Distribution and characterization of different molecular products of pro-somatostatin in the hypothalamus and posterior pituitary lobe of the Mongolian gerbil (Meriones unguiculatus)

Antisera raised against various synthetic peptide fragments of the pro-somatostatin molecule were used to visualize immunohistochemically the distributions of different pro-somatostatin fragments in the hypothalamus and posterior pituitary of the Mongolian gerbil. To define the nature of the immunoreactive somatostatin-related molecular forms, gel chromatography combined with radioimmunoassays of hypothalamic and posterior pituitary extracts was performed. Within the hypothalamus, only trace amounts of somatostatin-28 and somatostatin-28(1-12) were present, whereas pro-somatostatin(1-76), pro-somatostatin(1-64), and somatostatin-14 peptides were present in equimolar amounts. In contrast, the posterior pituitary lobe contained equal amounts of somatostatin-14, somatostatin-28, and somatostatin-28(1-12) but no pro-somatostatin(1-76), indicating that pro-somatostatin is further processed during the axonal flow to posterior pituitary nerve terminals. The gel chromatographic data were further substantiated by immunohistochemical data. Thus, perikarya containing all of these five immunoreactivities were strictly confined to the periventricular area and parvocellular subset of the paraventricular nucleus. However, the number of somatostatin-28- and somatostatin-28(1-12)-immunoreactive perikarya was approximately 20% of the number of somatostatin-14- and pro-somatostatin(1-64)-immunoreactive cells. In other hypothalamic areas only somatostatin-14 and pro-somatostatin(1-64) immunoreactivities were detectable in cell bodies. These cell bodies were encountered in the organum vasculosum laminae terminalis; the suprachiasmatic, ventromedial, arcuate, perifornical, and posterior hypothalamic nuclei; and the median preoptic and retrochiasmatic areas. In situ hybridization histochemistry revealed that the cellular distribution of pro-somatostatin mRNA corresponds to that of somatostatin-14 and pro-somatostatin immunoreactivity, suggesting that the immunoreactive material observed within the cell bodies is synthetized there and that the differences in density of immunoreactivities may be explained by intracellular processing of pro-somatostatin. Somatostatinergic nerve fibers and terminals in hypothalamic areas and the posterior pituitary lobe were immunoreactive to all of the employed antisera. From the present results, obvious differences between intrahypothalamic and hypothalamo-pituitary somatostatinergic neurons emerge. Within hypothalamic neurons not projecting to the median eminence and the posterior pituitary lobe, pro-somatostatin is posttranslationally processed in the cell body predominantly into pro-somatostatin(1-64) and somatostatin-14. Otherwise, within periventricular neurons projecting to the median eminence and the posterior pituitary lobe, pro-somatostatin is posttranslationally processed during the axonal flow into pro-somatostatin(1-64), somatostatin-14, somatostatin-28, and somatostatin-28(1-12).

Circulating galanin: origin, metabolism, and pharmacokinetics in anesthetized pigs

The concentration of galanin-like immunoreactivity (GAL-LI) was 12.9 +/- 0.9 pmol/l in porcine arterial plasma (n = 9) and ranged from 1 to 14 pmol/g in extracts of porcine gastrointestinal tract (n = 5), the colon being the richest gut segment. A significant (P less than 0.05) arteriovenous concentration difference of circulating endogenous GAL-LI occurred across the kidney (15.1 +/- 2.3 vs. 6.2 +/- 0.5 pmol/l) and a hind leg (15.7 +/- 2.5 vs. 10.2 +/- 1.0 pmol/l), whereas a negative gradient was observed across the intestine (12.5 +/- 2.0 vs. 17.7 +/- 3.3 pmol/l) of anesthetized pigs. Passage through the brain, liver, or lungs did not change the concentration of endogenous GAL-LI significantly. During basal circumstances, the major source of circulating GAL-LI is therefore the gut. During infusion of 20 pmol.kg-1.min-1 of synthetic porcine galanin, a significant extraction occurred across the kidney (64.8 +/- 4.3%), hind leg (20.3 +/- 3.8%), and liver (19.7 +/- 4.3%). The overall metabolic clearance rate was 37.8 +/- 3.7 ml.min-1.kg-1. The half-life of galanin in plasma was 4.6 +/- 0.3 min, and the apparent distribution space was 255.6 +/- 31.4 ml/kg. Incubation studies in vitro showed that the concentration of galanin, added to blood and plasma at 37 degrees C, was halved in 1 h, unless stabilized with EDTA and aprotinin.

All products of proglucagon are elevated in plasma from uremic patients

We measured and characterized the proglucagon (PG) products in plasma obtained from nine uremic patients and six control subjects in the fasting state. The concentrations of PG products measured by direct RIAs were significantly higher in the uremic patients than in the normal subjects; the concentration of total glucagon immunoreactivity in plasma was 209 +/- 20 vs. 70 +/- 11 pmol/L, the glucagon-like peptide-1 immunoreactivity was 154 +/- 33 vs. 41 +/- 13 pmol/L, and the concentration of pancreatic-type glucagon immunoreactivity was 53 +/- 6 vs. 30 +/- 7 pmol/L. By chromatography, the predominating PG products in both uremic and normal plasma were shown to be glicentin [corresponding to PG-(1-69)] and the major PG fragment [presumably corresponding to PG-(72-158)]. In addition, glucagon-like peptide-1 [presumably corresponding to PG-(72-107) amide] was a major product in uremic plasma. Our results suggest that the kidneys play an important role in the removal from plasma of these products of PG.

Somatostatin is an essential paracrine link in acid inhibition of gastrin secretion

We studied the functional coupling between antral somatostatin and gastrin cells in pigs using isolated perfused preparations of the antrum with intact supply of the vagus nerves. Luminal acidification significantly inhibited gastrin secretion to 61 +/- 3% of basal secretion and increased somatostatin output 9-fold. Intra-arterial infusion of somatostatin to concentrations of 10(-10) and 10(-9) mol/l inhibited gastrin secretion to 18 +/- 9 and 33 +/- 11% of basal secretion. Electrical stimulation of the vagus nerves and intra-arterial infusion of gastrin-releasing polypeptide (GRP; 10(-9) mol/l) significantly increased both gastrin and somatostatin secretion. Addition to the perfusate of Fab fragments of somatostatin antibodies abolished the effect of somatostatin at 10(-10) mol/l and the acid inhibition of gastrin secretion, but had no effect on the response to vagus stimulation of GRP infusion. We conclude that a local release of somatostatin is essential for the acid-induced inhibition of gastrin secretion, whereas changes in the local somatostatin concentration are unlikely to play a major role in vagally or GRP-induced gastrin secretion.

