Insulin receptors on pancreatic acinar cells in guinea pigs

Exocrine Pancreatic Function in Girls with Anorexia Nervosa

OBJECTIVES

To assess pancreatic exocrine function in patients with anorexia nervosa using a breath test with 13C-labeled mixed triglycerides (MTG-BT) and to determine the relationship between the test results and selected biochemical and hormonal parameters.

MATERIAL AND METHODS

Anthropometric measurements, biochemical and hormonal parameters (serum leptin, soluble leptin receptor (sLR), acylated and desacylated ghrelin, free leptin index (FLI)), and MTG-BT were performed in a group of 31 girls with the restrictive type of AN, as well as 38 healthy girls (C).

RESULTS

The average cumulative dose of 13C-triglycerides recovered with exhaled air (%CD) was similar in both study groups, while the average time from 13C-triglycerides administration to peak 13CO2 excretion in expired air (time to peak (TTP)) was significantly longer in patients with AN compared to C. In both groups, %CD correlated negatively with FLI. TTP correlated negatively with sLR and FLI in the AN and with serum insulin and HOMA-IR values in the C.

CONCLUSIONS

In girls with AN, the pancreatic efficiency of lipase secretion was found to be normal, while the kinetics of this enzyme secretion were disturbed. These changes may result from disorders in the functioning of the adipose-insular and islet-acinar axes.

Age-associated changes in pancreatic exocrine secretion of the isolated perfused rat pancreas

Gut functions, such as gastrointestinal motility, gastric secretion and pancreatic secretion, were reduced with age. Glucose tolerance is impaired, and the release of insulin and β-cell's sensitivity on glucose are reduced with age. However, a lot of controversial data have been reported as insulin concentrations after glucose ingestion are either higher or no different in elderly and young subjects. Thus, this study was aimed to investigate whether aging could affect pancreatic exocrine secretion and its action mechanisms. An isolated perfused rat pancreatic model was used to exclude the effects of external nerves or hormones. Pancreatic secretion was increased by CCK under 5.6 mM glucose background in the isolated perfused pancreas of young (3 months), 12 months and 18 months aged rats. There was no significant difference between young and aged rats. In 3 months old rats, CCK-stimulated pancreatic secretion was potentiated under 18 mM glucose background. However, the potentiation effects of endogenous insulin and CCK were not observed in 12 and 18 months old rats. Exogenous insulin also potentiated CCK-stimulated pancreatic secretion in 3 months old rats. Similarly, exogenous insulin failed to potentiate CCK-stimulated pancreatic secretion as that of 3 months old rats. Wet weight of pancreas and amylase content in pancreatic tissue were not changed with age. These results indicate that pancreatic exocrine secretion is reduced with age and endogenous insulin secretion and/or action is involved in this phenomenon.

The complex exocrine-endocrine relationship and secondary diabetes in exocrine pancreatic disorders

The pancreas is a dual organ with exocrine and endocrine functions. The interrelationship of the endocrine-exocrine parts of the pancreas is a complex one, but recent clinical and experimental studies have expanded our knowledge. Many disorders primarily of the exocrine pancreas, often solely in the clinical realm of gastroenterologists are associated with diabetes mellitus (DM). Although, the DM becoming disorders are often grouped with type 2 diabetes, the pathogenesis, clinical manifestations and management differ. We review here data on the association of exocrine-endocrine pancreas, the many hormones of the pancreas and their possible effects on the exocrine functions followed by data on the epidemiology, pathogenesis, and management of DM in chronic pancreatitis, cystic fibrosis, pancreatic cancer, and clinical states after pancreatic surgery.

The islet-acinar axis of the pancreas: more than just insulin

Although the role of the islets in the regulation of acinar cell function seemed a mystery to investigators who observed their dispersion among pancreatic acini, over time an appreciation for this intricate and unique structural arrangement has developed. The last three decades have witnessed a steadily growing understanding of the interrelationship of the endocrine and the exocrine pancreas. The islet innervation and vascular anatomy have been more fully characterized and provide an appropriate background for our current understanding. The interrelationship between the endocrine and exocrine pancreas is mediated by islet-derived hormones such as insulin and somatostatin, other humoral factors including pancreastatin and ghrelin, and also neurotransmitters (nitric oxide, peptide YY, substance P, and galanin) released by the nerves innervating the pancreas. Although considerable progress has been achieved, further work is required to fully delineate the complex interplay of the numerous mechanisms involved. This review aims to provide a comprehensive update of the current literature available, bringing together data gleaned from studies addressing the actions of individual hormones, humoral factors, and neurotransmitters on the regulation of amylase secretion from the acinar cell. This comprehensive view of the islet-acinar axis of the pancreas while acknowledging the dominant role played by insulin and somatostatin on exocrine secretion sheds light on the influence of the various neuropeptides on amylase secretion.

