Investigation of the interaction between cholinergic and nitrergic neurotransmission in the pig gastric fundus

Berberine ameliorates the neurological dysfunction of the gastric fundus by promoting calcium channels dependent release of ACh in STZ-induced diabetic rats

Background

It has been reported diabetic gastroparesis is related to diabetic autonomic neuropathy of the gastrointestinal tract, and berberine (BBR) could ameliorate diabetic central and peripheral neuropathy. However, the influence of BBR on the function and motility of the gastric fundus nerve is unclear.

Methods

A diabetic rat model was constructed, and HE staining was used to observe the morphological changes in the gastric fundus. The changes in cholinergic and nitrogen-related neurochemical indexes and the effects of BBR on them were measured using Elisa. The effects of BBR on the neural function and motility of gastric fundus were investigated by electric field stimulation (EFS) induced neurogenic response in vitro.

Results

In the early stage of STZ-induced diabetic rats, the contractile response of gastric fundus induced by EFS was disorder, disturbance of contraction amplitude, and the cell bodies of neurons in the myenteric plexus of gastric fundus presented vacuolar lesions. Administration with BBR could improve the above symptoms. BBR further enhanced the contraction response in the presence of a NOS inhibitor or the case of inhibitory neurotransmitters removal. Interestingly, the activity of ACh could affect NO release directly and the enhancement of BBR on contractile response was canceled by calcium channel blockers completely.

Conclusions

In the early stage of STZ-induced diabetic rats, the neurogenic contractile response disorder of the gastric fundus is mainly related to cholinergic and nitrergic nerve dysfunction. BBR promotes the release of ACh mainly by affecting the calcium channel to improve the neurological dysfunction of the gastric fundus.

Quercetin relaxes human gastric smooth muscles directly through ATP-sensitive potassium channels and not depending on the nitric oxide pathway

BACKGROUND

Quercetin has recently become a remarkably popular subject of research due to its broad beneficial pharmacological properties. The goal of our study was to observe its effects on contractility of human gastric smooth muscles in reference to the NO pathway and direct influence of potassium channels.

METHODS

Tissues were obtained from patients undergoing sleeve gastrectomy due to morbid obesity (n = 10 aged 24-56; BMI 47.16 ± 1.84). The following parameters were evaluated in the recordings: area under the curve (AUC), average baseline muscle tone, and relative change in muscle contraction.

KEY RESULTS

Quercetin induced noticeable, dose-dependent relaxation of the carbachol treated gastric strips. The substantial effect was noted at concentrations higher than 10^-7  mol/L and maximal at 10^-4  mol/L (81.82 ± 3.32%; n = 10; p < 0.0001) of the control. Neither NOS blockers nor guanylyl cyclase blockers had inhibitory effects on the relaxation of strips induced by examined polyphenol. Glibenclamide inhibited the relaxing effect of quercetin, significant at concentrations higher than 5⋅10^-5  mol/L. Preincubation with charybdotoxin or apamin extended the relaxing effect of quercetin (from 10^-6  mol/L). Tamoxifen, in turn, significantly increased muscle relaxation at all quercetin concentrations.

CONCLUSIONS & INFERENCES

In conclusion, the current study was the first to show that quercetin-induced relaxation of human gastric smooth muscle occurs directly through K⁺_ATP channels and independently to NO pathways. The present results suggest that quercetin is a potential nutraceutical in the treatment of functional gastrointestinal dyspepsia and other minor gastric muscle motility disturbance.

Acetylcholine exerts inhibitory and excitatory actions on mouse ileal pacemaker activity: role of muscarinic versus nicotinic receptors

