Effects of gastrin-releasing peptide on basal and stimulated thyroid hormone secretion in the mouse

Recently, gastrin releasing peptide (GRP) was demonstrated to occur within normal thyroidal C cells. In the present study, the effects of GRP on basal and stimulated thyroid hormone secretion were investigated in the mouse according to the McKenzie technique. Iodine-deficient mice were pretreated with 125I and thyroxine. GRP was found dose-dependently to increase the basal radioiodine levels after iv injection, reflecting a stimulation of basal thyroid hormone secretion. The effect was maximal at a dose level of 3.0 nmol/animal, and at 2 h after injection, when GRP had increased blood radioiodine levels to 152 +/- 8% compared with 96 +/- 5% in controls (P less than 0.001). GRP seemed to exert additive effects on thyroid hormone secretion with vasoactive intestinal peptide and with TSH at a threshold dose level. In contrast, GRP did not influence the stimulatory effects of either a half-maximal dose level of TSH or noradrenaline. Furthermore, neither L-propranolol nor methylatropine influenced the GRP-induced thyroid hormone secretion. It is concluded that GRP has the capacity to stimulate basal thyroid hormone secretion in the mouse.     

The effect of gastrin-releasing peptide on growth hormone secretion in the rat

Several investigators have reported gastrin-releasing peptide (GRP)-like immunostaining in several regions of the rat brain. The objective of this study was to determine the possible effects of this peptide on GH release. Porcine GRP was injected intraventricularly (third ventricular) in a volume of 2 microliters into ovariectomized female rats. A significant decrease in basal GH release, as evidenced by decreased plasma GH levels, was observed within 10 min which lasted for 90 min after the injection of 2 micrograms (0.7 nmol) GRP (P less than 0.001). In addition, all GH pulses were abolished during this time. In subsequent experiments, varying doses of GRP were administered, and human pancreatic GH-releasing factor (GRF) was injected iv at a dose of 0.1 microgram/kg 20 min later to determine the responsiveness of the pituitary. The minimal effective dose of GRP to lower plasma GH was approximately 10 ng (3.6 pmol); however, the GH-releasing action of GRF was blocked by even the lowest dose of the peptide tested (5 ng; 1.8 pmol). To determine if GRP had any direct action on the pituitary, overnight-cultured pituitary cells from ovariectomized animals were incubated for 1 h with GRP in various concentrations. There was a slight dose-dependent stimulation of GH release with concentrations of GRP ranging from 10(-9)-10(-6) M; however, the GH-releasing action was much less than that of GRF. To confirm the direct stimulatory effect of GRP on GH release, dispersed pituitary cells were perifused with medium containing 2 X 10(-6) M GRP. An immediate increase in GH release was observed in the perfusate. Since GRP has a direct stimulatory action to release GH in the pituitary, but ivt injection of the peptide inhibits GH release and blocks the response to GRF, we suggest that GRP may act on periventricular structures to release somatostatin, which reduces GH release and blocks the response to GRF.     

Effect of islet hormones on secretin-stimulated exocrine secretion in isolated perfused rat pancreas

To clarify the effect of islet hormones on pancreatic ductular cell function, we measured the exocrine secretion elicited by 10 pM secretin in the presence or absence of islet hormones using an isolated perfused rat pancreas model. Insulin significantly increased secretin-stimulated pancreatic juice secretion, but not protein secretion. The potentiating effect of insulin on pancreatic juice secretion was concentration-dependent, and the maximal effect was observed with 1 μM insulin. Ouabain, a specific Na⁺,K⁺-ATPase inhibitor, caused concentration-dependent inhibition of the potentiating effect of insulin without affecting secretin action. Glucagon (100 nM) significantly inhibited secretin-stimulated pancreatic juice secretion and also tended to inhibit protein secretion. A somatostatin analog, SMS 201-995 (10 nM) significantly inhibited both the pancreatic juice and protein secretion stimulated by secretin. The inhibitory effect of SMS 201-995 was concentration-dependent and was maximal at 1–10 nM. These results demonstrate that insulin potentiates the secretory response to secretin, at least partly by increasing Na⁺,K⁺-ATPase activity, whereas glucagon and somatostatin inhibit this response. Thus, pancreatic islet hormones regulate the secretory function of pancreatic ductular and centroacinar cells.     

