Insulin and glucagon secretion in rats: effects of calcitonin gene-related peptide

Immunoreactive calcitonin gene-related peptide (CGRP) has been shown to occur in intrapancreatic nerves and islet somatostatin cells in the rat. Therefore, we investigated the effects of CGRP on insulin and glucagon secretion in the rat. CGRP was infused i.v. at one of 3 dose levels (4.3, 17 or 68 pmol/min). Infusion of CGRP alone was found to elevate basal plasma levels of both insulin and glucagon. In contrast, CGRP impaired the plasma insulin responses to both glucose (7 mg/min; P less than 0.001) and arginine (8.5 mg/min; P less than 0.001), and inhibited the arginine-induced increase in plasma glucagon concentrations (P less than 0.001). Since CGRP and somatostatin are colocalized within the D-cells, we also infused CGRP and somatostatin together at equimolar dose levels (17 pmol/min), with glucose (7 mg/min). By that, the increase in plasma insulin concentrations decreased more rapidly than during infusion of either peptide alone. Since alpha 2-adrenoceptor activation is known to inhibit glucose-stimulated insulin secretion, we also infused CGRP together with the specific alpha 2-adrenoceptor antagonist yohimbine (37 nmol/min). In that way, the plasma insulin-lowering effect of CGRP was prevented. We have shown in the rat: (1) that CGRP stimulates basal insulin and glucagon secretion; (2) that CGRP inhibits stimulated insulin and glucagon secretion; (3) that CGRP and somatostatin more rapidly induce a potent inhibitory action on glucose-stimulated insulin secretion when given together; and (4) that the alpha 2-adrenoceptor antagonist, yohimbine, counteracts the inhibitory action of CGRP on glucose-stimulated insulin secretion. We suggest that CGRP is of importance for the regulation of insulin and glucagon secretion in the rat. The mechanisms behind the islet effects of CGRP can not be established by the present results, though they apparently require intact alpha 2-adrenoceptors.     

Responses of the rat pituitary-adrenal axis to hypotensive infusions of corticotropin-releasing factor, vasoactive intestinal peptide and other depressor agents.

We have assessed in male rats the response of the hypothalamo-pituitary-adrenal axis to hypotension induced by 30 min i.v. infusions of corticotropin-releasing factor (CRF; 0.1, 0.2 and 0.5 nmol/kg/min), calcitonin gene-related peptide (CGRP; 0.25 nmol/kg/min), vasoactive intestinal peptide (VIP; 0.25 nmol/kg/min) and nitroprusside (NP; 150 micrograms/kg/min). Infusions of CRF produced dose-dependent decreases in mean arterial blood pressure of 10, 35 and 43 mmHg at 30 min, and the other treatment had depressor effects comparable with the higher CRF doses (between -35 and -44 mmHg). Plasma ACTH levels were increased from 383% to 595% by CGRP, NP and the three different CRF infusions (P less than 0.001 vs. controls), whereas they were raised more than 10-fold by VIP administration (P less than 0.001 vs. other treatments), a level 60% higher than the maximum achieved with CRF. Corticosterone levels were increased by 112% to 146% following infusion of the three different CRF doses, CGRP and NP (P less than 0.001 vs. controls), and by 240% after VIP (P less than 0.001 vs. other treatments). Plasma aldosterone values were increased by 112% to 140% after infusion of NP and the two higher CRF doses (P less than 0.01 vs. controls), and by 223% following VIP (P less than 0.05 vs. CRF 0.2 and NP). CGRP infusion, although resulting in similar haemodynamic changes, did not alter circulating aldosterone. The levels measured after CGRP were identical to those observed after the infusion of atrial natriuretic peptide (ANP; 1 nmol/kg/min), a known inhibitor of aldosterone secretion. These results demonstrate that the combination of hypotension and direct pituitary stimulation by CRF does not increase circulating ACTH levels above those obtained with hypotension alone (NP and CGRP), whereas VIP, which has only minimal direct effects on corticotroph function, markedly enhanced the ACTH response, suggesting that it may modulate ACTH release by an indirect mechanism. Evaluation of aldosterone levels after the different infusions indicates that CGRP prevented the rise normally associated with acute hypotension, thus confirming recent observations in other species that stimulated aldosterone secretion can be inhibited by CGRP.     