The effect of acetylcholine (ACh) on pacemaking and spontaneous contractions in the gastrointestinal tract is not well characterized. The current study aims to profile the effect of several muscarinic and nicotinic receptor agonists and antagonists on pacemaker potentials in the ICR mouse ileum. Pacemaker potentials of whole thickness mouse ileal segments were recorded extracellularly using a 60-channel microelectrode array (MEA) platform. A spatiotemporal analysis integrated the frequency, amplitude, and velocity measurements of pacemaker currents. Comparative data were obtained by recording spontaneous smooth muscle tone in a conventional organ bath. On the MEA, ACh (0.3-300 μM) and bethanechol (0.3-300 μM) significantly reduced ileal pacemaker potentials. The inhibitory effect of ACh was mimicked by donepezil (300 μM) but not nicotine (0.3-7 mM). Atropine (300 μM), but not hexamethonium (300 μM), reversed the inhibitory actions of ACh and bethanechol and revealed excitatory properties manifested as increases in pacemaker frequency. A spatial analysis also revealed that atropine, but not hexamethonium, reversed the ACh-induced distortion of pacemaker propagation activity. Atropine (0.001-3 mM) and hexamethonium (0.3-7 mM) alone were inactive. In the organ bath, ACh (300 nM) and bethanechol (30 μM) induced ileal tonic contractions, while inhibiting basal spontaneous contractions at 300 μM. Atropine (1 μM), but not hexamethonium (1-300 μM), reversed both the tonic contractions and the inhibition of the spontaneous contractions of ACh and bethanechol and revealed an excitatory effect manifested as an increasing in the frequency of contractions. Muscarinic, but not nicotinic, receptors appear to mediate the inhibitory actions of ACh on mouse ileal pacemaker potentials.NEW & NOTEWORTHY The study discovered an acute action of acetylcholine on pacemaker potentials that is mediated by muscarinic receptors on the mouse ileum. Bethanechol, but not nicotine, mimicked the inhibitory actions of acetylcholine on pacemaker potentials. Atropine, but not hexamethonium, reversed the inhibitory actions of acetylcholine. When introduced after acetylcholine, atropine exhibited excitatory actions that increased the pacemaker frequency. Acetylcholine and bethanechol distorted the propagation activity and pattern, and this was also reversed by atropine. These actions of acetylcholine on pacemaker potentials may contribute to pathophysiology in bowel diseases.

Contribution of endogenous nitrergic and peptidergic influences to the altered neurally-induced gastric contractile responses in strips from dystrophic (mdx) mice

Gastrointestinal motor disorders have been reported to occur in dystrophic (mdx) mice. The aim of the present study was to investigate the contribution of endogenous nitrergic and peptidergic components to the gastric contractile responses in strips from wild type (WT) and mdx mice. In both preparations, electrical field stimulation (EFS) induced frequency-dependent excitatory responses that were abolished by atropine or tetrodotoxin. The amplitude of the neurally-induced contractile responses was greater in strips from mdx mice in respect to the WT ones. In both preparations, at the end of the stimulation period strip tension decayed below the pre-stimulus level (off-relaxations). The nitric oxide (NO) synthesis inhibitor L-NNA increased the amplitude of the EFS-induced contractile responses without influencing off-relaxations. alpha-chymotrypsin and PACAP 6-38 abolished off-relaxations and also caused a reduction in amplitude of the contractile responses, whereas VIP receptor antagonists were ineffective. The efficacy of L-NNA, alpha-chymotrypsin or PACAP 6-38 on the excitatory responses was lower in strips from mdx mice in respect to the WT ones. alpha-chymotrypsin, in the presence of L-NNA, was no longer able to decrease the amplitude of the neurally-induced contractile responses but still abolished off-relaxations in both preparations. Direct muscular responses to methacholine were similar in amplitude in the two preparations and were not influenced by L-NNA or alpha-chymotrypsin. The results indicate that both endogenous NO and peptides influence the EFS-induced cholinergic responses: a stronger peptidergic modulatory action on a weaker nitrergic neurotransmission is suggested to occur in strips from mdx mice in respect to the WT ones and to contribute to the altered gastric contractile responses.

Investigation of fundo-antral reflex in human beings

AIM: To examine the sensory and motor response(s) of the stomach following fundic distention and to assess whether cholinergic mechanisms influence these responses.

METHODS: Fundic tone, gastric sensory responses and antral motility were evaluated in eight healthy volunteers after a probe with two sensors was placed in the antrum and a highly compliant balloon in the fundus. Isobaric balloon distentions were performed with a barostat. Study was repeated in six volunteers after intravenous atropine was given.

RESULTS: Fundic distention induced large amplitude antral contractions in all subjects. The area under the curve was higher (P<0.05) during fundic distention. First sensation was reported at 12±4 mmHg, moderate sensation at 18±4 mmHg and discomfort at 21±4 mmHg. Discomfort was associated with a decrease in antral motility. After atropine was given, the area under the curve of pressure waves and fundic tone decreased (P<0.05). Sensory thresholds were not affected.

CONCLUSIONS: Fundic balloon distention induces an antral motor response, the fundo-antral reflex, which in part may be mediated by cholinergic mechanisms.

