Peptidergic and nitrergic inhibitory neurotransmissions in the hamster jejunum: regulation of vasoactive intestinal peptide release by nitric oxide

Gut Microbiota in Ischemic Stroke: Role of Gut Bacteria-Derived Metabolites

Ischemic stroke (IS) remains a leading cause of death and long-term disability globally. Several mechanisms including glutamate excitotoxicity, calcium overload, neuroinflammation, oxidative stress, mitochondrial damage, and apoptosis are known to be involved in the pathogenesis of IS, but the underlying pathophysiology mechanisms of IS are not fully clarified. During the past decade, gut microbiota were recognized as a key regulator to affect the health of the host either directly or via their metabolites. Recent studies indicate that gut bacterial dysbiosis is closely related to hypertension, diabetes, obesity, dyslipidemia, and metabolic syndrome, which are the main risk factors for cardiovascular diseases. Increasing evidence indicates that IS can lead to perturbation in gut microbiota and increased permeability of the gut mucosa, known as "leaky gut," resulting in endotoxemia and bacterial translocation. In turn, gut dysbiosis and impaired intestinal permeability can alter gut bacterial metabolite signaling profile from the gut to the brain. Microbiota-derived products and metabolites, such as short-chain fatty acids (SCFAs), bile acids (BAs), trimethylamine N-oxide (TMAO), lipopolysaccharides (LPS), and phenylacetylglutamine (PAGln) can exert beneficial or detrimental effects on various extraintestinal organs, including the brain, liver, and heart. These metabolites have been increasingly acknowledged as biomarkers and mediators of IS. However, the specific role of the gut bacterial metabolites in the context of stroke remains incompletely understood. In-depth studies on these products and metabolites may provide new insight for the development of novel therapeutics for IS.

Inhibitory Neural Regulation of the Ca 2+ Transients in Intramuscular Interstitial Cells of Cajal in the Small Intestine

Gastrointestinal motility is coordinated by enteric neurons. Both inhibitory and excitatory motor neurons innervate the syncytium consisting of smooth muscle cells (SMCs) interstitial cells of Cajal (ICC) and PDGFRα+ cells (SIP syncytium). Confocal imaging of mouse small intestines from animals expressing GCaMP3 in ICC were used to investigate inhibitory neural regulation of ICC in the deep muscular plexus (ICC-DMP). We hypothesized that Ca2+ signaling in ICC-DMP can be modulated by inhibitory enteric neural input. ICC-DMP lie in close proximity to the varicosities of motor neurons and generate ongoing Ca2+ transients that underlie activation of Ca2+-dependent Cl- channels and regulate the excitability of SMCs in the SIP syncytium. Electrical field stimulation (EFS) caused inhibition of Ca2+ for the first 2-3 s of stimulation, and then Ca2+ transients escaped from inhibition. The NO donor (DEA-NONOate) inhibited Ca2+ transients and Nω-Nitro-L-arginine (L-NNA) or a guanylate cyclase inhibitor (ODQ) blocked inhibition induced by EFS. Purinergic neurotransmission did not affect Ca2+ transients in ICC-DMP. Purinergic neurotransmission elicits hyperpolarization of the SIP syncytium by activation of K+ channels in PDGFRα+ cells. Generalized hyperpolarization of SIP cells by pinacidil (KATP agonist) or MRS2365 (P2Y1 agonist) also had no effect on Ca2+ transients in ICC-DMP. Peptidergic transmitter receptors (VIP and PACAP) are expressed in ICC and can modulate ICC-DMP Ca2+ transients. In summary Ca2+ transients in ICC-DMP are blocked by enteric inhibitory neurotransmission. ICC-DMP lack a voltage-dependent mechanism for regulating Ca2+ release, and this protects Ca2+ handling in ICC-DMP from membrane potential changes in other SIP cells.

