5-HT activates vagal afferent cell bodies in vivo: role of 5-HT2 and 5-HT3 receptors.

Occipital artery (OA) injections of 5-HT elicit pronounced reductions in heart rate and mean arterial blood pressure (MAP) in urethane-anesthetized rats by activation of vagal afferent cell bodies in the ipsilateral nodose ganglion. In contrast, internal carotid artery (ICA) and i.v. injections elicit similar cardiovascular responses by activation of peripheral vagal afferent terminals. The aim of this study was to examine the roles of 5-HT3 and 5-HT2 receptors in the 5-HT-induced activation of vagal afferent cell bodies and peripheral afferent terminals in urethane-anesthetized rats. OA, ICA and i.v. injections of 5-HT elicited dose-dependent reductions in heart rate and MAP that were virtually abolished after i.v. administration of the 5-HT3 receptor antagonists, MDL 7222 or ICS 205-930. The responses elicited by the OA injections of 5-HT were markedly diminished after i.v. injection of the 5-HT2 receptor antagonists, xylamidine or ketanserin, whereas the responses elicited by i.v. or ICA injections of 5-HT were not affected. The present findings suggest that (1) 5-HT3 and 5-HT2 receptor antagonists gain ready access to nodose ganglion cells upon i.v. administration, and (2) functional 5-HT3 and 5-HT2 receptors exist on the cell bodies of vagal afferent neurons mediating the cardiovascular responses elicited by OA injections of 5-HT. These findings also support a wealth of evidence that 5-HT3 receptors exist on the peripheral terminals of vagal afferents, and although they do not discount the possibility that 5-HT2 receptors exist on peripheral vagal afferent terminals, it appears that activation of these receptors does not have pronounced effects on 5-HT3 receptor activity on terminals that mediate the hemodynamic responses to 5-HT.

Occipital artery injections of 5-HT may directly activate the cell bodies of vagal and glossopharyngeal afferent cell bodies in the rat.

The primary objective of this study was to determine whether circulating factors gain direct access to and affect the activity of vagal afferent cell bodies in the nodose ganglia and glossopharyngeal afferents cell bodies in the petrosal ganglia, of the rat. We found that the occipital and internal carotid arteries provided the sole blood supply to the nodose ganglia, and that i.v. injections of the tracer, Basic Blue 9, elicited strong cytoplasmic staining in vagal and glossopharyngeal afferent cell bodies that was prevented by prior ligation of the occipital but not the internal carotid arteries. We also found that occipital artery injections of 5-HT elicited pronounced dose-dependent reductions in heart rate and diastolic arterial blood pressure that were (1) virtually abolished after application of the local anesthetic, procaine, to the ipsilateral nodose and petrosal ganglia, (2) markedly attenuated after transection of the ipsilateral vagus between the nodose ganglion and brain and virtually abolished after subsequent transection of the ipsilateral glossopharyngeal nerve between the petrosal ganglion and the brain, (3) augmented after ipsilateral transection of the aortic depressor and carotid sinus nerves, and (4) augmented after transection of all ipsilateral glossopharyngeal and vagal afferent nerves except for vagal cardiopulmonary afferents. These findings suggest that blood-borne 5-HT in the occipital artery gains direct access to and activates the cell bodies of vagal cardiopulmonary afferents of the rat and glossopharyngeal afferents of undetermined modalities.

Blockade of voltage-sensitive Ca(2+)-channels markedly diminishes nitric oxide- but not L-S-nitrosocysteine- or endothelium-dependent vasodilation in vivo.

