Nervous control of pancreatic endocrine secretion in pigs. II. The effect of pharmacological blocking agents on the response to vagal stimulation

The glucose dependent glucagon and insulin responses to electrical vagal stimulation in anesthetized splanchnicotomized young pigs were studied after administration of various pharmacological blocking agents. Hexamethonium completely abolished the responses, regardless of the glucose level. Atropine was without effect on the glucagon as well as the insulin response, regardless of stimulation frequency, glucose level, or dose of atropine. Neither propranolol nor a combination of propranolol and phenoxybenzamine inhibited the response. Our findings indicate that neither adrenergic fibres nor fibres impinging on muscarinic cholinergic receptors are involved in the pancreatic endocrine response to vagal stimulation.

Nervous control of gastro-pancreatic somatostatin secretion in pigs

The influence of the autonomic nervous system on the secretion of somatostatin from the antral and the fundic parts of the stomach and from the pancreas of the pig was investigated in experiments involving electrical stimulation of the vagal nerves and the splanchnic nerves in (1) intact, anesthetized pigs and (2) isolated perfused preparations of (a) antrum with intact vagal supply, (b) pancreas with intact vagal supply, (c) pancrease with intact sympathetic supply. The results clearly demonstrated that parasympathetic activity inhibits D-cell function in all gastro-pancreatic tissues; antral gastrin secretion was inversely correlated to somatostatin secretion and it is suggest that antral D-cell secretion participates in the control of gastrin secretion; the inhibitory effect of Gastric Inhibitory Polypeptide (GIP) as well as intraluminal HCl on gastrin secretion may be exerted via the stimulatory effect of both on somatostatin secretion. The sympathetic innervation of the pancreas is also clearly inhibitory to the pancreatic somatostatin secretion, whereas sympathetic nervous activity influences little the gastric somatostatin release.

Nervous control of pancreatic endocrine secretion in pigs. I. Insulin and glucagon responses to electrical stimulation of the vagus nerves

The increases in the concentrations of insulin and pancreatic glucagon in portal venous and arterial plasma in response to electrical stimulation of the vagus nerves were studied in anesthetized splanchnicotomized young pigs. The responses were frequence dependent; threshold frequency was below 1 Hz and maximum response was reached at 8-12 Hz. With maximal stimulation responses of magnitudes comparable to the responses to maximal arginine (glucagon) and glucose stimulation (insulin) were observed. However, both the insulin and the glucagon response were critically dependent on the blood glucose concentration during the stimulation: the glucagon response was inversely correlated to blood glucose, whereas the insulin response was positively correlated to blood glucose at concentrations above 4.5 mmol . 1(-1). Below this glucose concentration there was no detectable insulin response and above 8.0 mmol . 1(-1) no glucagon response to vagal stimulation. A stimulated secretion of glucagon as well as insulin was maintained for up to 30 min stimulation, but insulin secretion tended to decrease, whereas glucagon secretion tended to increase. Above blood glucose concentrations of 4 mmol . 1(-1), blood glucose concentrations increased slightly in response to vagal stimulation, whereas no change was noted during stimulations performed at lower blood glucose concentrations.

Effect of sulfation of CCK-8 on its stimulation of the endocrine and exocrine secretion from the isolated perfused porcine pancreas

The secretory effect of sulfated and nonsulfated cholecystokinin octapeptide (CCK-8) was studied on the isolated perfused porcine pancreas. Both CCKs in concentrations from 10(-11) to 10(-8) mol/l in the presence of glucose (7.5, 5.0 or 3.5 mmol/l) were without effect on insulin and glucagon release. The exocrine secretion was stimulated by both CCKs in a dose-dependent manner, but sulfated CCK-8 was considerably more potent. The study shows that CCK-8, a major constituent of endogenous CCK, does not contribute to the incretin mechanism, irrespective of degree of sulfation. In contrast, CCK-8 is a potent stimulator of exocrine pancreatic secretion. For this effect sulfation is crucial.

Tyrosine A14[125I]monoiodoinsulin: Preparation, Biologic Properties, and long-term stability

125I-insulin was prepared by reacting 17.4 nmol porcine insulin (100 micrograms) with 5 mCi 125I (about 2.4 nmol) using the lactoperoxidase method. The reaction product was subjected to gel electrophoresis and the band containing A14 [125I]monoiodoinsulin was eluted. This preparation showed a specific activity of about 1.5 Ci/mumol as evaluated by radioimmunoassay and bioassay, i.e., about 75% of the theoretical maximum. The content of radioactive derivatives other than A14 monoiodoinsulin was less than 2%. The binding affinity of tracer A14 monoiodoinsulin to adipocytes, hepatocytes, and cultured human lymphocytes was twice as high as that of A19 monoiodoinsulin. Binding to antibodies was examined to 10 guinea pig anti-insulin sera. Three sera did not distinguish between the two tracers, whereas seven exhibited higher binding of the A14 tracer. A detailed analysis of one of the discriminating sera showed that the average affinity constant was about 2.5 times lower for the A19 tracer than for the A14 tracer. The A14 monoiodoinsulin tracer is remarkably stable. After 200 days the specific activity had declined to about half of its original value which is consistent with the hypothesis that the physical decay of [125I]monoiodoinsulin (T 1/2 equals 60 days) extinguishes the activity of the molecule without causing major damage of other molecules. By this time 96% of the radioactivity migrated with insulin when subjected to gel filtration on Sephadex G-50, 4% was in the void volume, and nothing in the total column volume or later. Binding to receptors was indistinguishable from that obtained at time zero. It is concluded that Tyr A14[125I]monoiodoinsulin represents an advance in biologic work as compared with previous tracers for insulin.

Simultaneous recording of the gastro-entero-pancreatic hormonal peptide response to food in man

The serum or plasma concentrations of gastrin, gastric inhibitory polypeptide (GIP), gut glucagon-like-immunoreactivity (gut GLI), secretin, vasoactive intestinal polypeptide (VIP), insulin, glucagon, and pancreatic polypeptide (PP) were recorded simultaneously following the ingestion of a normal, mixed meal in seven healthy, normal weight men. The concentrations of PP and gastrin increased within 10 min. Subsequently GIP, insulin, glucagon, and gut GLI increased in the order mentioned. The mean concentrations of secretin and VIP were not affected by the meal, athough transient decreases in secretion concentrations could be detected in all subjects. The concentrations of the other hormones remained elevated for 4 hr or more. Perhaps the period of observation following food stimulation of gastro-entero-pancreatic hormones should be extended.