Purinergic neuromuscular transmission in the gastrointestinal tract; functional basis for future clinical and pharmacological studies

Nerve-mediated relaxation is necessary for the correct accomplishment of gastrointestinal (GI) motility. In the GI tract, NO and a purine are probably released by the same inhibitory motor neuron as inhibitory co-transmitters. The P2Y1 receptor has been recently identified as the receptor responsible for purinergic smooth muscle hyperpolarization and relaxation in the human gut. This finding has been confirmed in P2Y1 -deficient mice where purinergic neurotransmission is absent and transit time impaired. However, the mechanisms responsible for nerve-mediated relaxation, including the identification of the purinergic neurotransmitter(s) itself, are still debatable. Possibly different mechanisms of nerve-mediated relaxation are present in the GI tract. Functional demonstration of purinergic neuromuscular transmission has not been correlated with structural studies. Labelling of purinergic neurons is still experimental and is not performed in routine pathology studies from human samples, even when possible neuromuscular impairment is suspected. Accordingly, the contribution of purinergic neurotransmission in neuromuscular diseases affecting GI motility is not known. In this review, we have focused on the physiological mechanisms responsible for nerve-mediated purinergic relaxation providing the functional basis for possible future clinical and pharmacological studies on GI motility targeting purine receptors.

Nitrergic inhibition of tachykininergic neuro-muscular transmission via cyclic GMP in the hamster ileum

The present study was designed to explore the inhibitory mechanism by nitric oxide (NO) of the tachykininergic neuro-muscular transmissions in the hamster ileum. In the presence of guanethidine (1 µM), atropine (0.5 µM), nifedipine (0.1 µM) and apamin (100 nM), electrical field stimuli (EFS; 0.5 ms duration, 15 V) evoked non-adrenergic, non-cholinergic excitatory junction potentials (EJPs) in circular smooth muscle cells. The EJPs were markedly inhibited by the tachykinin NK1 receptor antagonists [D-Pro(4), D-Trp(7,9)]-SP(4-11) (3 µM). Both the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 200 µM) and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 µM), did not affect on the resting membrane potentials, but enhanced the tachykininergic EJPs. In the presence of L-NAME (200 µM), exogenously applied NO (10 µM) and the membrane permeable analogue of guanosine 3',5'-cyclic monophosphate (cGMP), 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP, 3 mM), significantly inhibited the tachykininergic EJPs. Application of EFS (0.5 msec duration, 15 V) with trains of 20 pulses at 20 Hz increased amount of released substance P (SP). The release of SP was further increased by the treatment of L-NAME or ODQ, but markedly reduced by exogenously applied NO and 8-Br-cGMP. These results suggest that the endogenous NO may inhibit the tachykininergic neuro-muscular transmissions by the decrease of SP release from the tachykininergic neurons, possibly through a guanylate cyclase-cGMP-dependent mechanism in the hamster ileum.

Inhibitory purinergic transmission in mouse caecum: role for P2Y1 receptors as prejunctional modulators of ATP release

Using conventional microelectrode recording techniques, we investigated, in the circular muscle of the mouse caecum, the neurotransmitter(s) involved in the neurally-evoked inhibitory junction potentials (IJPs) and the existence of possible prejunctional mechanisms controlling neurotransmitter release. Electrical field stimulation with single pulses elicited IJPs, consisting only of a "fast" hyperpolarization, while using train stimuli (30-50 Hz) the initial fast hyperpolarization was followed by a slower hyperpolarization. The fast and the slow component were selectively antagonized by apamin, a blocker of calcium-activated potassium channels, and N(omega)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, respectively. Fast IJPs were antagonized also by P2 purinoceptor antagonists, suramin or 4-[[4-formyl-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-2-pyridinyl]azo]-1,3-benzenedisulfonic acid tetrasodium salt (PPADS), P2Y purinoceptor desensitization by adenosine 5'-O-2-thiodiphosphate (ADPbetaS). 2'-Deoxy-N(6)-methyl ADP diammonium salt (MRS 2179), P2Y1 purinoceptor antagonist, at the concentration of 1 microM increased the amplitude of the fast IJP, while at the concentration of 10 microM induced a reduction. 8,8'-[Carbonylbis[imino-3,1-phenylenecarbonylimino (4-fluoro-3,1-phenylene) carbonylimino]] bis-1,3,5-naphthalenetrisulfonic acid hexasodium salt (NF 157) and 2,2-dimethyl-propionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethyl-propionyl-oxymethyl)-propyl ester (MRS 2395), P2Y11 and P2Y12 purinoceptor antagonist, were without any effect. ATP-induced hyperpolarization was affected by apamin and by P2Y purinoceptor desensitization, but not by MRS 2179. 2-(Methylthio)ATP tetrasodium salt hydrate (2-MeSATP), P2Y1 purinoceptor agonist, at a concentration which did not cause changes in the membrane potential, reduced the amplitude of the fast IJPs. This effect was prevented by MRS 2179. Paired nerve stimulation, either using single pulses or train stimuli, did not cause any alteration of the second-evoked IJP. In conclusion, in the circular muscle of the mouse caecum, ATP is responsible for the fast IJP while nitric oxide is responsible for the slow IJP. ATP-mediated response is dependent on ADPbetaS-sensitive P2Y receptors, which are in part P2Y1, but not P2Y11 or P2Y12 receptor subtypes. In addition, the most substantial finding of this study is the functional demonstration that ATP released by nerve stimulation activates P2Y1 receptors, located prejunctionally, limiting its release by motoneurons.

