of HCl. Electrical field stimulation (EFS) produced a biphasic contractile response of the isolated guinea pig vas deferens; viz. the first rapid phasic contractile response and the second slow maintained tonic contractile response. The phasic contractile response to EFS was significantly augmented by HCl 10mM. These results may indicate that acidification of the medium potentiates the neurochemical transmission between the nerve terminals and the smooth muscle of vas deferens via sensitization of P2X (presumably P2X1 or P2X2) receptors existing in the smooth muscle.     

Effects of the functional elimination of sarcoplasmic reticulum on the manganese-dependent norepinephrine-induced contractions of the guinea pig vas deferens

We investigated the effects of inhibitors of the sarcoplasmic reticulum (SR) functions on the tonic contractions induced by norepinephrine (NE) in the Ca(2+)-depleted Mn(2+)-loaded vas deferens of the guinea pig in the absence of both Ca2+ and Mn2+ (Mn(2+)-dependent NE-contraction). In control preparations without Ca(2+)-depletion and Mn(2+)-loading, either cyclopiazonic acid (CPA, 10 microM) or ryanodine (RYA, 3 microM) inhibited the initial phasic and tonic components but not the large phasic component of NE-induced contraction in normal medium containing 2.2 mM Ca2+. In contrast, CPA did not affect the Mn(2+)-dependent NE-contractions. The inhibitory effect of RYA slowly developed with each repetition of the Mn(2+)-dependent NE-contraction and the magnitude of the inhibition was slight. A23187 (10 microM) inhibited the NE-induced contractions of the control preparations in the same manner as CPA and RYA. Although A23187 did not induce contractions in the Mn(2+)-loaded preparations, A23187 augmented the Mn(2+)-dependent NE-contractions. The augmented tonic contractions returned to the resting level by washing NE and A23187. The augmentation remained for 3 successive contractions in the absence of A23187. However, the 2nd application of A23187 did not augment the contraction. These results suggest that neither Mn(2+)-release from SR nor Mn(2+)-influx from the extracellular space contributes to the Mn(2+)-dependent NE-contractions. We concluded that NE induces Mn(2+)-dependent contractions by increasing Mn2+ sensitivity of contractile processes but not by increasing intracellular Mn2+ concentration.     

Synchronization of cell division in eight-cell bovine embryos produced in vitro: effects of 6-dimethylaminopurine

The effects of NS 1619, a newly developed activator of large-conductance Ca2+-activated K+ channels, were investigated on single smooth muscle fibers dissociated enzymatically from rat vas deferens and on contractions of the epididymal half of vas deferens. K+ currents were recorded using whole-cell patch-clamp methods in near-physiological K+ solutions (5.4 mM extracellular K+/145 mM intracellular K+). When cell membrane voltage was stepped to test potentials (-60 to +60 mV) from a holding potential of -10 mV, NS 1619 increased the outwardly rectifying K+ current in a concentration-dependent manner. The increased portion of the K+ current by NS 1619 was totally abolished by charybdotoxin (100 nM) but not by glibenclamide (3 microM). NS 1619 reduced electrically stimulated contractile responses of rat vas deferens in a concentration-dependent manner, and charybdotoxin but not glibenclamide partially inhibited the effect of NS 1619. NS 1619 (50 microM) inhibited the noradrenaline-induced contraction. Charybdotoxin (100 nM) partially reduced the NS 1619-induced inhibition while glibenclamide (3 microM) had no effect. NS 1619 (10-100 microM) reduced the high K+-induced contractions in a noncompetitive manner. The present results indicate that NS 1619 activates charybdotoxin-sensitive Ca2+-activated K+ channels and probably inhibits Ca2+ influx. These two effects might account largely for the observed mechanical inhibition induced by NS 1619 in the epididymal half of isolated rat vas deferens.     

