T. Skak-Nielsen

Gastrin-Releasing Peptide in the Porcine Pancreas

The presence of gastrin-releasing peptide (GRP) was studied in extracts of porcine pancreata. Gel filtration and high-pressure liquid chromatographic profiles of these extracts as monitored with both C-terminally and N-terminally directed radioimmunoassays against GRP showed pancreatic GRP to consist of one main form, namely the 27-amino acid peptide originally extracted from porcine stomach, and small amounts of a C-terminal fragment identical with the C-terminal 10-amino acid peptide. Gastrin-releasing peptide-like immunoreactivity released from the isolated perfused porcine pancreas during electrical vagal stimulation was shown by gel filtration to consist of the same two forms. By use of immunocytochemical techniques employing an antiserum directed against its N terminus, GRP was localized to varicose nerve fibers in close association with the exocrine tissue of the porcine pancreas in particular. Some fibers were found penetrating into pancreatic islets also. Immunoreactive nerve cell bodies as well as fibers were found within intrapancreatic ganglia. The potency of GRP in stimulating exocrine as well as endocrine secretion from the porcine pancreas, its presence in close contact with both acini and islets, and its release during vagal stimulation indicate that GRP may have a role in the parasympathetic regulation of endocrine and exocrine secretion from the pig pancreas.

Localization in the gastrointestinal tract of immunoreactive prosomatostatin

Antisera against 5 different regions of the entire prosomatostatin molecule were used for immunohistochemical mapping of prosomatostatin-containing structures in the pig gastrointestinal tract, and for radioimmunological and chromatographical analysis of the products of prosomatostatin in extracts of ileal mucosa. The latter showed that the antisera were capable of identifying components containing N-terminal as well as C-terminal parts of prosomatostatin. Endocrine cells were identified with all antisera in most parts of the gastrointestinal tract, and varicose nerve fibres were observed in all parts of the small intestine but not in the stomach and the colon. The colon contained very few immunoreactive structures. Immunoreactive nerve cell bodies were found in the submucous plexus of the small intestine. All immunoreactive endocrine cells in the stomach and the duodenum and all immunoreactive nerves were stained by all 5 antisera whereas the small intestinal endocrine cells did not stain for the most N-terminal region of prosomatostatin. The results suggest that all gastrointestinal somatostatin is derived from the same precursor molecule, which, however, in the small intestinal endocrine cells is processed differently from that of the other tissues.

Role of gastrin-releasing peptide in the neural control of pepsinogen secretion from the pig stomach

A new experimental model, the isolated perfused antrectomized pig stomach with intact vagal innervation, was shown to produce pepsinogen and gastric acid upon electrical stimulation of the vagus nerves and by intravascular administration of carbachol (from a basal value of 111 +/- 24 units of pepsin per minute and 0.044 +/- 0.012 mEq H+/min to 393 +/- 75 units of pepsin per minute and 0.102 +/- 0.022 mEq H+/min upon vagal stimulation). Vagal stimulation also increased the release of the neuropeptide gastrin-releasing peptide to the venous effluent from 0.42 +/- 0.12 to 3.1 +/- 0.95 pmol/min. Intravascular infusions of gastrin-releasing peptide at a concentration of 10(-8) mol/L resulted in a threefold increase in pepsinogen secretion and a small increase in acid output. Because gastrin-mediated effects of gastrin-releasing peptide are excluded with this preparation, our results show that gastrin-releasing peptide acts either directly or through another unknown local mediator on the pepsinogen-secreting cells. Gastrin-releasing peptide may thus participate in the vagal control of pepsinogen secretion.

Vagal control of the release of somatostatin, vasoactive intestinal polypeptide, gastrin-releasing peptide, and HCl from porcine non-antral stomach

We studied the secretion of somatostatin and HCl and the release of vasoactive intestinal polypeptide (VIP) and gastrin-releasing peptide (GRP) from isolated, vascularly perfused, porcine non-antral stomach. Electric vagus stimulation increased acid secretion and the release of VIP and GRP and inhibited somatostatin secretion as determined in the venous effluent. Atropine abolished the HCl response and reversed the somatostatin inhibition to a three-fold increase, whereas GRP and VIP responses were unchanged. Both intra-arterial carbachol (10(-6) M) and GRP (10(-8) M) increased acid secretion and inhibited somatostatin secretion. VIP (10(-8) M) increased somatostatin secretion and had no effect on acid secretion. By immunohistochemistry, somatostatin was localized to both open-type and closed-type cells equally spread in the various parts of the gastric glands without particular relation to the parietal cells. Numerous GRP- and VIP-immunoreactive nerve fibers were seen between the glands. It is concluded that the fundic and antral secretion of somatostatin, investigated in a previous study, are differently regulated. The relation of fundic somatostatin release to acid secretion seems to be complex.

