Response of plasma glicentin to intraduodenal administration of glucose in piglets

Controversial results concerning the secretion of glicentin prompted us to investigate the response of circulating glicentin to intraduodenal administration of glucose in piglets. A 20% solution of glucose (2 g/kg) was administered into the duodenum of six piglets in a fully conscious state. As blood glucose rose, plasma insulin increased to a peak of 21 +/- 4 microU/ml. Plasma glucagon, determined by C-terminal-specific antiserum, was 70 +/- 30 pg/ml at fasting and slightly increased after the glucose load. Plasma immunoreactive glucagon measured by cross-reacting glucagon antiserum increased from the baseline of 1563 +/- 260 to a peak of 4738 +/- 415 pg/ml at 120 min. Plasma glicentin determined by antiserum R 64 was 463 +/- 81 pmol/l at baseline and reached a peak level of 1081 +/- 174 pmol/l at 90 min. The percent changes of plasma glucagon from the fasting level measured by cross-reacting antiserum and glicentin were 296 and 233%, respectively. There was a significant correlation between plasma glucagon measured by cross-reacting antiserum and glicentin (r = 0.817, P less than 0.001). Chromatography of plasma obtained during glucose load revealed the heterogeneity of glicentin. It can be concluded from the present study that glicentin is clearly secreted in response to intraluminal administration of glucose.     

Effect of 2-deoxy-D-glucose on plasma somatostatin levels in conscious dogs

The effects of 2-deoxy-D-glucose (2-DG) on plasma levels of somatostatin-like immunoreactivity (SLI) were examined in conscious normal dogs. After an iv infusion of 2-DG (400 mg/kg . h for 15 min), plasma SLI rose significantly from a mean baseline of 130 +/- 5 pg/ml (mean +/- SEM) to a mean peak of 204 +/- 25 pg/ml (P less than 0.005) at 25 min. Plasma insulin and glucagon also increased significantly. Atropine (200 microgram/kg . h for 35 min, iv) and hexamethonium (5 mg/kg, iv) markedly suppressed the SLI response to 2-DG, suggesting that it might be mediated, at least in part, by the autonomic nervous system. In contrast, the plasma insulin and plasma glucagon responses to this glucose analog were only slightly affected by atropine or hexamethonium pretreatment. Carbachol (0.2 mg, sc) caused a mean maximal increase in SLI of 43 +/- 14% (P less than 0.005) and atropine (200 micrograms/kg . h, iv) caused a mean maximal decrease of 25 +/- 2% (P less than 0.001) from the respective baseline levels. Plasma insulin and glucagon rose promptly after carbachol and were unchanged by atropine. To assess th contribution of 2-DG-stimulated gastric acid secretion in the 2-DG-induced SLI rise 2-DG was infused during the infusion of the H2-receptor antagonist cimetidine (3.0 mg/kg . h). Plasma SLI, nevertheless, increased significantly from a mean baseline of 112 +/- 6 pg/ml to a mean peak of 158 +/- 19 pg/ml (P less than 0.005) at 20 min, although the magnitude of the response was substantially reduced (P = NS). These observations suggest that in the conscious dog, 2-DG stimulates SLI secretion in part via cholinergic mechanism.     

Plasma release of atrial natriuretic peptide in response to blood volume expansion

The response of plasma atrial natriuretic peptide (ANP) concentration to acute intravascular volume expansion was measured in ten male Wistar rats. An infusion of 3 ml polygelene colloidal solution at 37 degrees C over 45 s produced peak venous pressure rises of 1.5 cm water. A highly significant (P less than 0.001) rise of immunoreactive plasma ANP from 24.4 +/- 2.2 (mean +/- S.E.M.) pmol/l to a peak of 70.0 +/- 10.5 pmol/l occurred within 2.5 min. Plasma ANP concentrations had virtually returned to basal levels (32.7 +/- 2.7 pmol/l) 30 min after this acute volume load. A further infusion of 10 ml polygelene colloidal solution in 2 min produced peak venous pressure rises of 10 cm water and caused a dramatic and significant (P less than 0.001) increase of plasma ANP concentration to a peak of 534.8 +/- 38.5 pmol/l, occurring 7.5 min after infusion. The plasma ANP concentration had fallen but remained above basal levels 30 min later (137.2 +/- 26.4 pmol/l). Similar results were obtained using an identical protocol but with whole rat blood instead of polygelene solution as the volume-expanding agent. Gel column chromatography suggested that the majority of the immunoreactive ANP in rat plasma was of similar molecular size to rat alpha-ANP (1-28). These results support the hypothesis that blood volume expansion is a potent stimulus for the release of ANP into plasma.     