Regulation of adrenergic nerve-mediated contraction of canine pulmonary artery by K+ channels

The aim of the present study was to investigate the role of certain subtypes of K+ channels in nerve-evoked contractions of pulmonary artery in vitro. The lobar or segmental pulmonary arteries were dissected from dogs, cut into ring segments, and the contractile responses to electrical field stimulation (EFS) and noradrenaline were measured under isometric conditions. Addition of iberiotoxin, a big conductance Ca2+-activated K+ channel blocker, and apamin, a small conductance Ca2+-activated K+ channel blocker, did not change the resting tension but augmented the contractile responses to EFS, so that the electric stimulus frequency required to produce a half-maximal contraction (ES50) was decreased from 18.2+/-3.5 to 7.4+/-2.3 Hz (p<0.01) and from 16.8+/-2.2 to 11.4+/-2.0 Hz (p<0.05), respectively, whereas glibenclamide, an adenosine triphosphate (ATP)-sensitive K+ channel blocker, had no effect. In contrast, none of the K+ channel blockers altered the contractile response to noradrenaline. Incubation of tissues with iberiotoxin and apamin increased the release of 3H-noradrenaline evoked by EFS. We conclude that big conductance Ca2+-activated K+ channels and small conductance Ca2+-activated K+ channels may play a role in the regulation of adrenergic neurotransmission in the pulmonary artery, probably by inhibiting the exocytotic release of noradrenaline from the adrenergic nerve terminals.     

Autoinhibition, sympathetic cotransmission and biphasic contractile responses to trains of nerve stimulation in the rodent vas deferens

1. The present review critically discusses the evidence for and against the various hypotheses that have been proposed to explain the biphasic contractile response of the rodent vas deferens to trains of electrical field stimulation (EFS). 2. It is widely accepted that the initial component of the biphasic response of the rodent isolated vas deferens to trains of EFS is mediated by ATP and the second slower tonic contractions is mediated by noradrenaline (NA). This theory is based on the ability of antagonists of the post-junctional receptors for these neurotransmitters to inhibit the respective components of the biphasic response and on the ability of exogenous application of either ATP or NA to mimic the responses of each phase. 3. Prejunctional autoinhibition has also been proposed as the cause of the biphasic response. This is based primarily on the ability of alpha 2-adrenoceptor antagonists to transform responses from biphasic to monophasic and on the ability of neuronal NA uptake inhibitors to accentuate the separation of the two phases. 4. Atypical or extrajunctional NA receptors have also been proposed to be the mediators of the component of the response to nerve stimulation that is resistant to the traditional alpha-adrenoceptor antagonists. 5. Different contractile mechanisms and/or sources of calcium have also been postulated to cause the biphasic response. Blockers of intracellular Ca2+ mobilization are able to block the initial component, while blockers of extracellular Ca2+ entry inhibit the second tonic phase. 6. It is concluded that because alpha 1-adrenoceptor antagonists and blockers of P2 purinoceptors have also been shown to block both phases of the response to trains of EFS, prejunctional auto-inhibitory mechanisms perhaps provide the most sound explanation for the phenomenon of the biphasic contractile response to trains of EFS.     

Role of nitric oxide on cholinergic component of bronchial tone in pig

In vitro studies demonstrated that stimulation of intrinsic nerves of airway smooth muscle results in a predominantly contractile response, followed by a relaxant response which involves cholinergic, adrenergic and non-adrenergic non-cholinergic (NANC) nerve activation. Thus, in this paper it is determined whether endogenous nitric oxide (NO) modulates cholinergic neurotransmission in isolated pig airway smooth muscle. Bronchial rings were suspended in organ baths for isometric measurement of tension and the contractions were induced using electrical field stimulation (EFS) techniques. Then, the effects of L-NG-nitroarginine (L-NOARG, 10 microM), an inhibitor of NO synthase, and L-arginine (L-ARG, 1 mM), a precursor of NO synthesis, were evaluated. The cholinergic contractions induced by electrical field stimulation (EFS: 60 V, 2 ms, 60 Hz) of pig lobar bronchial preparations increased (29%) in the presence of L-NOARG (10 microM). This effect may be released by nerves in pig large airways during EFS.     