Glucagon immunoneutralization in diabetic rats normalizes urea synthesis and decreases nitrogen wasting

To study the effect of glucagon neutralization on urea synthesis in diabetic rats, animals with newly induced (75 mg/kg streptozocin) experimental diabetes mellitus were divided into two groups. One group was given one weekly injection of nonimmune rabbit serum (n = 6), and the other group was given one weekly injection of a specific high-titer antibody against pancreatic glucagon (n = 6). Four weeks later, serum-treated diabetic rats had fasting glucagon concentrations 2-3 times higher than nondiabetic controls given one weekly injection of saline (control). Plasma glucagon binding capacity of diabetic rats given glucagon antibodies was 10-15 times higher than the glucagon concentration. A second group of nondiabetic controls were given nonimmune serum. Blood glucose concentration and urinary glucose output were identical in both groups of diabetic animals. Food intake doubled in both groups of diabetic rats. In control rats, the accumulated nitrogen balance, determined weekly for 4 wk, was positive at 81 +/- 3.1 mmol/96 h; in serum-treated diabetic rats, the accumulated nitrogen balance was negative, -8.3 +/- 2.4 mmol/96 h throughout the 4 wk, whereas it was higher at 4.7 +/- 2.3 mmol/96 h in the glucagon antibody-treated diabetic rats (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of immunoreactive pancreastatin in porcine tissues

Pancreastatin is a 49 amino acid peptide with a C-terminal glycine amide originally isolated from porcine pancreas. There are strong indications that pancreastatin is derived from chromogranin A, since the amino acid sequence 240-288 in porcine chromogranin A contains pancreastatin flanked by typical signals for proteolytic processing. In the present study the distribution and molecular nature of immunoreactive pancreastatin were examined in selected porcine tissues. For this purpose a radioimmunoassay specific for the C-terminal sequence of porcine pancreastatin, that did not cross-react with porcine chromogranin A was used in combination with gel permeation chromatography and reverse-phase high-pressure liquid chromatography (HPLC). We demonstrated the presence of pancreastatin, a C-terminal pancreastatin fragment and N-terminally extended molecular forms in the examined tissues. Pancreastatin predominated in the pancreas and stomach antrum, while N-terminally extended molecular forms were mainly present in the stomach body, jejunum and adrenal gland. The specific distribution pattern of the molecular forms probably reflects a tissue-specific processing of chromogranin A.

Role of the vasoactive intestinal peptide in a neuroendocrine regulation of the adrenal cortex

Using a method for isolation and perfusion of pig adrenal glands with preserved nerve supply, we measured the release of cortisol and aldosterone and of the vasoactive intestinal peptide (VIP) after electrical stimulation of the splanchnic nerves. Additionally, the effect of VIP (at final concentrations of 10(-10)-10(-7) M) in the perfusion medium on the release of cortisol and aldosterone was investigated. The amount of VIP contained within the adrenal was measured by chromatography, and the localization of VIP in the adrenal gland was investigated immunohistochemically. Stimulation of the splanchnic nerves provoked a significant release of VIP (2.7- to 17-fold) and of the corticosteroids cortisol (2.5- to 6.7-fold) and aldosterone (1.6- to 2.8-fold). VIP added to the perfusion medium stimulated secretion of both corticosteroids with a maximal effect at 10(-8) M. Cortisol release increased 20- to 58.5-fold over basal, aldosterone release increased 2.9- to 4.9-fold over basal. This VIP-stimulated release had the same range of magnitude as the release stimulated by adrenocorticotropic hormone in physiological concentrations (10(-10) M). The mean concentration of VIP-like immunoreactivity in the adrenal glands was 8.9 +/- 2.1 pmol/g wet weight. Immunohistochemical investigations showed immunoreactive cells within the adrenal medulla as well as VIP-ergic nerve fibers in the cortex of the adrenal gland. These data show that the adrenal cortex can be stimulated independent of the hypothalamus-pituitary-adrenal axis via a neuroadrenocortical axis. In this regulatory pathway, the VIP-ergic innervation of the adrenal cortex may be a potent stimulatory element.

Nerve fibers in the rat posterior pituitary lobe contain prosomatostatin (1-64)

The neurohormone and neurotransmitter somatostatin arises from the processing of a larger precursor, prosomatostatin (proSS). An immunohistochemical investigation in the rat, using a well-characterized antiserum raised against a synthetic peptide identical to the 20-36 residues of the proSS molecule, revealed the presence of immunoreactive nerve fibers and nerve terminals in the median eminence, infundibulum, infundibular stalk and posterior pituitary lobe. The largest number of immunoreactive nerve fibers and nerve terminals was observed in apposition to the portal vessels, whereas a moderate number of proSS-immunoreactive fibers was identified in the infundibular stalk and in the proximal part of the posterior pituitary lobe. The proSS-immunoreactive nerves entered the posterior pituitary lobe from the infundibular and pituitary stalks and were followed to rostral and ventral aspects of the organ. In contrast, positive fibers were rarely identified in caudal and posterior parts. Extracts of rat posterior pituitaries subjected to gel chromatography and reversed-phase high-pressure liquid chromatography (HPLC) analysis showed the presence of a single proSS-immunoreactive molecule corresponding to the size of proSS(1-64). The functional significance of the proSS(1-64) in the hypothalamus and pituitary is at present unknown, but its location in the hypothalamo-hypophyseal system suggests that this end product of the processing of proSS is released into the portal and perhaps also the general circulation.

Plasma glucagon and glucose recovery after hypoglycemia: the effect of total autonomic blockade

The role of the autonomic nervous system in the glucagon response to hypoglycemia has not been fully clarified. We have studied the effect of total pharmacological blockade of the autonomic nervous system (concomitant alpha- and beta-adrenergic blockade with simultaneous atropine injection) and of isolated alpha-adrenergic blockade on hormonal responses to hypoglycemia and on blood glucose recovery after hypoglycemia in healthy subjects. Neither of the pharmacological blockades had any significant effects on plasma glucagon responses to hypoglycemia nor had they any effect on the rate of blood glucose recovery after hypoglycemia. We conclude that the autonomic nervous system has no major influence on the glucagon response to hypoglycemia in healthy man. Changes in autonomic nervous activity are not essential for blood glucose recovery after hypoglycemia in healthy man.

Galanin and galanin extended at the N-terminus with seven and nine amino acids are produced in and secreted from the porcine adrenal medulla in almost equal amounts

Galanin is present in high concentrations in porcine adrenals, but nothing is known about the processing and secretion of other products of the 123-amino acid precursor preprogalanin. Using, in combination, RIA against galanin, a variety of chromatographic procedures, mass spectrometry, and amino acid sequencing, we studied the processed and the secreted products of preprogalanin. From the tissue extracts we isolated in equimolar amounts and sequenced two major pools of galanin immunoreactive peptides: galanin and two N-terminally extended forms, preprogalanin-(24-61) and preprogalanin-(26-61). The same peptides were identified upon gel chromatography and analytical HPLC in effluents collected during electrical stimulation of the intact splanchnic nerve supply of an isolated perfused preparation of porcine adrenals. The processing of preprogalanin in porcine adrenals thus includes the formation and release of galanin, preprogalanin-(24-61), and preprogalanin-(26-61). The signal peptidase cleaves the preprogalanin at either Gly23 or Gly25.

