Increased somatostatin release from pancreases of alloxan diabetic rats perfused in vitro

Regulation of rat pancreatic CCKB receptor and somatostatin expression by insulin

The cholecystokinin B receptor (CCK(B)R) is localized on pancreatic endocrine somatostatin delta-cells. Pancreatic somatostatin content was increased in diabetic rats. The mechanisms involved in this phenomenon are unknown, and we believe insulin is involved. In this study, four groups of rats were used: controls, streptozotocin-induced diabetic, streptozotocin-induced diabetic with insulin, and streptozotocin-induced diabetic with insulin and its cessation. Rats were killed after 7-28 days of treatment for diabetes, and somatostatin mRNA expression and pancreatic somatostatin content, CCK(B)R mRNA and protein expression evaluation in total pancreas and purified islets, and the cellular localization of somatostatin and CCK(B)R in islets was measured. Data indicate that diabetes is established after 7 days, is controlled by insulin, and reappears after treatment cessation. Pancreatic somatostatin mRNA expression and somatostatin content were increased during diabetes, normalized during insulin treatment, and reaugmented after treatment cessation. Gland and islet CCK(B)R mRNA and protein almost disappeared during diabetes; CCK(B) mRNA reappeared in response to insulin, but the protein did not. Confocal microscopy confirmed data obtained on somatostatin and CCK(B)R as established biochemically in the course of the treatments. In conclusion, these data strongly suggest that insulin can negatively control pancreatic somatostatin mRNA and hormone content and positively control CCK(B)R mRNA; the CCK(B)R protein appears to be delayed.

Role of somatostatin and its analogues in the pathogenesis and treatment of diabetes mellitus

Somatostatin secreted by pancreatic D cells is a potent inhibitor of insulin, glucagon and growth hormone secretion, as well as other cells. The role of abnormal pancreatic D-cell function in diabetes mellitus is unclear. However, development of long-acting selective somatostatin analogs might prove useful in the treatment of diabetes.

In vivo somatostatin, vasopressin, and oxytocin synthesis in diabetic rat hypothalamus

The in vivo labeling of somatostatin-14, somatostatin-28, arginine vasopressin, and oxytocin was studied in rat hypothalamus after third ventricular administration of [35S]cysteine to streptozotocin-diabetic and normal rats. Immunoreactive somatostatin levels in hypothalamus were unaffected by diabetes, as was the incorporation of [35S]cysteine into hypothalamic somatostatin-14 and somatostatin-28. In contrast, immunoreactive vasopressin levels in hypothalamus and posterior pituitary (and oxytocin levels in posterior pituitary) were below normal in diabetic rats. Moreover, [35S]cysteine incorporation into hypothalamic vasopressin and oxytocin (probably mainly in the paraventricular nucleus because of its proximity to the third ventricular site of label injection) was significantly above normal. The increments in vasopressin and oxytocin labeling were reversed by insulin administration. In vivo cysteine specific activity and the labeling of acid-precipitable protein did not differ between normal and diabetic animals; effects of diabetes on vasopressin and oxytocin labeling were therefore not caused by simple differences in cysteine specific activity. These results suggest that diabetes 1) does not influence the production of somatostatin peptides in hypothalamus but 2) stimulates the synthesis of vasopressin and oxytocin. For vasopressin at least, the increase in synthesis may be a compensatory response to the known increase in its secretion that occurs in uncontrolled diabetes.

Growth hormone and somatostatin in the plasma of transiently diabetic ducks: basal variation and response to glucose

In the duck, subtotal pancreatectomy induces a transient diabetes, with decreased insulin and glucagon basal levels as well as responses to glucose. At the same time, a transient increase in basal peripheral somatostatin occurs, followed by an increase in growth hormone in the postdiabetic state. Intravenous glucose induces a slight decrease in somatostatin secretion in normal, but not in diabetic animals, and no significant variation in growth hormone secretion at any state. An obvious role of growth hormone or somatostatin in the development of this transient diabetes in the duck could not be detected in this study.