Response of plasma glicentin to fat ingestion in piglets

In order to elucidate the response of plasma glicentin to fat ingestion, butter, glycerol or palmitate was administered into the duodenum of piglets in a fully conscious state and plasma glicentin and glucagon were determined. Butter instillation did not change blood glucose. Plasma triglyceride rose gradually 120 min after butter loading. Plasma insulin and glucagon measured by antiserum specific to the C-terminal slightly increased following butter administration and plasma total glucagon and glicentin increased gradually and significantly. The increments of total glucagon and glicentin were 179 and 158%, respectively. However, chromatography of porcine plasma obtained during fat loading revealed heterogeneity of glicentin-related peptides. Glycerol ingestion induced a slight rise of plasma total glucagon. Administration of palmitate revealed an increase in plasma total glucagon and glicentin. The present study clearly demonstrates the secretion of glicentin following fat ingestion, which might be caused by the hydrolysates of triglyceride, as suggested in previous dog experiments.     

RESPONSE OF CIRCULATING SOMATOSTATIN, INSULIN, GASTRIN AND GIP, TO INTRADUODENAL INFUSION OF NUTRIENTS IN NORMAL MAN

We have studied the effect of direct infusion of nutrients into the duodenum of normal subjects on circulating plasma somatostatin, insulin, gastrin and gastric inhibitory polypeptide (GIP) levels. Six normal subjects were given on four separate occasions 150 ml of isotonic solutions containing 100 calories of carbohydrate, protein, or fat, and a control solution of saline, by infusion into the second part of the duodenum. Plasma somatostatin rose slightly after carbohydrate, mean basal 30 +/- 3 pg/ml, peak 46 +/- 16 pg/ml at 15 min; and more markedly after protein, peak 57 +/- 9 pg/ml at 30 min. However, fat was the most potent intraduodenal stimulus to plasma somatostatin release into circulation, peak 101 +/- 11 pg/ml at 30 min. The plasma insulin rise was greatest after carbohydrate, peak 68 +/- 10 i.u., but there was a significant rise after protein also, peak 34 +/- 6 i.u. Plasma gastrin rose significantly after protein only, peak 70 +/- 22 pg/ml. Plasma GIP rose markedly after carbohydrate, basal 506 +/- 50 pg/ml, peak 1480 +/- 120 pg/ml. Protein was also a potent stimulus of circulating plasma GIP release, peak 1200 +/- 190 pg/ml, while fat was the least potent, peak 730 +/- 190 pg/ml. Thus, calorie for calorie, fat is the most potent intraduodenal nutrient stimulus of circulating somatostatin. We postulate therefore that somatostatin may be an enterogastrone--a circulating hormone released by intraduodenal fat which inhibits gastric acid secretion. Fat is the least potent intraduodenal nutrient stimulus of circulating GIP release. This is evidence against the hypothesis that circulating GIP acts as an enterogastrone.     

Inhibition of secretin release and pancreatic bicarbonate secretion by somatostatin infusion in man.

Five healthy students were investigated on two different days with or without a constant infusion of somatostatin (500 microgram/h) into an arm vein a fluoroscopically placed Lagerl?f tube was used for the collection of gastric and duodenal juice. After 30-min basal period, 40 ml 100 mmol/l HCl was infused into the midpart of the duodenum over 5 min through a thin catheter attached to the tube. Plasma immunoreactive secretin was measured by radioimmunoassay employing 125I-labelled synthetic secretin, antibody against synthetic secretin, and standards prepared from pure natural porcine secretin. Secretin levels without somatostatin infusion were 4.6+/-0.7 pmol/l (mean+/-S.E.M.) basally and rose to a peak of 21.8+/-6.2 pmol/l after duodenal acidification (p less than 0.05) and with somatostatin infusion were 4.4+/-0.4 pmol/l basally and rose to a peak of 6.7+/-1.7 pmol/l (n.s.) after duodenal acidification. Pancreatic bicarbonate output increased from 8.0+/-2.5 mumol/min (mean+/-S.E.M.) to 283+/-44 mumol/min without somatostatin infusion (p less than 0.05) and from 6.7+/-2.1 mumol/min to 70+/-13 mumol/min somatostatin (p less than 0.05). This study shows that somatostatin (500 microgram/h can inhibit the release of secretin and the pancreatic bicarbonate secretion after duodenal acidification in man.     

