Role of the Hypophysis in Regulation of Pancreatic and Gastric Somatostatin

Abstract

Since hypophysectomy and GH deficiency are associated with decreases in hypothalamic content and release of SRIF, it was of interest to determine whether these hormonal alterations also affect peripheral tissue levels of SRIF. Hypophysectomized (hypox) rats were studied at various times after surgery and compared with age-matched controls. Pancreatic, gastric, and hypothalamic SRIF levels were measured by RIA and expressed as nanograms per mg protein or nanograms per organ. Decreased levels of hypothalamic SRIF were observed in hypox animals at all time periods after surgery. In contrast, pancreatic SRIF concentrations increased within 1 week of hypophysectomy, and the tissue content increased as much as 3-fold after 20 weeks. Measurement of the SRIF content of isolated rat islets of Langerhans revealed a 67% increased content/islet in hypox rats compared with controls. The gastric SRIF concentration was not changed early, but subsequently, the total organ content was significantly decreased compared with that in controls. The changes in stomach and pancreas SRIF contents became more marked with duration of pituitary deficiency. Studies in genetically dwarfed Snell mice, lacking primarily GH but also other anterior pituitary hormones, were similar to the findings noted in hypox rats; the SRIF concentration was significantly increased in the pancreas and decreased in the stomach and hypothalamus. It is probable that deficiencies in other hormones as well as GH are involved in producing the changes in pancreatic SRIF in hypox and dwarfed animals. This contention was supported in that replacement of T3 (5 micrograms/kg . day) reduced pancreatic SRIF concentration by 30%, while GH plus T3 produced a significantly greater (60%) decrease in pancreatic SRIF in hypox rats.

The effect of hypophysectomy on pancreatic islet hormone and insulin-like growth factor I content and mRNA expression in rat

“…Thus, GH deficiency after hypophysectomy results in a decrease in the hypothalamic somatostatin content in vivo and its release in vitro (Berelowitz et al 1981). In contrast, pancreatic somatostatin has been reported to be increased in rats 4-6 weeks after hypophysectomy (Recant et al 1984). The latter result agrees with the results of the present study with respect to the pancreatic somatostatin peptide content.…”

“…In contrast, islets isolated and cultured 4 weeks after hypophysectomy contained less insulin per microgram of protein than islets from normal rats (Martin and Gagliardino 1967). Pancreatic somatostatin per gram of tissue was found to be unchanged (Berelowitz et al 1981) whereas Recant et al (1984) found elevated somatostatin whether expressed per milligram of protein or per whole pancreas of hypox rats. To our knowledge, no data are available regarding pancreatic glucagon content in hypox rats.…”