Basal and tolbutamide-induced plasma somatostatin in healthy subjects and in patients with diabetes and impaired glucose tolerance

Peripheral levels of basal and tolbutamide-induced somatostatin have been measured in patients with diabetes or impaired glucose tolerance (IGT) and compared with those in normal individuals. Basal somatostatin was significantly higher in patients with Type 1 diabetes than in age-matched control subjects. This increase was most pronounced at diagnosis, and appeared to be related to metabolic control in insulin-treated patients. No increase was noted in patients with Type 2 diabetes or with IGT. Intravenous bolus injection of tolbutamide enhanced peripheral somatostatin levels in healthy volunteers in a biphasic manner. Patients with IGT also exhibited a biphasic response but the amplitude of the first phase was higher. No secretory response was detected in 27/29 Type 1 diabetic patients at diagnosis; a somatostatin response to tolbutamide became detectable again in Type 1 patients with normalization of their basal somatostatin levels but was then paradoxically related to poor blood glucose control. In Type 2 diabetes, basal somatostatin levels were similar to age-matched control subjects, but decreased upon intravenous tolbutamide administration.

Pancreatic A- and D-cell response to arginine during acute alloxan-induced intra-islet insulinopenia

This study was performed to investigate the role of pancreatic B-cell function on glucagon and somatostatin response to arginine. Isolated perfused rat pancreas was used for the experiment. Acute B-cell destruction was induced in vitro by 0.56 mM alloxan infused directly into the vascular system of the perfused pancreas. This resulted in a fall in basal insulin release and in a complete absence of hormone response to 20 mM arginine. Glucagon and somatostatin release during metabolic stimulus was superimposable on that observed in the control experiments (no alloxan infusion). We conclude that a normal B-cell function is not required for glucagon and somatostatin response to arginine.

Plasma somatostatin and plasma glucagon in long-term IDDM without residual B-cell function. No effect of different long-term metabolic control

To further study the elevated plasma somatostatin (SRIF)--and reduced plasma glucagon concentrations found in IDDM patients without residual B-cell function compared to normal controls, we investigated 39 such patients, randomly assigned to three different insulin treatment regimens; conventional therapy with two injections a day (CTh), insulin pump (CSII) and multiple injections (MI), for 1 year. They were given an arginine infusion (0.5 g/kg/20 min). The mean basal plasma SRIF values in the CTh, CSII and MI groups were 20.8 +/- 3.3, 18.6 +/- 1.8 and 20.6 +/- 2.8 pmol/l and the mean basal plasma glucagon values were 30 +/- 5.7, 19 +/- 2.3 and 27 +/- 4.7 pmol/l, respectively. Both SRIF and glucagon increased in all groups in relation to arginine infusion. For both hormones, the mean values were highest in the CTh group, lowest in the CSII group, although the differences were not significant. The mean HbA1 values for the last 3 months within the test were 10.0 +/- 0.5, 8.8 +/- 0.3 and 9.1 +/- 0.5%, respectively, in the same order as above. The CTh group had significantly higher HbA1 values than the CSII group (p less than 0.02). We conclude that small differences in long-term blood glucose control are of inconsiderable importance for the islet hormonal response to arginine found in IDDM without B-cell function.

Pancreatic hormones in streptozotocin-diabetic rats

Pancreatic polypeptide (PP) levels of plasma and pancreas were studied in the rat after streptozotocin (STZ) injection. In 4 weeks of observation, plasma PP was elevated up to 4 times the control values with marked hyperglycemia and insulinopenia. At 4 weeks, intravenous (i.v.) glucose tolerance tests and i.v. insulin tolerance tests were performed. In the glucose tolerance test, control rats responded with a 10-fold increase in plasma insulin and 15% decrease in plasma PP levels, whereas STZ-diabetic rats produced no increase of plasma insulin and an approximately 50% reduction of plasma PP levels with marked hyperglycemia. In the insulin tolerance test, diabetic rats showed a marked increase in plasma PP levels and less increase in plasma insulin levels than the controls. In diabetic rats, pancreatic insulin levels were reduced to about 3.5% of control, whereas those of somatostatin (SRIF), PP and glucagon were elevated to 8.3, 2.7 and 1.4 times control, respectively. In a morphometric study, islet areas of diabetic rats were seen to be reduced to about 10% of control. With in vitro perfused pancreatic slices, STZ-diabetic pancreas released much more glucagon and PP than control pancreas. Thus, STZ injection in the rat caused marked beta-cell damage as well as hyperplasia of SRIF, PP and glucagon cells, with glucagon and PP hypersecretion.