Emptying of the gastric substitute, glucagon-like peptide-1 (GLP-1), and reactive hypoglycemia after total gastrectomy

Postprandial glucagon-like peptide-1 (GLP-1), pancreatic glucagon, and insulin were measured in 27 tumor-free patients 43 months (median) after total gastrectomy and in four controls using a 99technetium-labeled 100-g carbohydrate solid test meal. Emptying of the gastric substitute was measured by scintigraphy. Fourteen patients suffered from early dumping symptoms, and five of them also reported symptoms suggestive of reactive hypoglycemia (late dumping). The median emptying half-time (T1/2) of the gastric substitute was 480 sec. Sigstad's dumping score was 8.5 +/- 1.6 (mean +/- SE) in patients with rapid emptying (T1/2 less than 480 sec), and 3.0 +/- 1.5 in patients with slow emptying of the gastric substitute (P = 0.02). The peak postprandial concentration of GLP-1 was 44 +/- 20 pmol/liter in controls, 172 +/- 50 in patients without reactive hypoglycemia, and 502 +/- 116 in patients whose glucose fell below 3.8 mmol/liter during the second postprandial hour. Plasma GLP-1 concentrations peaked at 15 min, and insulin concentrations at 30 min after the end of the meal. A close correlation between integrated GLP-1 responses and integrated insulin responses (r = 0.68) was observed. Multiple regression revealed that three factors were significantly associated with the integrated glucose concentrations during the second hour (60-120 min): Early (first 30 min) integrated GLP-1 (inverse correlation; P = 0.006), age (P = 0.006), and early integrated pancreatic glucagon (P = 0.005). There was a close (inverse) relationship of T1/2 with early integrated GLP-1 and pancreatic glucagon, but not with insulin. Gel filtration of pooled postprandial plasma of gastrectomized individuals revealed that all glucagon-like immunoreactivity eluted at Kd 0.30 (Kd, coefficient of distribution), the elution position of glicentin. Almost all of the GLP-1 like immunoreactivity eluted at Kd 0.60, the elution position of gut GLP-1. The authors contend that GLP-1-induced insulin release and inhibition of pancreatic glucagon both contribute to the reactive hypoglycemia encountered in some patients following gastric surgery. Rapid emptying seems to be one causative factor for the exaggerated GLP-1 release in these subjects.

Neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), but not galanin, are autonomic cotransmitters in the porcine pancreas

The neuropeptide galanin has been identified as a potential sympathetic cotransmitter in the canine pancreas. Immunoreactive galanin, also present in nerve fibers of the pig pancreas, was therefore measured in the effluent from isolated perfused pig pancreas with preserved sympathetic (splanchnic) or parasympathetic (vagal) innervation with radioimmunoassays directed against both the N-terminus and the C-terminus of galanin. Electrical vagus stimulation increased the pancreatic exocrine secretion, the secretion of insulin and glucagon, and the release of VIP, but did not influence galanin release. Splanchnic nerve stimulation increased perfusion pressure and glucagon secretion, inhibited insulin secretion, and increased the release of NPY, but galanin release was not affected. We conclude that the pancreatic galanin nerve fibers belong neither to the sympathetic nor to the parasympathetic divisions of the efferent nerve supply to the pig pancreas.

Substance P and neurokinin A are codistributed and colocalized in the porcine gastrointestinal tract

Immunoreactive substance P and neurokinin A were measured with radioimmunoassay in extracts of different segments of porcine gastrointestinal tract using C-terminally directed antisera. In all segments, the concentrations of substance P and neurokinin A were similar. The largest concentrations of both peptides were found in the mid-colon. By gel chromatography and reversed-phase high pressure liquid chromatography the immunoreactivity in extracts from ileum eluted as homogenous peptides at the positions of synthetic substance P and neurokinin A, respectively. No neurokinin B was found. By immunohistochemistry of porcine duodenum, jejunum, ileum and mid-colon, identical localization patterns were found for substance P and neurokinin A, and the two peptides demonstrated by double immunofluorescence to be colocalized in the enteric nervous system of the ileum. We conclude that the tachykinins substance P and neurokinin A are codistributed and colocalized in the procine gastrointestinal tract and suggest that the two peptides are produced from a common precursor, beta- and/or gamma-preprotachykinin, in the same neurons.

Identification, characterization and release of GRP gene-associated peptides from the normal porcine and human gastro-intestinal tract

Using a radioimmunoassay directed towards human proGRP (42-53) on acetic acid extracts, immunoreactivity was measured throughout the porcine GI-tract in concentrations that were parallel to those of GRP (gastrin-releasing peptide or 'mammalian bombesin'). Gel filtration and HPLC studies of human and porcine tissue extracts revealed that the immunoreactivity was mainly due to a peptide with a molecular size of 8-9 kDa. The peptide did not contain the GRP sequence, making it a major fragment of the GRP C-flanking part of proGRP. Furthermore, a peptide of similar size with proGRP (42-53) immunoreactivity was released from isolated, perfused preparations of porcine antral and non-antral stomach and pancreas in parallel with GRP in response to electrical stimulation of the vagus nerves. Our results suggest that a processing of preproGRP occurs in normal, adult human and porcine tissues, that is similar to that previously demonstrated in small cell lung carcinomas and human fetal lungs. The finding that the immunoreactive proGRP fragment is released from the tissues upon appropriate stimulation raises the question of a possible physiological role for proGRP products other than GRP.

Release of galanin from isolated perfused porcine adrenal glands: role of splanchnic nerves

We found a high concentration of galanin in extracts of porcine adrenal glands (114 pmol/g). By immunohistochemistry, galanin was localized to groups of medullary cells previously shown to produce norepinephrine. To study mechanisms for the release of galanin, we developed the following in vitro model: isolated perfused porcine adrenals with intact splanchnic nerve supply. When the nerves were electrically stimulated, epinephrine and norepinephrine secretion increased 276- and 291-fold, respectively, and galanin release increased up to 1,300-fold. Acetylcholine at 10(-6) M stimulated galanin release, and hexamethonium almost abolished the response to nerve stimulation. Galanin infusions had no effect on epinephrine and norepinephrine secretion in concentrations of 10(-8) and 10(-7) M, but increased both cortisol and aldosterone secretion (P less than 0.05). Splanchnic nerve stimulation in anesthetized pigs increased the concentration of galanin in the caval vein but not in arterial plasma. It is concluded that galanin, coreleased with catecholamines from the adrenal glands, may have endocrine functions but that galanin may also have local regulatory functions in the adrenals.

Human galanin: primary structure and identification of two molecular forms

From acid/ethanol extracts of surgical specimens of human large intestine we isolated two peptides, in approximately equal amounts, that reacted with an antiserum against porcine galanin. By amino acid analysis, sequence analysis and mass spectrometry, the larger of the two peptides was found to consist of 30 amino acid residues, the sequence of which was identical to that of porcine galanin except for the following substitutions: Val16, Asn17, Asn26, Thr29 and Ser30. Unlike porcine galanin, the carboxy-terminus was not amidated. The smaller peptide corresponded to the first 19 amino acid residues counted from the N-terminus of the 30 residue peptide (again without amidation). The structural analysis was repeated on another batch of tissue with identical results. By HPLC analysis of extracts of specimens from a further 4 patients, the same peptides were identified. Thus, human galanin includes two peptides of 19 and 30 amino acids that share the sequence of the N-terminal 15 residues with other mammalian galanins, but exhibit characteristic differences in the remaining part of the molecules.