Pancreatic glucoregulatory hormones in cirrhosis of the liver: portal vein concentrations during intravenous glucose tolerance test and in response to a meal

We studied the relationship between the pancreatic glucoregulatory hormones, insulin and glucagon, and glucose intolerance through the response to food and intravenous glucose in 11 patients with verified hepatic cirrhosis. Blood samples were obtained from the portal vein and the superior vena cava. The results of the systemic vein hormone determinations were compared to results obtained from peripheral vein determination in 10 age-, sex- and weight-matched controls admitted to hospital for minor surgery and to results from ambulant, normal subjects. In the cirrhotics collateral shunting was elevated by transhepatic portography. The cirrhotics and the matched controls had similar glucagon levels and responses, but showed hyperresponsiveness to a meal compared to ambulant normal subjects. Compared to the matched controls the cirrhotics showed glucose tolerance and hyperinsulinism, but compared to normal subjects the hospitalized controls were also glucose intolerant and demonstrated hyperinsulinism. In the cirrhotics, the portal vein/vena cava ratio for insulin was negatively correlated to the degree of collateral shunting. No relationship was found between the degree of portosystemic shunting and fasting concentrations of glucagon and insulin, and the insulin response to glucose. The glucagon response to the meal, was correlated to severity of cirrhosis. The rate constant for glucose disappearance (K-value) was not related to the insulin response, to severity of disease or to degree of shunting. It was, however, correlated to the suppressibility of glucagon secretion as measured in the portal vein. Our results indicate that the glucoregulatory disturbances in compensated cirrhosis are partly caused by non-specific factors which are independent of cirrhosis; the portal-vein hormone responses, however, support the contention that glucagon secretion influences glucose tolerance in cirrhotics.

Evidence that glicentin contains the entire sequence of glucagon

Glicentin (a highly purified 100-amino acid peptide with glucagon-like immunoreactivity from porcine gut) was subjected to limited digestion with trypsin and carboxypeptidase B, and the resulting peptides were studied by gel filtration and region-specific glucagon radioimmunoassays. Similar digests of glucagon and purified fragments of glucagon were studied in parallel. Glicentin gave rise to peptides that corresponded closely to the 1-17 and 19-29 fragments of glucagon. Also, 125I-labelled glicentin and 125I-labelled glucagon gave rise to identical fragments after trypsin treatment. On the basis of this and other evidence [Jacobsen, Demandt, Moody & Sundby (1977) Biochim. Biophys. Acta 493, 452-459] it is concluded that glicentin contains the entire glucagon sequence at residues number 64-92 and thus fulfills one of the requirements for being a 'proglucagon'.

Oxygen supply, oxygen consumption, and endocrine and exocrine secretions of the isolated, perfused, porcine pancreas

We studied the effect of varying oxygen supply on the endocrine and exocrine secretions of the isolated perfused porcine pancreas utilizing completely synthetic perfusion medium with and without the addition of erythrocytes. With synthetic medium oxygenated to a Po2 of 500 mmHg, oxygen consumption was constant for flow rates at or above 0.5 ml x min-1 x g-1 (wet weight). Addition of erythrocytes to the medium did not increase oxygen consumption at flow rates above this level. Furthermore, the secretion of fluid, bicarbonate and protein in response to secretin and acetylcholine was not influenced by addition of erythrocytes. Similarly, the secretion of insulin, glucagon, pancreatic polypeptide, and somatostatin in response to arginine and acetylcholine was unchanged; arginine stimulated the secretion of all four peptides, whereas acetylcholine stimulated the secretion of insulin and pancreatic polypeptide and inhibited glucagon and somatostatin secretion. The results indicate that the porcine pancreas is respiring adequately, when perfused with a completely synthetic perfusion medium at flows above about 0.5 ml x min-1 x g-1 and Po2 about 500 mmHg, and that addition of erythrocytes is not necessary for the study of its secretory functions.

Neural regulation of pancreatic hormone secretion by the C-terminal tetrapeptide of CCK

In pancreatic islets a peptide corresponding to the C-terminal tetrapeptide amide of cholecystokinin and gastrin, Trp-Met-Asp-Phe-NH2, is present in nerve terminals. This tetrapeptide amide is uniquely potent as a releaser of insulin and the other islet hormones, whereas larger cholecystokinins and gastrins as well as tetrapeptide analogues are considerably less potent. We suggest that neural release of the tetrapeptide amide is implicated in regulation of pancreatic hormone secretion.

Secretory effects of gastrins on isolated perfused porcine pancreas

The effects of the four main forms of gastrin (component I, gastrin-34, gastrin-17, and gastrin-14) on insulin, glucagon, and exocrine secretion were measured on the isolated perfused porcine pancreas. All gastrins were studied in concentrations ranging from 10(-11) to 10(-8) M. Depending on the glucose concentration in the perfusate, all four gastrins increased insulin or glucagon secretion in a dose-dependent manner in concentrations above 10(-10) M. These concentrations are slightly above the arterial concentrations in normal pig and man, but they correspond to gastrin concentrations measured in patients with achlorhydria and gastrinomas. The exocrine secretion was stimulated by all gastrins in a dose-dependent manner. The lowest concentrations that stimulated flow rate significantly were within the physiologic range, 10(-11) and 10(-10) M. All gastrins induced maximal flow rate at a concentration of 10(-9) M. The sulfated form of gastrin-17 had the greatest efficacy. The results indicate that all gastrins may influence the exocrine secretion under normal conditions and the endocrine secretion in diseases with endogenous hypergastrinemia.

Effect of arginine infusion on endogenous pancreatic glucagon and gastric acid secretion in duodenal ulcer patients and normal subjects

The effect of intravenous infusion of L-arginine on pentagastrin-stimulated gastric acid secretion was studied in 15 duodenal ulcer patients and 12 healthy subjects. In both groups L-arginine enhanced plasma concentrations of pancreatic glucagon equally and to levels similar to those seen after a protein-rich meal and inhibited the acid response in duodenal ulcer patients and in normal subjects. The study supports previous findings suggesting that pancreatic glucagon is a physiological inhibitor of gastric acid secretion but does not support the hypothesis of a defect in this inhibitory system in duodenal ulcer patients.

