The pathway by which cholecystokinin octapeptide (CCK-8) inhibits motility of the proximal stomach and the role of this pathway in the CCK-induced delay in gastric emptying of a liquid meal has been studied in rats by selective destruction of vagal afferent C-fibers using bilateral perineural application of the sensory neurotoxin, capsaicin, 3 or 4 days prior to the experiment. The capsaicin treatment significantly attenuated the decrease in intragastric pressure in urethan-anesthetized rats in response to CCK-8 (0.1-100 pmol iv) compared with vehicle-treated controls. Removal of the celiac-superior mesenteric ganglion completely abolished the inhibitory action of CCK-8 on gastric motility in these rats. In contrast, only celiac ganglionectomy in combination with vagotomy abolished the CCK-8 effect in vehicle-treated controls. Intravenous injection of CCK-8 (300 pmol) 5 min before intragastric administration of a methylcellulose solution decreased gastric emptying by 55% in conscious control or vehicle-treated rats. Perivagal capsaicin treatment abolished the delay in gastric emptying induced by CCK-8. In addition, capsaicin treatment alone significantly increased gastric emptying. These results demonstrate that CCK-8 decreases gastric motility in the gastric corpus and delays gastric emptying by a capsaicin-sensitive vagal afferent pathway. These same afferent fibers may also play a physiological role in the gastric emptying of liquids.

In vitro gastric vagal afferents' (GVAs) unit activities were recorded from the ventral GVA nerve strands in rats. The responsiveness of 16 GVA terminals to close intra-arterial injection of vehicle (0.1 ml), leptin (350 pmol), and cholecystokinin (CCK)-8 (10 pmol) was analyzed to generate a spike count-versus-time histogram. Data of 5-min spike counts before and after each treatment were normalized by dividing the latter by the former. A quotient (Q) > 1 indicates an excitatory effect, Q < 1 indicates an inhibitory effect, and Q close to 1 indicates no effect. Two types of GVA terminals were identified. Type 1 (n = 8) responded to leptin with Q > 1; CCK-8 pretreatment did not consistently alter leptin sensitivity. In contrast, Type 2 (n = 8) responded to leptin with Q < 1 or close to 1, and CCK-8 pretreatment increased the leptin sensitivity so that the terminals responded to subsequent leptin with Q > 1. These data suggest that Type 1 and Type 2 GVA terminals may provide afferent neural signals, which, in turn, will be involved in body weight and food intake control systems, respectively.

The effects of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, on the vagal cholinergic increase in gastric mucosal blood flow (GMBF) and acid secretion induced by intracisternal injection of the thyrotropin-releasing hormone (TRH) analogue, RX 77368, were studied. GMBF and acid secretion were measured simultaneously by the hydrogen gas clearance technique and titration of gastric perfusate in urethan-anesthetized rats. RX 77368 (30 ng) injected intracisternally stimulated gastric acid secretion and GMBF for 90 and 180 min respectively. GMBF was increased from basal 63 +/- 4 to 166 +/- 14 ml.min-1.100 g-1 at 60 min postinjection. L-NAME (3 mg/kg) injected intravenously 15 min before RX 77368 completely prevented the increase in GMBF induced by the TRH analogue, whereas the acid response was not modified. The effect of L-NAME was reversed by L-arginine but not by the stereoisomer D-arginine. These results show that the increase in GMBF, but not the stimulation of acid secretion, induced by central vagal activation is mediated through a product of L-arginine-NO pathway.

Recently, gastrin releasing peptide (GRP), Ala-Pro-Val-Ser-Val-Gly-Gly-Gly-Thr-Val-Leu-Ala-Lys-Met-Tyr-Pro-Arg-Gly-Asn-His-TrpAla-Val-Gly-His-Leu-Met-NH2, a mammalian bombesin, was isolated from porcine gastric mucosa and sequenced by McDonald et aL9 This polypeptide was manually synthesized by solid-phase methodology, using a benzhydrylamine-styrene-1% divinylbenzene copolymer. Deprotection and cleavage from the resin were accomplished by HF.The crude peptide was purified by gel filtration and reverse-phase, high-performance liquid chromatography (RP-HPLC). Homogeneity of the synthetic peptide was demonstrated by RP-HPLC, sequence analysis, peptide mapping, and amino acid analysis. The peptide was further characterized by thin-layer chromatography, paper electrophoresis, optical rotation, ultraviolet spectroscopy, and 300-MHz Fourier transform proton nuclear magnetic resonance spectroscopy. The circular dichroism spectra of GRP indicated that the polypeptide chain was largely random with no evidence for a-helical structure. The primary structure was confirmed by amino acid analysis of the tryptic peptide fragments, sequence analysis of GRP and its Met(0) derivative using a modified 890 C spinning-cup sequencer, and C-terminal end group determination. GRP released gastrin when administered systemically and decreased gastric acid secretion when given intracisternally in rats. GRP also mimicked CNS-mediated actions of bombesin to influence thermoregulation or glucoregulation, most likely because of the common C-terminal homology of these peptides. This assumption was supported by the observation that the synthetic acetylated octapeptide [Ac-HisZ0]-GRP (20-27) showed pharmacological effects similar to those exhibited by GRP and amphibian bombesin.Bombesin, a tetradecapeptide first isolated and characterized from the skin of the frog Bombina bombina2 has been shown in mammals to influence various neural and visceral functions. Acting through the central nervous system, bombesin is a potent stimulus to disrupt therm~regulation,~ to stimulate adrenal epinephrine ~e c r e t i o n ,~ which results in lowering of plasma insulin and elevation of plasma glucagon and glucose? and to suppress gastric acid secretiom6 Bombesin when injected peripherally also stimulates gastrin release, gall bladder contraction, antidiuresis, and intestinal motor activity.' It is now recognized on the basis of immunologic data that bombesin has counterparts in mammalian brain and gastrointestinal tissues.* McDonald et a1.9 have recently isolated and sequenced a porcine intestinal, 27 amino acid containing peptide, termed gastrin releasing peptide (GRP), which stimulates the release of gastrin (1) The conventions and nomenclature used are those of the IUPAC-IUB Commission on Biochemical Nomenclature ("Collected Tentative Rules and Recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature", 2nd ed.; American Rivier, J.; Brown, M. hoc. Natl. Acad. Sci.(7) Enpamer, V.; Melchiorri, P.; Erspamer, G. F.; Negri, L. "Gastrointestinal Hormon...

Plasma modifications of adenohypophyseal hormones were investigated in groups of female and male rats stressed for 15, 30 min, 1, 2, 4 or 6 h, either by cold (4°C), forced muscular exercise (FME), or immobilization. GH levels in both female and male rats were consistently decreased by the 3 stressing agents. Immobilization in the female and the 3 stressors in the male elicited an early secretory response of prolactin (Prl), while only in immobilized female rats plasma LH levels showed an early, short-lived increment. A more prolonged exposure to stress had an inhibitory influence on plasma Prl and LH levels in both sexes. FSH concentrations were not modified in females, but were decreased in male rats submitted to either one of the 3 stressors. In both male and female rats plasma TSH levels rose during cold exposure, while they were decreased by FME and by immobilization. Our data indicate that the character of the hormonal secretory response during stress is nonspecific. Indeed, to the exception of the specific stimulation of TSH release by cold, stress-induced hormonal changes are not related to the nature but rather to the intensity and duration of the stressing agent.