C-cell hyperplasia accompanying thyroid diseases other than medullary carcinoma: an immunocytochemical study by means of antibodies to calcitonin and somatostatin

Eighteen normal thyroid glands and unaffected thyroid tissue adjacent to 37 follicular cell-derived benign and malignant tumors and to ten thyroid metastases were studied immunocytochemically with calcitonin (CT) and prosomatostatin/somatostatin (SMS) antibodies. CT- and SMS-immunoreactive cells were found in 100% of cases, though with ample variations in number. Most but not all SMS-immunoreactive cells also contained CT. Diffuse and/or nodular C-cell hyperplasia was seen in 30% of pathological thyroid glands; in concomitance with follicular adenomas, the mean C-cell number more than doubled that found in normal glands. Furthermore the proportion of SMS-immunoreactive C-cells increased from about 1% of CT-immunoreactive cells in normal adult thyroid glands to 2.5% in follicular adenomas, 3% in follicular carcinomas, 4.6% in papillary carcinomas, and 5.7% in metastases. The findings suggest that C-cell hyperplasia may be causally related to pathologic disorders affecting follicular cells. Furthermore, the demonstration that the intrathyroidal SMS cell mass is readily affected by alterations of the follicular structure of the gland suggests a possible regulatory role of SMS in the thyroidal microenvironment.

Gastrin-releasing peptide is a transmitter mediating porcine gallbladder contraction

We studied the role of gastrin-releasing peptide (GRP) for porcine gallbladder motility. Immunohistochemistry visualized nerve fibers containing GRP-like immunoreactivity in muscularis. GRP concentration dependently stimulated contractions of muscularis strips (ED50, 2.9 nM). Neuromedin B was less potent (ED50, 0.1 microM), suggesting existence of GRP-preferring receptors. GRP-induced contractions were unaffected by muscarinic antagonism (1 microM atropine), axonal blockade (1 microM tetrodotoxin), cholecystokinin (CCK) receptor antagonism (10 microM MK-329), or substance P desensitization (1 microM), supporting the existence of myogenic GRP receptors. The bombesin (BN) analogue D-Phe6-BN-(6-13)propylamide (PA) stimulated contractions (ED50, 3.3 nM) with low efficacy (29% of that of GRP). D-Phe6-BN-(6-13)PA (1 microM) shifted GRP concentration-response curves one log to the right. D-Phe6-BN-(6-13)PA interacted specifically with GRP receptors; while abolishing responses to GRP (1 nM), responses to substance P (0.1 microM) and CCK-8 (1 nM) were unchanged. Electrical stimulation (10 Hz, 0.5 ms, 10 V) caused a rapid onset-slow offset, tetrodotoxin-sensitive excitation. Atropine reduced the amplitude to 58% and caused a delayed, slow onset-slow decline response. D-Phe6-BN-(6-13)PA reduced the amplitude to 59% and caused a very rapid onset-rapid decline response. Atropine plus D-Phe6-BN-(6-13)PA abolished responses to nerve stimulation. Nerve stimulation caused significant release of GRP-like immunoreactivity. Thus two neural inputs were defined: a cholinergic rapid onset-rapid offset excitation and a delayed, slow onset-slow offset excitation caused by release and subsequent binding of GRP to GRP-preferring receptors.

Oxidation/reduction explains heterogeneity of pancreatic somatostatin

Somatostatin 14 (SS 14) has been isolated from pancreatic extracts, but open gel filtration immunoreactive SS often elutes in two peaks. We isolated both peaks, but upon sequence analysis only authentic SS 14 could be identified. By further gel filtration experiments it turned out that both synthetic and extractable SS appeared homogeneous at neutral pH 7.5, but showed an additional, earlier peak in acetic acid. After addition of mercaptoethanol, all of the SS eluted at this earlier position regardless of the pH. We conclude that partial reduction/oxidation of SS explains the heterogeneity.

Differential effects of secretin-fragments imply a dual mechanism of action for secretin

The effects of synthetic peptides, representing different parts of the secretin molecule in isolated mouse pancreatic islets have been investigated in perifusion studies. In the presence of 10 mM D-glucose the C-terminal nonapeptide Leu-Gln-Arg-Leu-Leu-Gln-Gly-Leu-Val-NH2 (S19-27) showed a 2-fold higher activity than that earlier shown for S22-27 and had the same effect on the dynamic pattern of insulin release as secretin, while the elongating sequence Leu-Gln-Arg (S19-21) had no effect on the insulin release. The nonapeptide Leu-Ser-Arg-Leu-Arg-Asp-Ser-Ala-Arg (S10-18) had no influence on the insulin release. Glucagon release seen after intact secretin could not be shown for any of the smaller fragments. Accumulation of cAMP in the islets as seen with secretin, could at 10 mmol/L D-glucose only be demonstrated with S22-27 or S19-27 but not with S10-18 or S1-6. Our results indicate that full size secretin has to be present to stimulate glucagon release while insulin-releasing activity can be confined to the C-terminal part of the hormone.

Proglucagon products in plasma of noninsulin-dependent diabetics and nondiabetic controls in the fasting state and after oral glucose and intravenous arginine

We investigated the major products of proglucagon (PG) processing in plasma in the fasting state, after intravenous arginine and after an oral glucose load in noninsulin-dependent diabetics (NIDDM) and in weight matched controls using specific radioimmunoassays and analytical gel filtration. In the fasting state the glucagonlike peptide-1 (GLP-1) immunoreactivity was significantly elevated in the NIDDM group compared with the control group. Both after intravenous arginine and after an oral glucose load a rise in the plasma concentrations of all immunoreactive moieties measured was seen. All integrated incremental responses after intravenous arginine were identical in the two groups. After oral glucose the insulin concentrations in plasma were lower and the concentrations of all proglucagon products were higher in the NIDDM group compared to the control group. The gel filtration analysis showed that arginine stimulated the secretion of pancreatic glucagon (PG 33-61), major proglucagon fragment (PG 72-158) and probably GLP-1 (PG 72-107 amide) in both groups, whereas oral glucose stimulated the secretion of glicentin (PG 1-69) and intestinal GLP-1 (PG 78-107 amide), an insulinotropic hormone. The elevated levels of immunoreactive GLP-1 in diabetics in the fasting state were mainly due to an increased concentration of major proglucagon fragment.

Short time effects of growth hormone on glucose metabolism and insulin and glucagon secretion in normal man

The present study was undertaken in order to evaluate the acute metabolic and hormonal effects of human growth hormone in healthy subjects. Glucose turnover, plasma glucose, FFA, insulin, C-peptide, glucagon, and somatostatin concentrations were determined in the fasting state after a bolus injection of placebo or growth hormone in quantities producing increases in plasma growth hormone levels within the normal physiological range. We found that growth hormone administration resulted in negligible changes in plasma glucose, no significant changes in appearance or disappearance rates of glucose, a moderate increase in FFA and a moderate fall in plasma insulin, C-peptide and glucagon concentrations, while plasma somatostatin levels were unchanged. These findings suggest that rapid changes in plasma growth hormone concentrations, corresponding to the fluctuations seen during normal daily life, may play a role in the short time regulation of blood glucose concentration through an inhibition of insulin and glucagon secretion.