Effect of gastrin-releasing peptide (GRP) on guinea pig gallbladder contrction in vitro

Few studies have reported the effects of gastrin-releasing peptide (GRP)/bombesin on the guineas pig gallbladder, and the results are contradictory. Because such contradictory results may, in part, be due to technical factors, we investigated the effect of GRP on guinea pig gallbaladder smooth muscle, using a improved horizontal organ bath. The guinea pigs were killed and the gallbladder was removed. Four longitudinal uscle strips (2×12mm) were suspended in Krebs-Ringer solution at 37°C and aerated with 95% O₂ and 5% CO₂. The mechanical activity of the strips was recorded isotonically by displacement-voltage transducers. via L-arms, to which a piezoelectric element with a frequency of 100Hz and movement of 50μm was applied. GRP contracted gallbladder muscle strips dose dependently, but the calculated maximal response was 22.4% and 20.1% of the acetylcholine-and cholecystokinin octapeptide (CCK8)-induced responses, respectively. The GRP-induced contraction was unaffected by the muscarinic blocker, atropine, or by the CCK receptor antagonist, loxiglumide. It is concluded that GRP weakly, but apparently directly, stimulates guinea pig gallbladder contraction.     

On the role of gastrin-releasing peptide in meal-stimulated exocrine pancreatic secretion.

The contribution of gastrin-releasing peptide (GRP) in the physiologic pancreatic response to a meal is unknown. We therefore investigated whether immunoneutralization of GRP could influence the exocrine pancreatic response to a meal as well as plasma concentrations of the peptide hormones neurotensin (NT) and cholecystokinin (CCK). Modified Herrera fistulas were implanted in five mongrel dogs. After a standard meal, we analyzed plasma NT, CCK, and GRP, and protein and enzyme (amylase, lipase, trypsin) content of exocrine pancreatic juice. An unspecific rabbit immunoglobulin solution was administered intravenously as a control. This experiment was repeated with a specific anti-GRP-immunoglobulin. The i.v. administration of the anti-GRP-antibody significantly inhibited meal-stimulated pancreatic secretion. Integrated protein output decreased from 58.4 to 36.8 g/180 min (p < 0.05), as did amylase (2,102 to 1,145 KU/180 min; p < 0.05), lipase (2,258 to 1,172 KU/180 min; p < 0.05), and trypsin (5,321 to 4,990 U/180 min). Postprandially released NT decreased from 8,271 to 5,825 pmol/180 min (p < 0.05). In contrast, integrated amounts of CCK remained relatively stable with 473 to 611 pmol/180 min. The neuropeptide GRP is one of the biologically important regulatory factors influencing meal-stimulated pancreatic secretion, as well as the postprandial plasma level of the peptide hormone NT in the dog. These mentioned effects of postprandially released GRP seem not to be mediated by CCK in an endocrine manner.     

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

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

Role of acetylcholine and gastrin-releasing peptide (GRP) in gastrin secretion

Using an isolated rat stomach infusion model, we investigated the role of gastrin-releasing peptide (GRP) and acetylcholine in the secretion of gastrin (which plays a major role in gastric acid secretion), and the relationship between gastrin secretion and stomach pH. Bombesin, which has a structure analogous to that of GRP, was used in the experiment. We also investigated whether acetylcholine has muscarine-like or nicotine-like action. Our findings pointed to the presence of an alternative, GRP-mediated, route for stimulating gastric secretion from G cells, other than the acetylcholine-mediated route. We injected bombesin to confirm the presence of such a GRP-mediated route; significantly increased gastrin secretion was observed, even under acidic conditions, in the gastric lumen, which has been considered to show almost no gastric secretion. This secretion was not inhibited by atropine. The results suggested that there are two routes for inducing gastrin secretion from G cells: an acetylcholine-mediated route and a GRP-mediated route (intramural peptide neurons). As GRP induced gastrin secretion, regardless of stomach pH, GRP was considered to be more closely related to gastrin secretion. The results also suggested that a muscarine-like action, particularly in the M3 receptor-mediated route, plays a significant role in acetylcholine-mediated gastrin secretion and that nicotine-like action is not involved in gastrin secretion.     