Circulating amino acids and pancreatic endocrine function after ingestion of a protein-rich meal in obese subjects

We measured plasma amino acid together with insulin, glucagon, pancreatic polypeptide (PP), and glucose concentrations after the ingestion of a protein meal in lean and obese subjects. The basal plasma amino acid levels were similar in both groups. The postprandial increase in the plasma amino acid levels in the obese subjects was only 15-50% of that in the lean subjects. The mean basal and peak postprandial plasma insulin levels were significantly higher (72 and 165 pmol/L) in the obese group than in the lean group (36 and 115 pmol/L; P less than 0.05-0.01). The postprandial rise in plasma glucagon was largely attenuated in the obese subjects, and there was no difference in plasma PP and glucose levels in the 2 groups. To further evaluate the role of circulating amino acids on pancreatic endocrine function in obese and lean subjects, an amino acid mixture consisting of 15 amino acids was infused iv. During the infusion the plasma amino acid levels were comparable in both groups. Plasma insulin rose by 36 +/- 7 (+/- SE) pmol/L (5 +/- 1 microU/mL) in the lean and 129 +/- 22 pmol/L (18 +/- 3 microU/mL) in the obese subjects, whereas plasma glucagon, PP, and glucose levels were similar in both groups. In view of the 3.6-fold greater insulin responses in the obese subjects, it is likely that circulating amino acids contribute to their hyperinsulinemia in spite of the reduced postprandial rise of amino acids in this group (50-85%). Thus, under physiological conditions amino acids have to be considered as an important regulatory component of postprandial insulin release in obese subjects.     

Leptin increases circulating glucose, insulin and glucagon via sympathetic neural activation in fasted mice.

OBJECTIVE: A number of recent studies suggest that leptin has effects on glucose metabolism and pancreatic hormone secretion. Therefore, the effect of leptin administration on circulating glucose, insulin and glucagon in fed and fasted mice was investigated. The potential contribution of the sympathetic nervous system to the effects of leptin was also examined. DESIGN: Recombinant human or murine leptin was administered intraperitoneally (300 microg/mouse per 12 h over 24 h) to fed or fasted, normal or chemically sympathectomized NMRI mice. Blood samples were collected at baseline and after 24 h. MEASUREMENTS: Plasma concentrations of glucose, insulin and glucagon. RESULTS: In the fed state (n = 24), leptin administration did not affect glucose, insulin or glucagon concentrations after 24 h. Fasting (n = 24) reduced body weight by 2.2+/-0.4 g, plasma glucose by 3.7+/-0.4 mmol/l, plasma insulin by 138+/-35 pmol/l, and plasma glucagon by 32+/-7 pg/ml. In fasted mice, human leptin (n = 24) increased plasma glucose by 1.5+/-0.2 mmol/l (P = 0.041), plasma insulin by 95+/-22 pmol/l (P = 0.018), and plasma glucagon by 16+/-3 pg/ml (P = 0.025), relative to saline-injected control animals. Murine leptin exerted similar stimulating effects on circulating glucose (+1.0+/-0.2 mmol/l, P = 0.046), insulin (+58+/-17 pmol/l, P = 0.038) and glucagon (+24+/-9 pg/ml, P = 0.018) as human leptin in fasted mice (n = 12) with no significant effect in fed mice (n = 12). Human leptin did not affect circulating glucose, insulin or glucagon in fasted mice after chemical sympathectomy with 6-hydroxydopamine (40 mg/kg iv 48 h prior to fasting; n = 12). CONCLUSION: Leptin increases circulating glucose, insulin and glucagon in 24 h fasted mice by a mechanism requiring intact sympathetic nerves.     

