Insulin, glucagon and somatostatin in fetal rat islets maintained free-floating in culture: immunocytochemistry and radioimmunoassay

Effect of thawing rate and post-thaw culture on the cryopreserved fetal rat islets: Functional and morphological correlation

The ability of the fetal pancreatic islet cells to multiply rendered them a potential tissue for transplantation studies to cure diabetes. A bank of fetal islets could be created with proper storage in liquid nitrogen. The aim of this study is to evaluate the effect of thawing rate and post-thaw culture on the structural and functional integrity of isolated cryopreserved islets of rat fetuses. Fetal rat islets were isolated by the collagenase digestion, cultured for three days, and then cryopreserved using dimethylsulphoxide as cryoprotectant and the step-rate cooling to -40 degrees C before immersing them in liquid nitrogen. The islets were thawed by the slow or fast warming rates using hyperosmolar sucrose solution and then cultured for 1 or 2 days. Insulin and C-peptide contents of the slow thawed islets were higher than those of the control. In the fast thawed islets the contents were similar to those of the control. Insulin and C-peptide release in response to glucose for the slow thawed islets were lower than those of the control and in the fast thawed islets they were similar to that of the control. Histological examination showed irregular periphery and fragmented central part of the large slowly thawed islets, which showed also variable immunohistochemical reaction to anti-insulin serum, ranging from strongly positive reaction to markedly weak reaction. Fast thawed islets showed mostly regular periphery and their reaction to the anti-insulin serum was slightly weaker than that of the control islets. It was concluded that fast thawing and post-thaw culture is much better than slow thawing, as indicated by nearly normal insulin and C-peptide content and release and intact structural integrity.

Triiodothyronine down-regulates thyrotropin-releasing hormone (TRH) synthesis and decreases pTRH-(160-169) and insulin releases from fetal rat islets in culture

TRH is localized with insulin in beta-cells. It is synthesized as a prohormone containing five copies of TRH and seven cryptic peptides, including pro (p)-TRH-(160-169). Thyroid hormone regulates the expression of several genes encoding peptide hormones. We found that circulating T3 concentrations were inversely correlated with TRH levels in two physiopathological situations. There are low concentrations of circulating thyroid hormone and very high concentrations of TRH and pTRH-(160-169) during development, and experimental hypothyroidism results in higher concentrations of prepro (pp)-TRH messenger RNA (mRNA) and TRH content in the adult rat pancreas than are present in the euthyroid pancreas. The present study was carried out to investigate the interaction between T3 and pancreatic TRH during the functional maturation of islets in culture and to validate the data obtained in vivo. T3 decreases ppTRH mRNA in islets in a dose-dependent manner. The primary impact of T3 on islet function may be mediated by ppTRH mRNA, as short term T3 treatment had no effect. Long term T3 treatment reduced the islet TRH content and the amounts of pTRH-(160-169) and insulin released. This secretory pattern and coordinated regulation of pTRH-(160-169) and insulin suggests that pTRH-(160-169) plays a specific role in the regulation of insulin secretion.

Sorbin in the porcine gastrointestinal tract and pancreas: an immunocytochemical analysis

Sorbin is a 153-amino acid peptide that was initially discovered in the porcine duodenum. We have reported previously that this peptide regulates intestinal electrolyte transport and have described accumulation sites in the rat digestive tract. In the present study, we investigated the anatomical distribution and the site(s) of sorbin production in the porcine digestive tract using immunocytochemistry. The use of polyclonal antisera, which by cross-reaction studies were shown to be specific for different regions of the molecule, revealed a diversified distribution. Sorbin predominated in endocrine cells preferentially localized in the pyloric glands, duodenal crypts of Lieberkühn, and pancreatic islets; in the gastrointestinal tract, sorbin coexisted with Met-enkephalin or with substance P in a small fraction of serotonin-storing [enterochromaffin (ED)] cells, i.e. EC2 cells and EC1 cells, respectively; in the pancreas, sorbin coexisted with insulin in the beta-cells, also considered as serotonin-storing cells in the pig, and with EC cells in the exocrine pancreas. An enteric neuronal system containing sorbin was also reported. Our results demonstrate that sorbin is a component of the serotonin-storing cell type in the porcine gastrointestinal tract and pancreas, and suggest potential directions to investigate the functions of this new regulatory peptide.