Apoptosis in the male gonad

1. Previous work has shown that enalaprilat, an inhibitor of angiotensin-converting enzyme (ACE), potentiated the actions of alpha 1-adrenoceptor antagonists; it was hypothesized that angiotensin II (AngII) modulated the activity of alpha 1-adrenoceptors. This hypothesis was tested in Sprague-Dawley rat isolated perfused tail arteries using the AT1 receptor antagonist losartan and the AT2 receptor antagonist PD123319. 2. Losartan had no alpha 1-adrenoceptor antagonist effects at concentrations below 1 mumol/L. Similarly, losartan (0.1 mumol/L) had no effect on the alpha 1-adrenoceptor antagonist action of doxazosin (1, 10 nmol/L) nor on the potentiation of doxazosin by enalaprilat (1 mumol/L). 3. PD123319 (0.1 mumol/L) had no alpha 1-adrenoceptor antagonist effect but altered the mode of action of the alpha 1-adrenoceptor antagonist doxazosin: PD123319 changed doxazosin from a competitive to a non-competitive antagonist, as evidenced by the reduced slope of the dose-response curve for the alpha 1-adrenoceptor agonist phenylephrine. 4. These results suggest that AngII can modulate alpha 1-adrenoceptor function in rat tail arteries via an indirect action at AT2 receptors. However, the present results do not rule out the involvement of bradykinin, endothelin or prostaglandin in the modulation of alpha 1-adrenoceptor function by angiotensin II.     

Angiotensin II inhibits glomerular adenylate cyclase via the angiotensin II receptor subtype 1 (AT1)

We examined the role of angiotensin II (AII) receptor subtypes in the regulation of hormone-stimulated cyclic AMP (cAMP) accumulation in isolated rat glomeruli. All inhibited cAMP formation induced by histamine, serotonin and parathyroid hormone, but not by prostaglandin E2 or calcitonin gene-related peptide. Angiotensin III but not the angiotensin fragments (1-7) and (3-8) also showed inhibitory activity. The inhibition of histamine-induced cAMP accumulation by AII was concentration-dependent and was absent in glomeruli isolated from pertussis toxin-treated rats. The effect of AII on histamine-induced cAMP levels was not mimicked by the protein kinase C activator, phorbol-12-myristate-13-acetate, nor was the effect of AII inhibited by the protein kinase C inhibitors, staurosporine and H-7. The angiotensin II receptor subtype 1 (AT1) antagonists, SK&F 108566 and losartan, attenuated the inhibitory effect of AII on histamine-stimulated cAMP accumulation, whereas the AT2 selective antagonists, CGP 42112A, WL-19 and PD 123319, had no effect. Displacement of [125I]AII from glomerular membrane using the subtype-selective antagonists confirmed that the glomerular AII receptor has characteristics of an AT1 subtype. The results suggest that AII, through activation of the AT1 receptor, may act to maintain the contractile state of glomerular mesangial cells by attenuating the increase in cAMP levels induced by some hormones.     

Inhibition of sympathetic outflow by the angiotensin II receptor antagonist, eprosartan, but not by losartan, valsartan or irbesartan: relationship to differences in prejunctional angiotensin II receptor blockade

It is well established that angiotensin II can enhance sympathetic nervous system function by activating prejunctional angiotensin II type I (AT1) receptors located on sympathetic nerve terminals. Stimulation of these receptors enhances stimulus-evoked norepinephrine release, leading to increased activation of vascular alpha 1-adrenoceptors and consequently to enhanced vasoconstriction. In the present study, the effects of several chemically distinct nonpeptide angiotensin II receptor antagonists were evaluated on pressor responses evoked by activation of sympathetic outflow through spinal cord stimulation in the pithed rat. Stimulation of thoracolumbar sympathetic outflow in pithed rats produced frequency-dependent pressor responses. Infusion of sub-pressor doses of angiotensin II (40 ng/kg/min) shifted leftward the frequency-response curves for increases in blood pressure, indicating augmented sympathetic outflow. Furthermore, pressor responses resulting in spinal cord stimulation were inhibited by the peptide angiotensin II receptor antagonist, Sar1, Ile8 [angiotensin II] (10 micrograms/kg/min). These results confirm the existence of prejunctional angiotensin II receptors at the vascular neuroeffector junction that facilitate release of norepinephrine. The nonpeptide angiotensin II receptor antagonist, eprosartan (0.3 mg/kg i.v.), inhibited the pressor response induced by spinal cord stimulation in a manner similar to that observed with the peptide antagonist, Sar1, Ile8[angiotensin II]. In contrast, equivalent doses (0.3 mg/kg i.v.) of other nonpeptide angiotensin II receptor antagonists, such as losartan, valsartan, and irbesartan, had no effect on spinal cord stimulation of sympathetic outflow in the pithed rat. Although the mechanism by which eprosartan, but not the other nonpeptide angiotensin II receptor antagonists, inhibits sympathetic outflow in the pithed rat is unknown, one possibility is that eprosartan is a more effective antagonist of prejunctional angiotensin II receptors that augment neurotransmitter release. Because eprosartan is more effective in inhibiting sympathetic nervous system activity compared to other chemically distinct nonpeptide angiotensin II receptor antagonists, eprosartan may be more effective in lowering systolic blood pressure and in treating isolated systolic hypertension.     