Effect of glicentin-related peptides on glucagon secretion in anaesthetized dogs

Summary Recent studies have demonstrated that glicentin is released during nutrient ingestion. However, the biological function of glicentin remains unclear. In order to clarify the role of glicentin in the enteroinsular axis, the effect of glicentin-related peptides was investigated using in vivo local circulation of canine pancreas. Peaks I and II of gut glucagon-like immunoreactivity, partially purified from porcine intestinal extract by affinity chromatography and gel filtration, synthesized hexadecapeptide of N-terminal glicentin (1–16) and synthesized octapeptide of C-terminal glicentin (62–69) were administered for 10 min into the pancreaticoduodenal artery of canine pancreas. Blood samples were then drawn from the pancreaticoduodenal vein. The administration of peak I of glucagon-like immunoreactivity during arginine infusion in a dosage of 20 ng reduced the glucagon secretion by 42 pmol/1 (p<0.05), whereas peak 11 of glucagon-like immunoreactivity (20 ng) slightly increased the plasma level of insulin, although not significantly. The administration of glicentin (1–16) in a dosage of 400 ng during saline infusion did not alter the plasma insulin level, but reduced the plasma glucagon level in the pancreaticoduodenal vein by 29 pmol/1 (p<0.05). In addition, glicentin [62–691 in a dosage of 400 ng exerted a decrease in both the plasma insulin (40 mU/1,p<0.05) and glucagon level (27 pmol/l,p<0.05). The present study demonstrates the suppression of pancreatic glucagon release during the infusion of peak I glucagon-like immunoreactivity and N- or C-terminal glicentin-related peptide. Therefore, it is suggested that glicentin released during nutrient intake might inhibit the secretion of glucagon.     

Dopaminergic regulation of alpha-melanocyte-stimulating hormone and N-acetyl-beta-endorphin secretion in the fetal lamb

alpha MSH is present in high concentrations in the intermediate lobe of the fetal pituitary and has been implicated as a regulator of fetal adrenal steroidogenesis and fetal growth. However, there are few data regarding alpha MSH levels in fetal plasma or the control of fetal alpha MSH secretion. We measured alpha MSH immunoactivity in the plasma of chronically catheterized fetal lambs (gestational age, 116-138 days), newborn lambs, and adult sheep both in the baseline state and after dopamine receptor blockade with metoclopramide. The effect of metoclopramide on the release of another proopiomelanocortin-derived peptide, N-acetyl-beta-endorphin (N-acetyl-beta EP), which is synthesized together with alpha MSH in the intermediate lobe, was also studied. Baseline fetal plasma alpha MSH was significantly greater than maternal alpha MSH [35.6 +/- 2.2 (+/- SEM) vs. 10.0 +/- 1.0 pg/ml]. In eight studies in five fetal lambs, alpha MSH rose to a peak level of 121 +/- 23 pg/ml 15 min after metoclopramide administration to the fetus. Simultaneous maternal alpha MSH levels did not change, suggesting that the alpha MSH in fetal plasma was of fetal pituitary origin. Gel filtration of pooled fetal plasma extracts revealed that the alpha MSH immunoactivity eluted in the same position as the alpha MSH standard. Metoclopramide caused the secretion of nearly equimolar amounts of alpha MSH and N-acetyl-beta EP into fetal plasma. In four fetal lambs, basal N-acetyl-beta EP levels of 156 +/- 34 pg/ml rose to 305 +/- 65 pg/ml 15 min after metoclopramide treatment. Metoclopramide also stimulated plasma alpha MSH in newborn and adult sheep. In six newborn lambs, alpha MSH rose from 45.2 +/- 13 to 211 +/- 38 pg/ml 15 min after metoclopramide treatment, whereas in four adult sheep, a basal alpha MSH level of 11.1 +/- 2.2 pg/ml rose to 20.1 +/- 2.7 pg/ml 15 min after metoclopramide. In addition, metoclopramide stimulated fetal and neonatal PRL secretion, but had no effect on plasma vasopressin concentrations or acid-base and blood gas values. These studies indicate that immunoreactive alpha MSH and N-acetyl-beta EP are secreted into ovine fetal plasma and that the secretion of these peptides in the fetus appears to be under tonic dopamine inhibition, as is the case in the adult sheep and newborn lamb.     

Substantial rise of plasma beta-endorphin levels after insulin-induced hypoglycemia in human subjects.