Effect of sparteine sulfate on insulin secretion in normal men

This study aimed at evaluating the influence of sparteine sulfate either upon basal plasma glucose and insulin or glucose-induced insulin secretion in normal man. Thirteen overnight fasted volunteers took part in this study; five of them were submitted to sparteine sulfate bolus (15 mg in 10 ml of saline solution) followed by a slow infusion (90 mg/100 ml X 60 min) and eight subjects underwent two different glucose pulses (20 gr. i.v.) in absence or in presence of sparteine, infused as described above. In basal conditions, along with sparteine infusion, plasma glucose showed a progressive and significant decrease (P less than 0.0001) and plasma insulin was significantly higher from min 10 to 120' (P less than 0.0005-0.001). Even during the glucose-induced insulin secretion, in the presence of sparteine infusion, plasma glucose levels were significantly lower while plasma insulin levels were significantly higher when compared to those observed after glucose alone. The acute insulin response (AIR) was 42 +/- 10 microU/ml after glucose alone vs 67 +/- 9 microU/ml after glucose plus sparteine (P less than 0.05). Total insulinemic areas were significantly different being 1410 +/- 190 vs 2250 +/- 310 microU/ml/min (P less than 0.001) during glucose and glucose plus sparteine infusion, respectively. This study thereby, demonstrates that in normal man sparteine sulfate, administrated by intravenous infusion, is able to increase either basal or glucose-induced insulin secretion.     

Age-related increase of calcitonin gene-related peptide in rat thyroid and circulation.

Elevated calcitonin levels in thyroid gland extracts and in plasma accompanied by C-cell hyperplasia are frequently found in old rats, in particular those raised in laboratory conditions. In parallel with calcitonin, we demonstrate here that the thyroidal content and plasma levels of immunoreactive calcitonin gene-related peptide (i-CGRP) significantly increase with age in rats (p less than 0.0001). C18 Sep-Pak-extractable i-CGRP level in plasma was 35% of the total i-CGRP. Gel permeation chromatography and rp-HPLC studies revealed a number of immunoreactive molecular forms of CGRP and only 40-50% of the acid-extracted immunoreactivity was coeluted with the synthetic CGRP(1-37). The i-CGRP level measured in plasma was highly correlated with the thyroidal content of CGRP (p less than 0.001) and also with the age of the rat (p less than 0.001), suggesting an age-related increase of contribution of CGRP from thyroid gland into the circulation.     

Calcitonin gene-related peptide in human obesity.

We studied plasma calcitonin gene-related peptide (CGRP) levels in obese women before (n = 24) and after (n = 13) weight loss, and in normal weight controls (n = 15). Furthermore, the influence of two isocaloric meals (high carbohydrate vs. high fat) on plasma CGRP concentrations was studied. The CGRP concentration in the obese group (32.26 +/- 2.01 pg/ml) was significantly (p less than 0.0001) higher than in the control group (21.64 +/- 0.15 pg/ml). After weight loss (14.3 +/- 0.72% of original weight) CGRP concentrations remained unchanged. Only the high-fat meal caused a significant (p less than 0.02) rise in CGRP levels. Our results indicate that elevated plasma CGRP levels may constitute a primary phenomenon in obese women, and that fat intake may be associated with increased CGRP secretion.     

