Vasoactive intestinal polypeptide causes relaxation of the pyloric sphincter in the rabbit

Intravenous vasoactive intestinal polypeptide lowers pulmonary-to-systemic vascular resistance ratio in a neonatal piglet model of pulmonary arterial hypertension

BACKGROUND

Several studies of vasoactive intestinal polypeptide (VIP) demonstrated its potent vasodilative effects on pulmonary and systemic circulation. However, no hemodynamic studies were performed to depict the effects of VIP in an in vivo model of pulmonary arterial hypertension (PAH), thereby limiting a complete understanding of the overall hemodynamic effects of VIP in PAH.

METHODS AND RESULTS

The pulmonary and systemic hemodynamic effects of intravenous infusion of 100 ng/kg per minute of VIP in control and pulmonary hypertensive piglets at 6 to 8 weeks of age were assessed. Pulmonary arterial hypertension was induced after the instillation of meconium solution in the subjects' trachea and was characterized by the establishment of a persistently elevated pulmonary arterial pressure, diminished cardiac output, and elevated pulmonary-to-systemic vascular resistance (PVR/SVR) ratio.

CONCLUSIONS

Continuous intravenous infusion of VIP markedly decreased PVR/SVR ratio in pulmonary hypertensive subjects; however, it lowered blood pressure without causing any significant changes in PVR/SVR ratio in control subjects. Collectively, these results suggest an overall pulmonary vasodilative effect of VIP in PAH.

Origins and projections of nerve fibres in rat pyloric sphincter

Nerve fibres play an important role in the regulation of gastric emptying. The aims of this study were to clarify the distribution, projections and origin of neuronal type nitric oxide synthase (NOS)-, tyrosine hydroxylase (TH)-, vesicular acetylcholine transporter (VAchT)- and peptide-containing nerve fibres of the rat pyloric sphincter. Extrinsic and local denervations of the sphincter were performed in order to reveal the origin and projections of the various nerve fibre populations. Pylorus from control and denervated animals were processed for the immunocytochemical demonstration of cholecystokinin (CCK), enkephalin, gastrin-releasing peptide (GRP), somatostatin, calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), pituitary adenylate cyclase-activating peptide (PACAP), substance P (SP), vasoactive intestinal peptide (VIP), galanin, NOS, VAchT and TH. VAchT, TH, nNOS, and all of the peptides investigated were found in nerve fibres innervating the pyloric sphincter, and coexistence of several putative neurotransmitters were revealed. Extrinsic denervation caused a total loss of NPY/TH-, SP/CGRP- and SP/CGRP/VIP/NOS/PACAP-containing nerve fibres. Local denervation immediately proximal to the sphincter markedly reduced the numbers of VIP/NOS/galanin- and VIP/NOS/galanin/PACAP +/- NPY-containing fibres within the sphincter suggesting an origin of these fibres in myenteric ganglia in the antral region; denervation at the level of the oxyntic-pyloric border had no effect. Local denervation immediately distal to the sphincter caused a marked decrease in VAchT-, SP/enkephalin-, enkephalin-, somatostatin-, CCK- and GRP-containing fibres within the sphincter suggesting that these emanate from the duodenum. The latter procedure also reduced the number of SP/CGRP-containing fibres of extrinsic origin within the pyloric sphincter.

Nitric oxide synthase is absent in only a subset of cases of pyloric stenosis

PURPOSE

The aim of this study was to study nitric oxide synthase (NOS) immunohistochemistry in the pyloric muscle and establish the role of nitric oxide in pyloric stenosis.

METHODS

Pyloric muscle biopsy specimens were obtained from 20 patients with pyloric stenosis during pyloromyotomy. Ten control specimens without pyloric disease were obtained from autopsy performed less than 4 hours after death on age-matched babies who died of other causes. Tissues were fixed in 4% paraformaldehyde immediately. A monoclonal antibody against the neuronal form of NOS (bNOS) was used for immunohistochemistry.

RESULTS

Immunohistochemistry showed activity of bNOS in the control specimens and some pyloric stenosis specimens. This shows that NOS is present in the pylorus in normal cases as well as in a few cases of pyloric stenosis.

CONCLUSIONS

NOS deficiency leading to lack of locally available nitric oxide causes a failure of smooth muscle relaxation. This may account for the cause of pyloric stenosis in infants. However, this study shows that this is true probably only in a subset of cases. The etiology of pyloric stenosis may still be multifactorial. Further investigations are required regarding the etiology of pyloric stenosis. J Pediatr Surg 36:616-619.