The effect of antral distension on the endocrine pancreas in man

Isolated antral distension by a 150 cm3 balloon in man significantly elevated the plasma concentrations of pancreatic polypeptide and glucagon in portal venous blood. The concentrations of plasma pancreatic glucagon, plasma insulin, and plasma glucose were unchanged in peripheral venous blood during antral distension with or without a background infusion of pentagastrin. Antral distension significantly increased the plasma concentration of pancreatic polypeptide in peripheral venous blood. Antral distension also inhibited basal and pentagastrin-stimulated gastric acid secretion in healthy subjects. The release of pancreatic hormones evoked by antral distension cannot explain the concomitant inhibition of gastric acid secretion. The results support and extend the concept of a gastro-pancreatic reflex to the endocrine part of the pancreas with release of at least pancreatic polypeptide and glucagon.

Vasoactive intestinal polypeptide in vagally mediated pancreatic secretion of fluid and HCO3

The role of nerves that liberate vasoactive intestinal polypeptide (VIP) in the porcine pancrease as mediators of the atropine-resistant action of the vagus on flow and bicarbonate (HCO3) secretion was examined. Efferent electrical stimulation of the vagus in atropinized pigs produced a profuse flow of pancreatic juice with high HCO3 content concomitantly with a significant increase in pancreatic VIP output from 13 to 113 fmol/min. Intravenous administration of somatostatin (SRIF) during continuous electrical vagal stimulation caused a parallel suppression of the VIP release and the pancreatic fluid and HCO3 secretion to prestimulatory values. The SRIF-induced reduction in fluid and HCO3 secretion seemed to be mediated via an inhibition of the VIP release rather than through a direct effect on the exocrine cells, inasmuch as SRIF did not influence the VIP-provoked exocrine response from the in vitro isolated perfused porcine pancreas. The results support the view that VIP is transmitter in the vagally induced atropine-resistant water and HCO3 secretion from the porcine pancreas.

Functional studies in patients with the glucagonoma syndrome

Four patients with glucagon-producing tumours of the pancreas were investigated. Fasting plasma glucagon concentrations ranged from 209--625 pmol/l. Plasma insulin concentrations were normal except in one patient, where the tumour also produced insulin (558 pmol/l). Intravenous glucose (25 g/m2) depressed the glucagon concentration in two patients, while no change was noted in the others. Intravenous arginine stimulated glucagon secretion in three patients, but not in the fourth. Intravenous somatostatin suppressed glucagon secretion in all three patients investigated. All patients had abnormally low plasma levels of individual amino acids; glucogenic and branched-chain amino acids were equally depressed. Surgical removal of the tumours led to complete recovery from dermatosis and the glucagon levels were normalized. Postoperative tests were performed in three patients. The alpha-cell responsiveness to iv glucose was restored. Glucose tolerance (Kg-value) was improved in one patient (0.73 to 1.65), persistently low in one patient (0.75 to 0.72) and impaired in the third patient (1.35 to 1.09). It is concluded that none of these functional tests will be of diagnostic value in cases suspected of glucagonomas. The results also show that glucose homeostasis is remarkably unaffected by the extreme hyperglucagonaemia of these patients and that hypoaminoacidaemia is an important consequence of chronic hyperglucagonaemia.

The effect of different diets and of insulin on the hormonal response to prolonged exercise

The importance of carbohydrate availability during exercise for metabolism and plasma hormone levels was studied. Seven healthy men ran on a treadmill at 70% of individual maximal oxygen uptake having eaten a diet low (F) or high (CH) in carbohydrate through 4 days. At exhaustion the subjects were encouraged to continue to run while glucose infusion increased plasma glucose to preexercise levels. Forearm venous blood, biopsies from vastus muscle and expiratory gas were analyzed. Time to exhaustion was longer in CH- (106 +/- 5 min (S.E.)) than in F-expts. (64 +/- 6). During exercise, overall carbohydrate combustion rate, muscular glycogen depletion and glucose and lactate concentrations, carbohydrate metabolites in plasma, and estimated rate of hepatic glucose production were higher, fat metabolites lower, and the decrease in plasma glucose slower in CH- than in F-expts. Plasma norepinephrine increased and insulin decreased similarly in CH- and F-expts., whereas the increase in glucagon, epinephrine, growth hormone and cortisol was enhanced in F-expts. Glucose infusion eliminated hypoglycemic symptoms but did not substantially increase performance time. During the infusion epinephrine decreased markedly and glucagon even to preexercise levels. Infusion of insulin (to 436% of preexercise concentration) in addition to glucose in F-expts. did not change the plasma levels of the other hormones more than infusion of glucose only but reduced fat metabolites in plasma. At exhaustion muscular glycogen depletion was slow, and the glucose gradient between plasma and sarcoplasma as well as the muscular glucose 6-phosphate concentration had decreased.

CONCLUSIONS

The preceding diet modifies the energy depots, the state of which (as regards size, receptors and enzymes) is of prime importance for metabolism during prolonged exercise. Plentiful carbohydrate stores favor both glucose oxidation and lactate production. During exercise norepinephrine increases and insulin decreases independent of plasma glucose changes whereas receptors sensitive to glucose privation but not to acute changes in insulin levels enhance the exercise-induced secretion of glucagon, epinephrine, growth hormone and cortisol. Abolition of cerebral hypoglycemia does not inevitably increase performance time, because elimination of the hypoglycemia may not abolish muscular energy lack.