Prejunctionally mediated inhibition of neurotransmission by isoprenaline in rat vas deferens

Effects of isoprenaline on monophasic contractions evoked by electric field stimulation were studied in rat isolated prostatic vas deferens. Isoprenaline reduced electrically evoked contractions (EC50: 0.27 +/- 0.05 microM), and propranolol concentration-dependently antagonized the effect of isoprenaline. In contrast, isoprenaline (0.3-3 microM) did not affect the contractile response induced by exogenous noradrenaline or ATP, while forskolin (100 nM) attenuated agonist-induced contraction. In some tissues, adrenergic and purinergic components of the electrically evoked contraction were isolated by exposure to alpha,beta-methylene ATP (3 microM) and prazosin (3 microM), respectively. Isoprenaline induced a greater inhibition of purinergic than adrenergic component of the electrically evoked contraction. Iberiotoxin (50 nM), glibenclamide (3 microM), 4-aminopyridine (0.3 mM) and tetraethylammonium ions (1 mM) attenuated the effect of isoprenaline. These results indicate that isoprenaline-induced inhibition of the electrically evoked (both purinergic and adrenergic) contraction was mediated primarily through activation of prejunctional beta-adrenoceptors, which probably inhibited release of contractile transmitters from sympathetic nerves supplying vas deferens. Lack of effect of isoprenaline on agonist-induced contraction does not favour a functional role of beta-adrenoceptors in vas smooth muscle.     

Presynaptic modulation by L-glutamate and GABA of sympathetic co-transmission in rat isolated vas deferens

1. The modulatory effects of L-glutamate and its structural analogues, and of gamma-aminobutyric acid (GABA), on sympathetic co-transmission were studied in the rat isolated vas deferens exposed to electrical field stimulation (EFS). 2. Application of exogenous L-glutamate caused a concentration-dependent (1 microM-3 mM) inhibition of the rapid twitch component of the biphasic EFS contraction. However, L-glutamate (1 microM-3 mM) had a minimal effect on the phasic contraction induced by exogenous adenosine 5'-triphosphate (ATP, 150 microM) and noradrenaline (50 microM). Unlike L-glutamate, D-glutamate had no effect on the EFS contraction. 3. The L-glutamate-induced inhibition of the EFS contractions was significantly attenuated by the glutamate decarboxylase (GAD) inhibitor 3-mercapto-propionic acid (150 microM) and was abolished in the presence of the GABA transaminase (GABA-T) inhibitor, 2-aminoethyl hydrogen sulphate (500 microM). 4. The L-glutamate-induced inhibition of the electrically evoked contraction was not affected by the adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)(30 nM), reactive blue 2 (30 microM) or the GABAA receptor antagonist bicuculline (50 microM). However, the GABAB receptor antagonist 2-hydroxysaclofen (50 microM) significantly inhibited the L-glutamate effect. 5. Similar to L-glutamate, GABA also caused a concentration-dependent (0.1-100 microM) inhibition of the EFS contractions. This GABA-induced inhibition was not affected by either the GABAA receptor antagonist bicuculline (50 microM) or reactive blue 2 (30 microM). However, a significant attenuation of the GABA-mediated effect was recorded with the GABAB receptor antagonist 2-hydroxysaclofen (50 microM). Contractions of the vas deferens induced by exogenous ATP and noradrenaline were not affected by GABA (0.1-100 microM). 6. The L-glutamate analogues, N-methyl-D-aspartate (NMDA) (1 microM-1 mM) and quisqualate (Quis 0.1 microM-0.3 mM) had no effect, whilst kainate (Kain, 1 microM-1 mM) caused an inhibition of the EFS-induced contractions. Effects of Kain could be abolished by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dioxine (CNQX, 10 microM). NMDA, Quis and Kain had no effect on the exogenous ATP- or noradrenaline-induced contractions. 7. It is concluded that the excitatory amino acid L-glutamate modulates the electrically evoked vas deferens contraction through conversion to the inhibitory amino acid GABA by a specific GABA transaminase. The GABA formed may then act on GABAB receptors and cause inhibition of the contraction through a presynaptic mechanism.     