Metabolic clearance rate and plasma half life of alpha-human atrial natriuretic peptide in man

The disappearance and metabolic clearance rate (MCR) of alpha human atrial natriuretic peptide (alpha h-ANP) has been studied in normal man by radioimmunoassay of the atrial peptide in plasma and plasma extracts. After an intravenous (iv) bolus injection of 100 micrograms alpha h-ANP, levels of immunoreactive alpha h-ANP (IR-alpha hANP) in unextracted plasma fell rapidly and exponentially during the first 10 min (t1/2 = 2.5 min), after which levels declined more slowly to reach basal values 30 min after injection. Venous plasma extracts, purified by Sep Pak cartridges, were used to calculate the MCR of IR-alpha hANP under steady state conditions of constant iv infusion (200 micrograms over 60 min) in healthy volunteers. Calculated MCR from venous samples was 2.4 L/min and volume of distribution 10.7 L. After cessation of infusions, the disappearance rate (rapid phase) of IR-alpha hANP was 3.1 min. These studies show that alpha h-ANP is rapidly metabolized at rates similar to other vasoactive hormones such as angiotensin II and vasopressin.     

Digestive motor effects and vascular actions of CGRP in dog are expressed by different receptor subtypes

Calcitonin gene-related peptide (CGRP) is a 37 AA peptide localized in blood vessels and nerves of the GI tract. Activation of CGRP receptors (subtypes 1 or 2) usually induces vasodilation and/or muscle relaxation, but its effects in dog and on gastroduodenal motility are still unclear. This study looked for the effect of CGRP and the antagonist CGRP8-37, specific for CGRP type 1 receptor, 1) on GI motility (interdigestive and postprandial), and 2) on hemodynamy, in conscious dogs. During the interdigestive period, the infusion of CGRP1-37 (200 pmol/kg/h) or CGRP8-37 (2000 pmol/kg/h) did not modify the duration of the migrating motor complex nor the release nor the motor action of plasma motilin. The gastric emptying of a solid meal (15 g meat/kg) was reduced by the administration of CGRP1-37 (AUC: 2196 +/- 288.6 versus 3618 +/- 288.4 with saline or T12: 78 +/- 7.3 versus 50 +/- 4.3 min; P < 0.01) and this effect was reversed by the antagonist CGRP8-37. CGRP1-37 significantly (P < 0. 01) diminished arterial pressures (118 +/- 1.6/64 +/- 1.4 vs. 125 +/- 1.4/75 +/- 1.2 mmHg with saline) and accelerated the basal cardiac rhythm (110 +/- 1.4 versus 83 +/- 1.6 beats/min). However, CGRP8-37 failed to block the cardiovascular effects of CGRP1-37. In dog, CGRP could influence digestive motility by slowing the gastric emptying of a meal through an action on CGRP-1 receptors. Hemodynamic effects of CGRP were not blocked by CGRP8-37 and seem therefore mediated by CGRP-2 receptor subtype.     

Effects of substance P and calcitonin gene-related peptide on the pulmonary circulation.

To assess the in vivo effects of the neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) on the pulmonary vascular bed, the hemodynamic responses to both CGRP and SP were examined in the in situ-perfused lung lobe of open-chest anesthetized pigs. Peptides were infused into the lobar artery under conditions of elevated pulmonary vascular tone by prostaglandin F2 alpha (PGF2 alpha, 20 micrograms/min). Pulmonary airway lobar dynamic compliance (Cdyn) and airway resistance (Re) were computed from simultaneously measured airway pressure and airflow entering the lobe through a Carlens endobronchial divider. PGF2 alpha infusion slightly reduced Cdyn (-20%) and increased Re (+11%) while lobar arterial pressure rose from 14 +/- 1 to 31 +/- 2 mmHg (n = 12). In these conditions, lobar artery infusion of SP (0.5-50 pmol/min) or CGRP (15-5,000 pmol/min) produced a dose-dependent decrease in the pressor response to PGF2 alpha, reaching -54 +/- 3 and -64 +/- 7%, respectively, without alterations in lung mechanics. On a molar basis, SP was more effective than CGRP; its vasodilatory effect was more rapid and of shorter duration. Higher CGRP infusion rates were not studied because of marked systemic hypotension. SP infused at 150, 500, and 1,000 pmol/min significantly reduced Cdyn by 12 +/- 2, 24 +/- 4, and 62 +/- 7%, respectively, but also induced a rise in lobar arterial pressure and a fall in systemic arterial pressure. The results show that both SP and CGRP are potent pulmonary vasodilators. In contrast to CGRP, which did not affect lung mechanics, high infusion rates of SP decreased Cdyn and increased Re.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diagnostic relevance of the amino-terminal cleavage peptide of procalcitonin (PAS-57), calcitonin and calcitonin gene-related peptide in medullary thyroid carcinoma patients