The aim of this study was to determine the hemodynamic responses elicited by systemic injections of (i) the nitric oxide (NO)-donors, sodium nitroprusside (10 nmol/kg, i.v.) and (Z)-1-(N-methyl-N-(6(N-methylammoniohexyl)amino))diazen-1-ium-1, 2-diolate (MAHMA NONOate, 25 nmol/kg, i.v.), (ii) the endothelium-derived S-nitrosothiol, L-S-nitrosocysteine (100 nmol/kg, i.v.), and (iii) the endothelium-dependent agonist, acetylcholine (1.0 microg/kg, i.v.), in anesthetized rats, before and after injection of the voltage-sensitive Ca(2+)-channel (Ca(VS)(2+)-channel) blocker, nifedipine (500 nmol/kg, i.v.). Before injection of nifedipine, the agents produced similar falls in mean arterial blood pressure, and in hindquarter and mesenteric vascular resistances. The depressor and vasodilator responses elicited by sodium nitroprusside and MAHMA NONOate were markedly attenuated by nifedipine. The falls in mean arterial blood pressure and mesenteric resistance elicited by L-S-nitrosocysteine and acetylcholine were not attenuated but the falls in hindquarter resistance were slightly attenuated by nifedipine. The cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.v.), did not affect the actions of sodium nitroprusside, MAHMA NONOate, L-S-nitrosocysteine or acetylcholine or the effects of nifedipine on the hemodynamic actions of these compounds. The decomposition of sodium nitroprusside (0.2 nmol/ml), MAHMA NONOate (0.5 nmol/ml) and L-S-nitrosocysteine (2 nmol/ml) to NO upon addition to rat blood was not affected by nifedipine (10 microM). These findings suggest that (i) exogenously applied NO relaxes resistance arteries in vivo by inhibition of Ca(VS)(2+)-channels whereas L-S-nitrosocysteine and the non-prostanoid endothelium-derived relaxing factor (EDRF) released by acetylcholine acts by additional mechanisms, and (ii) this EDRF may be an S-nitrosothiol which acts independently of its decomposition to NO.

Redox regulation of S-nitrosocysteine-mediated vasodilation in vivo.

This study examined the effects of the lipophobic electron acceptor, nitroblue tetrazolium (2x5 micromol/kg, i.v.) on the vasodilation produced by the putative endothelium-derived S-nitrosothiol, L-S-nitrosocysteine (400 nmol/kg, i.v.), and the nitric oxide (NO) donor, (Z)-1-N-methyl-N-[6(N-methylammoniohexyl)amino]&z. sfnc;diazen-1-ium-1,2-diolate (MAHMA NONOate, 25 nmol/kg, i.v.), in anesthetized rats. The administration of nitroblue tetrazolium resulted in delayed but long-lasting increases in vascular resistances. The L-S-nitrosocysteine-induced vasodilator responses were markedly diminished whereas the MAHMA NONOate-induced responses were not affected by nitroblue tetrazolium. These results support the possibility that L-S-nitrosocysteine interacts with membrane thiols that are subject to nitroblue tetrazolium-induced oxidation (i.e., disulfide-bridge formation) and that nitroblue tetrazolium-induced vasoconstriction may involve a loss of potency of endothelium-derived S-nitrosothiols.

In vivo evidence that L-S-nitrosocysteine may exert its vasodilator effects by interaction with thiol residues in the vasculature.

This study examined the effects of the lipophobic thiol chelator, para-hydroxymercurobenzoic acid (25 and 50 micromol/kg, i.v.) on the falls in mean arterial blood pressure and regional vascular resistances produced by L-S-nitrosocysteine (400 nmol/kg, i.v.) and the nitric oxide (NO)-donors, (Z)-1-&z. sfnc;N-methyl-N-[6(N-methylammoniohexyl)amino]&z.sfnc; diazen-1-ium-1, 2-diolate (MAHMA NONOate, 25 nmol/kg, i.v.) and sodium nitroprusside (10 microg/kg, i.v.), in urethane-anesthetized rats. The L-S-nitrosocysteine-induced responses were markedly diminished whereas the MAHMA NONOate- and sodium nitroprusside-induced responses were minimally affected by para-hydroxymercurobenzoic acid. These results suggest that the vasodilator actions of L-S-nitrosocysteine involves the interaction with membrane thiols in vascular smooth muscle of resistance arteries and that para-hydroxymercurobenzoic acid does not markedly affect NO-mediated vasodilation.

Modulation of temperature-induced tone by vasoconstrictor agents.