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

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

醛糖还原酶抑制剂对小鼠胰岛体外培养时胰岛素分泌的影响

观察了ＩＣＩ１２８４３６（Ｓｔａｔｉ），一种新型醛糖还原酶抑制剂（ＡＲＩ），使体外培养时小鼠胰岛山梨醇形成减少后，葡萄糖诱发快速与慢速相胰岛素释放的变化情况。培养４８或９６小时后，葡萄糖诱发快速或慢速相胰岛素释放，ＡＲＩ组（１０ｍｇ／Ｌ）与对照组胰岛比较均无显著性差异。说明ＡＲＩ虽可使胰岛山梨醇形成减低，但其对葡萄糖诱发胰岛素释放无明显影响。提示胰岛山梨醇可能无确切促进胰岛素分泌的作用。     

Effect of cysteamine on gastric nerve fibers containing gastrin-releasing peptide in the rat

In rats, changes in gastric nerve fibers containing gastrin-releasing peptide (GRP) in cysteamine-induced duodenal ulcer were investigated in relation to the dynamics of gastrin-producing cells (G-cells). Marked increases in gastric acid secretion and serum gastrin level were observed from 2h after the administration of cysteamine. The number of G-cells was significantly decreased from 2h after the injection of cysteamine. Two and 4h after the administration of cysteamine, the G-cells showed ultrastructural changes characterized by a markedly decreased number of secretory granules. Circulating GRP levels were significantly elevated from 2h after the administration of cysteamine. In the control group given vehicle only, nerve fibers showing immunoreaction for GRP formed a fine network in the gastric wall and were densely distributed in the oxyntic mucosa, located close to capillaries and demonstrated varicosities that contained either small clear vesicles or GRP-immunopositive vesicles with large cores. Eight h after the administration of cysteamine, there was depleted GRP immunoreactivity, evidenced by a markedly decreased number of vesicles, with large electron-dense cores, in the oxyntic mucosa. These findings suggest that, in cysteamine-induced doudenal ulcer, alterations in gastric nerve fibers containing GRP may be related to hypergastrinemia.     

Effect of diacylglycerol lipase inhibitor RHC 80267 on pancreatic mouse islet metabolism and insulin secretion

Summary The effect of interference with diacylglycerol metabolism was investigated in pancreatic mouse islets. In the presence of the diacylglycerol lipase inhibitor RHC 80267, glucose-induced insulin secretion was reduced 50–60%; whereas carbacholin-induced insulin secretion was unaffected. Addition of the diacylglycerol kinase inhibitor R 59022 did not change glucose-stimulated insulin secretion but abolished the inhibition seen in the presence of RHC 80267. RHC 80267 increased islet glucose utilisation, measured as formation of tritiated water from 5-[³H]-glucose, 3-fold but did not affect glucose oxidation to CO₂, lactate production or islet ATP levels. Glucose utilisation in leucocytes and hepatocytes was not increased by addition of RHC 80267. Islet lipid production from glucose was augmented 4-fold in the presence of RHC 80267 but only accounted for about 5% of the increase in glucose utilisation. The activity of adenylate cyclase and phosphoinositide-specific phospholipase C was unaffected by RHC 80267. Concentrations of RHC 80267 below 35 mol/l did not alter the activity of phospholipase A₂; whereas higher concentrations of the drug inhibited phospholipase A₂ activity approx 25%. The data support the hypothesis that production of arachidonic acid from diacylglycerol may be involved in regulation of insulin secretion.Abbreviations RHC 80267 (1,6-di(O-(carbamoyl)cyclohexanone oxime)hexane) - R 59022 6-[2-[4-[(4-fluorophenyl)phenylmethylene]-1-piperidinyl]ethyl]-7-methyl-5H-thiazolo[3,2-]pyrimidin-5-one     

Effects of cholecystokinin and gastrin antagonists on pancreatic exocrine secretion stimulated by gastrin-releasing peptide.

The effects of a specific cholecystokinin (CCK) receptor antagonist (L364,718) and a gastrin receptor antagonist (L365,260) on gastrin-releasing peptide-10 (GRP-10)-stimulated pancreatic secretion were investigated in the anesthetized rat. GRP-10 stimulated pancreatic exocrine secretion in a dose-dependent manner. A dose of 1.0 nmol/kg/h elicited a significant increase in pancreatic protein output. L364,718 (2.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous CCK-8 (3.0 nmol/kg/h) on pancreatic secretion, did not suppress the excitatory effect of GRP-10. L365,260 (5.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous gastrin (20 micrograms/kg/h) on gastric acid secretion, did not suppress the excitatory effect of GRP-10 either. We concluded that CCK or gastrin do not mediate the excitatory mechanism of bombesin/GRP on pancreatic secretion. Since CCK and gastrin are the most probable candidates for excitatory mediator of bombesin/GRP, these results support the hypothesis that bombesin/GRP directly stimulates the exocrine pancreas in the rat.     