We have identified the amino-terminal cleavage peptide of procalcitonin (PAS-57) in the plasma of normal human subjects and of medullary thyroid carcinoma (MTC) patients together with calcitonin (CT) and CT gene-related peptide (CGRP). Major components on reversed-phase high-pressure liquid chromatography had the retention times of synthetic PAS-57, CT and CGRP as well as of precursor proteins. Plasma levels of PAS-57 (290 +/- 50 pgeq/ml; mean +/- S.E.M.), CT (27 +/- 8 pgeq/ml) and CGRP (8.4 +/- 0.8 pgeq/ml) were respectively 2.3-, 1.6- and 1.5-fold higher in normal men (n = 10) than in women (n = 8). In response to 1 min intravenous calcium infusions (2 mg per kilogram body weight) PAS-57 and CT were increased 3.5- and 2.7-fold (P less than 0.001), respectively, but CGRP remained unchanged. In MTC patients (n = 57) with raised levels of PAS-57 and CT, the molar ratio between PAS-57 and CT was 1.7-times higher than in normal subjects (P less than 0.01). We have found that PAS-57 is a predominant CT/CGRP gene derived product in the circulation of normal subjects and of MTC patients and a potential new MTC tumor marker.     

Pharmacokinetics and organ catabolism of cholecystokinin octapeptide in pigs

The pharmacokinetics and organ catabolism of cholecystokinin octapeptide (CCK8) were studied in pigs. In conscious animals, intravenous infusion of increasing doses of CCK8 (2.9-232.3 pmol.kg-1.min-1) resulted in a linear increase of plasma CCK-like immunoreactivity (CCK-LI). At the cessation of infusion of the largest dose of CCK8, plasma CCK-LI promptly returned to near basal values. The half-disappearance time (t1/2), metabolic clearance rate (MCR) and distribution volume (DV) were estimated to be 0.55 +/- 0.03 min, 134.8 +/- 10.8 ml.kg-1.min-1 and 107.9 +/- 13.0 ml.kg-1, respectively. In another group of anesthetized animals, infusion of CCK8 at similar doses produced higher plateau plasma CCK levels and the t1/2, MCR and DV were calculated to be 0.68 +/- 0.06 min, 32.5 +/- 3.9 ml.kg-1.min-1 and 45.2 +/- 5.6 ml.kg-1, respectively. Estimates of first-pass immunological degradation through various vascular beds were in the range 27-66%, with in decreasing order the kidney, liver, hindleg, followed by the brain and gut. These results indicate that immunoreactive CCK8 is rapidly cleared from plasma during passage through several vascular beds. The peptide is only partly inactivated during hepatic transit and so may exert hormonal effects upon its release from intestinal stores.     

Effect of central hypertonic stimulation on plasma atrial natriuretic peptide and oxytocin in conscious rats

The effect of the intracerebroventricular (i.c.v.) injection of hypertonic sodium chloride on plasma atrial natriuretic peptide (ANP) and oxytocin (OT) was evaluated in conscious freely moving rats. A hypertonic or isotonic NaCl solution was injected into the third ventricle. Blood pressure and heart rate were monitored and blood samples were collected. I.c.v. injection of the hypertonic solution resulted in a significant increase in mean arterial pressure (105.3 +/- 2.9 mmHg at time 0 to 124.2 +/- 4.4 mmHg at 5 min, P less than 0.01) and heart rate (350.0 +/- 25.0 bpm at time 0 to 420.8 +/- 13.6 bpm at 20 min, P less than 0.01). Plasma OT increased 4-fold over the basal values 5 min after the injection (4.5 +/- 1.1 to 20.1 +/- 3.2 pg/ml, P less than 0.01), while there was no significant change in plasma ANP (37.3 +/- 9.1 to 46.6 +/- 12.6 pg/ml, n.s.). The control injection produced no significant changes in any parameters. These results show that hemodynamic changes are not necessarily associated with alterations in plasma ANP. Furthermore they suggest that central osmoreceptors are not involved in the control of ANP secretion.     