Pancreatic somatostatin

This is a review of pancreatic somatostatin which is limited in its scope and therefore focuses upon some selected issues. Throughout the entire review the same basic questions recur: Why do islets contain somatostatin? What is the physiological role of somatostatin and what does this peptide have to do with diabetes? Clear answers to these questions do not emerge, but a number of hunches are explored. The review provides a very brief look at somatostatin secretion, a discussion of the potential interactions which islet D cells might have with other islet cell types, consideration of how knowledge of islet anatomy may help us understand the D cell, and finally some comments about what happens to the D cell in diabetes and fasting.

Pancreatic immunoreactive somatostatin and diabetes mellitus

Pancreatic secretions were collected during endoscopic retrograde cholangiopancreatography from 15 subjects without pancreatic, biliary, or hepatic diseases, 11 patients with non-insulin-dependent diabetes, and 11 patients with insulin-dependent diabetes. Pancreatic secretion was stimulated by the intravenous administration of one unit of secretin per kilogram of body weight. Immunoreactive somatostatin (IRS) in the pancreatic juice of the nondiabetic subjects ranged from 43 to 97 pg/ml, in non-insulin-dependent diabetics from 5 to 3872, and in the insulin-dependent diabetics from 0 to 2093. IRS in insulin-dependent diabetics under good plasma glucose control ranged from 0 to 281 pg/ml, compared to those under poor control who ranged from 518 to 2093 pg/ml. These results indicate that IRS in pancreatic juice is higher in poorly controlled insulin-dependent diabetics than in well controlled insulin-dependent diabetics and nondiabetics. Whether these changes in IRS are purely secondary phenomena or play some pathogenetic role in the disturbed metabolism of diabetes remains to be proven. The chromatographic profile of IRS in pancreatic juice on both gel filtration and high-performance liquid chromatography has indicated that these IRS moieties represent somatostatin 14 and somatostatin 28.

Abnormal D cell secretion in alloxan-diabetes: influence by drug and aberrant metabolism

Abnormalities of somatostatin secretion in diabetes may be secondary to B cell damage with resulting insulinopenia or other effects of diabetogenic agents, including toxicity toward the somatostatin-producing D cells. These possibilities were evaluated in isolated perfused pancreas from normal and alloxan-diabetic rats. In normal rats 3-isobutyl-1-methylxanthine (IBMX, 1 mM), alpha-ketoisocaproic acid (KIC, 5 mM), D-glucose (27 mM), and D-glyceraldehyde (5 mM) stimulated somatostatin release. In diabetic rats 3 days after alloxan, IBMX and KIC elicited somatostatin release, whereas glucose or glyceraldehyde were without effect. In diabetic rats 14 days after alloxan, an otherwise (in normal and 3-day diabetic rats) nonstimulatory concentration of IBMX (0.05 mM) markedly stimulated somatostatin release, whereas as in 3-day diabetic rats glucose was ineffective. Insulin treatment for 2 days did not affect the somatostatin response to glucose in normal rats, did not restore a somatostatin response to glucose 3 days after alloxan, but partially restored (P less than 0.01) a response to glucose (28% of normal) 14 days after alloxan. Insulin in vitro (1 mU/ml, 20 min) failed to restore a glucose effect. Administration of alloxan (1.0 mM) for 5 min to pancreases from normal rats inhibited glucose-induced somatostatin response from 1,562 +/- 401 to 206 +/- 83 pg/15 min (P less than 0.01), whereas the response to IBMX (1 mM) was not significantly decreased. Following different time courses, both an effect of alloxan and of metabolic derangement inhibit somatostatin responses to glucose in alloxan diabetes.