Galanin and vasoactive intestinal polypeptide: coexistence and corelease from the vascularly perfused pig ileum during distension and chemical stimulation of the mucosa

By immunohistochemistry and double staining technique, almost complete coexistence of galanin-like immunoreactivity (GAL-LI) and vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) was demonstrated in submucosal ganglionic cells and mucosal nerve fibers of the porcine ileum. The release of the two neuropeptides was studied in isolated, vascularly perfused pig ileum. Distension (increasing intraluminal pressure by 10 mm Hg) and intraluminal instillation of homologous gallbladder bile, amino acids, 0.1 M HCl, hypertonic NaCl (3,400 mosm x kg-1) and hypertonic glucose (1,100 mosm x kg-1) all increased the release of GAL-LI and VIP-LI into the venous effluent in parallel. Being the most potent stimulus, bile increased the output of GAL-LI from 0.74 +/- 0.12 to 2.44 +/- 0.81 pmol/min (mean +/- SE, p = 0.018) and the output of VIP-LI from 3.29 +/- 0.19 to 12.68 +/- 4.01 pmol/min (p less than 0.001), respectively. In conclusion, the coexistence and parallel release of GAL and VIP suggest that GAL/VIP neurons may be involved in intramural secretory and motor reflexes.

Immunocytochemical localization and identification of prosomatostatin gene products in medullary carcinoma of human thyroid gland

Thirty-three cases of histologically proven calcitonin-positive medullary thyroid carcinoma were studied immunocytochemically for the occurrence of prosomatostatin-related peptides. Positive cells, identified with a panel of antisera raised against four different regions of the prosomatostatin molecule, were found in 100% of the tumors. Most but not all somatostatin-positive cells were also immunoreactive for calcitonin. Notably, seven patients harboring somatostatin-rich tumors revealed a more favorable clinical course. The results (1) indicate that somatostatin production is a universal concomitant of thyroid medullary carcinoma, (2) suggest that these cells are likely to produce a somatostatin precursor molecule similar to mammalian prosomatostatin, and (3) imply that somatostatin-reactive cells may have as yet unknown roles in these tumors, possibly in the realm of paracrine and autocrine regulation of cell growth.

Endocrine, metabolic and cardiovascular responses to adrenaline after abdominal surgery

Adrenaline-induced changes in heart rate, blood pressure, plasma adrenaline and noradrenaline, cortisol, glucagon, insulin, cAMP, glucose lactate, glycerol and beta-hydroxybutyrate were studied preoperatively and 4 and 24 h after skin incision in 8 patients undergoing elective cholecystectomy. Late postoperative responses of blood glucose, plasma cAMP, lactate and glycerol to adrenaline infusion were reduced, whereas other responses were unaffected. Blood glucose appearance and disappearance rate as assessed by [3H]3-glucose infusion was unchanged pre- and postoperatively. The increase in glucose appearance rate following adrenaline was similar pre- and postoperatively. These findings suggest that several beta-receptor-mediated responses to adrenaline are reduced after abdominal surgery.

Effects of splanchnic nerve stimulation on the adrenal cortex may be mediated by chromaffin cells in a paracrine manner

The effects of nerve activation and of the catecholamines epinephrine and norepinephrine on adrenal corticosteroid release were investigated in intact isolated perfused pig adrenals with preserved nerve supply. To study the contact zones of medullary and cortical tissues, porcine adrenals were examined on the histological and ultrastructural levels. Splanchnic nerve activation stimulated in parallel the release of epinephrine (from a basal value of 0.31 +/- 0.11 to 8.13 +/- 0.60 microgram/min) and norepinephrine (from 0.76 +/- 0.68 to 12.94 +/- 3.58 micrograms/min) and the release of the corticosteroids cortisol (from 0.62 +/- 0.19 to 2.00 +/- 0.35 micrograms/min) and aldosterone (from 3.34 +/- 0.59 to 7.53 +/- 1.63 ng sigma in). Also, perfusion of the isolated adrenals with catecholamines provoked a significant release of the corticosteroids. Epinephrine (10(-6) M) stimulated the release of cortisol (from 0.59 +/- 0.31 to 2.66 +/- 0.34 micrograms/min) and aldosterone (from 2.12 +/- 0.42 to 4.68 +/- 0.92 ng/min). Norepinephrine (10(-6) M) stimulated the release of cortisol (from 0.26 +/- 0.07 to 1.28 +/- 0.10 micrograms/min) and aldosterone (from 1.28 +/- 0.37 to 3.57 +/- 0.80 ng/min). Using an immunostaining for synaptophysin, which is specific for neuroendocrine cells, chromaffin cells could be detected within all three zones of the adrenal cortex. The two endocrine tissues appear to be closely interwoven. On the ultrastructural level, medullary cells are in apposition to cortical cells, with close cellular contacts. These results show that the release of corticosteroids cortisol and aldosterone can be stimulated through the sympatho-adrenal system. Taking into consideration the close colocalization of cortical and medullary tissues, this stimulation may be mediated by chromaffin cells in a paracrine manner.

Somatostatin release induced by gastrin-releasing peptide in man. Effect of proximal gastric vagotomy and cholinergic blockade

The influence of intragastric pH on the basal release of somatostatin has been studied in healthy controls and in duodenal ulcer patients. In addition the somatostatin response to gastrin-releasing peptide infusion has been evaluated both regarding the effect of intragastric pH and the influence of vagal innervation and muscarinic blockade. No difference was found in basal blood levels, when changing the intraluminal pH, although a slightly higher basal somatostatin concentration was noticed in patients with duodenal ulcer disease. Neither proximal gastric vagotomy nor cholinergic blockade had any effect on basal somatostatin concentrations. GRP infused in stepwise increasing doses from 20 pmol/kg/h to 400 pmol/kg/h induced a small but significant response. This effect of GRP was most evident, when the stomach was perfused with 0.1 M HCl. The small, somatostatin response to GRP infusion was not influenced by vagal denervation of the parietal cell area, neither by cholinergic blockade. Despite the previously observed effects of vagotomy and cholinergic blockade on gastrin release induced by GRP, a corresponding inverse effect on somatostatin is not apparent.

Porcine pancreastatin has no effect on endocrine secretion from the pig pancreas

We investigated the effects of porcine pancreastatin on the endocrine and unstimulated exocrine secretion of isolated, perfused porcine pancreas. Pancreastatin in a concentration of 10(-8) mol/l had no effect on basal secretion of insulin, glucagon and somatostatin at a perfusate glucose concentration of 5 mmol/l (n = 4) and neither at 10(-8) nor 10(-7) mol/l influenced the hormone responses to acute elevations of perfusate glucose concentration from 3.5 to 11 mmol/l (n = 7). This elevation strongly stimulated insulin secretion and inhibited glucagon secretion. Exocrine secretion was not affected by pancreastatin. The results suggest that pancreastatin does not directly influence pancreatic secretion.