Glucose dependent insulinotropic polypeptide (GIP) infused intravenously is insulinotropic in the fasting state in type 2 (non-insulin dependent) diabetes mellitus

The effects of an intravenous infusion of porcine GIP on beta-cell secretion in patients with untreated type 2 diabetes mellitus have been studied. The subjects were studied on two separate days. After a 10 h overnight fast and a further 120 min basal period they were given an intravenous infusion of porcine GIP (2 pmol.kg-1.min-1) or control solution in random order from 120-140 min. Frequent plasma glucose, insulin, C-peptide and GIP measurements were made throughout and the study was continued until 200 min. Plasma glucose levels were similar throughout both tests. During the GIP infusion there was an early significant rise in insulin concentration from 0.058 +/- 0.006 nmol/l to 0.106 +/- 0.007 nmol/l (P less than 0.01) within 6 min of commencing the GIP infusion and insulin levels reached a peak of 0.131 +/- 0.011 nmol/l at 10 min (P less than 0.01). Insulin levels remained significantly elevated during the rest of the GIP infusion (P less than 0.01-0.001) and returned to basal values 20 min post infusion. No change in basal insulin values was seen during the control infusion. C-peptide levels were similarly raised during the GIP infusion and the increase was significant just 4 min after commencing the GIP infusion (P less than 0.05). GIP levels increased from 16 +/- 3 pmol/l prior to the infusion to a peak of 286 +/- 24 pmol/l 20 min later. At 4 min when a significant beta-cell response was observed GIP levels were well within the physiological range.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperglycaemic clamp and insulin binding to isolated monocytes before and after glibenclamide treatment of mild type II diabetics

The therapeutic action of 3.5 mg glibenclamide (HB 420) once a day for six weeks was evaluated in ten mild NID diabetics previously treated with diet only. Stable HbA1, insulin secretion during hyperglycaemic clamp (100 mg/dl over the baseline in the first study, and at the same level in the second one), peripheral sensitivity expressed as the amount of dextrose infused per Kg per min (M-coefficient), the glucose metabolic clearance rate (MCR) and the M/I ratio were measured. Circulating monocytes were separated to assess insulin binding before and after treatment. The results included a significant decrease in HbA1 (7.5 +/- 0.3 against 8.4 +/- 0.4%, P less than 0.005), increased steady-state (100-120 min.) plasma insulin (31 +/- 4.4 against 25.7 +/- 3.9 microU/ml), a significant increase in M-coefficient (4.02 +/- 0.62 against 2.49 +/- 0.31 mg/Kg/min, P less than 0.01), and MCR (1.90 +/- 0.34 against 1.18 +/- 0.18 ml/Kg/min, P less than 0.025) and an increase in the M/I ratio (14.6 +/- 1.9 against 11.2 +/- 1.7). All subjects displayed an increase in total insulin binding (4.03 +/- 0.31% against 2.79 +/- 0.34%, P less than 0.001) and affinity constants (Ke = 8.3 +/- 0.6 against 6.6 +/- 0.4 X 10(7) M-1, P less than 0.05). Since the M/I ratio increased in only 7/10 subjects and since there was no significant correlations between the percentage increase in M and MCR and the plasma insulin increase, whereas the increase in R0 was significant, it is felt that the euglycaemizing action of low doses of glibenclamide is primarily peripheral.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulation of canine pancreatic polypeptide, gastrin, and gastric acid secretion by ranatensin, litorin, bombesin nonapeptide and substance P