The effect of angiotensin AT1 receptor blockade in the brain on the maintenance of blood pressure during haemorrhage in sheep

The effect of systemic or intracerebroventricular (ICV) infusion of the angiotensin AT1 receptor antagonist losartan on blood pressure during hypotensive haemorrhage was investigated in five conscious sheep. Mean arterial pressure (MAP) was measured during haemorrhage (15 mL kg-1 body wt). Losartan (1 or 0.33 mg h-1) was given to sheep by ICV, intravenous or intracarotid administration, beginning 60 min before and continuing during the haemorrhage. During control infusion of ICV artificial cerebrospinal fluid, MAP was maintained until 13.16 +/- 0.84 mL kg-1 blood loss, when a rapid reduction of at least 15 mmHg in arterial pressure occurred (the decompensation phase). ICV infusion of losartan at 1 mg h-1 caused an early onset of the decompensation phase after only 9.8 +/- 0.8 mL kg-1 of blood loss compared with control. Intravenous infusion of losartan (1 mg h-1) also caused an early onset (P < 0.05) of the decompensation phase at 10.2 +/- 1.0 mL kg-1 blood loss. This dose of losartan inhibited the pressor response to ICV angiotensin II, but not to intravenously administered angiotensin II, indicating that only central AT1 receptors were blocked. Bilateral carotid arterial administration of losartan at 0.33 mg h-1 caused an early onset of the decompensation phase during haemorrhage at 11.06 +/- 0.91 mL kg-1 blood loss (P < 0.05), which did not occur when infused by intravenous or ICV routes. The results indicate that an angiotensin AT1-receptor-mediated mechanism is involved in the maintenance of MAP during haemorrhage in sheep. The locus of this mechanism appears to be the brain.     

Central pathology review in clinical trials for patients with malignant glioma. A Report of Radiation Therapy Oncology Group 83-02

We previously described delayed pressor response (DPR) 3 h after endothelin (ET)-1 injection in normotensive rats. In the current study, we examined effects of the ETA receptor antagonist BQ123 (0.01 mumol/kg/min intravenously, i.v.), phosphoramidon (100 mumol/kg i.v.), the neutral endopeptidase inhibitor SQ28603 (112 mumol/kg + 0.04 mumol/kg/min i.v.), the angiotensin-converting enzyme inhibitor enalaprilat (10 mumol/kg i.v.), and the thromboxane receptor antagonist, SQ29548 (0.5 mumol/kg + 0.5 mumol/kg/h i.v.) on DPR. Vehicle and ET-1 (1.0 nmol/kg i.v.) were administered on day 1; vehicle or drug and ET-1 were administered on day 2. BQ123 inhibited DPR 36% (vehicle 44 +/- 5, BQ123 28 +/- 3 mm Hg); phosphoramidon inhibited DPR 56% (vehicle 45 +/- 4, and phosphoramidon 20 +/- 5 mm Hg). DPR was unchanged after SQ28603 (vehicle 39 +/- 2 and SQ28603 44 +/- 2 mm Hg), enalaprilat (vehicle 39 +/- 2 and enalaprilat 38 +/- 7 mm Hg), or SQ29548 (vehicle 46 +/- 6 and SQ29548 43 +/- 3 mm Hg). The results suggest that DPR 3 h after ET-1 injection in rats is mediated in part through ETA receptors. DPR does not appear to involve thromboxane or synthesis of angiotensin II (AII), but may be related to synthesis of ET-1.     