Immunohistochemical detection of ganglia in the rat stomach serosa, containing neurons immunoreactive for gastrin-releasing peptide and vasoactive intestinal peptide

SummaryGanglia, not previously described, were identified in the rat stomach serosa along the minor curvature. The ganglia consisted of varying number of cell bodies lying in clusters along or within nerve bundles. The ganglia were shown to contain GRP and VIP immunoreactive nerve fibers and cell bodies and also some NPY immunoreactive fibers, whereas they were devoid of somatostatin immunoreactivity. Nerve ligation experiments indicated that the ganglia are intrinsic to the stomach.

Processing and Secretion of Prosomatostatin by the Pig Pancreas

Antisera and radioimmunoassays against five different regions of prosomatostatin (proSS) were used for chromatographical analysis and for immunohistochemical mapping of the products of proSS in the pig pancreas. Secreted products of proSS were studied by analysis of effluent from isolated perfused pig pancreas obtained during isoproterenol stimulation. All cells that were stained with one antiserum also stained with the other antisera. Immunoreactive nerves were not observed. Isoproterenol increased equally the secretion of proSS 20–36, proSS 65–76, and proSS 7%92 immunoreactivity. The major molecular forms identified in pancreatic extracts and released from the pancreas were proSS W92; proSS 65–76; an N-terminally extended form of proSS 65–76; and two larger forms comprising the proSS 20–36 sequence (but not the 1–13 sequence) with and without the proSS 65–76 sequence. hoSS 1–10, 1–32 and 65–92 (somatostatin 28) were not identified.

Role of gastrin-releasing peptide in pepsinogen secretion from the isolated perfused rat stomach

We studied the effects of the neuropeptide gastrin-releasing peptide on pepsinogen secretion using an isolated perfused rat stomach with intact vagal innervation. Following electrical stimulation of the vagus nerves, the pepsin output to the luminal effluent increased from 94 +/- 7 to 182 +/- 24 units pepsin/min and the release of immunoreactive gastrin-releasing peptide to the venous effluent increased from 0.059 +/- 0.014 to 0.138 +/- 0.028 pmol/min. Infusion of gastrin-releasing peptide at 10(-8) M significantly increased pepsin output (from 87 +/- 17 to 129 +/- 22 units pepsin/min) and simultaneous infusion of gastrin-releasing peptide and carbachol at 10(-8) and 10(-6) M, respectively, resulted in an increase to almost 4 times the basal values. Atropine reduced but did not abolish the pepsin response to vagal stimulation and to infusion of gastrin-releasing peptide. Our results suggest that gastrin-releasing peptide participates in the vagal control of pepsinogen secretion.

The Role of Gastrin‐Releasing Peptide in Pancreatic Exocrine Secretion

Although the pancreas receives a dense supply of nerve fibers, the extent of neural control of pancreatic exocrine secretion has been difficult to assess. For a long time, emphasis has been on the endocrine control of secretion, nourished by the discovery of the rather large number of gut peptides that may influence pancreatic secretion and by the fact that exocrine denervation, e.g., truncal vagotomy, does not seem to bring about pancreatic insufficiency. However, it appears that there is an abundance of mechanisms controlling exocrine secretion,’ which means that seemingly “intact” secretory responses may be obtained even when one mechanism is bypassed. In addition, it appears that the organization of the pancreatic innervation rather closely resembles that of the intestinal innervation, for which the designation “little brain” has been used because of its complexity and because of its ability to generate true reflexes after extrinsic denervatiom2 It follows that long reflexes may not be essential for a certain level of neural control. Finally, the inaccessibility of the gland, its relatively low secretory volume and the viscosity of the juice secreted present technical problems that may have discouraged investigators from attempting to examine the extent of neural control.’ However, as recently reviewed,’.’ there is ample evidence for the importance of the neural control of pancreatic exocrine secretion. In rats, cats, and pigs, electrical stimulation of the vagus nerves elicits pancreatic secretory responses that vary between 40 and 100% of the maximal responses to secretin and/or cholecystokinin.’ Reflex stimulation of pancreatic secretion may be elicited by sham feeding in many mammalian species, including dogs and human^.^ Although pancreatic insufficiency does not result from vagotomy, this operation nevertheless profoundly changes pancreatic ~ecre t ion .~ Similarly, in the dog, the muscarinic cholinergic antagonist, atropine, abolishes important secretory responses to various components of meal ingestion;’ and cholinergic agonists potently stimulate in particular the secretion of pancreatic enzymes.’” It has been known for some time that some of the effects of nerve stimulation are resistant to the inhibitory effect of atropine in cats and pigs?-’ Also, the secretory effects of sham feeding in humans are to a great extent resistant to the action of anticholinergic drugs.4 Hexamethonium, the nicotinic receptor antagonist, effectively blocks the effects of vagal stimulation, suggesting that such effects are transmitted through cholinergic nicotinic receptors in autonomic ganglia? Possibly, therefore, the second neuron is non-cholinergic. It is also believed to be non-adrenergic on the basis of studies with adrenal blockers.’ Thus, a system of non-adrenergic,