The effect of water temperature on the hormonal response to prolonged swimming

The relationship between thermoreception, hormonal secretion and muscular activity was studied. 6 men swam 60 min in 21, 27 and 33 degrees C water at a speed requiring 68% of VO2 max (determined in 27 degrees C water). Rectal temperature increased in 33 degrees C (1.3 +/- 0.2 degrees C, mean and S.E.) and 27 degrees C (0.7+/- 0.1 degrees C) expts. but decreased in 21 degrees C expts. (0.8 +/- 0.3 degrees C). Changes in esophageal and muscle temperatures parallelled changes in rectal temperature. Plasma noradrenaline was higher in 33 degrees C than in 27 degrees C expts. and growth hormone, cortisol and glucagon concentrations increased in 27 degrees C and 33 degrees C expts. only. Insulin concentrations were uniformly depressed during swimming at the different water temperatures. In 21 degrees C expts. noradrenaline and adrenaline concentrations were higher than in 27 degrees C expts. VO2, carbohydrate combustion and peak lactate were slightly lower in 33 degrees C expts. Plasma glucose decreased slightly and FFA and glycerol concentrations increased identically in all expts. Heart rate increased continuously during swimming in 27 degrees C and 33 degrees C expts., but not in 21 degrees C expts. In conclusion the rise in body temperatures normally observed during exercise enhances the exercise induced increases in the plasma concentrations of noradrenaline, cortisol, growth hormone and glucagon. Decreased body temperatures may elicit catecholamine secretion as a direct consequence of thermoreception. Shivering may account for previously observed decreases in insulin secretion during cold stress but not for increases in cortisol and growth hormone.

Gel filtration pattern of immunoreactive glucagon secreted by the isolated, perfused, porcine pancreas

The isolated pancreatic glands from six pigs were perfused in a single pass system and then stimulated with arginine. Samples of the early response perfusate were subjected to gel filtration. Glucagon was determined radioimmunologically in the column effluents using four different antisera with various capacities to recognize other molecular forms of pancreatic type glucagon immunoreactivities. One antiserum crossreacted with purified gut type glucagon. More than 93% of the assayed glucagon in the effluent was eluted within the distribution of pancreatic glucagon when chromatographed under identical conditions. In fifteen experiments there was no detectable immunoreactivity corresponding to the void volume, whereas in the remaining seven experiments less than 7% was eluted at this position. The immunoreactivity in the void volume was detected variably by the four antibodies. No immunoreactivity was detected between the void volume and the elution position of pancreatic glucagon. It is concluded that the arginine stimulated porcine pancreas almost exclusively secretes one molecular species of glucagon, which probably is the 29-amino acid peptide.

Plasma enteroglucagon after jejunoileal bypass with 3:1 or 1:3 jejunoileal ratio

Enteroglucagon concentration in peripheral blood was determined before and after a test meal in 24 morbidly obese patients. Eighteen had jejunoileal bypass, 6 with a 3:1 and 12 with a 1:3 jejunoileal ratio of the functioning segment, and 6 were unoperated. All three groups exhibited an increment of enteroglucagon concentration after the meal. Both the fasting values and the postprandial integrated increments were higher in operated patients than in unoperated patients and higher after 1:3 bypass than after 3:1 bypass. The findings agree with the hypothesis that enteroglucagon secretion is stimulated by exposure of the lower bowel to upper-bowel content, and that the effect of enteroglucagon is, as seen after bypass operation, stimulation of growth and reduction of motility of the intestine.

Fat-induced jejunal inhibition of gastric acid secretion and release of pancreatic glucagon, enteroglucagon, gastric inhibitory polypeptide, and vasoactive intestinal polypeptide in man

The effect of intrajejunal (i.j.) infusion of fat on meal-stimulated gastric acid secretion and release of pancreatic glucagon (PG), enteroglucagon (EG), gastric inhibitory polypeptide (GIP), and vasoactive intestinal polypeptide (VIP) was studied in seven healthy volunteers. I.j. fat markedly inhibited meal-stimulated acid secretion as compared to a control study with i.j. saline infusion. The acid inhibition was accompanied by augmental plasma concentrations of EG, GIP, and VIP but not of PG, suggesting that EG, GIP, and VIP may be among mediators of fat-induced jejunal inhibition of acid secretion. Concentration-time relationship makes it unlikely that the observed inhibition could be ascribed to any single peptide studied.

Increased glucose disposal after jejuno-ileostomy

Nine patients were studied 1.5--3 years after jejuno-ileostomy for obesity by an intravenous glucose infusion technique designed to imitate blood glucose concentrations after glucose ingestion. Whereas serum insulin and gastrin concentrations were normal, blood glucose concentrations were significantly depressed compared to preoperative levels as well as to levels in matched normal subjects. Thus, in the fasting state mean concentrations (+/- S.E.M.) of blood glucose, serum insulin and gastrin in the patients were, respectively, 3.3 +/- 0.2 mmol/l, 95 +/- 22 pmol/l and 38 +/- 4 pmol/l. The corresponding concentrations in the matched normals were 4.3 +/- 0.2 mmol/l, 70 +/- 18 pmol/l and 39 +/- 6 pmol/l. The glucose concentrations in the patients were low in all situations, i.e. in the fasting state, after oral glucose ingestion and during the intravenous glucose infusion. The results indicate that jejuno-ileostomy in obesity greatly facilitates peripheral glucose disposal. The mechanism behind this phenomenon is not yet known.

Nervous control of pancreatic exocrine secretion in pigs

The pancreatic secretion of fluid, bicarbonate and protein in response to electrical stimulation of the vagus and splanchnic nerves, to exogenous and endogenous secretin and to various pharmacological agents was studied in anesthetized young pigs (21 kg). Vagal stimulation increased flow, bicarbonate output and protein output in a frequency dependent manner; the half maximal effective frequency was 2--4 Hz and the maximal effective frequency 12 Hz. The secretory response to vagal stimulation was potentiated by physiological elevations of the arterial concentration of secretin brought about by injection of secretin or by acidification of the duodenal bulb. Simultaneous stimulation of the splanchnic nerves strongly inhibited the response to vagal stimulation; splanchnic nerve stimulation alone had no demonstrable effect. The flow and bicarbonate response to vagal stimulation was unaffected by atropine, but abolished by hexamethonium. Protein output was strongly inhibited by both agents. The response to intraarterial infusion of acetylcholine resembled that elicited by vagal stimulation but it was smaller and it was completely abolished by atropine and unaffected by hexamethonium. Alpha- and beta-adrenergic blockade stimulated rather than inhibited the secretory response to vagal stimulation. The portal vein plasma concentration of secretin was not affected by vagal stimulation. The results indicate that the protein response, and the flow and bicarbonate response to vagal stimulation are not brought about by the same mechanism. An increased release of secretin is not involved. Peptidergic (VIP-containing) nerves may contribute.