One of the primary cardiovascular adjustments to hyperthermia is a sympathetically mediated increase in vascular resistance in the viscera. Nonneural factors such as a change in vascular tone or reactivity may also contribute to this response. Therefore, the aim of this study was to determine whether vascular smooth muscle tone is altered during heating to physiologically relevant temperatures >37 degrees C. Gradually increasing bath temperature from 37 degrees C (normothermia) to 43 degrees C (severe hyperthermia) produced graded contractions in vascular ring segments from rat mesenteric arteries and thoracic aortae. In untreated rings these contractions were relatively small, whereas hyperthermia elicited near-maximal increases in tension when rings were constricted with phenylephrine or KCl before heating. In phenylephrine-treated mesenteric arterial rings, the contractile responses to heating were markedly attenuated by the Ca2+ channel antagonists nifedipine and diltiazem. Diltiazem also blocked the contractile responses to heating in thoracic aortic rings. These results demonstrate that hyperthermia has a limited effect on tension generation in rat vascular smooth muscle in the absence of vascular tone. However, in the presence of agonist-induced tone, tension generation during heating is markedly enhanced and dependent on extracellular Ca2+. In conclusion, these data suggest that local regulation of vascular tone can contribute to the hemodynamic adjustments to hyperthermia.

Effect of heating on vascular reactivity in rat mesenteric arteries.

Vasoconstriction in the viscera is one of the primary cardiovascular adjustments to heating. Local temperature can influence vascular responsiveness to catecholamines and sympathetic nerve activity. Therefore, we hypothesized that heating would alter vascular reactivity in rat mesenteric arteries. Concentration-response curves to norepinephrine, phenylephrine, potassium chloride (KCl), calcium, acetylcholine, and sodium nitroprusside were obtained in vascular ring segments from rat mesenteric arteries at 37 and 41 degrees C. In some rings, basal tension increased slightly during heating. Heating to 41 degrees C did not alter the contractile responses to norepinephrine in endothelium-intact or -denuded rings but augmented the responses to KCl and calcium in endothelium-intact rings. The potentiating effect of heating on the responses to KCl and calcium was eliminated after endothelium removal. In contrast, the relaxant responses to acetylcholine and sodium nitroprusside were significantly attenuated at 41 degrees C. Collectively, these results demonstrate that heating alters vascular reactivity in rat mesenteric arteries. Furthermore, these data imply that heating reduces the ability of vascular smooth muscle to relax, possibly due to a decrease in sensitivity to nitric oxide.

Nitric oxide as an autocrine regulator of sodium currents in baroreceptor neurons.

Arterial baroreceptors are mechanosensitive nerve endings in the aortic arch and carotid sinus that play a critical role in acute regulation of arterial blood pressure. A previous study has shown that nitric oxide (NO) or NO-related species suppress action potential discharge of baroreceptors. In the present study, we investigated the effects of NO on Na+ currents of isolated baroreceptor neurons in culture. Exogenous NO donors inhibited both tetrodotoxin (TTX) -sensitive and -insensitive Na+ currents. The inhibition was not mediated by cGMP but by NO interaction with channel thiols. Acute inhibition of NO synthase increased the Na+ currents. NO scavengers (hemoglobin and ferrous diethyldithiocarbamate) increased Na+ currents before but not after inhibition of NO synthase. Furthermore, NO production in the neuronal cultures was detected by chemiluminescence and immunoreactivity to the neuronal isoform of NO synthase was identified in fluorescently identified baroreceptor neurons. These results indicate that NO/NO-related species function as autocrine regulators of Na+ currents in baroreceptor neurons. Modulation of Na+ channels may represent a novel response to NO.

Cerebrovascular relaxation responses to endothelium-dependent and -independent vasodilators after normothermic and hypothermic cardiopulmonary bypass in the rabbit.

BACKGROUND: Cardiopulmonary bypass causes activation of leukocytes and increased concentrations of proinflammatory mediators, which may result in endothelial dysfunction. Because hypothermia attenuates many inflammatory processes, the authors hypothesized that hypothermic cardiopulmonary bypass would be associated with better endothelial function than normothermic cardiopulmonary bypass. METHODS: Isoflurane-anesthetized New Zealand White rabbits were randomized to undergo 90 min of either normothermic (37 degrees C, n=9) or hypothermic (27 degrees C, n=9) cardiopulmonary bypass with terminal rewarming. A third group served as anesthetized normothermic non-cardiopulmonary bypass surgical controls (n=8). Basilar artery and descending thoracic aorta were isolated from each animal. In vitro vessel relaxation responses to increasing concentrations of acetylcholine (which induces endothelial release of nitric oxide) and nitroprusside (which provides exogenous nitric oxide) were measured in phenylephrine-precontracted vessel rings. RESULTS: There were no differences in vessel relaxation responses between normothermic and hypothermic cardiopulmonary bypass groups in basilar artery or aorta. In contrast, basilar arteries from non-cardiopulmonary bypass controls had increased relaxation responses to both acetylcholine (P=0.004) and nitroprusside (P=0.031) compared with the pooled cardiopulmonary bypass animal data. CONCLUSIONS: The authors observed no differences in endothelial or vascular smooth muscle function between normothermic and hypothermic cardiopulmonary bypass groups. Compared with non-cardiopulmonary bypass controls, cardiopulmonary bypass appeared to decrease basilar artery smooth muscle relaxation in response to endogenous and exogenous nitric oxide.