To elucidate whether insulin-induced hypoglycemia enhances the release of beta-endorphin in man, plasma extracts obtained from healthy subjects and patients with Graves' disease before and 45 min after insulin injection were subjected to gel chromatography, and the fractions obtained were measured by RIA for beta-endorphin. In four healthy subjects, basal plasma beta-endorphin levels were less than 3 to 3.1 pg/ml, and the levels rose substantially to 47.5 +/- 12.4 pg/ml (mean +/- SE) 45 min after insulin injection. Basal plasma beta-endorphin levels in three hyperthyroid patinets (less than 3 to 3.8 pg/ml) did not seem to be different from those in healthy subjects; however, the rise after insulin injection tended to be higher in cases of hyperthyroidism, with a peak value of 68.5 +/- 9.7 pg/ml. Plasma beta-lipotropin and ACTH levels also rose in parallel with beta-endorphin in response to insulin-induced hypoglycemia in both healthy subjects and hyperthyroid patients. It would thus appear that beta-endorphin, like ACTH or beta-lipotropin, is released in human subjects by hypoglycemic stress.     

Oxytocin stimulates glucagon and insulin secretion in fetal and neonatal sheep

In adults of several species arginine vasopressin (AVP) and oxytocin (OT) stimulate pancreatic secretion of immunoreactive plasma glucagon (IRG). In fetal sheep AVP is an important stress hormone and may be simultaneously secreted with OT; however, their effects on IRG secretion are not known. We sought to determine if AVP and/or OT affected pancreatic IRG secretion in fetal and neonatal sheep. Either AVP or OT was infused for 30 min in chronically catheterized fetal and neonatal sheep, obtaining peripheral arterial and/or portal venous blood samples before; 10, 15, and 30 min during; and 15, 30, and 60 min after infusion for measurements of blood gases, hematocrit, IRG, immunoreactive plasma insulin (IRI) and plasma glucose. AVP did not affect IRG or IRI in fetal sheep (mean +/- SE, 133 +/- 1 days gestation), but small increases occurred in portal venous blood of lambs (2-49 days old). In contrast, OT (4.6 +/- 0.3 mU/min.kg; n = 12) increased fetal plasma IRG from 72 +/- 5 to 86 +/- 6 and 97 +/- 7 pg/ml (P less than 0.001) and IRI from 16 +/- 2 to 20 +/- 3 and 20 +/- 2 microU/ml (P less than 0.02) at 15 and 30 min, respectively; 157 +/- 11 microU OT/min.kg had no effect. In lambs (2-49 days old), 3.0 mU OT/min.kg increased arterial (n = 15) IRG from 139 +/- 19 to 367 +/- 43 and 483 +/- 76 pg/ml (P less than 0.01) and portal IRG (n = 8) from 167 +/- 39 to 341 +/- 72 and 502 +/- 148 pg/ml (P less than 0.01), respectively. Arterial and portal IRI also rose (P less than 0.01) from 36 +/- 4 to 82 +/- 12 and 105 +/- 32 microU/ml and from 29 +/- 5 to 65 +/- 13 and 51 +/- 7 microU/ml, respectively. Glucose was unchanged in all experiments. In fetal and neonatal sheep, AVP has minimal effects on IRG and IRI release. In contrast, OT increases both substantially; furthermore, there is a difference in fetal and neonatal responsiveness. OT may be important in modulating glucagon and insulin secretion during and after parturition.     

The effect of vagal stimulation on the release of cholecystokinin in anaesthetized pigs

The effect of electrical vagal stimulation on the release of cholecystokinin (CCK) was studied in nine anaesthetized pigs. Plasma CCK concentrations were measured radioimmunologically by means of an antiserum specific for the sulphated tyrosine region of CCK. Stimulation of both vagal nerves for 10 min induced an increase in CCK concentrations from 1.9 +/- 0.4 pmol/l to a peak value of 3.6 +/- 0.4 pmol/l in portal vein plasma and from 1.5 +/- 0.3 to 2.7 +/- 0.4 pmol/l in arterial plasma. Mean integrated increments during stimulation were 12.0 +/- 2.5 pmol/l/10 min (p less than 0.01) and 8.3 +/- 1.0 pmol/l/10 min (p less than 0.001), respectively. The results suggest a vagal innervation of the CCK cell in the upper small intestine.     