Interactions between anemone toxin II and veratridine on single neuronal sodium channels

Restenosis is the single most important factor limiting a favorable long-term outcome following mechanical revascularization. The vascular endothelium, through the release of key regulatory compounds, may regulate vascular structure by exerting fundamental control over collagen synthesis following injury to the vessel wall. We tested the hypothesis that endothelin (ET-1), an endothelium-derived peptide previously shown to be increased in pathological states, differentially stimulates porcine coronary vascular smooth muscle cell collagen types I and III synthesis. Monocultures of porcine coronary vascular smooth muscle were exposed to varying concentrations of endothelin over a 24-96-h time period. The medium was assayed for soluble collagen types I and III using a sensitive and specific ELISA method. Experiments were also done with the ET-1 antagonists PD 145065 and BQ123. Cell counts and viability were serially monitored. Experiments were also conducted with angiotensin II (A-II). A-II and ET-1 stimulated cell proliferation. ET-1 maximally stimulated collagen type I synthesis at 48 h at an optimal concentration of 10(-8) M, with no significant stimulation of collagen type III synthesis. The ETA specific antagonist BQ123 significantly inhibited the stimulatory effects of ET-1. A-II also stimulated collagen type I synthesis above basal levels, but was less efficacious than endothelin (95 +/- 5%, A-II, v 189 +/- 14% ET-1). In contrast to ET-1, A-II stimulated collagen type III synthesis (31 +/- 6% above basal, compared to -4 +/- 5% for ET-1). Results are also reported using smooth muscle cells from porcine aorta. The data demonstrate that ET-1 and A-II stimulate collagen synthesis by coronary artery vascular smooth muscle, and that they exert a differential effect over the two types of collagen that are present in the intima following balloon injury. Thus, the over expression of key regulatory compounds by endothelium following balloon injury could enhance collagen deposition and, consequently, play an integral role in intimal hyperplasia and restenosis.     

Endopeptidase 24.11 inhibition does not modify uterotonic effects of endothelins in rat uterus

We investigated effects of the endopeptidase 24.11 inhibitor, SCH 39370, on uterotonic effects of endothelins (ETs) and sarafotoxin S6b. Responses of uteri from non-pregnant rats were inhibited by the ETA receptor antagonist, BQ123 (1 microM) but not the ETB receptor antagonist, BQ 788 (1 microM). ET-1, sarafotoxin S6b and ET-2 were more potent than ET-3 in tissues from non-pregnant and pregnant rats. SCH 39370 (10 microM) did not affect uterotonic responses to these peptides in either group, but inhibited those of big ET-1 in non-pregnant rat tissues, indicating inhibition of conversion of big ET-1 to ET-1. These data indicate that endopeptidase 24.11 does not inactivate the endothelin peptides in the rat uterus.     

Chronic parvovirus infection mimicking myelodysplastic syndrome in a child with subclinical immunodeficiency

1. The effect of cyclo(D-Trp-D-Asp-Pro-D-Val-Leu) (or BQ123), a selective ETA receptor antagonist, on the vasoconstrictor and diuretic responses elicited by endothelin-1 (ET-1) was examined in conscious sheep with chronic indwelling renal arterial cannulae. 2. Using low dose close renal arterial infusion, ET-1 has potent effects on the kidney causing a marked decrease in effective renal plasma flow and an increase in urine output and free water clearance in the normally hydrated animal. 3. The vasoconstrictor response to renal arterial infusion of ET-1 at 5 micrograms/h was blunted by renal arterial infusion of the ETA receptor selective antagonist, BQ123 (400 micrograms/h). 4. In contrast, the effect of ET-1 on urine production and free water clearance was not affected by this dose of BQ123. 5. The differential effect of BQ123 on renal blood flow and urine production suggests that these effects of endothelin on the kidney are mediated through different receptor mechanisms.     