Evidence for a role of inducible nitric oxide synthase in gastric relaxation of mdx mice

Alterations of gastric mechanical activity have been reported in mdx mouse, animal model for Duchenne muscular dystrophy. This study examined if alterations in the vasoactive intestinal polypeptide (VIP) system are present in mdx stomach. Gastric mechanical activity was recorded in vitro as changes of endoluminal pressure and neurally or pharmacologically evoked relaxations were analysed in mdxvs normal stomach. Reverse-transcription polymerase chain reaction was used to detect inducible nitric oxide synthase (iNOS) expression. Relaxations to sodium nitroprusside in mdx stomach showed no difference in comparison with normal preparations. In normal stomach, VIP produced relaxation, which was reduced by VIP6-28, antagonist of VIP receptors, but was not modified by Nomega-nitro-L-arginine methyl ester (L-NAME), 1-H-oxodiazol-[1,2,4]-[4,3-a]quinoxaline-1-one (ODQ) or by N-(3-(aminomethyl)-benzyl)acetamidine (1400W) and aminoguanidine, inhibitors of iNOS. In contrast, in mdx stomach VIP responses were antagonized not only by VIP6-28, but also by L-NAME, ODQ, 1400W or aminoguanidine. In normal stomach, the slow relaxation evoked by stimulation at high frequency was reduced by VIP6-28, but it was unaffected by 1400W or aminoguanidine. In mdx stomach, it was reduced by VIP6-28 or 1400W, which did not show additive effects. iNOS mRNA was expressed only in mdx stomach. The results suggest that in mdx gastric preparations, iNOS is functionally expressed, being involved in the slow relaxation induced by VIP.

Beneficial effects of vasodilators in preventing severe acute pancreatitis shock

OBJECTIVES

To investigate the effect of treatment with several vasodilatory substance on the changes in mean arterial pressure (MAP) of severe acute pancreatitis.

METHODS

Pancreatitis was induced in rats by 5% sodium taurocholate retrograde infusion through the pancreatic duct, which produces a significant decrease in arterial blood pressure.

RESULTS

Three hours after the induction of pancreatitis, a fall of approximately 25 mm Hg in MAP was observed, with no changes of MAP in untreated controls. The administration of the nitric oxide synthesis inhibitor, N-nitro-L-arginine methyl ester (25 mg/kg), previously to the induction of pancreatitis, produced a marked fall in MAP leading to the death of all the animals. When several vasodilatory substances, S-nitroso-N-acetylpenicillamine (200 microg x kg x h), calcitonin gene-related peptide (10 microg/kg), and vasoactive intestinal polypeptide (8 microg x kg x h) were administered previously to the induction of pancreatitis, the MAP fall induced by pancreatitis was not observed. The improvement of physiological conditions observed in vasodilator-treated animals is in agreement with histological data, which show only minor structural changes in the pancreas from these animals, in contrast with the severe alterations observed in untreated pancreatitic rats.

CONCLUSION

: Vasodilation confers protection against the systemic circulatory derangement derived from the development of severe acute pancreatitis.