The effect of inhaled nitric oxide therapy on bleeding time and platelet aggregation in neonates.

The effect of inhaled nitric oxide (iNO) on bleeding time and platelet aggregation was studied in nine newborn infants with resolving pulmonary hypertension. Infants treated with iNO at 40 ppm for 30 minutes had bleeding times that were nearly twofold longer than those obtained 24 hours after iNO was discontinued. iNO had no effect on in vitro platelet aggregation studies.

Hemodynamic effects of L- and D-S-nitroso-beta,beta-dimethylcysteine in rats.

This study examined whether S-nitroso-beta,beta-dimethylcysteine (S-nitrosopenicillamine; SNPEN) may activate stereoselective S-nitrosothiol receptors within the vasculature. We examined 1) the hemodynamic effects produced by the L- and D-isomers of SNPEN (12.5-400 nmol/kg iv), the L- and D-isomers of the parent thiols [L- and D-penicillamine (PEN); 12.5-400 nmol/kg iv], and the nitric oxide (NO) donor sodium nitroprusside (SNP; 1-10 micrograms/kg iv) in conscious rats; 2) the hemodynamic effects produced by these compounds in urethan-anesthetized rats; and 3) the relative decomposition of L- and D-SNPEN to NO on addition to rat blood or cultured porcine aortic smooth muscle (PASM) cells. We found that 1) L-SNPEN was a more potent hypotensive and vasodilator agent within the mesenteric bed and within sympathetically intact and sympathetically denervated hindlimb beds of conscious rats than was D-SNPEN; 2) the hypotension and vasodilation produced by L-SNPEN was similar in conscious and anesthetized rats, whereas the effects of D-SNPEN and SNP were augmented by urethan-anesthesia; 3) L- and D-PEN did not affect hemodynamic parameters in conscious or anesthetized rats; and 4) L- and D-SNPEN decomposed equally to NO on addition to rat blood or PASM cells. These results suggest that the vasodilator effects of SNPEN involve the interaction of this S-nitrosothiol with stereoselective recognition sites within the vasculature and that urethan alters the mechanisms by which L- and D-SNPEN relax vascular smooth muscle.

Stereoselective actions of S-nitrosocysteine in central nervous system of conscious rats.

This study examined whether the stereoselective actions of S-nitrosocysteine (SNC) in the central nervous system involves the activation of stereoselective SNC recognition sites. We examined the effects produced by intracerebroventricular injection of the L- and D-isomers of SNC (L- and D-SNC) on mean arterial blood pressure, heart rate, and vascular resistances in conscious rats. We also examined the hemodynamic effects produced by intracerebroventricular injections of 1) L-cystine, the major non-nitric oxide (NO) decomposition product of L-SNC, 2) the parent thiols L- and D-cysteine, and 3) the bulky S-nitrosothiol L-S-nitroso-gamma-glutamylcysteinylglycine [L-S-nitrosoglutathione, (L-SNOG)]. Finally, we examined the decomposition of L- and D-SNC and L-SNOG to NO on their addition to brain homogenates. The intracerebroventricular injection of L-SNC (250-1,000 nmol) produced falls in mean arterial pressure, increases in heart rate, and a dose-dependent pattern of changes in hindquarter, renal, and mesenteric vascular resistances. The intracerebroventricular injections of D-SNC, L-cystine, and L-SNOG produced only minor effects. The intracerebroventricular injection of L-cysteine produced pressor responses and tachycardia, whereas D-cysteine was inactive. L- and D-SNC decomposed equally to NO on addition to brain homogenates. L-SNOG decomposed to similar amounts of NO as L- and D-SNC. These results suggest that SNC may activate stereoselective SNC recognition sites on brain neurons and that S-nitrosothiols of substantially different structure do not stimulate these sites. These recognition sites may be stereoselective membrane-bound receptors for which L-SNC is the unique ligand.