New insights for dinucleotide backbone binding in conserved C5''-H . . . O hydrogen bonds

OBJECTIVE: Although a number of pharmacologic agents have been shown to reduce intimal hyperplasia in animal models of restenosis, to date no systemic agent has conclusively been shown to be effective in humans. Recently, considerable attention has been directed towards endothelin (ET), a potent vasoconstrictor and a powerful mitogen for vascular smooth muscle cells, as a mediator of intimal hyperplasia. Endothelin-1 has been shown to be mitogenic for human saphenous vein smooth muscle cells, and expression also is elevated in human vein graft stenosis. The aim of this study was the investigation of whether ET receptor antagonists can attenuate neointima formation in a laboratory model of vein graft intimal hyperplasia and the determination of whether the effects are mediated by a specific ET receptor subtype. METHODS: We used an organ culture of human saphenous vein, a well-validated model of vein graft intimal hyperplasia. Paired segments of human long saphenous vein were cultured with and without the following antagonists: bosentan, a nonselective ET receptor antagonist; BQ 123, a specific endothelin-A antagonist; or BQ 788, a specific endothelin-B (ETB) antagonist. After 14 days in the culture, the segments were fixed and processed and the sections were immunostained to facilitate the measurements of neointimal thickness with a computerized image analysis system. RESULTS: The nonselective antagonist bosentan and the ETB selective antagonist BQ 788 significantly reduced neointima formation by 70% (P = .001) and 50% (P = .03), respectively, but the ETA antagonist BQ 123 had no significant effect on the reduction of neointima formation (P = 1.0). CONCLUSION: The results of this study imply an important role for ET as a mediator of human vein graft intimal hyperplasia and imply further that a specific ETB antagonist may have a therapeutic potential for the prevention of vein graft stenosis.     

AT2-antagonist sensitive potentiation of angiotensin II-induced vasoconstrictions by blockade of nitric oxide synthesis in rat renal vasculature

1. Although the actions of angiotensin II (Ang II) on renal haemodynamics appear to be mediated by activation of the AT1 receptor subtype, AT2 binding sites have also been evidenced in the adult kidney vasculature. As NO is known to mask part of the renal effects of vasoconstrictor drugs, we queried whether the Ang II-induced vasoconstrictions could occur via multiple receptor subtypes during inhibition of NO synthesis. We explored the effect of AT1 and AT2 receptor (AT-R) antagonists on Ang II-induced pressure increases during NO synthase or soluble guanylyl cyclase inhibition in rat isolated kidneys perfused in the presence of indomethacin at constant flow in a single-pass circuit. 2. In the absence of NO blockade, the AT1-R antagonist L-158809 (500 nM) antagonized the Ang II-induced vasoconstrictions, while the AT2-R antagonist PD-123319 (500 nM) had no effect. 3. Perfusing kidneys in the presence of either NO synthase inhibitors, L-NAME (100 microM) or L-NOARG (1 mM), or soluble guanylyl cyclase inhibitor, LY-83583 (10 microM), significantly increased both molar pD2 (from 9.40+/-0.25 to 10.36+/-0.11) and Emax values (from 24.9+/-3.1 to 79.9+/-4.9 mmHg) of the concentration-response curve for Ang II-induced vasoconstriction. 4. In the presence of L-NAME, 500 nM L158809 abolished the Ang II-induced vasoconstrictions whatever the concentration tested. On the other hand, 500 nM PD-123319 reversed the left shift of the concentration-response curve for Ang II (molar pD2 value 9.72+/-0.13) leaving Emax value unaffected (91.3+/-7.6 mmHg). 5. In the presence of L-NAME, the potentiated vasoconstriction induced by 0.1 nM and the augmented vasoconstriction induced by 10 nM Ang II were fully inhibited in a concentration-dependent manner by L-158809 (0.05-500 nM). By contrast, PD-123319 (0.5-500 nM) did not affect the 10 nM Ang II-induced vasoconstriction and concentration-dependently decreased the 0.1 nM Ang II-induced vasoconstriction plateauing at 65% inhibition above 5 nM antagonist. 6. Similar to PD-123319, during NO blockade the AT2-R antagonist CGP-42112A at 5 nM decreased by 50% the 0.1 nM Ang II-induced vasoconstriction and at 500 nM had no effect on 10 nM Ang II-induced vasoconstriction. 7. In conclusion, the renal Ang II-induced vasoconstriction, which is antagonized only by AT1-R antagonist in the presence of endogenous NO, becomes sensitive to both AT1- and AT2-R antagonists during NO synthesis inhibition. While AT1-R antagonist inhibited both L-NAME-potentiated and -augmented components of Ang II-induced vasoconstriction, AT2-R antagonists inhibited only the L-NAME-potentiated component.     

