Secretion of insulin and of glucagon by the perfused pancreas of newborn rats: effect of vasoactive intestinal peptide Vip]

A method is described for perifusion of the splenic part of the pancreas from 48-64 hour-old rat. In different basal conditions, the secretion of insulin and glucagon is stable and reproducible for 90 mn. The addition of the vasoactive intestinal peptide (VIP) to these perifusion media, at a concentration as low as 2 ng/ml, determines a remarkable increase of insulin and of glucagon secretion. These results suggest the possibility of a VIP action in the physiology of endocrine pancreas.     

A glucagon-secretin-like peptide stimulates the intrinsic nervous plexus of guinea pig gallbladder

The role of vasoactive intestinal peptide (VIP), as a possible neurotransmitter of the intrinsic nerve plexus in the guinea pig gallbladder, was investigated by monitoring spontaneous contractile activity. VIP receptor antagonist (4 Cl-D-Phe6, Leu 17)-VIP did not produce any effect on muscular tone and spontaneous activity, whereas (N-Ac-Tyr1, D-Phe2)-GRF-(1-29)-NH2, (14-GRF analog), which is known to stimulate digestive enzyme secretion by interacting with the VIP-preferring receptors, greatly increased the amplitude and frequency of waves as well as the muscular tone. Since VIP receptor antagonist acts selectively as a competitive antagonist for the action of VIP, we conclude that the gallbladder inhibitory intrinsic plexus neurotransmitter is not VIP, but a member of the glucagon-secretin family of peptides.     

A glucagon-secretin-like peptide stimulates the intrinsic nervous plexus of guinea pig gallbladder

Summary The role of vasoactive intestinal peptide (VIP), as a possible neurotransmitter of the intrinsic nerve plexus in the guinea pig gallbladder, was investigated by monitoring spontaneous contractile activity. VIP receptor antagonist (4 Cl-D-Phe⁶, Leu¹⁷)-VIP did not produce any effect on muscular tone and spontaneous activity, whereas (N-Ac-Tyr¹, D-Phe²)-GRF-(1-29)-NH₂, (14-GRF analog), which is known to stimulate digestive enzyme secretion by interacting with the VIP-preferring receptors, greatly increased the amplitude and frequency of waves as well as the muscular tone. Since VIP receptor antagonist acts selectively as a competitive antagonist for the action of VIP, we conclude that the gallbladder inhibitory intrinsic plexus neurotransmitter is not VIP, but a member of the glucagon-secretin family of peptides.     

Vasoactive intestinal peptide (VIP) occurs in nerves of the pineal gland

Summary Nerves staining with antibodies against vasoactive intestinal peptide (VIP) were detected in the pineal gland of the rabbit, cat and pig. VIP nerves were numerous in the cat but few in the rabbit and pig. A particularly rich VIP nerve supply was noted in the pineal stalk of the cat. The nerves were predominantly located around small blood vessels. Occasionally, nerve fibres were seen in the glandular parenchyma without obvious relation to blood vessels.Grant support from the Swedish Medical Research Council (04X-4499).     

The effect of Apamin® on nonadrenergic,noncholinergic nervous vasodilatations in the cat small intestine

Summary The intestinal vasodilation evoked by mechanical mucosal stimulation or by transmural electrical field stimulation was abolished by close i.a. injection of Apamin, a polypeptide originally isolated from bee venom. Apamin also blocked the vasodilatation induced by close i.a. infusion of vasoactive intestinal polypeptide (VIP). It is suggested that Apamin is a VIP receptor antagonist.This research was sponsored by grants from the Swedish Medical Research Council (14X-2855), from the Swedish Society for Medical Sciences, from Magnus Bergvalls Stiftelse and from the Medical Faculty, University of Göteborg.     

Endocrine and exocrine pancreatic function after camostate-induced growth of the organ

It is well known that oral administration of camostate induces hyperplasia and hypertrophy of the rat pancreas. It is not clear, however, whether pancreatic hormone and enzyme secretion are affected by camostate treatment.In rats, daily administration of 200 mg camostate/kg b. wt for 14 days significantly increased pancreatic weight and pancreatic content of DNA, protein, amylase, lipase, trypsin and chymotrypsin, as well as the amount of insulin, glucagon and somatostatin. In the intact animal, blood glucose levels and serum concentrations of insulin and glucagon in response to an oral glucose load were not impaired after camostate treatment. In the isolated perfused pancreas, however, insulin and glucagon secretions were reduced, whereas somatostatin release was not affected. The volume of pancreatic juice produced by the unstimulated isolated perfused organ, as well as protein and enzyme secretion, were increased after camostate treatment. Likewise, the isolated perfused pancreas from camostate-treated rats secreted a larger volume of pancreatic juice and more protein in response to cholecystokinin (CCK), while enzyme secretion was affected in a non-parallel manner: amylase release was markedly reduced, lipase release was unchanged, and release of trypsin and chymotrypsin was increased.     