Secretory effects of VIP on isolated perfused porcine pancreas

We studied the secretion of insulin, glucagon, and the exocrine secretion of the isolated perfused porcine pancreas in response to vasoactive intestinal polypeptide (VIP) in concentrations ranging from 30 to 18,750 pmol/liter at various concentrations of glucose in the perfusion medium. VIP stimulated the insulin and glucagon secretion in a dose-dependent manner. The response pattern was critically dependent on the glucose concentration. In the presence of a glucose concentration of 7.5 mmol/liter, VIP enhanced insulin release without affecting glucagon release. Maximal insulin release was obtained at a VIP concentration of 3,750 pmol/liter. At a glucose concentration of 5.0 or 3.5 mmol/liter, VIP enhanced glucagon release but not insulin release. VIP stimulated the exocrine secretion in a secretin-like manner. The lowest concentration of VIP observed to increase pancreatic exocrine secretion was 30 pmol/liter, whereas the maximal pancreatic exocrine responses were not obtained.

Secretory effects of secretin on isolated perfused porcine pancreas

The effect of pure natural porcine secretin on endocrine and exocrine pancreatic secretion was studied in the totally isolated perfused porcine pancreas. The exocrine pancreatic responses to secretin correspond well with those obtained in the anesthetized pig. The lowest concentration of secretin observed to increase pancreatic secretion was 2.8 pmol/liter, whereas the maximum pancreatic responses were obtained at a secretin concentration of 92 pmol/liter. The infusion of secretin in concentrations ranging from 2.8 to 278 pmol/liter in the presence of a constant concentration of glucose (7.5, 5.0, or 3.5 mmol/liter) was without effect on the insulin and glucagon release. Infusion of secretin at a concentration of 834 pmol/liter in the presence of glucose at 7.5 mmol/liter provoked a significant (P less than 0.01) short-lived increase in insulin secretion. However, there was no effect on the glucagon secretion. The results of this study indicate that neither the augmented insulin response nor the suppression of glucagon elicited by oral glucose depend on secretin.

Reflex adrenergic control of endocrine pancreas evoked by unloading of carotid baroreceptors in cats

The effects of unloading of the carotid baroreceptors on arterial plasma glucose concentration as well as on portal plasma immunoreactive glucagon (IRG) and insulin (IRI) concentrations were studied in anestethized, vagotomized cats either by sectioning the sinus nerves or by lowering the pressure in the isolated carotid sinuses. Complete elimination of the carotid baroreceptor discharge by cutting the sinus nerves caused an increase in the arterial plasma glucose concentration by 100% and an increase in the portal IRG level by about 200%, whereas the portal IRI concentration decreased to 50% of its basal value. These baroreceptor-induced changes of the plasma IRG and IRI levels seemed to be graded in relation to the drop in carotid blood pressure and they were clearly detectable when the pressure was lowered from 120 to 90 mmHg in the isolated carotid sinus preparation. The described reflex hyperglycemia, hyperglucagonemia and hypoinsulinemia were mediated to the pancreas and liver mainly by the sympatho-adrenal system, since cutting the splanchnic nerves above the adrenal glands abolished the hyperglycemia and hypoinsulinemic responses and markedly depressed the magnitude of the hyperglucagonemic response. In adrenalectomized cats, complete unloading of the baroreceptors evoked both hyperglucagonemia and hypoinsulinemia although the magnitude of the hormonal responses was diminished. In animals where the pancreas and liver were sympathectomized but the adrenal glands left intact, cutting the sinus nerves evoked a doubling of the IRG level and a slight increase in plasma glucose, but no significant change of the IRI level. I.v. infusion of adrenaline (1 microgram/kg X min) or noradrenaline (5 microgram/kg X min) caused pronounced increases in IRG and plasma glucose and a clear-cut reduction of IRI. We conclude that the function of the endocrine pancreas in the cat can be influenced by variations in the blood pressure by means of a reflex control which originates from arterial baroreceptors. This reflex adjustment of the endocrine pancreas is mediated chiefly by two links of the sympatho-adrenal system, namely by catecholamine-release from the adrenal medulla and, more importantly, by a direct adrenergic nerve fibre influence on the alpha- and beta- cells.

Influence of the autonomic nervous system on the release of vasoactive intestinal polypeptide from the porcine gastrointestinal tract

1. The release of vasoactive intestinal polypeptide from the gastrointestinal tract in response to stimulation of the vagus nerves, the splanchnic nerves and to intra-arterial infusion of acetylcholine (ACh) was examined in pigs. 2. Stimulation of the vagus nerves caused an abrupt increase in the release of vasoactive intestinal polypeptide. The amount of the peptide released depended on the frequency at which the nerves were stimulated. Maximum release was obtained at 8 Hz. 3. Atropine and beta-adrenergic blocking agents failed to diminish the vagally induced release of vasoactive intestinal polypeptide, while the response was completely blocked by hexamethonium and increased after alpha-adrenergic blockade and after splanchnicotomy. 4. Intra-arterial infusion of ACh closely imitated the response to vagal stimulation, but the release of vasoactive intestinal polypeptide induced by ACh was abolished by atropine. 5. Stimulation of the splanchnic nerves caused a decrease in the release of vasoactive intestinal polypeptide, an action which was annulled by alpha-adrenergic blockade, but still present after the adrenal glands were isolated from the circulation. The inhibitory effect of splanchnic stimulation significantly diminished the vagally induced release of vasoactive intestinal polypeptide. 6. The results demonstrate a dual innervation with opposing effects on the neurones containing vasoactive intestinal polypeptides. The possible physiologic implication of this finding is discussed.

Exchange of metabolites in the leg of exercising juvenile diabetic subjects

1. Exchange of metabolic substrates was studied across the leg at rest and during a bicycle exercise demanding 50% of the maximal oxygen uptake in seven patients with juvenile diabetes and six control subjects. The leg blood flow and the femoral arterial and venous substrate concentrations were measured in the fasting state and, in the diabetic subjects, 24 h after the last administration of insulin.

2. At rest a close correlation was seen in the control subjects between the leg glucose uptake and the arterial insulin concentration. The diabetic subjects, including three patients in whom it could be shown that the insulin concentrations were extremely low, had a resting glucose uptake in the same order of magnitude as the control subjects. The glucose uptake was inversely related to the arterial concentrations of non-esterified fatty acids in both groups.