Comparison of somatostatin distribution in pancreatic duct ligated rats and streptozotocin diabetic rats

The somatostatin content in the pancreas and gastrointestinal tract was examined in normal, streptozotocin (STZ)-diabetic and pancreatic duct ligation (PDL) rats. The somatostatin content in the pancreas and gastric antrum in the STZ-diabetic group showed a higher concentration compared with those in the normal control group (p less than 0.001). The somatostatin content in the duodenum in the PDL group showed a higher concentration compared with those in the sham-operated group (p less than 0.02). There was no significant increase in the lower gastrointestinal tract in the normal, STZ and PDL groups. These facts suggest that the concentration of somatostatin varies according to tissues and organs and that the distribution of somatostatin in chronic pancreatic injury caused by PDL is different from that in diabetes mellitus cases or controls.

Alterations in somatostatin and other islet cell functions in the spontaneously diabetic BB Wistar rat: biochemical and morphological characterization

In the present study we have attempted to assess the functional status of somatostatin cells in relation to the function of the other islet cell types (B, A, and PP cells) in the BB Wistar rat. Somatostatin-like immunoreactivity (SLI), glucagon, and insulin were measured in extracted plasma obtained from the hepatic portal vein (PV) and inferior vena cava (IVC) of acutely diabetic untreated rats, insulin-treated diabetic rats and nondiabetic controls. Extracts of the pancreas were assayed for SLI, glucagon, and insulin, and the pancreatic populations of A, B, D, and PP cells were evaluated by morphometry. Extrapancreatic somatostatin changes were assessed by measurement of SLI in extracts of the whole gut, hypothalamus, and retina. Direct studies of SLI, glucagon, and insulin secretion in response to glucose, arginine, and theophylline were carried out using the isolated perfused pancreases of two separate groups of untreated diabetic and nondiabetic rats. Our results showed that in the severely insulin deficient BB Wistar rat (1) pancreatic concentrations of SLI, glucagon, and insulin were reduced; (2) the B cells are virtually eliminated and the D cells severely reduced early in diabetes; A and PP cells are resistant initially but eventually sustain major losses as observed in terminal islets; (3) retinal SLI is reduced, but SLI in gut and brain appears unchanged; (4) the secretion of SLI, glucagon, and insulin from the perfused pancreas is diminished 60%, 36%, and 99%, respectively; (5) PV and IVC blood levels of SLI and glucagon are elevated despite decreased pancreatic secretion; (6) The trans-hepatic gradient of SLI is reduced; and (7) Insulin treatment normalizes the elevated PV and IVC levels of SLI and glucagon. It is concluded that the elevated PV and IVC levels of SLI are secondary to insulin deficiency and result from increased SLI secretion most probably from the gut and from diminished hepatic metabolism. The origin of the hyperglucagonemia is less certain, but as in the case of SLI, important contributions from extra-pancreatic secretion appears likely.

Plasma somatostatin increases during hypoglycaemia in insulin-dependent patients with and without B-cell function

Responses of somatostatin-like immunoreactivity (SLI) to hypoglycaemia were investigated in seven type 1 (insulin-dependent) patients with residual B-cell function, eight patients without B-cell function, and six healthy controls. A higher basal level of SLI was found in the group with B-cell function when compared with the group without B-cell function. The basal level in the normal subjects was in between the two diabetic groups. All the diabetics had a somatostatin response to hypoglycaemia which was independent of residual B-cell function and no different from that of normal subjects.

Immunoreactive neurotensin levels in pancreas: elevation in diabetic rats and mice

Neurotensin levels in pancreas, but not other tissues, were increased in diabetic animals. The concentration of pancreatic immunoreactiveneurotensin was 138% higher in streptozotocin-diabetic rats, and 68% higher in genetically diabetic (db/db) mice as compared to their respective control animals. Daily administration of insulin (10-15 IU/kg) to diabetic rats completely reversed this effect, and pancreatic neurotensin levels in these animals returned to control values. These findings suggest that elevated levels of pancreatic neurotensin may contribute to some of the metabolic and hormonal disturbances occurring in diabetes.

Somatostatin and diabetes

Somatostatin, a tetradecapeptide originally isolated from the hypothalamus on the basis of its ability to inhibit the secretion of growth hormone, is now known to be widely distributed in various endocrine and gastrointestinal tissues and to have diverse actions, including inhibition of insulin and glucagon secretion. The location of somatostatin in pancreatic islet D cells suggests that it may act as a local regulator of insulin and glucagon secretion. Changes in islet D-cell function in experimentally-induced and spontaneous diabetes in animals suggest that the peptide may be involved in the pathogenesis of diabetes. Clinical studies with the peptide have provided insight into the physiologic roles of glucagon and growth hormone, and have indicated a potential therapeutic use for somatostatin in diabetes in man.