Pharmacological characterization of pre- and postsynaptic prostanoid receptors in pig gastric fundus

This study characterized the subtype of prostanoid receptors on the cholinergic neurones and smooth muscle cells in circularly oriented muscle strips of the pig gastric fundus. Tissues were electrically stimulated (40 V, 4 Hz, 0.25 ms, 2 min) to induce tritium outflow after incubation with [3H]-choline. Indomethacin increased the electrically induced tritium outflow, suggesting an inhibitory effect of endogenous prostanoids. In the presence of indomethacin, PGE2 > PGF2alpha >PGI2 inhibited tritium release while the TP-receptor agonist U-46619 and PGD2 had no effect. The EP2-receptor agonist butaprost had no effect while the EP1- and EP3-receptor agonist sulprostone mimicked the effect of PGE2. The effect of sulprostone was not affected by AH 6809, that antagonizes EP1- and EP2-receptors, suggesting the presence of presynaptic EP3-receptors on the cholinergic nerve endings. All prostanoid receptor agonists, except butaprost, contracted the tissues concentration-dependently; the rank order of potency (U-46619 > sulprostone > PGE2 > PGF2alpha > PGD2 = PGI2) suggests the presence of TP- and EP1- and EP3-receptors on the circular smooth muscle cells.

Effects of gastric electrical field stimulation with long pulses on gastric emptying in dogs

The aim was to investigate the effects of electrical field stimulation (EFS) with long and short pulses on gastric emptying, gastric contractility and vagal activity in dogs. Sixteen dogs were equipped with a duodenal cannula, electrodes and strain gauges (10 dogs) in the stomach. Each dog was fed with Ensure and gastric effluent was collected from the cannula. Electrical stimulation was applied via two electrodes (about 12 cm apart, one in the corpus and the other in the antrum) with long pulses (a frequency of 6 cycles min-1, pulse amplitude of 6 mA and width of 100 ms) in 10 dogs and with short pulses (frequency of 30 Hz and pulse width of 300 micros) in six dogs. The electrocardiogram was also recorded and heart rate variability was derived to assess the vagal activity. It was found that: (i). EFS with long pulses did not alter gastric emptying during stimulation but increased gastric emptying during the 45 min immediately after stimulation; (ii). EFS with long pulses increased gastric contractility in both proximal and distal antrum during and after the stimulation; (iii). EFS with long pulses resulted in an increase in vagal tone during the 45 min immediately after stimulation. However, there is no difference during the 45 min period of stimulation; (iv). EFS with short pulses had no effect on gastric emptying. We concluded that long pulse gastric electrical field stimulation with one electrode in the corpus and the other electrode in the antrum has postponed effects on gastric emptying of liquid, gastric contractility and vagal activity.

Prejunctional modulation of non-adrenergic non-cholinergic (NANC) inhibitory responses in the isolated guinea-pig gastric fundus

The inhibitory neurotransmission of the stomach was investigated in isolated guinea-pig gastric fundus. In preparations treated with guanethidine (1 micro mol L-1) and p-fluoro-hexahydro-sila-difenidol (1 micro mol L-1), electrical stimulation evoked neurogenic inhibitory responses not modified by hexamethonium (100 micro mol L-1), suggesting that inhibitory postganglionic non-adrenergic non-cholinergic (NANC) nerve fibres are involved. The nitric oxide (NO)-synthase inhibitor Nomega-nitro-l-argininine-methyl-ester hydrochloride (1-100 micro mol L-1) and the soluble guanylyl cyclase inhibitor ODQ (0.1-3 micro mol L-1) also abolished such relaxant response, suggesting the involvement of NO/Cyclic Guanosine 3',5' monophosphate (cGMP) system as the final mechanism of muscle relaxation. The alpha2-adrenoceptor agonist, UK 14 304 (10 nmol L-1-10 micro mol L-1) did not influence the electrical field stimulation (EFS)-evoked NANC responses. These latter responses were also refractory to a variety of receptor agonists and antagonists, acting at Gamma Aminobutyric Acid (GABA), serotonin 5HT1a, opioid micro , delta and kappa, muscarinic M1 and M2, histamine H2 and H3 and cannabinoid receptors. The NANC response was insensitive to the P/Q-type Ca2+-channel blocker omega-agatoxin TK (1 nmol L-1-0.1 micro mol L-1), but partially inhibited by the N-type Ca2+-channel blocker omega-conotoxin GVIA (0.1 nmol L-1-0.1 micro mol L-1), and by the L-type Ca2+-channel blockers nifedipine and calcicludine (0.1 nmol L-1-0.1 micro mol L-1). These data suggest that the NANC relaxation of the isolated guinea-pig gastric fundus is mediated by NO as the final inhibitory (neuro)transmitter at the longitudinal smooth muscle cells. The mechanism(s) promoting NO production is/are Ca2+-dependent, but apparently insensitive to presynaptic modulation. Both N- and L-type channels seem to occur in nitrergic nerve endings, where they contribute to trigger NO diffusion at the synaptic cleft.