Absence of effects of dibutyryl cyclic guanosine 3′,5′-monophosphate on release of α-amylase,45Ca efflux,and protein synthesis in rat pancreas in vitro

Summary Dibutyryl cyclic GMP did not affect basal, or carbachol stimulated secretion of α-amylase from rat pancreas. The nucleotide did not have a significant effect on⁴⁵Ca release from the pancreas nor did it alter the response to carbachol. The dibutyryl analogue of cyclic GMP did not duplicate or alter the inhibitory effect of carbachol on³H-leucine incorporation into pancreatic trichloroacetic acid-precipitable protein.

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Résumé L'effet du dibutyryl GMPc sur la sécrétion d'α-amylase, l'efflux du⁴⁵Ca et la synthèse de nouvelles protéines dans le pancréas du rat, ont été étudiés. Le dibutyryl GMPc n'affecte ni la sécrétion d'enzyme basale ni celle stimulée par le carbachol. Le nucléotide n'a pas un effet significatif sur le relàchement du⁴⁵Ca du pancréas et n'altère pas la réponse du carbachol. L'analogue ne mime pas et ne change pas l'effet du carbachol sur l'incorporation du³H-leucine dans les protéines précipitées par l'acide trichloroacétique.

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Supported by a grant from the Medical Research Council of Canada. The authors acknowledge the secretarial aide of MissC. Picard.     

The islet-acinar axis of the pancreas: Is there a role for glucagon or a glucagon-like peptide?

Intravenous glucagon inhibits exocrine pancreatic secretion in vivo, but exogenous glucagon does not affect exocrine secretion in vitro. Recent work, however, suggested that endogenous glucagon may be involved in the regulation of exocrine secretion even in vitro. We therefore investigated the effects of exogenous and endogenous glucagon on exocrine secretion by the isolated perfused rat pancreas in the presence of 1.8 mM glucose. Exogenous glucagon did not affect CCK-stimulated amylase output. 20 mM arginine stimulated glucagon release, but did not affect basal enzyme secretion. CCK-stimulated amylase output, however, was significantly inhibited in the presence of arginine. This inhibitory effect of arginine on exocrine pancreatic secretion could be blocked by glucagon antibodies, but not by nonspecific gammaglobulins. Thus exogenous glucagon failed to affect exocrine pancreatic secretion in vitro, but endogenously released glucagon or a glucagon-like peptide inhibited amylase release in the isolated perfused pancreas. We conclude that glucagon or a glucagon-like peptide may be a mediator in the islet-acinar axis.     

The topography of posttetanic potentiation in guinea-pig ileum

The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum offers, by its anatomical arrangement, the possibility of studying a new aspect of posttetanic potentiation (PTP); its topography. Evidence was sought and obtained that during PTP more distal junctional sites of cholinergic nerve terminals may be recruited into the transmitter secretion process.     

Absence of effects of dibutyryl cyclic guanosine 3',5'-monophosphate on release of alpha-amylase, 45Ca efflux, and protein synthesis in rat pancreas in vitro.

Dibutyryl cyclic GMP did not affect basal, or carbachol stimulated secretion of alpha-amylase from rat pancreas. The nucleotide did not have a significant effect on 45Ca release from the pancreas nor did it alter the response to carbachol. The dibutyryl analogue of cyclic GMP did not duplicate or alter the inhibitory effect of carbachol on 3H-leucine incorporation into pancreatic trichloroacetic acid-precipitable protein.     

Neuropeptides in pelvic afferent pathways

Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.     