Actions of S-nitrosocysteine in the nucleus tractus solitarii are unrelated to release of nitric oxide.

Cardiovascular effects elicited by microinjection of L-S-nitrosocysteine in the nucleus tractus solitarii (NTS) were compared and contrasted with those produced by the dextroisomer, other nitric oxide donors and nitric oxide itself. L-S-nitrosocysteine produced dose-related decreases of arterial pressure and heart rate. In contrast, D-S-nitrosocysteine, S-nitrosoglutathione, glyceryl trinitrate, and sodium nitroprusside produced minimal responses that were not dose-related. Likewise, injection of cystine and nitric oxide, two products of S-nitrosocysteine breakdown, produced no significant response. Headspace analysis using chemiluminescence revealed that L- and D-S-nitrosocysteine released identical amounts of nitric oxide when exposed to homogenates of whole rat brain. Responses to L-S-nitrosocysteine were not affected by local injection of oxyhemoglobin or the nitric oxide synthase inhibitor L-nitroarginine methylester. Although injection of L-cysteine into the NTS produced responses similar to those seen with injection of L-S-nitrosocysteine, blockade of excitatory amino acid receptors with kynurenic acid inhibited responses to cysteine but not those to the nitrosothiol. The study demonstrates that S-nitrosocysteine is biologically active in the NTS. Its action is independent of release of nitric oxide from the nitrosothiol but may be mediated through stereoselective sites on target neurons.

L- and D-S-nitroso-beta,beta-dimethylcysteine differentially increase cGMP in cultured vascular smooth muscle cells.

We examined the effects of the L- and D-isomers of S-nitroso-beta,beta-dimethylcysteine (L- and D-S-nitrosopenicillamine, 10(-7)-10(-5) M) on the guanosine 3',5'-cyclic monophosphate (cGMP) content of cultured porcine aortic smooth muscle cells and the decomposition of these stereoisomers to nitric oxide (NO). L-S-nitrosopenicillamine was a more potent generator of cGMP than D-S-nitrosopenicillamine although both stereoisomers equally decomposed to NO. The 10(-7) M concentration of L- or D-S-nitrosopenicillamine did not generate detectable amounts of NO although 10(-7) M L-S-nitrosopenicillamine but not D-S-nitrosopenicillamine generated significant amounts of cGMP. This study shows that the stereoisomeric configuration of S-nitrosopenicillamine is an important factor in its biological potency. The data suggest that the extracellular or intracellular generation of NO is not the only mechanism by which this S-nitrosothiol generates cGMP in vascular smooth muscle.

Stereoselective S-nitrosocysteine recognition sites in rat brain.

We examined the effects of intracisternal (i.c.) injections (10-250 nmol) of the L- and D-isomers of S-nitrosocysteine (L- and D-S-nitrosocysteine) on the mean arterial blood pressure and heart rate of conscious rats, and the decomposition of L- and D-S-nitrosocysteine to nitric oxide (NO) upon addition to brain homogenates. The i.c. injection of L-S-nitrosocysteine produced initial falls in mean arterial blood pressure and heart rate which were followed by increases in these parameters. The i.c. injection of D-S-nitrosocysteine did not produce initial falls in mean arterial blood pressure or heart rate but produced the subsequent increases in these parameters. L- and D-S-nitrosocysteine decomposed equally to NO. These results suggest that the initial effects of L-S-nitrosocysteine may be due to the activation of stereoselective recognition sites on brain neurons.

Use-dependent loss of acetylcholine- and bradykinin-mediated vasodilation after nitric oxide synthase inhibition. Evidence for preformed stores of nitric oxide-containing factors in vascular endothelial cells.