Four dogs with chronic gastric fistulas were give intravenous bombesin nonapeptide (B9), ranatensin, and litorin by constant infusion for 90 min at 1.2 micrograms x kg-1 on separate days. A dose response study with substance P (1.5, 3.0, 60, 18 and 54 micrograms x kg-1 x h-1) was also carried out and all tests compared to a standard protein meal (10g x kg-1). Plasma gastrin and PP were measured by radioimmunoassay and gastric acid by autobiuret titration. Substance P failed to stimulate gastric acid secretion or release either pancreatic polypeptide (PP) or gastrin. Basal gastrin levels were 8 +/-2 fmol/ml. The peak increment of gastrin released by bombesin was 95 +/- 16, ranatensin 22 +/- 6, litorin 18 +/- 4, and meal 39 +/- 5 fmol/ml. Bombesin caused significantly greater release of gastrin than a meal, litorin or ranatensin (P less than 0.01). Basal gastric secretion was 23 +/- 4 microequiv./min. B9 produced a peak acid secretion of 356 +/- 124 muequiv./min. There was no significant difference between the bombesin-like peptides (P less than 0.01). Basal plasma PP was 38 +/- 12 fmol/ml. B9 produced a peak PP increment of 600 +/- 50, litorin 137 +/- 36, ranatensin 98 +/- 11, and a meal 305 +/- 58 fmol/ml. B9 released significantly more PP than either litorin of ranatensin (P less than 0.01). The different amino acid sequences of the peptides are probably responsible for their potency. The substitution of a penultimate phenylalanine residue in litorin and ranatensin for leucine in bombesin does not prevent PP or gastrin release by bombesin-like peptides. Since bombesin-like peptides are widely distributed in the gastrointestinal tract of man and stimulate both acid and gut hormone secretion, it is possible that they might play a physiological role in the modulation of gastrointestinal function.     

Localisation and neural control of the release of calcitonin gene-related peptide (CGRP) from the isolated perfused porcine ileum

By immunohistochemistry, CGRP-like immunoreactive (CGRP-LI) nerve fibres were found in the lamina propria along small vessels and in the lamina muscularis mucosae in the porcine ileum. Immunoreactive nerve cell bodies were found in the submucous and myenteric plexus. Upon HPLC-analysis of ileal extracts, CGRP-LI corresponded entirely to porcine CGRP plus smaller amounts of oxidised CGRP. Using isolated vascularly perfused segments of the ileum, we studied the release of CGRP-LI in response to electrical stimulation of the mixed extrinsic periarterial nerves and to infusion of different neuroblockers. In addition, the effect of infusion of capsaicin was studied. The basal output of CGRP-LI was 2.9+/-0.7 pmol/5 min (mean+/-S.D.). Electrical nerve stimulation (8 Hz) significantly increased the release of CGRP-LI to 167+/-16% (mean+/-S.E.M.) of the basal output (n=13). This response was unaffected by the addition of atropine (10(-6) M). Nerve stimulation during infusion of phentolamine (10(-5) M) with and without additional infusion of atropine resulted in a significant further increase in the release of CGRP-LI to 261+/-134% (n=5) and 240+/-80% (n=9), respectively. This response was abolished by infusion of hexamethonium (3x10(-5) M). Infusion of capsaicin (10(-5) M) caused a significant increase in the release of CGRP-LI to 485+/-82% of basal output (n=5). Our results suggest a dual origin of CGRP innervation of the porcine ileum (intrinsic and extrinsic). The intrinsic CGRP neurons receive excitatory input by parasympathetic, possibly vagal, preganglionic fibres, via release of acetylcholine acting on nicotinic receptors. The stimulatory effect of capsaicin suggests that CGRP is also released from extrinsic sensory neurons.     