A reciprocal regulation of Ca(2+)-activated K(+) channel by insulin and somatostatin in guinea-pig pancreatic acinar cells

The effects of islet hormones, insulin and somatostatin, on the regulation of the opening of Ca(2+)-activated K(+) channels in the basolateral plasma membrane of primary cultured pancreatic acinar cells of guinea-pig were studied by cell-attached single-channel recording technique. A single application of insulin or somatostatin did not influence the opening of K(+) channel. The open-state probability (p) of K(+) channel induced by the application of acetylcholine (ACh) to the bath solution was increased by insulin in the presence of ACh. The enhancement effect of insulin on the increased frequency of the channel opening was not seen when concomitantly applied with protein kinase A inhibitor, Rp-cAMPS triethylamine. Insulin increased the p value of K(+) channel, which was reversed by an application of somatostatin (Tyr-somatostatin 28). The addition of ACh followed by forskolin or dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP) to the bath solution evoked an increase in the p value of K(+) channel. After increasing the channel opening, the addition of somatostatin reduced the p value, but not with dbcAMP. Taken together, the results suggest that insulin and somatostatin reciprocally modify the ACh-induced opening of the Ca(2+)-activated K(+) channel through a cyclic AMP-dependent signaling pathway.

Regulatory effect of cholecystokinin on subsequent insulin binding to pancreatic acini

We investigated the regulatory effect of cholecystokinin (CCK) on subsequent insulin binding to pancreatic acinar cells. Rat isolated acini were preincubated with various concentrations of CCK octapeptide (CCK-8) at 37 degrees C. Acini were then washed, resuspended in the binding buffer, and incubated with 8.3 pM 125I-labeled insulin for 60 min at 37 degrees C. Pretreatment with CCK-8 caused inhibition of subsequent 125I-insulin binding that was time and concentration dependent. Significant inhibition was observed with 3 pM CCK-8. Computer analysis of the competition-inhibition study with a nonlinear least-squares curve-fitting program revealed that CCK-8 pretreatment of acini reduced the receptor affinity of the high-affinity binding site. This inhibitory action of CCK-8 was not due to the alteration in degradation or internalization of the tracer. When acini were pretreated with 100 pM CCK-8 for 120 min at 4 degrees C, a reduction in the receptor affinity of the high-affinity binding site was also observed. In pancreatic membrane prepared from acini preincubated with 100 pM CCK-8 for 120 min at 37 degrees C, displacement of 125I-insulin (83 pM) by unlabeled insulin (24 degrees C, 1 h) revealed that CCK-8 inhibited 125I-insulin binding by altering the receptor affinity of the high-affinity binding site. In acinar preparations the inhibitory effect of CCK-8 on 125I-insulin binding was abolished when acini were preincubated with CCK-8 and CCK receptor antagonist L 374718 at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alloxan diabetes on exocrine pancreatic secretion in the anesthetized rabbit

The influence of the endocrine pancreas on the exocrine pancreatic secretion of both electrolytes and enzymes was studied in rabbits made diabetic by alloxan administration. No alterations were observed in the flow of pancreatic juice. Bicarbonate concentrations were considerably increased, whereas chloride concentrations were clearly reduced in the alloxan-diabetic rabbits compared with the control animals. Insulin treatment restored anion levels to normal. Similar, although less pronounced changes were seen in the output values of bicarbonate and chloride. There were no significant differences between the control and alloxan-treated animals in the output of sodium and potassium; however, potassium concentrations exhibited a significant rise both in untreated and insulin-treated diabetic rabbits compared with the controls. Total protein and amylase secretion decreased markedly in the diabetic animals. The secretion of amylase was not brought back to control values by additional administration of insulin. These results suggest that the endocrine pancreas plays an extremely important role in exocrine pancreatic function.

Immunocytochemical demonstration of insulin or insulin-like immunoreactivity in the rat prostate gland

The indirect immunocytochemical technique was used in conjunction with anti-insulin antisera to localize insulin-like immunoreactivity in tissue sections and primary cell cultures from rat prostate gland. Positive immunostaining for insulin-like reactivity was demonstrated in the epithelium of the prostate gland. There appeared to be some variation in the intensity and localization of the immunoreactivity within different regions of the gland. Prostatic epithelial cells grown in culture in an insulin-free medium displayed strong cytoplasmic immunostaining when treated with anti-insulin antisera, while nuclear staining was absent. These results demonstrate that insulin-like immunoreactivity is present in the epithelium of the prostate gland and suggest that there may be some local insulin or insulin-like synthesis in this organ.

Characterization of insulin receptors in isolated epithelial cells of rat ventral prostate: effect of fasting

Insulin receptors have been characterized in rat prostatic epithelial cells by using [125I]insulin and a variety of physicochemical conditions. The binding data at equilibrium (2 h at 15 degrees C) could be interpreted in terms of two populations of insulin receptors: a class of receptors with high affinity (Kd = 2.16 nM) and low binding capacity (28.0 fmol mg-1 protein), and another class of receptors with low affinity (Kd = 0.29 microM) and high binding capacity (1.43 pmol mg-1 protein). Proinsulin exhibited a 63-fold lower affinity than insulin for binding sites whereas unrelated peptides were ineffective. The specific binding of insulin increased by about 50 per cent after 96 h of fasting; this increase could be explained by an increase of both the number of the high affinity-low capacity sites and the affinity of the low affinity-high capacity sites. These results together with previous studies on insulin action at the prostatic level strongly suggest that insulin may exert a physiological role on the prostatic epithelium.