In the present study, we examined the possibility that the endothelium-dependent vasodilators acetylcholine and bradykinin release preformed pools of nitric oxide-containing factors. Successive injections of selected doses of acetylcholine (1.18 +/- 0.3 micrograms/kg IV) or bradykinin (5 micrograms/kg IV) caused reproducible hypotensive and vasodilator responses within sympathetically intact and sympathetically denervated hindlimbs of conscious rats. After administration of the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV), the first injection of acetylcholine or bradykinin produced pronounced depressor and vasodilator responses that, in the case of bradykinin, were greater than those observed before L-NAME administration. However, each successive injection of acetylcholine and bradykinin produced progressively smaller responses, such that the later injections elicited a markedly diminished hypotension and vasodilation. This "use-dependent" loss of endothelium-dependent vasodilation was not due to the diminished vasorelaxant potency of nitric oxide-containing factors because the vasodilator effects of the nitric oxide donor sodium nitroprusside (32 micrograms/kg IV) and the S-nitrosothiol compound S-nitro-socysteine (200 nmol/kg IV) were augmented in the presence of L-NAME. These results suggest that the use-dependent loss of the hemodynamic effects of acetylcholine and bradykinin in L-NAME-treated rats may be due to the release and subsequent depletion of a factor whose synthesis depends on the bioavailability of nitric oxide. Taken together, these results suggest that preformed pools of nitric oxide-containing factors exist within the endothelium of resistance vessels and that endothelium-dependent agonists exert their vasorelaxant effects at least in part by the mobilization of these performed pools.

Hemodynamic effects of L- and D-S-nitrosocysteine in the rat. Stereoselective S-nitrosothiol recognition sites.

The vasorelaxant effects of the endothelium-derived relaxing factor S-nitrosocysteine (SNC) may not be simply due to its decomposition to NO. The biological actions of SNC may also involve the transnitrosation of amino acids in the blood and in plasma membranes. The possibility that the SNC moiety possesses biological activity prompted us to examine whether the hemodynamic effects of this S-nitrosothiol involves the activation of stereoselective S-nitrosothiol receptors within the cardiovascular system. We examined (1) the hemodynamic effects produced by intravenous injections of the L and D isomers of SNC (L- and D-SNC, respectively; 100 to 800 nmol/kg), the L and D isomers of the parent thiols (L- and D-cysteine, respectively; 100 to 800 nmol/kg), the oxidized thiol L-cystine (100 to 800 nmol/kg), and the NO donor sodium nitroprusside (SNP, 1 to 36 micrograms/kg) in conscious freely moving rats, (2) the baroreceptor reflex-mediated changes in heart rate elicited in response to the falls in arterial pressure produced by L- and D-SNC and SNP in conscious rats, and (3) the relative decomposition of L- and D-SNC to NO upon addition to heparinized rat blood or upon direct application to cultured porcine aortic smooth muscle (PASM) cells. We now report that (1) L-SNC is a more potent hypotensive and vasodilator agent within the mesenteric bed and sympathetically intact and sympathetically denervated hindlimb beds of conscious rats than is D-SNC, (2) L- and D-SNC markedly inhibit baroreceptor reflex-mediated tachycardia in conscious rats and D-SNC is considerably more effective than L-SNC, (3) the intravenous injections of L- and D-cysteine or L-cystine do not affect arterial blood pressure or vascular resistances, and (4) L- and D-SNC decompose equally to NO upon application to rat blood or cultured PASM cells. These results suggest that the hemodynamic effects of endogenous SNC may involve its interaction with stereoselective S-nitrosothiol recognition sites within the vasculature and the baroreflex arc. These findings provide tentative evidence that membrane-bound S-nitrosothiol receptors may exist within the cardiovascular system.

Nitric oxide inhibits aromatase activity: mechanisms of action.

NO synthase is present in human ovarian granulosa-luteal cells and NO inhibits estradiol secretion by granulosa cells in culture. These findings suggest that NO is an autocrine regulator of ovarian steroidogenesis. The purpose of this investigation was to explore the mechanisms through which NO exerts an inhibitory effect on cytochrome P450 aromatase activity. To examine the effect of NO on aromatase mRNA levels, human granulosa-luteal cells were cultured in the presence or absence of the NO donor SNAP for 16 h. Using a probe for human aromatase, Northern blots revealed a 26% decrease in aromatase mRNA in cells exposed to SNAP. Because this modest decrease in mRNA is unlikely to explain a rapid and profound reduction in estradiol secretion that we have observed, we looked for direct effects of NO on cytochrome P450 aromatase activity. Aromatase activity was assayed in placental microsomes and granulosa-luteal cells by measuring the release of 3H2O from [1 beta-3H] androstenedione. NO (10(-4)-10(-3)M), added as a saturated saline solution, reduced aromatase activity by as much as 90% in a concentration-dependent, non-competitive manner. In contrast, carbon monoxide (CO), a gas known to bind to the heme iron in aromatase, had no effect on aromatase activity when added alone nor could CO reverse the NO-induced inhibition of aromatase. These data suggest that NO binding to the heme is insufficient to inhibit aromatase activity. NO has been reported to alter protein function by reacting with the sulfhydryl group of cysteines, forming a nitrosothiol group. Because a cysteine sulfhydryl group is thought to participate in the catalytic mechanism of all P450 enzymes, experiments were designed to test whether NO might inhibit aromatase via such a mechanism. Addition of increasing amounts of mercaptoethanol, a chemical with free sulfhydryl groups, blocked the NO-induced inhibition of aromatase in microsomes. N-Ethylmaleimide, a chemical which covalently modifies sulfhydryl groups, reduced aromatase activity in a concentration-dependent manner. We conclude that NO inhibits aromatase both by decreasing mRNA for the enzyme and by an acute, direct inhibition of enzyme activity. We hypothesize that the direct inhibition occurs as a result of the formation of a nitrosothiol on the cysteine residue adjacent to the heme in aromatase.