3. During exercise the glucose uptake increased in both patients and control subjects, but the increase was not related to arterial concentrations of insulin or non-esterified fatty acids.

4. The release of lactate, pyruvate, alanine and glycerol from the leg was not different in diabetic and control subjects neither at rest nor during exercise.

5. The ketonaemia was increased in the diabetic subjects, but the uptake of total ketone bodies was not different in the two groups. No increase in the uptake of total ketone bodies in control and diabetic subjects was found during exercise. The leg uptake of acetoacetate was a function of the substrate load and tended to be higher in diabetic subjects during exercise, when no net uptake of β-hydroxybutyrate was found.

6. The above results suggest that the glucose uptake in human skeletal muscle at rest depends on the concentration of insulin and possibly also of non-esterified fatty acids in arterial blood. In contrast the glucose uptake during exercise is not related to the concentration of insulin or non-esterified fatty acids, which may explain why no differences in this aspect are seen between the leg metabolism of diabetic and normal subjects.

Neutralization of glucagon by antiserum as a tool in glucagon physiology. Lack of depression of basal blood glucose after antiserum treatment in rats

The method of producing experimental glucagon deficiency by administration of glucagon antiserum was evaluated in rats. A pool of antisera was prepared, the affinity of which exceeded that of the glucagon receptors of liver cell membranes, whereas the binding capacity of the volume used amounted to more than one-third of the total glucagon content in the rat pancreas. That rapid, extensive, and lasting neutralization of glucagon had taken place after antiserum treatment was indicated by the following findings: When examined more than 1 h after the injection and after 60 min of exercise-stimulated glucagon production, all rats had excess free antibodies in plasma. The concentration of free glucagon was lowered to one-third of the concentration in control rats; at 37 degrees C plasma samples could bind 25% of additional 300 pmol/liter of glucagon in 10 s, and 69% in 120 s; the glycemic response to exogenous glucagon was abolished. Antiserum treatment, however, had no effect on blood glucose in rats fasted for 3 and 10 h, in chemically sympathectomized and adrenomedullectomized rats, and in 48-h-fasted, acutely adrenalectomized rats. The antiserum was found to contain 460 nmol/liter of antibody-bound glucagon, originating in the rabbit in which the antiserum was raised. However, antibody preparations from which the bound glucagon had been effectively removed were equally ineffective in lowering the basal blood glucose in rats, although in three-fourths of the rats the concentration of free glucagon was lowered beyond detection limit. The data indicate that the absolute concentration of glucagon in plasma is of minor importance for the maintenance of basal blood glucose in the rat.

Sympathetic control of metabolic and hormonal responses to exercise in rats

The importance of the sympatho-adrenal system for the pancreatic hormonal response to exercise and, furthermore, the role of glucagon and catecholamines for the hepatic glycogen depletion during exercise were studied. Rats were either surgically adrenomedullectomized and chemically sympathectomized with 6-hydroxydopamine or shamtreated. Two weeks later the rats had either rabbit-antiglucagon serum or normal rabbit serum injected. Subsequently the rats either rested or swam with a tail weight for 75 min. Immediately afterwards cardiac blood was drawn and liver and muscle tissue collected. In control rats in spite of an increase in blood glucose concentrati4ns during exercise plasma insulin concentrations were unchanged, while glucagon concentrations increased. In sympathectomized rats, compared to control rats, glucagon concentrations increased less, and insulin concentrations were higher, although glucose concentrations were lower during exercise. Sympathectomy completely abolished the exercise-induced decrease in liver and muscle glycogen concentrations, whereas neither glycogen depletion nor plasma catecholamine concentrations were influenced by the administration of glucagon antibodies. These findings indicate that the sympatho-adrenal system enhances glucagon secretion as well as muscular and hepatic glycogen depletion but inhibits insulin secretion in exercising rats. The increase in glucagon concentrations, however, does not enhance hepatic glycogen depletion at the work load used.

Vagal, cholinergic regulation of pancreatic polypeptide secretion

THE EFFECT OF EFFERENT, PARASYMPATHETIC STIMULATION UPON PANCREATIC POLYPEPTIDE (PP) SECRETION WAS STUDIED IN THREE WAYS: (a) Plasma PP concentrations increased in response to insulin-induced hypoglycemia in both normal subjects, from 11 pM (9.5-12.5) to 136 pM (118-147), n = 8 (median and interquartile range) and in duodenal ulcer patients, from 33 pM (21-52) to 213 pM (157-233), n = 7. The PP response to hypoglycemia was diminished by atropine in normal subjects (P < 0.005) and completely abolished by vagotomy in the duodenal ulcer patients. (b) Electrical stimulation, 8 Hz, of the vagal nerves in anesthetized pigs induced an increase in portal PP concentrations within 30 s from 32 pM (28-39) to 285 pM (248-294), n = 12. Minimal stimulatory frequency was 0.5 Hz and maximal stimulatory frequency 8-12 Hz. Atropine inhibited the PP response to electrical stimulation. Median inhibition with 0.5 mg of atropine/kg body wt was 74%, range 31-90%, n = 6. The response was eliminated by hexamethonium. Adrenergic alpha and beta blockade did not influence the release of PP in response to vagal stimulation. (c) Acetylcholine stimulated, in a dose-dependent manner, the secretion of PP from the isolated perfused porcine pancreas, half-maximal effective dose being 0.19 muM; maximal PP output in response to 5 min stimulation was 228 pmol, range 140-342 pmol, n = 5. Atropine completely abolished this response.The results of the present study together with the previously demonstrated poor PP response to food in vagotomized patients, indicate that vagal, cholinergic stimulation is a major regulator of PP secretion.

Inhibition of meal-stimulated gastric acid secretion in man by exogenous and endogenous pancreatic glucagon

The effect of intravenous infusion of glucagon (300 ng x kg(-1) x h(-1)), 1-arginine (0.6 g x kg(-1) x h(-1)) and of saline on meal-stimulated gastric acid secretion was studied in six healthy volunteers. Infusion of glucagon and 1-arginine enhanced plasma concentrations of pancreatic glucagon to 65--85 pmol/l, a level similar to that seen after a normal protein-rich meal. Both infusions significantly inhibited the acid response to the meal, most pronounced after 1-arginine. The difference in acid inhibition could not be ascribed either to differences in plasma glucagon concentrations or to differences in serum gastrin concentrations. The study supports the concept that pancreatic glucagon is a physiological inhibitor of gastric acid secretion.