Comparison of human immunodeficiency virus 1 DNA polymerase chain reaction and qualitative and quantitative RNA polymerase chain reaction in human immunodeficiency virus 1-exposed infants

The endothelial lining of the blood-brain barrier tightly controls the distribution of peptide hormones between the central nervous system and the circulation. By using primary cultures of brain microvessel endothelial cells, an in vitro model of the blood-brain barrier, we report here the uptake and transport of the octapeptide angiotensin II by a specific receptor population. With the angiotensin II antagonists losartan (AT1 specific) and PD 123,319 (AT2 specific), we showed that both the uptake and transport of angiotensin II were mediated by the AT1 receptor. Western blot analysis confirmed the existence of the AT1 receptor in our cell-culture model. Rhodamine 123 studies also suggested that both angiotensin II antagonists, but not angiotensin II, were substrates for the P-glycoprotein efflux system, thus restricting the transport of these compounds. These results suggest an AT1 receptor mediates uptake and transport of angiotensin II at the blood-brain barrier and may contribute to the regulation of cerebrovascular levels of the peptide.     

Mechanisms of endothelin-induced macromolecular leakage in microvascular beds of rat mesentery

Microvascular responses to endothelin-3 were investigated in the rat mesentery under fluorescence microscopy. Endothelin-3 in a range of 0.1-100 pM induced arteriolar constriction in a dose-dependent manner, and stimulated Ca2+ mobilization, demonstrated by fura-2-associated fluorography, in both arterioles and venules. Cyclo(-D-Trp-D-Asp-Pro-D-Val-Leu-) (BQ123), and endothelin ETA receptor antagonist, at a concentration of 10 microM inhibited the endothelin-3 (100 pM)-induced arteriolar constriction and Ca2+ mobilization in arterioles but not in venules. In venules, an early onset leakage of FITC (fluorescein isothiocyanate)-labeled albumin and subsequent reduction of red blood cell velocity without arteriolar constriction were observed after the superfusion of endothelin-3 with BQ123, suggesting that a non-endothelin ETA receptor mediates macromolecular leakage followed by a decrease in blood flow. Endothelin-3 with BQ123 neither stimulated leukocyte adhesion nor activated luminol-dependent chemiluminescence in venules, showing that endothelin-3-increased permeability may be induced by leukocyte-independent and oxyradical-independent mechanisms. These microvascular alterations of permeability and red blood cell velocity were significantly attenuated by the addition of phalloidin, an F-actin stabilizer, suggesting the involvement of endothelial cell contraction. Nicardipine (1,4-dihydro-2,6-dimethyl-4-[3-nitrophenyl]methyl-2- [methyl(phenylmethyl)amino]-3,5-pyridinedicarboxylic acid ethyl ester), a dihydropyridine-type Ca2+ channel antagonist, eliminated endothelin-3-induced arteriolar constriction; however, it did not affect albumin leakage promoted by endothelin-3 with BQ123, suggesting that a non-voltage-dependent Ca2+ channel(s) is involved in non-endothelin ETA receptor-mediated Ca2+ mobilization and contraction of venular endothelial cells. Overall, it is conceivable that endothelin ETA receptor and voltage-dependent Ca2+ channel are involved in endothelin-3-induced arteriolar constriction. In addition, the present results suggest that Ca2+ mobilization in venular endothelium, which is mediated by a non-endothelin ETA receptor, possibly endothelin ETB receptor and regulated by non-voltage-dependent Ca2+ channel(s), may cause endothelial cell contraction and subsequently increase macromolecular permeability in microvascular beds treated with endothelin-3.     