M1 receptor-mediated nitric oxide-dependent relaxation unmasked in stomach fundus from M3 receptor knockout mice

Muscarinic receptors can mediate both contractile and relaxant responses in smooth muscle. The stomach fundus from wild-type mice possesses a neuronal M(1) receptor that mediates relaxation to carbamylcholine and (4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride (McN-A-343) but is masked by M(3) receptor-mediated contraction to both agonists. When the M(3) receptor was deleted, cholinergic-induced relaxation was unmasked. M(1) receptor antagonism with pirenzepine, nitric oxide (NO) synthase inhibition with N(omega)-nitro-L-arginine methyl ester hydrochloride, and inhibition of neuronal activation with tetrodotoxin abolished relaxation to McN-A-343 in tissues from M(3) receptor knockout mice, supporting the neuronal localization of an M(1) receptor that activated NO release to effect relaxation. However, the cyclooxygenase inhibitor indomethacin did not affect contraction or relaxation to carbamylcholine in stomach fundus from wild-type or M(3) receptor knockout mice, indicating that cyclooxygenase products played no role in these responses. The neuronal M(1) receptor modulated relaxation induced by carbamylcholine and McN-A-343 but not relaxation induced by electric field stimulation of the stomach fundus. These data support the presence of M(1) receptor-mediated relaxation in the stomach and suggest that when the M(3) receptor is eliminated or blocked, M(1) receptor-mediated gastric relaxation may be enhanced, possibly leading to alterations in gastric emptying and subsequent effects on body weight.

Spontaneous mechanical activity and evoked responses in isolated gastric preparations from normal and dystrophic (mdx) mice

This study examined whether alterations of the spontaneous and evoked mechanical activity are present in the stomach of the mdx mouse, the animal model for Duchenne muscular dystrophy. The gastric mechanical activity from whole-organ of normal and mdx mice was recorded in vitro as changes of intraluminal pressure. All gastric preparations developed spontaneous tone and phasic contractions, although the tone of the mdx preparations was significantly greater. Atropine reduced the tone of the two preparations by the same degree. Nomega-nitro-l-arginine methyl ester (l-NAME) significantly increased the tone and spontaneous contractions only in the stomach from normal animals, but did not affect on the mdx preparations. Effects ofl-NAME on tone and contractility were preserved in the presence of tetrodotoxin. In both types of tissues electrical field stimulation (EFS) induced a biphasic response: cholinergic contraction followed by slow relaxation. In nonadrenergic noncholinergic conditions, EFS induced a rapid relaxation followed by a slow component in both types of tissues. l-NAME abolished the rapid component, reduced the slow component and unmasked tachychinergic contractions. No significant difference was found in evoked responses. The enteric neurotransmission is preserved in mdx gastric preparations, although alterations in the ongoing production of nitric oxide are present.

Generalized loss of inhibitory innervation reverses serotonergic inhibition into excitation in a rabbit model of TNBS-colitis

1. Inflammation may affect subpopulations of neurons of the myenteric plexus. 2. In the present study the effect of trinitrobenzene sulphonic acid (TNBS) induced colitis on nitrergic, purinergic and adrenergic inhibitory neurotransmission was studied as well as the consequences of the related changes on the response of 5-HT agonists using these neurotransmitters to mediate their effect. 3. Strips from normal and colitis rabbits (135 mg kg(-1) TNBS) were subjected to electrical field stimulation (EFS, 0.3 ms, 6V, 0.5 - 32 Hz, 10 s train). The response was measured isometrically in the absence or presence of L-NAME, suramin, guanethidine, the 5-HT agonists (5-HT(1/5A/7): 5-carboxamidotryptamine (5-CT), 5-HT(2): alpha-methyl-5-HT, 5-HT(3): 2-methyl-5-HT, 5-HT(4): 5-methoxytryptamine (5-MeOT)) or a combination. 4. In normal strips L-NAME (1 - 32 Hz), suramin (0.5 - 2, 8 Hz) and guanethidine (4, 16, 32 Hz) increased the response to EFS. This effect was abolished in inflamed strips and was accompanied by a decrease in nNOS expression. 5. In normal strips all 5-HT agonists induced pronounced (5-CT, alpha-methyl-5-HT) or small (2-methyl-5-HT, 5-MeOT) inhibitory neural responses. In inflamed strips this was reversed to cholinergic excitatory responses. 6. The effect of inflammation on the 5-HT(4) response was mimicked by preincubation of normal strips with L-NAME or suramin. Accordingly, in inflamed strips L-NAME or suramin did not affect the excitatory effects of 5-MeOT. 7. TNBS-colitis abolishes nitrergic, purinergic and adrenergic neurotransmission. This reverses serotonergic inhibition into excitation.