Significance of gastric endocrine tumor and age-related gut peptide alterations in Mastomys

The Mastomys (Praomys natalensis) species are a unique natural model in which the bioactivity of gastric carcinoids may be studied. Several investigators have previously demonstrated that these tumors contain large amounts of histamine. In this study we investigated the presence of peptides associated with the neoplasm. The levels and location of gastrin, gastric inhibitory peptide (GIP), neurotensin, peptide YY (PYY), pancreatic polypeptide (PP), glucagon, bombesin, vasoactive intestinal peptide (VIP) and somatostatin (SRIF) were investigated by radioimmunoassay and immunocytochemistry. In addition the distribution of these peptides were evaluated in the gastrointestinal tract of young and old animals to investigate possible age-related changes. PYY and enteroglucagon (EG) were significantly (P less than 0.001) elevated in both tumor tissue (676 +/- 152, 551 +/- 164 pmol/g) and plasma (620 +/- 160, 500 +/- 147 pmol/l) of tumor-bearing animals. Immunocytochemistry revealed PYY- and EG-like immunoreactivity in 20-30% of tumor cells. A significant decrease (P less than 0.05) in bombesin was noted in older animals, but no changes in gastric tissue content of PYY or EG could be detected between young and old animals. Gastrin was not detected in tumors and there were no significant changes in tissue or plasma levels with age. Small bowel concentrations of VIP and PYY were higher in the older mastomys (P less than 0.05). In contrast, colonic levels of bombesin, VIP, somatostatin and PYY were significantly lower (P less than 0.05) in older mastomys compared with young. The age-related changes in several peptides may reflect an adaptive response to acid hypersecretion. The multi-hormonal character of these neoplasms suggests that these tumors develop from a pluripotential stem cell.     

Possible thyrotrophs insensitivity to dopamine in hyperprolactinaemic amenorrhoeic patients

The study assessed the sensitivity of the thyrotrophs of hyperprolactinaemic patients to a physiological dose of dopamine (DA). Eight hyperprolactinaemic amenorrhoeic patients received 4-hour infusions of either DA (0.4 micrograms/kg x min) or glucose. Twelve normal women served as controls. In normal women the mean thyrotrophin (TSH) concentration declined significantly (P less than 0.05) from 81 +/- 6.6% of basal levels during glucose infusion to 59 +/- 5.8% of basal levels during DA infusion. In contrast DA infusion to hyperprolactinaemic patients caused no significant reduction in TSH levels compared to glucose infusion (DA infusion 68 +/- 4.7% of basal levels; glucose infusion 73 +/- 4.9% of basal levels). DA infusion caused a significant reduction in serum prolactin (PRL) levels both in hyperprolactinaemic patients (P less than 0.001) and normal women (P less than 0.02), but the PRL suppression was significantly (P less than 0.05) less pronounced in the hyperprolactinaemic patients, compared to normal women. We propose that the abnormal PRL as well as TSH secretion in hyperprolactinaemic amenorrhoeic patients may be due to a common defect. Both the lactotrophs and the thyrotrophs may be relatively insensitive to dopaminergic inhibition.     

Secretory bursts of growth hormone secretion in the dog may be initiated by somatostatin withdrawal