Somatostatin, insulin and glucagon after arginine stimulation in active and treated acromegaly

Ten acromegalic patients, 28-71 years old, were compared with 10 normal controls, 21-39 years old. In another study, 7 patients with active acromegaly, 19-70 years old, were investigated before and 4-9 months following transsphenoidal adenectomy and radiation. They were all investigated following an arginine infusion (0.5 g/kg/20 min). Although the mean plasma somatostatin (somatotrophin release inhibiting factor (SRIF] was somewhat higher in acromegalic patients compared to normal controls (mean basal values 21 +/- 3.8 and 16.6 +/- 2.1 pmol/l, respectively), the difference was not significant. The patients had higher serum insulin (peak values 118 +/- 23.9 and 63 +/- 11.8 mU/l, respectively) and lower plasma glucagon (peak values 171 +/- 29.0 and 310 +/- 52.7 pmol/l, respectively). Plasma SRIF increased during arginine infusion, but the concentrations were similar before and following the operation (mean basal values 18.2 +/- 2.6 and 15.2 +/- 2.3 pmol/l, respectively). Serum insulin was significantly higher before the operation (peak values 154 +/- 38.8 and 91 +/- 24.9 mU/l, respectively). Plasma glucagon was similar before and after the operation (peak values 143 +/- 23.4 and 127 +/- 22.7 pmol/l, respectively). Plasma SRIF is similar in active acromegaly and normal controls, and in acromegaly before and following treatment, despite differences in serum growth hormone (GH), serum insulin and plasma glucagon. This points towards a modulating role for GH on plasma SRIF, possibly by affecting the other islet cell hormones.     

Prandial regulation of ghrelin secretion in humans: does glucagon contribute to the preprandial increase in circulating ghrelin?

OBJECTIVE: Glucagon secretion is stimulated by fasting and inhibited postprandially, a pattern that mimics the secretory profiles of both ghrelin and GH. We thus hypothesized that glucagon may be a determinant of the changes in circulating ghrelin and GH that occur in relation to meals. The objective of the study was to explore this hypothesis by determining the ghrelin and GH response to a bolus of glucagon or saline in healthy subjects. SUBJECTS AND MEASUREMENTS: Nine healthy volunteers, mean age 47 years (range 33-58) and body mass index (BMI) 24 kg/m2 (range 20.9-27.6) were recruited and received either 1 mg glucagon (n = 9) or 1 ml saline (n = 6) subcutaneously on separate days between 0800 and 0830 h after an overnight fast. Venous blood was then sampled at 15-min intervals during the first hour, followed by 30-min intervals up to 4 h for glucose, insulin, GH, cortisol, somatostatin and ghrelin. RESULTS: Mean +/- SE basal ghrelin was 213.1 +/- 34.3 pmol/l and decreased significantly by 15 min after glucagon administration to 179.3 +/- 28 pmol/l (P = 0.01), then remaining suppressed relative to the basal value until 240 min after glucagon. Plasma insulin increased from a basal value of 46.7 +/- 7.7 pmol/l to a peak of 327.1 +/- 54.9 pmol/l (P < 0.0001). There was an inverse statistical relationship between the increase in insulin over the first 120 min and the decrease in ghrelin (P = 0.005), while somatostatin, GH and glucose were not significant contributors to the decrease in ghrelin (P > 0.05). Mean +/- SE basal GH was 7.3 +/- 2.9 microg/l and increased by 150 min after glucagon to a peak of 20.5 +/- 6.8 microg/l (P = 0.006). Changes in neither ghrelin nor glucose were related to the increase in GH (P = 0.7). Saline administration did not produce any significant change in ghrelin, insulin or somatostatin although the expected diurnal reduction in cortisol (P < 0.05) was observed. CONCLUSIONS: Our study found no evidence that glucagon stimulates ghrelin secretion in humans and supports the hypothesis that insulin is a negative regulator of ghrelin secretion in the postprandial state. We did not find a negative relationship between endogenous somatostatin and ghrelin despite earlier reports that exogenously administered somatostatin analogues suppress plasma ghrelin. Finally, glucagon-induced GH secretion is not mediated by an increase in plasma ghrelin.     