Characterization of pre- and postsynaptic muscarinic receptors in circular muscle of pig gastric fundus

1. This study investigated the subtype of muscarinic receptors on the cholinergic neurones and smooth muscle in the circular muscle of the pig gastric fundus. 2. Muscarinic antagonists, except MT-3, concentration-dependently inhibited the contractions induced by a given concentration of acetylcholine. Concentration-response curves by acetylcholine were shifted rightwards in a parallel manner without depression of the maximum by the muscarinic antagonists, except by MT-3 that induced a leftward shift. Correlation of the pIC(50) and pA(2) values with published pK(i) values for the five muscarinic receptor subtypes suggests that the muscarinic receptors on pig gastric fundus circular muscle belong to the M(3) subtype. 3. Electrically-evoked contractions (40 V, 4 Hz, 0.25 ms, 2 min) were concentration-dependently inhibited by the muscarinic antagonists except for methoctramine and AF-DX 116, that increased the amplitude of the electrically-induced contractions in lower concentrations. MT-3 tended to increase the electrically-induced contractions. 4. The antagonists, except MT-3, concentration-dependently increased the electrically-induced tritium outflow (40 V, 4 Hz, 0.25 ms, 2 min) after incubation of the tissues with [(3)H]-choline. MT-3 (3 x 10(-8) and 10(-7) M) decreased the electrically-induced tritium release. Correlation of the pIC(50) values with published pK(i) values for the different muscarinic receptor subtypes yielded a significant and comparable correlation for M(1), M(3), M(4) and M(5) receptors. 5. These results suggest that the postsynaptic receptors in circular muscle of the pig gastric fundus belong to the M(3) subtype. However, the presynaptic receptor could not be clearly defined, although it does certainly not belong to the M(2) subtype.

Potentiation of motilin-induced contraction by nitric oxide synthase inhibition in the isolated chicken gastrointestinal tract

The present experiments were designed to determine whether or not endogenous nitric oxide (NO) modifies the contractile response to chicken motilin (ch-MT) in the gastrointestinal (GI) tract (proventriculus and small intestine) of the chicken. ch-MT (1 nmol L(-1)-1 micromol L(-1)) caused contractions of longitudinal muscle strips of the proventriculus through both myogenic and neurogenic (mostly cholinergic) mechanisms. On the other hand, ch-MT (0.1 nmol L(-1)-100 nmol L(-1)) contracted the small intestine (duodenum, jejunum and ileum) only through a myogenic mechanism. L-Nitroarginine methylester (L-NAME) potentiated, and L-arginine inhibited, the ch-MT- induced contraction without affecting the responsiveness of acetylcholine (ACh) or 5-hydroxytryptamine in the proventriculus. Electrical field stimulation (EFS)- and 1,1-dimethyl-4-phenylpiperazinium (DMPP)- induced contractions were also potentiated by L-NAME. The potentiation by L-NAME was prevented by L-arginine but not by D-arginine. However, in the presence of atropine or tetrodotoxin, neither L-NAME nor L-arginine modified the responses to ch-MT and DMPP. In contrast to the proventriculus, L-NAME and L-arginine were both ineffective in modifying the ch-MT-induced contraction in the small intestine. These results indicate that NO synthase inhibition potentiates the contractile response of ch-MT, EFS and DMPP in the chicken proventriculus through reduction of endogenous NO-mediated presynaptic inhibition on neural ACh release. However, NOS inhibition did not modify the myogenic (direct) action of ch-MT in gastric and intestinal smooth muscles of the chicken.