Galanin in the porcine pancreas

Galanin, a 29 amino acid neuropeptide, was recently isolated from pig intestine. We studied the localization, nature and effect of galanin in pig pancreas. Galanin immunoreactive nerve fibers were regularly found in the pancreas. A peptide chromatographically similar to synthetic galanin was identified in pancreas extracts. The effect of galanin on the endocrine and exocrine secretion was studied in isolated pancreases, perfused with a synthetic medium containing 3.5, 5 or 8 mmol/l glucose and synthetic galanin (10(-10)-10(-8) mol/l). There was no effect on the basal exocrine secretion. The output of insulin, glucagon, somatostatin and pancreatic polypeptide (PP) was measured in the effluent. There was no effect on PP secretion. At a perfusate glucose concentration of 5 mmol/l, galanin at 10(-9) mol/l increased insulin secretion by 55 +/- 14% (mean +/- S.E.M., n = 5) of basal secretion, and at 10(-8) mol/l by 58 +/- 27% (n = 6). At 8 mmol/l glucose, insulin secretion increased by 25 +/- 10% (n = 6) and 62 +/- 17% (n = 8). At 5 mmol/l glucose glucagon secretion was increased by 15 +/- 3% (n = 5) by galanin at 10(-9) mol/l and by 29 +/- 11% (n = 5) by galanin at 10(-8) mol/l, and at 8 mmol/l glucose by 66 +/- 27% and 41 +/- 25%. Somatostatin secretion was inhibited to 72 +/- 2% (n = 5) of basal secretion by galanin at 10(-9) mol/l and to 65 +/- 7% (n = 7) at galanin at 10(-8) mol/l, both at 5 mmol/l glucose. At 8 mmol/l the figures were 83 +/- 6% and 70 +/- 10%. Insulin secretion in response to square wave increases in glucose concentration from 3.5 to 11 mmol/l (n = 5) increased 2-fold during simultaneous perfusion with galanin (10(-8) mol/l).

Inhibition of gastric acid secretion by jejunal glucose and its relation to osmolality and glucose load

Intrajejunal infusion of hypertonic glucose and hypertonic saline inhibits pentagastrin-stimulated gastric acid secretion in man. This effect is generally ascribed to the hyperosmolality of the solutions. Five volunteers were given 50 g glucose in osmolar concentrations of 2700 mosmol/l and 900 mosmol/l, and five were given 25 g glucose in osmolar concentrations of 2700 mosmol/l and 300 mosmol/l. Control studies with intrajejunal infusion of physiologic saline were performed in all subjects. Median inhibition of gastric acid secretion was 91% after 50 g glucose and 47% after 25 g glucose and was unrelated to the osmolar concentration. These findings suggest that the acid-inhibitory effect of intrajejunally administered glucose is related to the glucose load and not to the osmolar concentration. Plasma responses of intact neurotensin, immunoreactivity, NH2-terminal neurotensin immunoreactivity, enteroglucagon, and gastric inhibitory polypeptide were all related to the amount of glucose given. Glucagon and somatostatin, both of which are potent inhibitors of gastric secretion, were not released by intrajejunally administered glucose.

Galanin: distribution and effect on contractile activity and release of vasoactive intestinal polypeptide from the isolated perfused porcine ileum

In the pig ileum galanin (GAL)-like immunoreactivity was identified in nerve cell bodies of the submucous plexus and in nerve fibers of the circular and longitudinal muscle layer. Infusion of 5.10(-10)-10(-8) M of GAL into the arterial line of the isolated perfused porcine ileum decreased the frequency of spontaneous phasic contractions in a dose-dependent manner. The frequency of phasic contractions during maximal inhibition by GAL 10(-8) M was 13 +/- 4% (mean +/- SE) of basal frequency (p less than 0.05). The recovery from inhibition by GAL 10(-8) M lasted 16 +/- 1 min. Tonic contractions were not observed in this experimental set-up, neither by standard perfused catheter manometry nor by measurement of cross-sectional area of an intraluminally located balloon. Infusion of GAL 10(-8) M decreased the venous release of vasoactive intestinal polypeptide to 80 +/- 8% of basal release (p less than 0.05). It is concluded that GAL may participate in the regulation of small intestinal motility in the pig.

Pancreatic spasmolytic polypeptide, a potential growth factor for the intestine: neural control of secretion

We studied the effect of electrical stimulation of the vagus nerves and the effect of vasoactive intestinal polypeptide (VIP) on the secretion of pancreatic spasmolytic polypeptide (PSP) from isolated perfused porcine pancreas. We measured the concentration of PSP in the pancreatic juice and in the venous effluent by radioimmunoassay. The concentration in the pancreatic juice varied between 1 and 180 micrograms/ml, and in the venous effluent between 1 and 10 ng/ml. PSP is thus mainly an exocrine product. However, the concentrations in juice and venous effluent varied in parallel. Electrical vagus stimulation increased the output in the juice of PSP approximately 30 times. Atropine (10(-6) M) prevented the increase in PSP concentration during vagus stimulation, but only partially inhibited the output. VIP (10(-8) M) increased the output of PSP but decreased the concentration. We conclude from these results that PSP secretion is controlled by neural parasympathetic mechanisms that include both cholinergic and peptidergic pathways.

The relationship between some beta-adrenergic mediated responses and plasma concentrations of adrenaline and cyclic AMP in man

To test the hypothesis that increments in plasma cyclic AMP during beta-adrenergic stimulation reflect integrated second messenger function of the tissues activated by the agonist, graded adrenaline infusion resulting in plasma adrenaline concentrations within the physiological range was performed in 8 healthy subjects with and without concomitant beta-adrenoceptor blockade by iv propranolol. A significant correlation was found between increments in plasma adrenaline and plasma cyclic AMP in the experiments without beta-blockade; during concomitant beta-blockade the increase in plasma cyclic AMP concentrations at low adrenaline infusion rates was prevented, whereas a small increase in cyclic AMP was found at high adrenaline infusion rates, probably owing to incomplete beta-receptor blockade. Likewise, the adrenaline-induced increments in blood substrates (glucose, lactate, glycerol and beta hydroxybutyric acid) were significantly reduced but not completely prevented by beta-blockade. We conclude that an altered relationship between beta-agonist concentrations and plasma cyclic AMP may provide evidence for the existence of differences in beta-adrenergic sensitivity in man.

Identification of the neurotransmitter/neuromodulator functions of the neuropeptide gastrin-releasing peptide in the porcine antrum, using the antagonist (Leu13-psi-CH2 NH-Leu14)-bombesin

We studied the effects of a new bombesin/gastrin-releasing peptide (GRP) receptor antagonist, Leu13-psi-(CH2NH)-Leu14-bombesin, on the secretion of gastrin and somatostatin and on the motor activity of isolated perfused porcine antrum in response to infusions of GRP at 10(-10) or 10(-9) mol/l and in response to electric stimulation of the vagus nerves. GRP significantly increased the secretion of gastrin and somatostatin and increased the frequency of antral contractions threefold. At 0.5 x 10(-6) mol/l the antagonist completely abolished the effects on motality and gastrin secretion and strongly inhibited the effect on somatostatin secretion. Vagus stimulation significantly increased gastrin and somatostatin secretion and increased the contraction frequency threefold. The antagonist strongly inhibited the somatostatin response, abolished the motility effects and reversed the stimulatory effect on gastrin secretion to a significant inhibition. Assuming that the antagonist interacts specifically with GRP receptors, we conclude that our data strongly support the concept that GRP-producing nerves are essential for vagally induced secretion of gastrin and somatostatin from the antrum. The GRP nerves may also play a role in the control of gastric motor activity.