Extrapancreatic glucagons

From the mucosa of the gastrointestinal tract a number of peptides can be extracted, which are glucagon-like in their behavior towards antisera raised against the pancreatic hormone. The biochemistry and physiology of these peptides are critically reviewed. Although important advances have been made, facilitated by improved praparative and analytical techniques, many problems remain unresolved. It is, however, now well established that a peptide, which is indistinguishable from true, pancreatic glucagon (NW 3,485) is found in extrapancreatic gastrointestinal tissue from all species investigated. While abundant in dogs, especially in the gastric mucosa, much less is found in extra-pancreatic tissues of man and pig. Results from studies in dogs are therefore not necessarily relevant to other species. Human and porcine gut, however, contain other glucagon-like peptides (gut-type glucagon, enteroglucagon, gut GLI), one of which resembles true glucagon (MW 3,485) in its biological activity, but a definite physiological role for these peptides has not yet been established. The recent isolation and purification of one of the latter peptides undoubtedly will facilitate greatly future research in this field.

Elimination of porcine secretin in pigs

1. The elimination of immunoreactive secretin was studied in anaesthetized pigs by using constant infusions of pure natural porcine secretin. 2. The mean metabolic clearance rate was 15.4 ml min-1 kg-1, and was independent of the level at which it was determined. The mean distribution space was 64.4 ml/kg. The half-life of secretin after termination of the infusion averaged 2.6 min. 3. During intravenous infusion of secretin in a dose of 27.8 pmol h-1 kg-1 the renal extraction was 52%. Exclusion of the kidneys increased plasma secretin concentration from 26.5 pmol/l to 47.3 pmol/l and increased the half-life to 4.4 min. 4. Exclusion of the liver during infusion of secretin in a dose of 27.8 pmol h-1 kg-1 resulted in an increment in plasma secretin concentration of 7.8 pmol/l and an increase of the half-life to 3.6 min. 5. A gradient of endogenous secretin across the liver was present but no arteriovenous difference was found across the foreleg. 6. Incubation of secretin with whole blood or serum for 20 min at 37 degrees C did not result in any degradation of secretin.

Diminished hormonal responses to exercise in trained rats

Male rats (120 g) either were subjected to a 12-wk physical training program (T rats) or were sedentary controls (C rats). Subsequently the rats were killed at rest or after a 45- or 90-min forced swim. At rest, T rats had higher liver and muscle glycogen concentrations but lower plasma insulin. During exercise, blood glucose increased 60% in T rats but decreased 20% in C rats. Plasma glucagon and insulin concentrations did not change in T rats but plasma glucagon increased and insulin decreased markedly in C rats. Plasma epinephrine (90 min: range, 0.78-2.96 ng-ml-1, (T) vs. 4.42-15.67 (C)) and norepinephrine (90 min: 0.70-2.22 (T) vs. 2.50-6.10 (C)) were lower in T than in C rats. Hepatic glycogen decreased substantially and, as with muscle glycogen, the decrease was parallel in T and C rats. The plasma concentrations of free fatty acids were higher but lactate and alanine lower in T than in C rats. In trained rats the hormonal response to exercise is blunted partly due to higher glucose concentrations. In these rats adipose tissue sensitivity to catecholamines is increased, and changes in glucagon and insulin concentrations are not necessary for increased lipolysis and hepatic glycogen depletion during exercise.

Catecholamines and pancreatic hormones during autonomic blockade in exercising man

The importance of autonomic nervous activity for the pancreatic hormonal response to exercise in man was studied. 7 men ran at 58% of V(O2)max (determined without administration of drugs) to exhaustion during alpha-adrenergic blockade with phentolamine (P), during parasympathetic blockade with atropine (A), or without drugs (C). At rest phentolamine increased the plasma concentrations of both insulin and norepinephrine. During exercise norepinephrine concentrations increased and were in P experiments 3 times the concentrations in C experiments. Insulin always declined during exercise but in P experiments never decreased below basal levels. At identical times neither glucagon nor glucose differed significantly in the different expts. Thus during exercise alpha-adrenergic blockade increased insulin concentrations but did not diminish the glucagon response. Nor was this response increased when beta-receptor stimulation in P experiments was intensified by the particularly high catecholamine concentrations. The concentrations of FFA, glycerol and lactate were highest in P experiments and identical in A and C experiments. These findings indicate that during prolonged moderate exercise in man insulin secretion is depressed by stimulation of alpha-adrenergic receptors whereas glucagon secretion is not influenced by adrenergic receptors. Stimulation of beta-adrenergic receptors enhances lipolysis but neither lipolysis nor pancreatic hormonal secretion is influenced by cholinergic activity during exercise.

Regulation of gluconeogenesis and ketogenesis during rest and exercise in diabetic subjects and normal men

The splanchnic-hepatic metabolism of glucose, lactate, pyruvate, alanine, glycerol, non-esterified fatty acids (NEFA), ketone bodies and oxygen were investigated in five normal men and six juvenile diabetic subjects at rest and during exercise after an overnight fast. A linear relationship was found between load (arterial concentration multiplied by hepatic blood flow) and splanchnic-hepatic uptake of lactate, pyruvate, glycerol and NEFA. The uptake of alanine was highly sensitive to load, but was also regulated by the concentration of hepatic venous glucagon. The uptake of pyruvate was high in exercising diabetic subjects, who had a high lactate/pyruvate concentration ratio in hepatic venous blood. The rate of uptake of the total measured gluconeogenic precursors was significantly higher in the diabetic group at a given load. The rate of ketogenesis was linearly related to the NEFA load in both groups; however, the rate of ketogenesis was twofold at a given load in the diabetic group. The highest rates of ketogenesis were found coincident with the highest concentrations of glucagon in hepatic venous blood. The observed antiketogenic effect of exercise was due to a decreased load of NEFA, mainly caused by a decrease in the hepatic blood flow.