Influence of nitric oxide donors and of the alpha(2)-agonist UK-14,304 on acetylcholine release in the pig gastric fundus

This study in circular muscle strips of the pig gastric fundus aimed to measure the release of acetylcholine directly and to investigate whether NO and alpha(2)-adrenoceptor agonists can modulate acetylcholine release from cholinergic neurones. After incubation of the tissues with [(3)H]-choline, basal and electrically induced release of tritium and [(3)H]-acetylcholine were analyzed in a medium containing physostigmine (10(-5) M) as well as atropine (10(-6) M). The NO synthase inhibitor L-N(G)-nitroarginine methyl ester (3x10(-4) M), and the NO donors sodium nitroprusside (10(-5) M) and 3-morpholino-sydnonimine (10(-5) M) did not influence the basal release nor the electrically evoked release, indicating that NO does not modify [(3)H]-acetylcholine release. The alpha(2)-adrenoceptor agonist UK-14,304 (10(-5) M) significantly inhibited the electrically evoked release of [(3)H]-acetylcholine, and this effect was prevented by the alpha(2)-adrenoceptor antagonist rauwolscine (2x10(-6) M), suggesting that presynaptic alpha(2)-adrenoceptors are present on cholinergic neurones of the pig gastric fundus.

Role of nitric oxide- and vasoactive intestinal polypeptide-containing neurones in human gastric fundus strip relaxations

The morphological pattern and motor correlates of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) innervation in the human isolated gastric fundus was explored. By using the nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-diaphorase and specific rabbit polyclonal NO-synthase (NOS) and VIP antisera, NOS- and VIP-containing varicose nerve fibres were identified throughout the muscle layer or wrapping ganglion cell bodies of the myenteric plexus. NOS-immunoreactive (IR) neural cell bodies were more abundant than those positive for VIP-IR. The majority of myenteric neurones containing VIP coexpressed NADPH-diaphorase. Electrical stimulation of fundus strips caused frequency-dependent NANC relaxations. N(G)-nitro-L-arginine (L-NOARG: 300 microM) enhanced the basal tone, abolished relaxations to 0.3 - 3 Hz (5 s) and those to 1 Hz (5 min), markedly reduced ( approximately 50%) those elicited by 10 - 50 Hz, and unmasked or potentiated excitatory cholinergic responses at frequencies > or =1 Hz. L-NOARG-resistant relaxations were virtually abolished by VIP (100 nM) desensitization at all frequencies. Relaxations to graded low mechanical distension (< or =1 g) were insensitive to tetrodotoxin (TTX: 1 microM) and L-NOARG (300 microM), while those to higher distensions (2 g) were slightly inhibited by both agents to the same extent ( approximately 25%). In the human gastric fundus, NOS- and VIP immunoreactivities are colocalized in the majority of myenteric neurones. NO and VIP mediate electrically evoked relaxations: low frequency stimulation, irrespective of the duration, caused NO release only, whereas shortlasting stimulation at high frequencies induced NO and VIP release. Relaxations to graded mechanical distension were mostly due to passive viscoelastic properties, with a slight NO-mediated neurogenic component at 2 g distension. The difference between NO and VIP release suggests that in human fundus accommodation is initiated by NO. British Journal of Pharmacology (2000) 129, 12 - 20

Apoptosis in rat gastric antrum: evidence that regulation by food intake depends on nitric oxide synthase

The turnover of the epithelium of the gastrointestinal tract is regulated by a balance between cell multiplication and cell loss. We examined the effects of starvation on apoptosis in endocrine and other epithelial cells of rat antropyloric mucosa. Apoptosis was determined by the TUNEL reaction combined with immunocytochemical staining for gastrin and somatostatin. Apoptotic cell morphology was determined by bisbenzimide staining for DNA. Both gastrin and somatostatin cells showed a significantly lower apoptotic index than the general epithelium. This agrees with the longer turnover kinetics of gastric endocrine cells. On starvation, the apoptotic index of the general epithelium and of the gastrin but not of the somatostatin, cells increased significantly. This was prevented by the nitric oxide synthase (NOS) inhibitor L-NAME but not by its inactive stereoisomer D-NAME. Immunoreactive neuronal NOS was present in somatostatin cells, in nonendocrine cells predominating in the surface and pit epithelium, and in rare nerve fibers. Endothelial cell NOS was present in vessels, whereas the inducible isoform was barely detectable. Thus, endogenous NOS isoforms participate in regulating antropyloric epithelial apoptosis during starvation. The close paracrine relation between somatostatin cells and gastrin cells suggests that the former regulates apoptosis of the latter through release of NO.