Modulation of baroreceptor activity by nitric oxide and S-nitrosocysteine.

The goal of this study was to determine whether nitric oxide (NO) and the NO donor, S-nitrosocysteine (cysNO), modulate the activity of carotid sinus baroreceptors. Baroreceptor activity was recorded from the vascularly isolated carotid sinus in anesthetized rabbits. Baroreceptor activity decreased in a dose-dependent manner after injection of either NO or cysNO as constant pressure was maintained, and activity recovered spontaneously over time, within seconds to minutes. The baroreceptor pressure-activity relation was shifted significantly to the right by cysNO, with a profound suppression of activity at high pressure. Baroreceptor activity at 160 mm Hg averaged 76 +/- 8%, 60 +/- 6%, and 36 +/- 5% of the control maximum during exposure to 10(-4), 2 to 3 x 10(-4), and 10(-3) mol/L cysNO, respectively. The inhibition of activity by the L and D isomers of cysNO was equivalent and was blocked by reduced hemoglobin, suggesting that the effect was mediated by NO. The suppression of baroreceptor activity by cysNO was not related to vascular relaxation as measured by videomicrometer. Inhibition of soluble guanylate cyclase with methylene blue or 6-anilinoquinoline-5,8-quinone (LY83583, 10(-5) mol/L) did not attenuate and dibutyryl cGMP (10(-3) mol/L) did not mimic the suppression of baroreceptor activity by cysNO, suggesting a cGMP-independent mechanism. Activation of endogenous NO formation with thimerosal (10(-5) to 10(-4) mol/L) reduced maximum baroreceptor activity in five of eight experiments to 59 +/- 7% of the control maximum.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of the effect of anesthetic technique on reproductive success after laparoscopic pronuclear stage transfer. Propofol/nitrous oxide versus isoflurane/nitrous oxide.

BACKGROUND: Laparoscopic pronuclear stage transfer (PROST) is the preferred method of embryo transfer after in vitro fertilization in many infertility programs. There are scant data to recommend the use or avoidance of any particular anesthetic agent for use in women undergoing this procedure. The authors hypothesized that propofol would be an ideal anesthetic for laparoscopic PROST because of its characteristic favorable recovery profile that includes minimal sedation and a low incidence of postoperative nausea and vomiting. The purpose of the study was to compare propofol and isoflurance with respect to postanesthetic recovery and pregnancy outcomes after laparoscopic PROST. METHODS: One hundred twelve women scheduled for laparoscopic PROST were randomized to receive either propofol/nitrous oxide or isoflurane/nitrous oxide for maintenance of anesthesia. RESULTS: Visual analog scale scores for sedation were lower in the propofol group than in the isoflurance group at all measurements between 30 min and 3 h after surgery. More women experienced emesis and were given an antiemetic during recovery in the isoflurance group than in the propofol group. However, the percentage of pregnancies with evidence of fetal cardiac activity was 54% in the isoflurane group compared with only 30% in the propofol group (P = 0.023). Also, the ongoing pregnancy rate was greater in the isoflurane group than in the propofol group (54% vs. 29%, P = 0.014). CONCLUSIONS: Propofol/nitrous oxide anesthesia was associated with lower clinical and ongoing pregnancy rates compared with isoflurane/nitrous oxide anesthesia.