Gastrointestinal function regulation by nitrergic efferent nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Measurement of the propelled liquid by isolated hamster ileum as a parameter to evaluate peristalsis

We present a method to measure the volume of liquid propelled by peristaltic movements of isolated hamster ileum as a novel means to assess peristaltic activity. The oral and aboral ends of the dissected ileum were attached to cannulas fixed horizontally. The application of intraluminal pressure by raising the level of liquid in the bottle connected to the oral end evoked peristalsis and intermittent propulsion of the intraluminal liquid. The inhibition of intrinsic neurons by tetrodotoxin stopped propulsion; this indicated that the liquid propulsion was correlated with neuron-regulated peristalsis. The volume of liquid propelled by one complete peristaltic movement was significantly greater than that by incomplete peristalsis, whereas recordings of pressure changes were indistinguishable. Inhibitors of nitric oxide synthase decreased the volume of liquid propelled by peristaltic movements, suggesting a role of nitrergic neurons in peristalsis. Our data show that the method described above might be suitable for analyzing peristalsis.

Mediators of non-adrenergic non-cholinergic inhibitory neurotransmission in porcine jejunum

The purpose of this study was to determine the non-adrenergic non-cholinergic inhibitory neurotransmitter in pig jejunum. Intracellular electrical activity was recorded from circular smooth muscle cells. Inhibitory junction potentials (IJPs) evoked by electrical field stimulation were inhibited by tetrodotoxin (1 micromol L(-1)), omega-conotoxin GVIA (0.1 micromol L(-1)) tetrodotoxin, apamin (1 micromol L(-1)), 1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U-73122; 10 micromol L(-1)) but not by N omega-nitro-l-arginine (l-NNA; 100 micromol L(-1)), haemoglobin (10 micromol L(-1)), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 micromol L(-1)) or 9-(tetrahydro-2-furyl)adenine (SQ-22536; 10 micromol L(-1)). S-nitroso-N-acetylpenicillamine (SNAP) hyperpolarized the membrane potential. This was inhibited by ODQ (3 micromol L(-1)) and charybdotoxin (0.1 micromol L(-1)). Adenosine-5-triphosphate (ATP; 100 micromol L(-1)) and 2-methylthio ATP (2-MeS-ATP; 100 micromol L(-1)) did not hyperpolarize the membrane potential and 6-N-N-diethyl-beta- gamma -dibromomethylene-d-adenosine-5'-triphosphate (ARL67156; 100 micromol L(-1)) did not modify IJPs. Carbon monoxide (CO; 10%) and tricarbonyl dichlororuthenium dimer ([Ru(CO3Cl2)]2; 100 micromol L(-1)) hyperpolarized the membrane potential however zinc, copper and tin protoporphyrin IX (100 micromol L(-1)) did not alter IJPs. Vasoactive intestinal peptide (VIP) hyperpolarized the membrane potential but 4-Cl-d-Phe6-Leu17-VIP (1 micromol L(-1)) did not modify IJPs. Pituitary adenylate cyclase activating peptide (PACAP)38 (0.5 micromol L(-1)) hyperpolarized the membrane potential. This was inhibited by apamin (1 micromol L(-1)) but not by tetrodotoxin (1 micromol L(-1)). Pituitary adenylate cyclase activating peptide6-38 (1 micromol L(-1)) inhibited IJPs. These data suggest that inhibitory neurotransmission in pig jejunum is mediated partly by PACAP.

