Effect of somatostatin on pancreatic protein secretion induced by cholecystokinin

Somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic nerves in conscious rats

Somatostatin is known to be a potent inhibitor of pancreatic exocrine secretion, but the mechanism of its effect is not fully understood. The mechanism of the inhibition by centrally administered somatostatin was examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately, and with a duodenal cannula, an extrajugular vein cannula and a cerebroventricular cannula. Somatostatin was injected into the left lateral ventricle, and the inhibitory mechanism was examined using vagotomized rats and various drugs that affect sympathetic neurons. Intracerebroventricular administration of somatostatin significantly inhibited pancreatic exocrine secretion stimulated by bile-pancreatic juice diversion. The inhibitory effect was not abolished by vagotomy, pretreatment with propranolol, but was abolished by pretreatment with hexamethonium or phentolamine. The plasma level of somatostatin after its intracerebroventricular administration increased 3-fold, but its intravenous infusion at a rate giving a similar plasma somatostatin level to that produced by its intracerebroventricular injection, had no significant effect on pancreatic secretion. These results suggest that somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic efferent nerves and that alpha-adrenergic receptors have an important role in its inhibitory action.

Effect of somatostatin on plasma amino acid uptake by human pancreas

We studied the effect of somatostatin on amino acid uptake by pancreatic acinar cells in 12 healthy male volunteers, aged 20-48 yr. Pancreatic amino acid uptake was assessed by measuring free plasma amino acid concentration before and during pancreatic stimulation with secretin (1 CU/kg body wt.h) and cerulein (50 ng/kg body wt.h). Pancreatic stimulation with these peptides caused a significant decrease in plasma amino acid concentrations. Somatostatin, given at the dosages of 0.15 and 1.35 micrograms/kg body wt.h, significantly diminished this decrease. The effect of the higher dose of somatostatin was more marked than that produced by the lower dose, compatible with dose dependence. The results suggest that somatostatin is able to inhibit the amino acid uptake by the pancreatic acinar cells. This inhibitory effect could be an important mechanism by which the peptide decreases pancreatic enzyme secretion.

Effects of somatostatin and pancreatic polypeptide on exocrine and endocrine pancreas in the rats

The effects of somatostatin-14 (SS) and rat pancreatic polypeptide (rPP) on endocrine and exocrine functions of the pancreas, stimulated by 40 ng/kg cholecystokinin octapeptide during continuous infusion of 1 U/kg/h secretin, were investigated in the rat, in vivo. Protein output in the pancreatic juice and integrated insulin (IRI) secretion were inhibited, in a dose related fashion, by continuous infusion of SS, in doses of 0.5, 5 and 50 micrograms/100g/h. On the other hand, bicarbonate and volume output were not inhibited by SS. The rPP significantly inhibited not only the protein output but also the bicarbonate and volume output of the pancreatic juice in doses of 0.1 and 1 microgram/100g/h. Integrated IRI secretion was inhibited significantly by rPP, but the inhibition of IRI secretion was much greater in the portal than in the jugular vein. Plasma SS and rPP concentrations showed physiological ranges during infusion of doses of 0.5 and 0.1 microgram/100g/h of SS and rPP, respectively. Therefore, there was a marked difference between the inhibition by rPP and that by SS on the exocrine and endocrine pancreas. These observations suggest that SS and PP may play a physiological role in the pancreas and that their effects on the pancreas relate to different mechanisms.

Effect of somatostatin on amylase secretion from in vivo and in vitro rat pancreas

In the present study the effect of somatostatin on amylase secretion was determined using in vivo cannulation and isolated acini from rat pancreas. In vivo somatostatin-14 inhibited amylase secretion in basal state and that stimulated with CCK8 and acetylcholine. Somatostatin-14 and somatostatin-28 failed to inhibit amylase secretion from isolated acini in basal state and that stimulated with CCK8 and bethanechol. Somatostatin-14 did not increase 45Ca uptake or efflux of label from acini preloaded with 45Ca. Cellular cyclic AMP levels were not significantly increased. Somatostatin-14 did not alter the synthesis of proteins in vitro, as judged by incorporation of a mixture of fifteen 14C-labeled amino acids. Somatostatin-14 stimulated phosphoprotein phosphatase in higher doses, whereas no effect was observed at lower doses. Inhibition of secretion in vivo and lack of stimulation of amylase secretion in isolated acini suggest that the somatostatin effect in vivo is mediated by an indirect effect similar to other peptides, for example, opiates and neurotensin. Stimulation of phosphoprotein phosphatase suggests that somatostatin may bind to the acinar cells and affect functions other than secretion and synthesis of enzymes.

Effect of a cyclic hexapeptide analog (L363,586) of somatostatin on the function of pancreas grafts in dogs

Complications related to the exocrine secretions cause some pancreas grafts to fail in the early postoperative period. Somatostatin inhibits exocrine secretion, as well as insulin and glucagon release. L363,586 is a cyclic hexapeptide analog of somatostatin that is 50 to 100 times more potent than the native hormone in inhibiting islet hormone release. In a preliminary experiment in which permanent fistulas were created in two dogs, we demonstrated that L363,586 (0.3 micrograms/kg/60 min) results in a fourfold decrease in pancreatic exocrine secretion when measured for 210 min following a beef meal. In a separate experiment, five totally pancreatectomized dogs who received segmental pancreas autografts with pancreaticoductocystostomy 10 months previously had L363,586 (0.3 micrograms/kg/hr) administered by the Alzet osmotic pump subcutaneously for 7 days. Mean (+/-SE) daily serum amylase activity (IU/dl) during the week before the implant was 78 +/- 3, during the week of infusion was 65 +/- 2 (P less than 0.001), and during the week afterward was 76 +/- 2. In a prospective experiment, 12 totally pancreatectomized dogs received segmental pancreas autografts with anastomosis of the graft vessels to the iliac vessels and of the pancreatic duct to the bladder. L363,586 was administered by osmotic pump for 7 days to seven dogs at a dose of 0.3 micrograms/kg/hr. Mean (+/-SE) daily serum amylase levels at 1, 2, and 3 weeks posttransplant were 223 +/- 17, 81 +/- 3, and 82 +/- 5 in the L363,586-treated dogs and 229 +/- 18, 108 +/- 5, and 90 +/- 5 in the five untreated dogs (P less than 0.001 at 2 weeks).(ABSTRACT TRUNCATED AT 250 WORDS)