RECOVERY FROM GLUCOCORTICOID INHIBITION OF THE RESPONSES TO CORTICOTROPHIN-RELEASING HORMONE

We have characterized the recovery of the hypothalamic-pituitary-adrenal (HPA) axis from inhibition by short-term prednisolone administration. Prednisolone was given in a dosage averaging 25 mg at 12 h intervals orally for up to 2 weeks to adult volunteers. Human corticotrophin releasing hormone (hCRH) tests were performed at 0901 h using a bolus injection of 1 microgram/kg before and 24-48 h after discontinuing the prednisolone. In the initial control study, hCRH stimulated a two-fold rise in plasma ACTH and a 30% rise in plasma cortisol within 30 min (ACTH rose from 18.5 +/- 4.5, SEM, pg/ml to 36.5 +/- 12.6 pg/ml and cortisol from 415 +/- 58 to 531 +/- 69 nmol/l in response to hCRH. One dose of prednisolone had no effect on the ACTH or cortisol response to hCRH administered 24 h later. Twenty-four hours after discontinuing a 1 week course of prednisolone, baseline plasma ACTH (3.9 +/- 0.6 pg/ml) and cortisol (146 +/- 17 nmol/l) were markedly suppressed, as was the cortisol response to hCRH (peak 198 +/- 22). However, the plasma ACTH response to hCRH was not significantly suppressed. Forty-eight hours after discontinuing prednisolone, the recovery of ACTH secretion was complete (baseline 10.9 +/- 4.2, peak 36.4 +/- 14.8 pg/ml), but the cortisol response to hCRH was still depressed (peak 294 +/- 66 nmol/l). Recovery from a 2 week course of prednisolone had similar characteristics except plasma cortisol was depressed more profoundly. Plasma dehydroepiandrosterone (DHA) during hCRH tests and dehydroepiandrosterone sulphate (DHAS) paralleled plasma cortisol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Degradation of 125I-labelled prolactin in the rabbit: effect of nephrectomy and prolactin infusion

The concentrations of progesterone and oestradiol-17 beta in the maternal plasma of Bennett's wallaby, Macropus rufogriseus rufogriseus, were measured daily throughout gestation after reactivation of the diapausing corpus luteum by removal of the suckling pouch young (RPY). Progesterone increased from mean concentrations of 382-424 pmol/l (120-133 pg/ml) during lactation to reach peak concentrations of 908 +/- 172 (S.E.M.) pmol/l (285 +/- 54 pg/ml) (n = 8) 4 days after RPY and 971 +/- 220 and 971 +/- 229 pmol/l (305 +/- 69 and 305 +/- 72 pg/ml) (n = 7) 24 and 25 days after RPY respectively. The mean gestation length (RPY to birth) was 26.8 +/- 0.6 (S.D.) days (n = 6, range 25.75-27.50 days). Immediately after birth the plasma progesterone concentration declined to 299 +/- 51 (S.E.M.) pmol/l (94 +/- 16 pg/ml) (n = 6). Oestradiol-17 beta increased from mean concentrations of 291-553 pmol/l (80-152 pg/ml) during lactation to reach a peak concentration of 967 +/- 331 pmol/l (266 +/- 91 pg/ml) (n = 9) 1 day after RPY. The concentration declined from 7 days after RPY and fluctuated between mean concentrations of 273 and 480 pmol/l before reaching a minimum of 207 +/- 69 pmol/l (57 +/- 19 pg/ml) (n = 6) 19 days after RPY. A transient increase to 542 +/- 207 pmol/l (n = 7) occurred at 22 days after RPY. Plasma concentrations declined to a low of 156 +/- 55 pmol/l (43 +/- 15 pg/ml) (n = 6) 5 days after parturition. The mean concentration of plasma 13,14-dihydro-15-oxo-prostaglandin F2 alpha was less than 2.8 nmol/l (1 ng/ml) for all samples from 13 days after RPY until 4 days after parturition. The results suggest that oestradiol-17 beta may be important in the early stages of blastocyst reactivation to synergize with progesterone in stimulating uterine secretions. 13,14-Dihydro-15-oxo-prostaglandin F2 alpha is unlikely to be involved in the birth process and any luteolytic effect is likely to be from a local production of PGF2 alpha.     

Glucose-dependent insulinotropic polypeptide and insulin-like immunoreactivity in saliva following sham-fed and swallowed meals