Cholinomimetics produce seizures and brain damage in rats

Microinjections of the cholinergic agonists, carbachol and bethanechol, either into the amygdala or into the dorsal hippocampus produced sustained limbic seizures and brain damage in rats. Systemic administration of pilocarpine in rats resulted in a sequence of convulsive disorders and widespread brain damage as well. Scopolamine prevented the development of convulsive activity and brain damage produced by cholinomimetics. These results suggest that the excessive stimulation of cholinergic muscarinic receptors can lead to limbic seizures and brain damage. It is postulated that muscarinic cholinergic mechanisms are linked to the etiology of temporal lobe epilepsy and epileptic brain damage.     

Neuropeptides in pelvic afferent pathways

Summary Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double, staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are, involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.     

The effect of hexamethonium on the secretion induced by sodium deoxycholate in the rat jejunum

Summary The i.v. administration of hexamethonium reduces or abolishes net water secretion induced by sodium deoxycholate in the denervated rat jejunum. The findings suggest that a local nervous reflex may be involved in bile salt-induced intestinal secretion.This research was sponsored by grants from the Swedish Medical Research Council (14X-2855), from the Swedish Society for Medical Sciences, from Magnus Bergvalls Stiftelse and from the Medical Faculty, University of Göteborg.     

Pathways for excitatory and inhibitory innervation to the guinea-pig tracheal smooth muscle

Summary The trachea receives excitatory cholinergic innervation from the vagus nerve and the stellate ganglion. Inhibitory adrenergic fibres have the same sources. Those in the vagus nerve probably derive from high vagosympathetic anastomoses. Nonadrenergic inhibitory fibres have a preganglionic vagal supply.This study has been supported by grants from Magnus Bergvall Memorial Found and Harald and Greta Jeansson Foundation.     

Fluorogenic amines in the notochords of chick embryos treated by cholinergics]

The investigation of 3 day old notochords by the fluorescence method of Falck and Owman showed an increase of the fluorescence after treatment of the chick embryos at 48 hrs of incubation, with nicotine sulfate or carbachol. The addition of norepinephrine or L-Dopa emphasized the formaldehyde induced fluorescence. The simultaneous treatment with a cholinergic agent and atropine, propranolol or reserpine decreased or suppressed the fluorescence. These results demonstrate the existence of a relationship between the treatment with a cholinergic agent and the amount of chordal biogenic amines.     

Comparative cytochemical and pharmacological studies on the cholinergic innervation of the branchial heart of the cephalopodSepia officinalis (L.)

Summary The dense motor innervation of the obliquely striated muscle cells in the branchial heart of Coleoida is composed of activating and inhibiting parts. The inhibiting cholinergic system investigated in this study is characterized histo- and cytochemically by a high acetylcholinesterase activity (EC 3.1.1.7) in the glycocalices of the nerve fibers with transparent synaptic vesicles, the muscle cells and, to a lesser extent, the ovoid interstitial cells, the functions of which are endocytosis and storage of catabolic substances. The pharmacological results from the isolated organ indicate a more nicotinic type of Ach-receptor, which can be reversibly blocked by D-tubocurarine and -bungarotoxin, but not with the same intensity by tetraethylammonium or atropine.     

Immunohistochemical localization of pancreatic polypeptide (PP) in the brain of the larval instar of the hoverfly,Eristalis aenus (Diptera)

Summary 2 pancreatic polypeptide (PP) immunoreactive cells were observed in each half of the protocerebrum of the last (5th), larval instar of the hoverfly,Eristalis aenus. No PP immunoreactive nerve fibers could be detected in the brain.Support by a grant from the Swedish Medical Research Council (project No. 12X-102) and by a Swedish Institute scholarship.     

Cholinergic nerves in the rat portal vein

Summary The innervation of the rat portal vein was studied using the cholinesterase histochemical method 2 plexuses of cholinergic nerve fibers were found; an external plexus localized at the level of the outer adventitial layers and an inner plexus at the level of the adventitial-medial transitional zone and in the outer layers of the media.Acknowledgments. We thank Dr C. Cavallotti for his kind help and criticism. The kind help of Dr W. Collier and of the staff of the laboratory of Neurobiology as well as the bibliographic assistance of Istituto Superiore di Sanità (Serv. Documentazione, Dr Magliola) are gratefully acknowledged.     

Are there 2 cholinergic thermoregulatory centres in rats?

Summary An attempt was made to replicate the conflicting previous reports of hypo- and hyperthermic effects of intrahypothalamically administered carbachol. Despite using the same coordinates, injection parameters, and strain of rats reported by others, only hypothermia was conclusively demonstrated. It was concluded that the cholinergic system mediates heat loss mechanisms in rats.