Effect of islet activating protein on glucose tolerance,insulin secretion and insulin responsiveness in the NZO mouse

Summary The effect of islet activating protein on glucose tolerance, insulin secretion and insulin responsiveness was studied in the NZO mouse, a model of non-insulin dependent diabetes and obesity. A single IV injection of 5 ng/g body weight islet activating protein markedly lowered plasma glucose and the glucose response to IP glucose administration, measured 5 days later (mean±SEM, plasma glucose levels 0, 10, 30 and 60 min after glucose 6.0±0.9, 14.6±1.3, 14.1±1.3 and 13.2±1.7 mmol/l in islet activating protein-treated NZO mice versus 12.8±1.6, 27.8±3.4, 34.7±4.1, 39.1±3.8 mmol/l in carrier-treated NZO mice). There was no difference in fasting plasma insulin levels between islet activating protein and carrier-treated mice. No response of plasma insulin to glucose occurred in the carrier-treated mice, but a highly significant insulin response to glucose was seen in the islet activating protein-treated mice. The in vitro responsiveness of pancreatic islets of islet activating protein-treated NZO mice to glucose was improved, and the inhibitory effect of adrenaline on insulin secretion was reduced. The in vivo hypoglycaemic response to exogenous insulin was not improved by islet activating protein and a demonstrated defect in the insulin sensitivity and responsiveness of glucose utilization by isolated soleus muscle was not reversed by islet activating protein treatment. It is concluded that islet activating protein is highly effective in improving glucose tolerance and insulin secretion in NZO mice, and that the improvement in glucose tolerance occurs without demonstrable improvement in the responsiveness to exogenous insulin or sensitivity of soleus muscle to insulin.     

Effect of thyroid hormones on calcitonin secretion

A study of 140 patients with diffuse toxic goiter showed phasic change in plasma calcitonin concentration and blood calcitonin activity: an increase in these indices at early stages of disease with a subsequent decrease in a severe form of thyrotoxicosis. Basal calcitonin secretion by fragments of the thyrotoxic thyroid was much higher than that euthyroid gland. In incubation of paranodal tissue of the thyroid of patients with nodular euthyroid goiter and fragments of the thyroid of patients with thyrotoxicosis of moderate severity with thyroxin at concentration 10(-8) M the level of calcitonin secretion considerably increased, concentration 10(-6) M was ineffective. The thyroid taken peroperatively from patients with diffuse toxic goiter with thyrotoxicosis of a severe form turned out nonreactive with relation to thyroxin concentration 10(-8) M. Basal calcitonin secretion in the study group was within control values. Thyroxin showed the properties of a calcitonin-secretion stimulator. Signs of depletion of the thyroid calcitonin-producing capacity were revealed in the course of development of diffuse toxic goiter.     

Role of cholecystokinin, gastrin and gastrin-releasing peptide in the regulation of pancreatic secretion in cats.

This study performed on 6 conscious cats with chronic pancreatic fistulas was designed to determine the role of cholecystokinin (CCK), gastrin and gastrin-releasing peptide (GRP) in stimulation of pancreatic secretion in this species. Pancreatic response to GRP infused intravenously in graded doses appears to be mediated predominantly by CCK because a CCK receptor antagonist, L-364,718, abolished this response. Also, gastrin appears to mediate in part the secretory response to GRP because blockade of gastrin receptors by L-365,260, given at the dose that completely abolished the pancreatic response to exogenous gastrin, caused a significant reduction in the bombesin-induced pancreatic secretion. CCK and partly gastrin appear to mediate the postprandial pancreatic secretion in cats as the administration of L-364,718 and L-365,260 inhibited this secretion by over 90 and 30%, respectively. In contrast, GRP does not seem to contribute to food-induced pancreatic secretory stimulation, because the blockade of GRP receptors using novel bombesin/GRP antagonist (RC-3100) failed to affect this secretion. We conclude that CCK and partly gastrin, but not GRP, play an essential role in the postprandial pancreatic secretion.