Inhibitory pathways in the circular muscle of rat jejunum

1. Conflicting data have been reported on the contribution of nitric oxide (NO) to inhibitory neurotransmission in rat jejunum. Therefore, the mechanism of relaxation and contribution to inhibitory neurotransmission of NO, adenosine 5'-triphosphate (ATP), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) was examined in the circular muscle of Wistar-Han rat jejunum. 2. Mucosa-free circular muscle strips were precontracted with methacholine in the presence of guanethidine and exposed to electrical field stimulation (EFS) and exogenous NO, ATP, VIP and PACAP. All stimuli induced reduction of tone and inhibition of phasic motility. Only electrically induced responses were sensitive to tetrodotoxin (3 x 10(-6) m). 3. NO (10(-6)-10(-4) m)-induced concentration-dependent relaxations that were inhibited by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ; 10(-5) m) and the small conductance Ca(2+)-activated K(+)-channel blocker apamin (APA; 3 x 10(-8) m). 4. Relaxations elicited by exogenous ATP (10(-4)-10(-3) m) were inhibited by the P2Y purinoceptor antagonist reactive blue 2 (RB2; 3 x 10(-4) m), but not by APA and ODQ. 5. The inhibitory responses evoked by 10(-7) m VIP and 3 x 10(-8) m PACAP were decreased by the selective PAC(1) receptor antagonist PACAP(6-38) (3 x 10(-6) m) and APA. The VPAC(2) receptor antagonist PG99-465 (3 x 10(-7) m) reduced relaxations caused by VIP, but not those by PACAP, while the VPAC(1) receptor antagonist PG97-269 (3 x 10(-7) m) had no influence. 6. EFS-induced relaxations were inhibited by the NO-synthase inhibitor N(omega)-nitro-l-arginine methyl ester (3 x 10(-4) m), ODQ and APA, but not by RB2, PG97-269, PG99-465 and PACAP(6-38). 7. These results suggest that NO is the main inhibitory neurotransmitter in the circular muscle of Wistar-Han rat jejunum acting through a rise in cyclic guanosine monophosphate levels and activation of small conductance Ca(2+)-dependent K(+) channels.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

NANC inhibitory neurotransmission in mouse isolated stomach: involvement of nitric oxide, ATP and vasoactive intestinal polypeptide

1. The neurotransmitters involved in NANC relaxation and their possible interactions were investigated in mouse isolated stomach, recording the motor responses as changes of endoluminal pressure from whole organ. 2. Field stimulation produced tetrodotoxin-sensitive, frequency-dependent, biphasic responses: rapid transient relaxation followed by a delayed inhibitory component. 3. The inhibitor of the synthesis of nitric oxide (NO), l-NAME, abolished the rapid relaxation and significantly reduced the slow relaxation. Apamin, blocker of Ca2+-dependent K+ channels, or ADPbetaS, which desensitises P2y purinoceptors, reduced the slow relaxation to 2-8 Hz, without affecting that to 16-32 Hz or the fast relaxation. alpha-Chymotrypsin or vasoactive intestinal polypeptide 6-28 (VIP6-28), antagonist of VIP receptors, failed to affect the fast component or the delayed relaxation to 2-4 Hz, but antagonised the slow component to 8-32 Hz. 4. Relaxation to sodium nitroprusside was not affected by l-NAME, apamin or ADPbetaS, but was reduced by alpha-chymotrypsin or VIP6-28. Relaxation to VIP was abolished by alpha-chymotrypsin, antagonised by VIP6-28, but was not affected by l-NAME, apamin or ADPbetaS. Relaxation to ATP was abolished by apamin, antagonised by ADPbetaS, but was not affected by l-NAME or alpha-chymotrypsin. 5. The present results suggest that NO is responsible for the rapid relaxation and partly for the slow relaxation. ATP is involved in the slow relaxation evoked by low frequencies of stimulation. VIP is responsible for the slow relaxation evoked by high frequencies of stimulation. The different neurotransmitters appear to work in parallel, although NO could serve also as a neuromodulator that facilitates release of VIP.

Age-related alterations in soluble guanylyl cyclase and cGMP pathway in spontaneously hypertensive rats

BACKGROUND

Vascular contractility and blood pressure (BP) are regulated by soluble guanylyl cyclase (sGC) and cyclic guanosine monophosphate (cGMP) pathway, which can be influenced by heme oxygenase (HO)-derived carbon monoxide (CO). The age-related changes in sGC/cGMP pathway in tail artery smooth muscle cells (SMCs) in hypertension have not been systematically investigated.

METHODS

In the present study, spontaneously hypertensive rats (SHR) of 4, 8, and 20 weeks old were used. The basal and hemin-modulated levels of sGC and cGMP in tail artery tissues were examined.

RESULTS

Although BP of 20-week SHR was significantly elevated, sGC and cGMP levels were unaltered compared with age-matched Wistar-Kyoto rats (WKY). The levels of sGC and cGMP were significantly lower in 4- and 8-week SHR compared with age-matched WKY although BP of 4-week SHR was normotensive. Hemin administration resulted in a significant decrease in BP in 8-week (158.7 +/- 2.4 versus 123.5 +/- 1.3 mmHg, P < 0.01), but not in pre-hypertensive (4 weeks) or 20-week SHR or WKY at all ages. Coincidently, sGC and cGMP levels in 8-week SHRs were significantly elevated and so did the expression levels of HO-1. Hemin treatment did not increase the cyclic adenosine monophosphate (cAMP) content of tail artery from 8-week SHR. The constitutive HO-2 levels remained unchanged in 8- and 20-week SHR and age-matched WKY.