Nitrergic modulation of cholinergic responses in the opossum lower oesophageal sphincter

1. Electrical field stimulation (EFS) of the superfused lower oesophageal sphincter from opossum (Monodelphis domestica) elicited biphasic responses. The first phase (relaxation) was strictly dependent on the duration of the EFS. The second phase (contraction) started following termination of the EFS (< or = 15 Hz). EFS at frequencies above 15 Hz led only to contraction, which started immediately upon initiation of the stimulation. 2. In the presence of NG-nitro-L-arginine (L-NOARG; 0.1-300 microM), the relaxation phase was abolished and the contractile response started with the initiation of EFS (at all frequencies) and was greater in magnitude. The contractile response to EFS was completely blocked with scopolamine (10 microM). 3. Exogenous acetylcholine (1-100 microM) elicited concentration-dependent contractions of the sphincter in the presence of botulinum toxin. These contractions were abolished when EFS was applied during administration of acetylcholine. This inhibitory effect of EFS was completely reversed when the tissue was treated with L-NOARG (100 microM). 4. These results suggest that the cholinergic response in the opossum lower oesophageal sphincter is under nitrergic control.     

Tetrodotoxin-sensitive action potentials in smooth muscle of mouse vas deferens

Action potentials were recorded during impalements of some but not all smooth muscle cells of mouse vas deferens in response to both nerve stimulation and intracellular current injection. They were resistant to blockade by nifedipine (0.1-1.0 microM) but were blocked by tetrodotoxin (TTX, 0.2-1.0 microM) when this was added in the presence of nifedipine. It is suggested that voltage-dependent sodium (Na+) channels are present in mouse vas deferens that function to amplify calcium (Ca2+) influx through voltage-dependent Ca2+ channels.     

The voltage dependence of contraction at different stimulation rates in guinea-pig ventricular myocytes

Ventricular myocytes, isolated from the guinea-pig, were stimulated to contract by 100 ms long voltage clamp pulses from -80 to 0 mV at 0.5 and 3 Hz. An increase in frequency from 0.5 to 3 Hz led to a positive inotropic effect. Contraction-voltage relationships (CVR) were determined at each frequency. The CVR at 0.5 Hz was bell shaped and peaked between 0 and +20 mV, displaying a voltage dependence similar to the L-type Ca2+ current (ICa). At 3 Hz, contractions continued to increase at positive voltages, giving a more sigmoidal CVR. At 0.5 Hz, TTX reduced the size of steady-state contractions to 91 +/- 2% of control values, but had no effect on the shape of the CVR. At 3 Hz, TTX significantly reduced (P < 0.05) the magnitude of contractions at positive voltages (> or = +20 mV) but had no significant effect on contractions at voltages negative to 0 mV. These data illustrate that intracellular sodium activity (aNa(i)) and, in particular, Na+ entry due to the sodium current (INa) are important in determining the voltage dependence of contraction at positive voltages. Thapsigargin (2.5 microM), a blocker of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, reduced the size of steady-state contractions at 0 mV to 65 +/- 7% at 0.5 Hz. Increasing frequency to 3 Hz abolished the positive inotropy seen under control conditions. With thapsigargin present, contractions at 0.5 Hz were reduced at all potentials and the CVR was bell shaped. At 3 Hz the CVR was sigmoidal in shape. Contractions were significantly inhibited by thapsigargin at all potentials, but most significantly at more positive potentials (> or = +20 mV). These data show that, at normal body temperature, the shape of the CVR of guinea-pig ventricular myocytes changes with stimulation rate. Due to the voltage dependence of ICa, contractions evoked at positive voltages at 3 Hz must be supported by other mechanisms. The sensitivity of such contractions to TTX and thapsigargin suggests the involvement of both a Na(+)-dependent process and the SR. One possibility is that when aiNa and the Ca2+ content of the SR are raised at higher stimulation rates, enhanced Ca2+ entry via reverse Na(+)-Ca2+ exchange leads to a direct activation of the myofilaments and, to a lesser extent, the release of Ca2+ from the SR.     