Acute effects of alloxan- and streptozotocin-induced insulin deficiency on somatostatin and glucagon secretion by the perfused isolated rat pancreatico-duodenal preparation

The secretion of somatostatin and glucagon by the perfused rat pancreatico-duodenal preparation was examined in situ under control conditions and after the induction of acute insulin deficiency by alloxan or streptozotocin. A 10 min 0.625 mmol/l alloxan perfusion resulted in an immediate and transient increase in basal insulin and glucagon release and a slightly delayed and persistent increase in basal somatostatin secretion. The insulin responses to 16.7 mmol/l glucose, 1 mmol/l theophylline, and 19 mmol/l arginine alone or in combination were virtually eliminated by alloxan treatment. Somatostatin secretion in response to the stimuli was completely inhibited or markedly attenuated. The glucagon-suppressive effect of glucose was unaltered by alloxan and the stimulatory effect of arginine was enhanced. Addition of 1 microgram/ml porcine insulin to the perfusion medium did not modify the alterations in somatostatin and glucagon responses to arginine. Streptozotocin treatment 90 min prior to the onset of perfusion resulted in changes in somatostatin, glucagon, and insulin responses to glucose and arginine similar to those of alloxan. The present results are consistent with an effect of alloxan and streptozotocin on the D cell similar to that on the B cells, namely, interference with a glucose-mediated effect on hormone secretion.

Histogenesis of the endocrine pancreas in newborn rats after destruction by streptozotocin. An immunocytochemical study

Endocrine pancreatic tissue in newborn rats was studied 1 to 17 days after the destruction of B cells by an injection of streptozotocin. Regeneration of insulin cells was observed four days after streptozotocin injection, which was followed by recovery from the diabetic state and an increased pancreatic insulin content. Regeneration was characterised by new islets budding from small ducts. The pancreas of newborn rats, like the embryonic pancreas, thus retains a capacity to form endocrine tissue, although some degree of reduplication of preexisting B cells may also be involved in the process. Newborn rats injected with streptozotocin constitute an interesting model for the study of factors which may act on the regenerative potential of pancreatic endocrine tissue in the diabetic state.

Increased somatostatin secretion from pancreatic islets of streptozotocin-diabetic rats in response to glucose

Glucose stimulates somatostatin release from perifused pancreatic islets of diabetic rats 42-47 days after the induction of diabetes, and 48 h after withdrawal of insulin replacement therapy. The glucose effect is augmented by theophylline or glucagon. Basal somatostatin release and glucose-induced secretion are significantly higher in diabetic islets than in controls. It is suggested that glucose promotes somatostatin release by directly interacting with islet D cells but not via indirect pathways. Glucose-induced stimulation appears to be modulated by a D-cell adenylate cyclase/phosphodiesterase system. Reasons responsible for increased somatostatin secretion by diabetic islets include reduction in B-cell mass, suggesting that B cells may normally suppress the secretory activity of D cells.

Insulin, glucagon, and somatostatin secretion from isolated perfused rat and chicken pancreas-duodenum

Insulin, glucagon, and somatostatin secretion were evaluated in the following isolated perfused models: rat pancreas-duodenum (both normal and streptozotocin-diabetic animals) and the chicken pancreas with and without duodenum. Insulin secretion in response to glucose or arginine was greater from the normal rat than either the diabetic rat or the chicken. Glucagon release from both species was suppressed by glucose and stimulated by arginine except that poor inhibition by glucose was found in the diabetic rat. Somatostatin could be measured in the effluent from both normal and diabetic rats, but the responses to glucose and arginine were variable and modest. Clear increases of secretion in the rat were only observed in response to a combination of glucose, arginine, theophylline, and isoproterenol. In contrast, the chicken somatostatin secretion was markedly stimulated by glucose and by arginine. In conclusion, the perfused chicken pancreas-duodenum has been shown to secrete large amounts of somatostatin in comparison to the rat and should prove to be a useful system for the study of D-cell regulation.