Elevated plasma concentrations of C-flanking gastrin-releasing peptide in small-cell lung cancer

Many small-cell lung cancers (SCLCs) produce gastrin-releasing peptides (GRPs) (mammalian bombesin) but the plasma concentration of GRP is rarely elevated, possibly because of its rapid elimination. We developed a radioimmunoassay for the C-terminal flanking peptide of proGRP and measured its concentration in plasma from 71 patients with SCLC, in 27 healthy subjects and in 49 patients with other diseases including lung carcinomas. In addition, we studied the molecular size of immunoreactive C-flanking peptide in two SCLC cell lines and in plasma from SCLC patients. The concentration of immunoreactive C-flanking peptide in normal subjects and in control patients did not exceed 10 pmol/L and 26 pmol/L, whereas 72% of the SCLC patients had C-flanking peptide concentrations above 10 pmol/L. In patients with extensive disease (n = 35) the median concentration was 71 pmol/L (range, 10 to 940). ProGRP C-flanking peptide levels paralleled the clinical course in 12 patients. The molecule(s) responsible for the immunoreactivity had a molecular size of about 8 to 10 kd in both patient plasma and tumor cell lines, suggesting that the measured peptide(s) represented major fragment(s) if not the entire C-flanking peptide of proGRP. Thus this peptide(s) seems to be a useful marker for SCLC.

Release of PYY from pig intestinal mucosa; luminal and neural regulation

The localization, molecular nature and secretion of Peptide YY (PYY), a putative gut hormone belonging to the Pancreatic Polypeptide family of peptides, was studied in pigs. Immunoreactive PYY was identified in a population of endocrine cells in the mucosal epithelium of the pig ileum. Release of PYY was observed in isolated perfused pig ileum in response to luminal stimulation with glucose and vascular administration of the neuropeptide gastrin-releasing peptide (GRP). Electrical stimulation of the vagus nerve supply to the distal small intestine in intact anaesthetized pigs resulted in release of PYY into the circulation. Stimulation of the splanchnic nerves did not affect the basal release of PYY. PYY-immunoreactivity extracted from ileal tissue or released to plasma or perfusate from the ileum was indistinguishable from synthetic porcine PYY by gel filtration and reverse phase HPLC. It is concluded that the secretion of PYY in the pig ileum may be regulated not only by nutritional luminal factors, but also by postsynaptic parasympathetic nerves.

Proglucagon expression, posttranslational processing and secretion in SV40-transformed islet cells

HIT T15 is a B cell line derived from SV40 transformation of hamster islets. We describe here a HIT T15 variant, designated HIT T15-G, which appears to have evolved spontaneously and which expresses glucagon. Regulation of glucagon gene expression, posttranslational processing of proglucagon, and secretion of glucagon were studied in this cell line. Glucagon mRNA concentrations were increased approx. 2-fold following incubation of cells for 18 h in 10 microM forskolin but were unaffected by treatment with a phorbol ester (12-O-tetradecanoylphorbol 13-acetate; TPA) or with ionomycin. Proglucagon was processed to glucagon, and several large molecular weight forms of GLP-I and GLP-II which may include the major proglucagon fragment (MPF). The secretion of glucagon was stimulated by forskolin (5-fold), adrenalin (2-fold), arginine (3-fold) and KCl (2-fold) but was unaffected by glucose. These results suggest that the HIT T15-G cells may represent a less differentiated form of the parental HIT T15 cell line in which A cell phenotype is dominant but not complete.

Role of gastrin-releasing peptide in neural control of pancreatic exocrine secretion

We studied the effect of electrical stimulation of the vagus nerves on the exocrine secretion of isolated perfused porcine pancreas before and after procedures that almost completely blocked the effects elicited by infusions of gastrin-releasing peptide (GRP): desensitization of the pancreas for GRP (by perfusion with high concentrations of GRP); administration of an antagonist of GRP action [D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P]; and perfusion with Fab fragments of antibodies against GRP. Both desensitization and antagonist administration significantly (p less than 0.01) inhibited the effect of vagus stimulation on pancreatic protein secretion (by 42.1 and 33%). The inhibitory effect of anti-GRP perfusion was less pronounced (22% inhibition, 0.05 greater than p less than 0.1). The results support the notion that pancreatic, GRP-producing nerve fibers are involved in the neural control of pancreatic enzyme secretion.

Oxyntomodulin from distal gut. Role in regulation of gastric and pancreatic functions

We studied the effects of intravenous infusion of synthetic oxyntomodulin (proglucagon 33-69), a potential hormone from the ileal mucosa, on fasting and postprandial gastric acid secretion, gastric emptying, gastroduodenal motility, and pancreatic secretion of trypsin and lipase measured simultaneously in six normal volunteers using multilumen tubes for infusion of markers, manometry, and aspiration of gastric and duodenal contents. The infusion resulted in plasma concentrations of 203 +/- 21 pmol/liter (mean +/- SEM) of oxyntomodulin, regarded as high but not unphysiological concentrations of the peptide. Oxyntomodulin almost abolished basal acid secretion and inhibited postprandial acid secretion by 35 +/- 10%. Gastric emptying decreased significantly; the time for 50% to leave the stomach increased from 17.3 +/- 2.2 min to 34.7 +/- 8.0 min. The postprandial gastroduodenal motility was massively inhibited by oxyntomodulin. Postprandial trypsin and lipase output was significantly inhibited by 56 +/- 12% and 42 +/- 11%, respectively, during oxyntomodulin infusion. However, pancreatic enzyme output was linearly related to gastric emptying and oxyntomodulin did not influence this relationship, suggesting that oxyntomodulins effect was due to its effect on gastric emptying. Oxyntomodulin seems to play an important role in the small intestinal inhibitory control of gastropancreatic functions.

Complete sequences of glucagon-like peptide-1 from human and pig small intestine

In the small intestine, proglucagon is processed into the previously characterized peptide "glicentin" (proglucagon (PG) 1-69) and two smaller peptides showing about 50% homology with glucagon: glucagon-like peptide-1 and -2. It was assumed that the sites of post-translational cleavage in the small intestine of the proglucagon precursor were determined by pairs of basic amino acid residues flanking the two peptides. Earlier studies have shown that synthetic glucagon-like peptide-1 (GLP-1) synthesized according to the proposed structure (proglucagon 71-108 or because residue 108 is Gly, 72-107 amide) had no physiological effects, whereas a truncated from of GLP-1, corresponding to proglucagon 78-107 amide, strongly stimulated insulin secretion and depressed glucagon secretion. To determine the amino acid sequence of the naturally occurring peptide we isolated GLP-1 from human small intestine by hydrophobic, gel permeation, and reverse-phase high performance liquid chromatography. By analysis of composition and sequence it was determined that the peptide corresponded to PG 78-107. By mass spectrometry the molecular mass was determined to be 3295, corresponding to PG 78-107 amide. Furthermore, mass spectrometry of the methyl-esterified peptide showed an increase in mass compatible with the presence of alpha-carboxyl amidation. Thus, the gut-derived insulinotrophic hormone GLP-1 is shown to be PG 78-107 amide.