The effect of intraportal and peripheral infusions of glucagon on insulin and glucose concentrations and glucose tolerance in normal man

The effect of peripheral and intraportal infusions on 0.86 pmol/kg-min-1 of glucagon on plasma glucose, plasma insulin, and glucose tolerance was examined in four normal subjects. Peripheral glucagon concentrations increased by 60--90 pmol/1 during intraportal and 70--180 pmol/1 during peripheral infusions. The infusions caused increases in plasma glucose levels of approximately 1 mmol/1, and in plasma insulin levels of 75--100%, regardless of route of administration. Intravenous glucose tolerance tests carried out during the glucagon infusions showed that glucose tolerance remained within the normal range and was uninfluenced by the route of administration.

Lak of influence of glucagon on glucose homeostasis after prolonged exercise in rats

The significance of glucagon for post-exercise glucose homeostasis has been studied in rats fasted overnight. Immediately after exhaustive swimming either rabbit-antiglucagon serum or normal rabbit serum was injected by cardiac puncture. Cardiac blood and samples of liver and muscle tissue were collected before exercise and repeatedly during a 120 min recovery period after exercise. During the post-exercise period plasma glucagon concentrations decreased but remained above pre-exercise values in rats treated with normal serum, while rats treated with antiglucagon serum has excess antibody in plasma throughout. Nevertheless, all other parameters measured showed similar changes in the two groups. Thus after exercise the grossly diminished hepatic glycogen concentrations remained constant, while the decreased blood glucose concentrations were partially restored. Simultaneously concentrations in blood and serum of the main gluconeogenic substrates, lactate, pyruvate, alanine and glycerol declined markedly. During the post-exercise period NEFA concentrations in serum and plasma insulin concentrations remained increased and decreased, respectively, while plasma catecholamines did not differ from basal values. Muscle glycogen concentration decreased slightly. These findings suggest that in the recovery period after exhausiive exercise the increased glucagon glucagon concentrations in plasma do not influence gluconeogenesis.

Extraction, gel filtration pattern, and receptor binding of porcine gastrointestinal glucagon-like immunoreactivity

Different techniques for the extraction and initial purification of porcine gastrointestinal glucagon-like immunoreactivity (GLI) were compared with reference to yield, and preservation of number and pattern of GLI components. The conventional acid-ethanol technique combined with ethanol-ether purification gave high yields and a reproducible pattern of components. Large amounts of tissue were more easily extracted using another technique, based on extraction by boiling, extraction and precipitation with acetone, and--if necessary--salting out. By means of the latter two techniques mucosal tissue from all of the porcine gastrointestinal tract was extracted and subjected to gel filtration. Glucagon-like peptides were searched for using: 1. a radioimmunoassay which quantifies gut type glucagon (GTG), as well as pancreatic type glucagon (PTG), 2. a radioimmunoassay highly specific for pancreatic type glucagon (PTG), and 3. a radioreceptor assay based on binding of glucagon to porcine liver cell membranes. The oesophageal, the fundic, and the antro-pyloric parts of the gastric mucosa contained very small amounts of GLI. The cardiac gland region contained small amounts of a peptide indistinguishable from "true" glucagon. The duodenal mucosa contained small amounts of "true" glucagon and may be a smaller, glucagon-like peptide. The mucosa of the small intestine contained large amounts of both high and low molecular weight GTG and, in addition, PTG of high molecular weight and "true" glucagon. The colon also contained these components with "true" glucagon in high concentrations. Only small GTG and "true" glucagon were receptor-active, the former with less than its immunometric potency.

Glucose-induced decrease in glucagon and pinephrine responses to exercise in man

Seven men ran at 60% of individual maximal oxygen uptake to exhaustion during beta-adrenergic blockade with propranolol or without drugs. After propranolol administration the increases during exercise in plasma glucagon and epinephrine concentrations as well as the decrease in plasma glucose concentrations were faster than in control experiments. When euglycemia was maintained by glucose infusion during beta-adrenergic blockade, glucagon and epinephrine responses to exercise, although not abolished, were markedly reduced. The diminution of the exercise-induced decline in glucose concentrations correlated significantly with the diminution of the glucagon as well as the epinephrine responses. Thus decreased glucose concentrations may significantly enhance the secretion of glucagon and epinephrine during prolonged exercise in man. Since the diminution of the glucagon response produced by glucose infusion was not accompanied by significant alterations in the levels of nonesterified fatty acid (NEFA) and glycerol, increased glucagon secretion does not seem to be a major determinant of lipolysis during exercise in man. During glucose infusion, glycogen utilization rates in muscle (n = 4) tended to decrease, whereas carbohydrate combustion rate and concentrations of norepinephrine, insulin, alanine, and lactate were unchanged.

Pancreatic somatostatinoma. Clinical features and physiological implications

The first case of a tumour producing somatostatin-like immunoreactivity and bioactivity is presented. The pancreatic tumour was composed of cells indistinguishable from islet D cells. Radioimmunoassay of blood-samples obtained by tumour-vein catheterisation revealed very high levels of somatostatin immunoreactivity. On gel chromatography tumour extracts were found to contain at least 4 different immunoreactive components, one of which eluted in the position of synthetic somatostatin. Extracts from the tumour were potent in inhibiting insulin and glucagon secretion from isolated perfused porcine pancreas. Clinical abnormalities included hypochlorhydria, steatorrhoea, and diabetic glucose tolerance. Conceivably some of these abnormalities may be related to somatostatin hypersecretion from the pancreatic tumour.

Stimulation of glucagon and inhibition of insulin secretion evoked from carotid baroreceptors

The influence from carotid baroreceptors on portal immuno-reactive glucagon and insulin levels and on arterial plasma glucose concentration was studied in vagotomized cats by sectioning of the sinus nerves. Such a complete elimination of the afferent baroreceptor discharge caused a prompt and pronounced increase in the glucose and glucagon levels, whereas the insulin concentration significantly decreased. The role of vascular barorecptors in the hyperglycemic response to hemorrhage is discussed.

Release of vasoactive intestinal polypeptide (VIP) by electric stimulation of the vagal nerves

The concentration of immunoreactive VIP was measured in portal venous and peripheral arterial plasma in anesthetized pigs. Following electric stimulation of the vagal nerves the median concentration of VIP in portal plasma rose from 21 to 58 pmol l-1 and a simultaneous increase was found in arterial plasma. Atropine did not abolish this effect of vagal stimulation. The response is interpreted as increased release of VIP.