PACAP and VIP inhibit pyloric muscle through VIP/PACAP-preferring receptors

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with structural homology to vasoactive intestinal polypeptide (VIP). Two receptor types for PACAP have been described: PACAP preferring receptors are selective for PACAP; whereas VIP/PACAP preferring receptors have similar affinity for both PACAP and VIP. Both VIP and PACAP are present in enteric nerves at the pylorus. VIP is known to exert inhibitory effects on pyloric muscle; the effect of PACAP is unknown. The aims of this study were to determine the effect of PACAP on pyloric muscle and to characterize the PACAP receptor.

METHODS

Rabbit pyloric muscle strips were cut parallel to circular muscle fibres and placed in muscle baths. The effect of PACAP and VIP were quantitated as percent of basal motility index (MI).

RESULTS

PACAP-27, PACAP-38, and VIP had dose dependent inhibitory effects on the spontaneous phasic contractions of the pylorus. The PACAP-27- induced relaxation was inhibited by the PACAP receptor antagonist PACAP6-27, but was not affected by tetrodotoxin. VIP also had dose dependent inhibitory effects on pyloric muscle. The VIP relaxation was inhibited by PACAP6-27, but not affected by tetrodotoxin.

CONCLUSIONS

These studies indicate that, similar to VIP, PACAP inhibits pyloric muscle. The inhibitory effect of the PACAP receptor antagonist on both PACAP and VIP-induced relaxation suggest that PACAP and VIP act at the same receptor, a VIP/PACAP preferring receptor.

The enigma of pyloric stenosis. Some thoughts on the aetiology

A theory is advanced about the cause of pyloric stenosis of infancy (PS). Developmental changes will conspire to produce pathogenetic gastric hyperacidity within the first 4 weeks of life in babies who develop PS. The prime cause will be an increased gastric acidity due to a genetically determined supernormal parietal cell mass. This theory satisfactorily explains many known clinical features.

Nitric oxide synthesis inhibition: the effect on rabbit pyloric muscle

The relaxation mechanism of the pyloric smooth muscle is largely dependent on a nonadrenergic noncholinergic (NANC) inhibitory innervation mediated in part by nitric oxide (NO). The aim of the present study was to investigate the effect of NO antagonists on the contractility of the pyloric smooth muscle. In the clinical trial, 10 anesthetized experimental rabbits were infused intraarterially with the NO synthesis inhibitor N-nitro-L-arginine (L-NNA), at a concentration of 10(-4) mol/L; 10 controls received normal saline intraarterially. Pyloric contractility was assessed by balloon manometry. L-NNA infusion produced a dose-dependent increase in the frequency of the pyloric contraction. The maximal increase in frequency occurred during the slow L-NNA infusion rate of 146 ng/min (baseline-adjusted frequencies of experimental v control: 1.267 +/- 0.389 v 0.632 +/- 0.375; P = .001). The increased frequency level was sustained over the subsequent fast infusion rate of 292 ng/min (experimental v control: 1.362 +/- 0.604 v 0.704 +/- 0.579; P = .022). Both the duration and the amplitude of the pyloric contractions were not affected by the L-NNA infusion. These findings suggest that blockage of the L-arginine-NO pathway may have resulted in inhibition of the NANC-induced gastric muscle and relaxation of the pyloric sphincter. The authors speculate that the decreased NO production may be responsible for the sustained contraction of the pyloric smooth muscle with secondary hypertrophy, characteristic of hypertrophic pyloric stenosis.

Pancreatic polypeptide, microinjected into the dorsal vagal complex, potentiates glucose-stimulated insulin secretion in the rat

Specific binding sites for circulating pancreatic polypeptide (PP) have been found within the dorsal vagal complex (DVC) in the caudal medulla oblongata. Therefore, the effects of rat PP on pancreatic hormone secretion upon its microinjection into the DVC in halothane-anesthetized rats at doses of 0.4-40 pmol were investigated. At this range of doses, the changes in plasma concentrations of insulin, glucagon and glucose over basal levels did not differ from those after vehicle microinjection. In a separate series of experiments, vehicle and PP at doses of 0.4 and 4 pmol were microinjected into the right DVC 40 min after the continuous infusion of D-glucose had been started. In animals receiving continuous infusion of D-glucose, PP microinjected into the DVC (4 pmol), resulted in markedly higher insulin levels at corresponding time points compared to those with vehicle microinjected into the DVC. These data indicate, for the first time, that microinjection of PP into the DVC may potentiate glucose-stimulated insulin secretion in halothane-anesthetized rats.