On the regulatory functions of neuropeptide Y (NPY) with respect to vascular resistance and exocrine and endocrine secretion in the pig pancreas

We compared the effects of electrical stimulation of the splanchnic nerves and infusions of neuropeptide Y, noradrenaline or a combination of the two on pancreatic vascular resistance and exocrine and endocrine secretion. For these studies we used isolated perfused pig pancreas with preserved splanchnic nerve supply. The exocrine secretion was stimulated with physiological concentrations of secretin and cholecystokinin octapeptide. Noradrenaline and NPY at 10(-8) M both increased pancreatic perfusion pressure. Their effects were additive and similar in magnitude to that of electrical stimulation of the splanchnic nerves at 4-8 Hz. Nerve stimulation as well as NPY and noradrenaline infusions inhibited exocrine secretion, but an additive effect could not be demonstrated. Neither NPY nor noradrenaline could reproduce the stimulatory effect of nerve stimulation on glucagon secretion, nor the weak inhibitory effect on somatostatin secretion. NPY alone had no effect on insulin secretion and did not influence the inhibitory effect of noradrenaline. It is concluded that NPY is likely to cooperate with noradrenaline in the control of pancreatic blood flow, whereas its role in the control of pancreatic secretion is likely to be of minor importance, if any.

Prosomatostatin 1-64 is a major product of somatostatin gene expression in pancreas and gut

Prosomatostatin (pro-SS) is a peptide of 92 amino acids which contains the extensively studied somatostatin (SS) 1-28 and SS 1-14 at the C terminus. Little is known about the N-terminal part of pro-SS. In previous studies, using a radioimmunoassay against pro-SS 20-36 (sequence deduced from human cDNA sequence) we have identified a peptide with a molecular mass of approximately 8000 daltons in extracts of pancreas and intestinal mucosa. Using a variety of chromatographic procedures we have now isolated this peptide from extracts of pancreas and intestinal mucosa from pigs. The isolated peptides were sequenced on an Applied Biosystems gas phase sequenator and cleaved with the Asp-N endopeptidase for sequencing of C-terminal fragments. The peptides had an amino acid sequence identical to human pro-SS 1-64. In effluent from isolated perfused preparations of porcine small intestine and pancreas we identified upon appropriate stimulation pro-SS 20-36 immunoreactive peptides that by isocratic high pressure liquid chromatography appeared identical to pro-SS 1-64. An identical peptide was identified in pig plasma. Thus, in pancreas and gut pro-SS processing gives rise to the same pro-SS 1-64 molecule in spite of differential processing of the C terminus (SS 1-14 in pancreas and SS 1-28 in gut). The eventual hormonal role of pro-SS 1-64 may now be evaluated.

Pancreastatin-like immunoreactivity and insulin are released in parallel from the perfused porcine pancreas

Pancreastatin, a peptide isolated from the porcine pancreas, suppresses insulin release from pancreatic islets of the rat. Pancreastatin immunoreactivity has been localized to islet B and D cells in the porcine pancreas. We have developed a RIA for this peptide, using rabbit anti-porcine pancreastatin antibodies and 125I-Tyr-pancreastatin. Isolated pig pancreata were perfused with a nonrecirculating bicarbonate buffer solution containing 4% Dextran and 0.1% Albumin. Glucose (11 mmol/liter) induced a biphasic release of pancreastatin-like immunoreactivity (PLI). Electrical stimulation of the vagus nerves (8 Hz), as well as perfusion with acetyl choline (10(-6) mol/liter) in the presence of 5.5 mmol/liter glucose, also evoked prompt PLI responses. Furthermore, truncated GLP-1 (proglucagon 78-107; 10(-9) mol/liter) induced PLI release. All tested stimuli also elicited insulin secretion. To investigate whether the PLI measured could be ascribed to secretion of the low molecular weight pancreastatin (Mr 5,100) or to a possible precursor such as chromogranin A (Mr approximately 75,000), perfusates containing PLI were subjected to gel filtration on an Ultropac G3000SW column. All of the PLI was recovered at the elution position of the pancreastatin marker. In conclusion, PLI and insulin are released in parallel from the perfused porcine pancreas, exposed to stimuli known to affect insulin release.

GLP-1 (glucagon-like peptide 1) and truncated GLP-1, fragments of human proglucagon, inhibit gastric acid secretion in humans

Glucagon-like peptide 1 amide (GLP-1 amide), a predicted product of the glucagon gene (proglucagon 72-107-amide), and truncated GLP-1 (proglucagon 78-107-amide), recently isolated from porcine small intestine, were infused in doses of 100 and 400 ng/kg/hr and 12.5 and 50 ng/kg/hr, respectively, into eight volunteers to study pharmacokinetics and effects on pentagastrin-stimulated gastric acid secretion (plateau stimulation with pentagastrin at D50: 100 ng/kg/hr). The concentration of GLP-1 in plasma increased from 64 +/- 12 to 189 +/- 23 and 631 +/- 76 pmol/liter, respectively. The concentration of truncated GLP increased from approximately 7 pmol/liter to 28 +/- 3 pmol/liter during the high rate of infusion. A similar increase was seen in response to a mixed meal in eight normal volunteers. The metabolic clearance rate (MCR) of GLP-1 was 2.2 +/- 0.3 and 2.6 +/- 0.3 ml/kg/min, respectively, and the half-life in plasma was 17 +/- 2 min. The MCR of truncated GLP-1 was 13 +/- 2.8 ml/kg/min and the half-life 11.4 +/- 2.1 min. GLP-1 reduced the pentagastrin-stimulated acid secretion 16 +/- 9% during the low-rate infusion and 23 +/- 12% during the high rate (P less than 0.05). Truncated GLP-1 caused a 36 +/- 3% inhibition during the high infusion rate. Thus truncated GLP-1, a naturally occurring peptide, is a potent inhibitor of acid secretion in man and more so than GLP-1.

Effect of low-dose exogenous secretin and somatostatin on pentagastrin-stimulated gastric acid secretion in man

The inhibitory effect of intravenous infusion of secretin (0.05 CU kg-1h-1) and somatostatin (60 pmol kg-1h-1), given alone or in combination, on pentagastrin-stimulated (100 ng kg-1 h-1) acid secretion was studied in 10 healthy subjects. Secretin inhibited acid secretion by 54% (p less than 0.05), and somatostatin inhibited by 70% (p less than 0.05). The combined infusion of secretin and somatostatin decreased acid output by 64% (p less than 0.05). The differences between the three groups were not significant (p greater than 0.05). Median plasma concentrations of secretin and somatostatin were of the same magnitude as seen after duodenal acidification. The present study did not demonstrate any interaction between secretin and somatostatin in the inhibition of gastric acid secretion.