In 28 6-h experiments on 10 conscious resting trained male dogs, plasma growth hormone (GH) was determined at 5-min intervals by radioimmunoassay. For all experiments, the basal GH concentration in plasma was 0.80 +/- 0.06 ng mL-1. In each experiment, 1-3 secretory bursts of GH occurred, raising plasma GH 2.4 to 15.3 times basal concentrations (for all 43 bursts, 6.6 +/- 0.4 times the basal value). Metabolic clearance rates (MCR) and apparent distribution volumes (V) were determined, using stepwise infusions of canine GH. The MCR (3.99 +/- 0.30 mL kg-1 min-1) and V (57.9 +/- 5.5 mL kg-1) were used to transform the GH concentration versus time data into GH secretion rates, using a single compartment approach. Basal GH secretion rates for all 28 experiments were 3.12 +/- 0.24 ng kg-1 min-1. The secretory bursts yield peak GH secretion rates of 9.4 +/- 0.8 times basal secretion and these steep-sloped bursts last 25.1 +/- 1.2 min. Six-hour infusions of 0.15 microgram kg-1 min-1 of somatostatin (SRIF) abolished all secretory bursts but did not lower basal secretion rates. In five of seven SRIF infusion experiments in which samples were taken after the infusion ceased a secretory burst was seen in the hour following cessation of infusion (in four cases within 10 min). These secretory bursts lasted 23.0 +/- 2.9 min and were similar to those seen in control experiments. Infusions of SRIF at 0.05 microgram kg-1 min-1 had no effect. These results imply that during basal GH secretion, a surfeit of SRIF impinges on the somatotrophs, as extra SRIF does not further lower basal secretion. However, during secretory bursts, very little SRIF must be present, as exogenous SRIF blocks these bursts. The bursts are similar in duration to overshoots provoked in perifused dispersed rat somatotrophs by removal of an SRIF signal. It seems likely that their cause in vivo is similar. (All values are means +/- SEM.)     

Prolonged plasma half-life of insulin in patients with a genetic defect of high affinity binding sites

Plasma clearance of endogenous and intravenously administered insulin was studied in three sibs with severe insulin resistance secondary to an affinity defect of their insulin receptors, and in five healthy controls. Intravenous infusion of somatostatin was used to inhibit the insulin secretion. 0.3 U of insulin/kg body weight was administered as an intravenous bolus. Plasma glucose, immunoreactive insulin and C-peptide were determined subsequently at constant intervals. We found a prolonged plasma half-life of insulin in the three patients, being 33.5 +/- 11.8 min vs 8.2 +/- 2.2 min in controls, P less than 0.002, but a normal half-life of C-peptide. The result indicates, that the plasma insulin clearance is predominantly mediated by intact insulin receptors. We conclude, that insulin has a prolonged half-life in all patients with insulin resistance secondary to an impaired receptor function.     

Effect of the specific cholecystokinin-receptor antagonist loxiglumide on bombesin stimulated pancreatic enzyme secretion in man.

We have investigated the effects of the specific cholecystokinin (CCK) receptor antagonist loxiglumide on basal and bombesin stimulated pancreatic enzyme secretion, bilirubin output and plasma CCK release in six healthy subjects. The data were compared with those obtained in control experiments where saline was infused instead of loxiglumide. Basal amylase output (4.7 +/- 0.8 kU/45 min), trypsin output (2.9 +/- 0.8 kU/45 min) and bilirubin output (7.7 +/- 2.8 mmol/45 min) gradually declined during infusion of loxiglumide to values of 1.3 +/- 0.3 kU/45 min, 0.5 +/- 0.1 kU/45 min and 0.4 +/- 0.0 mmol/45 min, respectively, reaching statistical significance (P less than 0.05) in the 30 to 45-min period after the start of the loxiglumide infusion. In the control experiments saline infusion failed to influence basal amylase, trypsin and bilirubin output, while bombesin stimulated amylase output from 4.7 +/- 0.8 kU/45 min to 25.1 +/- 5.1 kU/45 min (P less than 0.05), trypsin output from 2.9 +/- 0.8 kU/45 min to 11.6 +/- 2.0 kU/45 min (P less than 0.05) and bilirubin output from 7.7 +/- 2.8 mmol/45 min to 68.0 +/- 16.0 mmol/45 min (P less than 0.05). Loxiglumide failed to significantly influence bombesin stimulated amylase output (36.7 +/- 9.0 kU/45 min) and trypsin output (8.3 +/- 2.9 kU/45 min), but almost abolished bilirubin output (9.7 +/- 3.6 mmol/45 min) (P less than 0.05). Basal plasma CCK (2.4 +/- 0.1 pM) was not significantly influenced by loxiglumide (2.4 +/- 0.2 pM).(ABSTRACT TRUNCATED AT 250 WORDS)