Atypical receptors mediate the response to endothelin-1 and sarafotoxin S6b in the human umbilical artery

The receptors mediating smooth muscle response to endothelin-1 and sarafotoxin S6b in the human umbilical artery were investigated in vitro. Both agonists induced contractions that were unaffected by the endothelin ET(B) receptor antagonist BQ 788 (10(-9), 10(-8), 10(-7) M). The non-selective endothelin ET(A/B) receptor antagonist PD 142893 (10(-7) M) decreased the contraction induced by endothelin-1. PD 142893 (10(-9) M) enhanced the contraction induced by sarafotoxin S6b whereas higher concentrations had no effect. Removing the endothelium did not affect the antagonising action of PD 142893 on endothelin-1-induced contractions while the enhancement of the sarafotoxin S6b-induced contraction was abolished. Sarafotoxin S6b induced relaxation in segments precontracted by 5-hydroxytryptamine and exposed to the endothelin ET(A) receptor antagonist BQ 123 (10(-7) M) and PD 142893 (10(-9) M) abolished this relaxation. These endothelial receptors seem neither to be classical endothelin ET(A) nor endothelin ET(B) receptors and they are not activated by endothelin-1.     

Vascular and excretory effects of angiotensin II in the rat isolated perfused kidney: influence of an AT1 and a nonselective AT receptor antagonist

Angiotensin II (AII) is a potent vasoconstrictor which, at physiological plasma concentrations, produces antinatriuresis, whereas high intrarenal concentrations cause natriuresis and diuresis. We examined the effects of a selective AT1 receptor antagonist, losartan, and a nonselective AT receptor antagonist, Sar1Thr8AII, on the response to infusion of AII in the isolated rat kidney perfused at constant pressure with a recirculating modified Krebs-Henseleit buffer. AII increased renal vascular resistance (RVR), glomerular filtration rate (GFR) and urinary volume (UV) and sodium excretion (UNaV) without changing the fractional excretion of water or electrolytes. Thus, changes in GFR can account for the natriuresis/diuresis. Both AII receptor antagonists prevented the increase in RVR. However, losartan was without effect on angiotensin-induced increases in GFR, UV or UNaV, whereas Sar1Thr8 AII also prevented the increases in GFR, UV and UNaV. The angiotensin receptor mediating the increase in GFR can be dissociated from that mediating the increase in RVR, providing functional evidence of angiotensin receptor subtypes in the rat kidney.     

Angiotensin II receptors and angiotensin II stimulation of ciliary activity in human fallopian tube

Using an antibody (6313/G2) directed against a specific sequence in the extracellular domain of the type 1 angiotensin II receptor (AT1), we demonstrated the presence of angiotensin II (AII) receptors in human fallopian tube. Immunoperoxidase staining for AT1 receptor showed positive staining in the epithelium of the tubal mucosa. The intensity of staining varied depending upon the hormonal status at the time of salpingectomy, being strongest in the proliferative phase of the ovarian cycle and weakest after menopause. Ligand binding assay confirmed that the AII receptor concentration was highest in the mucosa of fallopian tubes from premenopausal women. Mucosa from the ampullary segment had higher concentrations of AII receptor than the fimbrial and isthmic segments in both premenopausal and postmenopausal women. Displacement studies using specific AII receptor subtype antagonists showed that approximately 60% of the total activity could be displaced by CGP42112B (type 2 specific) and 40% by losartan (AT1 specific). Immunoblotting confirmed that the antibody detected a protein of approximately 60 kDa. Functional studies showed that AII had a stimulatory action on tubal ciliary beat frequency, but had no significant effect on myosalpingseal activity. This effect was achieved at nanomolar concentrations of AII; further increases in the AII concentration were without additional effect. The stimulatory effect of AII was inhibited by the specific AT1 antagonist losartan, whereas the type 2 antagonist, CGP42112B, had no effect. The data demonstrate that AII may play an important role in ovum transport and fertility.     

Cardiovascular effects produced by microinjection of angiotensins and angiotensin antagonists into the ventrolateral medulla of freely moving rats

In this study we determined the cardiovascular effects produced by microinjection of angiotensin peptides [Angiotensin-(1-7) and Angiotensin II] and angiotensin antagonists (losartan, L-158,809, CGP 42112A. Sar1-Thr8-Ang II, A-779) into the rostral ventrolateral medulla of freely moving rats. Microinjection of angiotensins (12.5-50 pmol) produced pressor responses associated to variable changes in heart rate, usually tachycardia. Unexpectedly, microinjection of both AT1 and AT2 ligands produced pressor effects at doses that did not change blood pressure in anesthetized rats. Conversely, microinjection of Sar1-Thr8-Ang II and the selective Ang-(1-7) antagonist, A-779, produced a small but significant decrease in MAP an HR. These findings suggest that angiotensins can influence the tonic activity of vasomotor neurons at the RVLM. As previously observed in anesthetized rats, our results further suggest a role for endogenous Ang-(1-7) at the RVLM. The pressor activity of the ligands for AT1 and AT2 angiotensin receptor subtypes at the RVLM, remains to be clarified.     

