Hypophysis and Function of Pancreatic Islets

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Abstract
Insulin secretion and biosynthesis of proinsulin and insulin were determined in isolated pancreatic islets of intact and hypophysectomized rats. Human (HGH) or porcine (PGH) growth hormone, ACTH, or human chorionic somatotrophin (HCS) was present in the incubation media at glucose concentrations of 0,50 or 100 and 300 mg%. Insulin secretion into the medium was determined by radioimmunoassay. Insulin biosynthesis was estimated from the amounts of 3H-leucine incorporated into the proinsulin and insulin fraction of the islet proteins which were separated on a Sephadex G 50 fine column. In the islets of intact animals, no significant stimulation of insulin secretion was found in the presence of HGH or PGH at any glucose concentration. On the other hand, insulin release was enhanced when ACTH or HCS was added to the incubation media. In islets of hypophysectomized rats, no increase of insulin secretion was observed with HGH or ACTH. Insulin biosynthesis was not significantly altered in the presence of any substance under all conditions tested, unlike the positive results of GH on insulin biosynthesis when hypophysectomized rats were pretreated in vivo as reported previously by us. It is concluded that GH is involved in the long-term regulation of pancreatic B-cell function, especially with respect to the sensitivity of the B-cells to glucose or other stimuli. 1 Supported by Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg, SFB Ulm 87

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