Gastrointestinal peptides, including insulin, glucagon and glucose-dependent insulinotropic polypeptide (GIP) have previously been reported in salivary glands. Recent evidence has suggested they might influence postprandial macronutrient metabolism. This study therefore investigated and compared postprandial hormone concentrations in saliva and plasma to determine whether their secretion was influenced by oral food stimuli. In a within-subject randomised cross-over comparison of hormone concentrations in plasma and saliva following a mixed meal, 12 subjects were given two 1708 kJ mixed meals. On one occasion the meal was chewed and swallowed (swallowed meal), on the other it was chewed and expectorated (sham-fed meal). Salivary and plasma levels of immunoreactive insulin, GIP and glucagon-like peptide-1 (GLP-1), total protein, alpha-amylase, glucose and non-esterified fatty acid were measured before and for 90 min following the meals. Saliva total protein and alpha-amylase rose following both meals, indicating that the stimulus for salivary protein release is related to the presence of food in the mouth. GLP-1 was not detected in saliva. Fasting salivary insulin levels were lower in saliva than plasma (28+/-6 vs 40+/-25 pmol/l respectively). Both increased following the swallowed meal but the rise in saliva was slower and less marked than in plasma (peak levels 96+/-18 and 270+/-66 pmol/l for saliva and plasma respectively, P<0.01). Both were unchanged following the sham-fed meal. GIP was detected in saliva. Fasting GIP levels were significantly higher in saliva than plasma (183+/-23 compared with 20+/-7 pmol/l, P<0.01). They decreased in saliva following both swallowed and sham-fed meals to nadirs of 117+/-17 and 71+/-12 pmol/l respectively, but rose following the swallowed meal to peak levels of 268+/-66 pmol/l. These findings are consistent with insulin in saliva being an ultrafiltrate of that circulating in blood, but GIP in saliva being the product of local salivary gland synthesis, whose secretion is influenced, directly or indirectly, by oral stimuli. The function of salivary GIP is unknown, but we speculate that it may play a role in the regulation of gastric acid secretion in the fasting state.     

Effect of bombesin on plasma insulin, pancreatic glucagon, and gut glucagon in man

The effect of bombesin on insulin, pancreatic glucagon, and gut glucagon was investigated in eight healthy volunteers and two pancreatectomized patients. Bombesin, infused iv at the constant rate of 5 ng kg-1 min-1, produced a sharp and statistically significant rise in the plasma insulin concentration. The peak was reached at 5 min (26 +/- 2.17 microU/ml; P less than 0.005 vs. basal values), followed by a prolonged and statistically significant (P less than 0.05) decrease in blood glucose. Pancreatic glucagon rapidly rose to a maximal value of 80.5 +/- 7.6 pmol/liter (P less than 0.005 vs. basal values). In contrast with the prompt increase in insulin and glucagon plasma levels, the peak in gut glucagon concentration (55.8 +/- 4.6 pmol/liter; P less than 0.005 vs. basal values) was reached 30 min after bombesin infusion was discontinued. In the two pancreatectomized patients, bombesin induced an increase in gut glucagon concentrations only. The results presented indicate that bombesin acts directly on the A and B cells of the pancreas, influencing glucose homeostasis; however, more complex mechanisms seem to be involved in gut glucagon secretion.     

Effects of intravenous infusion of amino acids on cholecystokinin release and gallbladder contraction in humans

We investigated the effect of intravenous infusions of the therapeutically available amino acid solutions Moripron and Morihepamin (Roussel Morishita, Osaka, Japan) on gallbladder contraction and cholecystokinin (CCK) release in healthy male volunteers. Plasma CCK levels were measured by radioimmunoassay, using the antibody OAL-656, which is specific for the aminoterminus of CCK-8 and thus recognizes biologically active forms of all CCKs. The volume of the gallbladder was calculated by ultrasonographic measurements. Intravenous infusion of Moripron at the rate of 3.33 ml/min for 60 min, caused gallbladder contraction, with a peak response of 31.3±8.6% of the fasting volume at 45–60 min, and a significant increase in plasma CCK concentration, from 1.8±0.2 pmol/l to a peak of 9.9±1.5 pmol/l, at 30–45 min. The maximum gallbladder contraction and the peak CCK release during the Moripron infusion were not significantly different from findings after a test meal. There was a close relationship between the peak plasma CCK concentration and the maximal gallbladder contraction during the administration of Moripron, and this agent, even when infused at the rate of 1.67 ml/min, significantly increased plasma CCK levels and gallbladder contraction. Intravenous infusion of Morihepamin had no significant influence on gallbladder volume or plasma CCK levels. The discrepancy in responses appeared to be related to differences in composition between Moripron and Morihepamin, and not to the total dose of amino acid. Intravenous infusions of amino acids appear to have different effects on gallbladder contraction and plasma CCK secretion depending on the amino acids composition. Our findings suggest that an intravenous infusion of Moripron could be used for the prophylaxis of acute acalculous cholecystitis and sludge formation due to reduced biliary motility in patients on total parenteral nutrition.