Decisions, decisions

Losartan is the first angiotensin II type 1 (AT1) receptor antagonist to become available for the treatment of hypertension. However, recent reports have revealed several cases of losartan-induced bronchoconstriction. We investigated to determine the mechanism of losartan-induced bronchoconstriction, considering in particular the involvement of endogenous nitric oxide (NO). In this study, we examined the effects of losartan on airway obstruction and endogenous NO production using anesthetized guinea pigs and cultured airway epithelial cells. Five minutes after administration of angiotensin II (Ang II), the bronchoconstriction induced by acetylcholine was not changed. In contrast, Ang II in the presence of losartan caused a significant increase in the acetylcholine responsiveness. Pretreatment with L-N omega-nitroarginine-methylester (L-NAME) potentiated acetylcholine-induced bronchoconstriction 5 min after administration of Ang II, and L-arginine reversed this action of L-NAME on the acetylcholine responsiveness. Moreover, Ang II administration increased NO concentration in expired air (12.5 +/- 1.5 ppb for saline, 40 +/- 5 ppb for Ang II, p < 0.01), and losartan significantly inhibited Ang II-stimulated NO release (20 +/- 3.5 ppb) from guinea pig airway. In cultured airway epithelial cells, Ang II also increased NO release (160 +/- 25 nM), and the effect of this Ang II-induced NO release was significantly inhibited by pretreatment with losartan (25 +/- 8 nM, p < 0.01). These findings suggest that losartan-induced bronchoconstriction may result from inhibition of endogenous NO release in the airway.     

Signal transduction mechanisms involved in angiotensin-(1-7)-stimulated arachidonic acid release and prostanoid synthesis in rabbit aortic smooth muscle cells

This study investigated the signal transduction mechanisms of angiotensin-(1-7) [Ang-(1-7)]- and Ang II-stimulated arachidonic acid (AA) release for prostaglandin (PG) production in rabbit aortic vascular smooth muscle cells. Ang II and Ang-(1-7) enhanced AA release in cells prelabeled with [3H]AA. However, 6-keto-PGF1 alpha synthesis produced by Ang II was much less than that caused by Ang-(1-7). In the presence of the lipoxygenase inhibitor baicalein, Ang II enhanced production of 6-keto-PGF1 alpha to a greater degree than Ang-(1-7). Angiotensin type (AT)1 receptor antagonist DUP-753 inhibited only Ang II-induced [3H]AA release, whereas the AT2 receptor antagonist PD-123319 inhibited both Ang II- and Ang-(1-7)-induced [3H]AA release. Ang-(1-7), receptor antagonist D-Ala7-Ang-(1-7) inhibited the effect of Ang-(1-7), but not of Ang II. In cells transiently transfected with cytosolic phospholipase A2 (cPLA2), mitogen-activated protein (MAP) kinase or Ca(++)-/cal-modulin-dependent protein (CAM) kinase II antisense oligonucleotides, Ang-(1-7)- and Ang II-induced [3H]AA release was attenuated. The CaM kinase II inhibitor KN-93 and the MAP kinase kinase inhibitor PD-98059 attenuated both Ang-(1-7)- and Ang II-induced cPLA2 activity and [3H]AA release. Ang-(1-7) and Ang II also increased CaM kinase II and MAP kinase activities. Although KN-93 attenuated MAP kinase activity, PD-98059 did not affect CaM kinase II activity. Both Ang II and Ang-(1-7) caused translocation of cytosolic PLA2 to the nuclear envelope. These data show that Ang-(1-7) and Ang II stimulate AA release and prostacyclin synthesis via activation of distinct types of AT receptors. Both peptides appear to stimulate CaM kinase II, which in turn, via MAP kinase activation, enhances cPLA2 activity and release of AA for PG synthesis.