Role of the Hypophysis in Regulation of Pancreatic and Gastric Somatostatin

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Abstract
Since hypophysectomy and GH [growth hormone] deficiency are associated with decreases in hypothalamic content and release of SRIF [GH release-inhibiting factor] 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 [radioimmunoassay] and expressed as ng per mg protein or ng 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 wk of hypophysectomy, and the tissue content increased as much as 3-fold after 20 wk. 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. Deficiencies in other hormones as well as GH may be involved in producing the changes in pancreatic SRIF in hypox and dwarfed animals. This contention was supported in that replacement of T3 [triiodothyronine] (5 .mu.g/kg .cntdot. day) reduced pancreatic SRIF concentration by 30%, while GH plus T3 produced a significantly greater (60%) decrease in pancreatic SRIF in hypox rats.