Pharmacokinetics of prednisolone transfer to breast milk

A possible interaction of salmon-calcitonin with opioid systems was studied in isolated tissues. Neurogenic contractions were elicited by electrical stimulation in guinea-pig ileum myenteric plexus-longitudinal muscle strips, rabbit vas deferens and mouse vas deferens. Bremazocine inhibited neurogenic contractions in all three tissues (presumably through kappa-receptors) [D-Pen2, D-Pen5]enkephalin and [Met5]enkephalin inhibited contractions in mouse vas deferens (presumably through delta-receptors), and [D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) inhibited contractions in guinea-pig ileum and mouse vas deferens (presumably through mu-receptors). All inhibitory effects were concentration-dependent. Salmon-calcitonin 0.1 IU/ml increased the effect of bremazocine in guinea-pig ileum and rabbit vas deferens and also increased the effects of [D-Pen2, D-Pen5]enkephalin and [Met5]enkephalin in mouse vas deferens. In contrast, salmon-calcitonin up to 0.4 IU/ml did not change the effect of bremazocine in mouse vas deferens and the effect of DAMGO in guinea-pig ileum and mouse vas deferens. It is concluded that salmon-calcitonin enhances agonist effects at opioid kappa- and delta- but not at opioid mu-receptors. The level of this interaction remains to be elucidated. The interaction may be the basis of the analgesic effect of salmon-calcitonin in vivo.     

Changes in electrophysiological properties and noradrenaline response in vas deferens of diabetic rats

The purpose of this study was to study changes in the sympathetic nerves of the vas deferens in 10-week-old streptozotocin-induced diabetic rats. To assess the activity of autonomic neurons, we recorded the amplitude and frequency of spontaneous junction potentials in vasa deferentia from age-matched controls and streptozotocin-induced diabetic rats. No change in the resting membrane potential of the smooth muscle of the vas deferens was found in streptozotocin-induced diabetic rats. The frequency of spontaneous junction potentials was significantly increased in the streptozotocin-induced diabetic rats and their amplitude was also markedly increased. The dose-response curve for the contractile response of the vas deferens to noradrenaline was significantly shifted to the right and the apparent affinity (pD2 value) was significantly decreased in streptozotocin-induced diabetic rats. These results suggest that degeneration of sympathetic neurons may occur in the vas deferens of 10-week streptozotocin-induced diabetic rats and that the greater amplitude of the spontaneous junction potentials may be related to an increase in Ca2+ mobilization, though the increase in Ca2+ mobilization does not lead to an enhanced contractile response.     

Value of the American College of Cardiology/American Heart Association stenosis morphology classification for coronary interventions in the late 1990s

We have reported that norepinephrine but not K+ induced a sustained and dose-dependent contraction without extracellular Ca2+ and Mn2+ in Ca2+-depleted Mn2+-loaded vas deferens from the guinea-pig. In the present study, we determined the phosphorylation of the 20-kDa myosin light chain and examined the effects of inhibitors of calmodulin and myosin light chain kinase on the Mn2+-dependent norepinephrine-induced contraction in order to evaluate the contribution of phosphorylation to this contraction. W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], ML-9 [1-(5-chloronaphthalene-1-sulfonyl)-homopiperazine] and wortmannin inhibited this contraction. However, the Mn2+-dependent norepinephrine-induced contraction developed without a significant increase in the phosphorylation of the 20-kDa myosin light chain. In beta-escin-permeabilized preparations, Mn2+ induced contractions that were inhibited by ML-9. These results suggest that the activation of myosin light chain kinase is essential for the development of Mn2+-dependent norepinephrine-induced contractions and that the phosphorylation of myosin light chain may act as a trigger for these contractions.     