CONCLUSION

The HO-activity inhibitor, chromium mesoporphyrin, abolished the BP-lowering and HO- stimulating effects of hemin in young SHR. Our results suggest that alteration in sGC/cGMP pathway in vascular SMCs precedes the occurrence of hypertension but returns to normal once hypertension is fully manifested.

Induction of heme oxygenase-1 and stimulation of cGMP production by hemin in aortic tissues from hypertensive rats

Heme oxygenase (HO) and carbon monoxide (CO) have been implicated in the modulation of various cardiovascular functions including blood pressure (BP) regulation. Up-regulating the HO/CO system lowers BP in young (8-week-old) but not in adult (20-week-old) spontaneously hypertensive rats (SHRs). The mechanisms for this selective effect are largely unknown. We investigated the effects of HO-1 inducer, hemin, on the HO/CO-soluble gyanylyl cyclase (sGC)/cGMP system in the aorta of prehypertensive (4-week-old) young and adult SHRs as well as age-matched Wistar-Kyoto rats (WKYs). Reduced expressions of HO-1, HO-2, and sGC proteins associated with depressed HO activity and cGMP levels were detected in young SHRs. These deficiencies were significantly reversed by hemin treatment. Macrophage infiltration of vascular tissues was more significant in adult SHRs than adult WKYs, but invisible in young SHRs and WKYs. Hemin treatment did not alter macrophage infiltration of vascular tissues in young SHRs. The same hemin administration resulted in a significant decrease in BP (from 148.6 +/- 3.2 to 125.8 +/- 2.6 mmHg, P <.01) in young SHRs, but not in prehypertensive or adult SHRs or WKYs of all ages. The HO inhibitor zinc protoporphyrin abrogated the hemin effect in young SHRs. Aortic tissues became desensitized to YC-1, an activator sGC, in adult SHRs. Thus, in young SHRs the expression and function of the HO/CO-sGC/cGMP system were suppressed, constituting a pathogenic mechanism for the development of hypertension. In adult SHRs, the HO/CO-sGC/cGMP system appeared normal, but desensitization of the sGC/cGMP pathway caused hypertension to prevail.

Nitrergic prejunctional inhibition of purinergic neuromuscular transmission in the hamster proximal colon

Neurogenic ATP and nitric oxide (NO) may play important roles in the physiological control of gastrointestinal motility. However, the interplay between purinergic and nitrergic neurons in mediating the inhibitory neurotransmission remains uncertain. This study investigated whether neurogenic NO modulates the purinergic transmission to circular smooth muscles of the hamster proximal colon. Electrical activity was recorded from circular muscle cells of the hamster proximal colon by using the microelectrode technique. Intramural nerve stimulation with a single pulse evoked a fast purinergic inhibitory junction potential (IJP) followed by a slow nitrergic IJP. The purinergic component of the second IJP evoked by paired stimulus pulses at pulse intervals between 1 and 3 s became smaller than that of the first IJP. This purinergic IJP depression could be observed at pulse intervals <3 s, but not at longer ones, and failed to occur in the presence of NO synthase inhibitor. Exogenous NO (0.3-1 microM), at which no hyperpolarization is produced, inhibited purinergic IJPs, without altering the nitrergic IJP and exogenously applied ATP-induced hyperpolarization. In the presence of both purinoceptor antagonist and nitric oxide synthase (NOS) inhibitor, intramural nerve stimulation with 5 pulses at 20 Hz evoked vasoactive intestinal peptide (VIP)-associated IJPs, suggesting that VIP component may be masked in the IJPs of the hamster proximal colon. Our results suggest that neurogenic NO may modulate the purinergic transmission to circular smooth muscles of the hamster proximal colon via a prejunctional mechanism. In addition, VIP may be involved in the neurotransmitter in the hamster proximal colon.