Fertility and contraception in Europe: the case of low fertility in southern Europe

We have investigated whether there are cannabinoid CB2 receptors that can mediate cannabinoid-induced inhibition of electrically evoked contractions in the mouse vas deferens or guinea-pig myenteric plexus-longitudinal muscle preparation. Our results showed that mouse vas deferens and guinea-pig whole gut contain cannabinoid CB1 and CB2-like mRNA whereas the myenteric plexus preparation seemed to contain only cannabinoid CB1 mRNA. JWH-015 (1-propyl-2-methyl-3-( -naphthoyl)indole) and JWH-051 (1-deoxy-11-hydroxy-delta8-tetrahydrocannabinol-dimethylheptyl+ ++), which have higher affinities for CB2 than CB1 cannabinoid binding sites, inhibited electrically evoked contractions of both tissues in a concentration related manner. This inhibition was attenuated by 31.62 nM of the cannabinoid CB1 receptor selective antagonist SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide hydrochloride] only in the myenteric plexus preparation. Vasa deferentia from delta9-tetrahydrocannabinol-pretreated mice (20 mg/kg i.p. once daily for two days) showed reduced sensitivity to JWH-015 and JWH-051. The results suggest that these compounds exert their inhibitory effects through cannabinoid CB1 receptors in the myenteric plexus preparation, but mainly through CB2-like cannabinoid receptors in the vas deferens.     

Influence of endothelial nitric oxide on adrenergic contractile responses of human cerebral arteries

The present study was designed to investigate the influence of the endothelium and that of the L-arginine pathway on the contractile responses of isolated human cerebral arteries to electrical field stimulation (EFS) and norepinephrine. Rings of human middle cerebral artery were obtained during autopsy of 19 patients who had died 3-8 h before. EFS (1-8 Hz) induced frequency-dependent contractions that were abolished by tetrodotoxin, prazosin, and guanethidine (all at 10(-6) M). The increases in tension were of greater magnitude in arteries denuded of endothelium. N(G)-monomethyl L-arginine (L-NMMA 10(-4) M) potentiated the contractile response to EFS in artery rings with endothelium but did not influence responses of endothelium-denuded arteries. L-arginine (10(-4) M) reversed the potentiating effects of L-NMMA on EFS-induced contractions. Norepinephrine induced concentration-dependent contractions, which were similar in arteries with and without endothelium or in arteries treated with L-NMMA. Indomethacin (3 x 10(-6) M) had no significant effect on the contractile response to EFS or on the inhibition by L-NMMA of acetylcholine-induced relaxation. These results suggest that the contractile response of human cerebral arteries to EFS is modulated by nitric oxide mainly derived from endothelial cells; although adrenergic nerves appear to be responsible for the contraction, the transmitter involved in the release of nitric oxide does not appear to be norepinephrine. The effects of L-NMMA in this preparation appear to be due to inhibition of nitric oxide formation rather than caused by cyclooxygenase activation.     

Teratocarcinosarcoma of the paranasal sinuses: a clinicopathologic and immunohistochemical study

We observed endothelin (ET)-induced contractile responses on prostatic and epididymal segments, as well as the facilitation of an electrically stimulated tone on prostatic segments of isolated rat vas deferens. In both segments, the selective ET(B)-receptor agonists, IRL 1620 and sarafotoxin S6c, produced only a small contraction or no contraction at a concentration of 1 microM. The rank order of contraction potencies (pD2 value) was ET-1 = ET-2 > ET-3 > sarafotoxin S6c = IRL 1620. The maximum responses of ET-induced contractions in the prostatic segments were larger than those in the epididymal segments. The contractile response to ET-3 was antagonized by pretreatment for 30 min with BQ-123 (10 nM), a selective ET(A) receptor antagonist, and BQ-788 (1 microM), a selective ET(B) receptor antagonist. The contractile responses to ET-1 were antagonized by pretreatment with BQ-123 (10 microM), but not with BQ-788 (1 microM). The ET-3-induced facilitation on the twitch response to electrical stimulation in the prostatic segment of the vas deferens was antagonized by BQ-123 (0.1 microM) and BQ-788 (1 microM). The ET-1-induced facilitation was antagonized by pretreatment with BQ-123 (3 microM), but not with BQ-788 (10 microM). These results suggest that in rat vas deferens the ET(A) receptors are divided into BQ-123-sensitive ET(A1) and BQ-123-insensitive ET(A2) subtypes, and the production of a contractile response of smooth muscle as well as the facilitation of neurotransmission are accomplished through mediation by ET(A1)- and ET(A2)-subtypes.