Elevated somatostatin in pancreatic islets of adrenalectomized dogs

Abstract

We have observed both hyperglucagonemia and hypoinsulinemia in adrenalectomized (Adx) dogs. To determine whether these hormonal alterations are related to changes in distribution of islet hormones in the pancreas, we examined the concentration and total mass of insulin, glucagon, and somatostatin in the head, body, and tail of the pancreas by immunoassay and immunocytochemistry. We studied 6 normal dogs, 5 Adx dogs deprived of cortisol for 24 h (Adx I) and 5 for 48-72 h (Adx II). In normal dogs, single and double immunocytochemical staining showed that, in contrast to some other species, B (insulin) cells are mostly in the central region of islet, whereas A (glucagon) and D (somatostatin) cells are distributed randomly. This topographic distribution was not altered by adrenalectomy. In normal dogs, insulin concentration (micrograms per g) and total mass (micrograms) were higher in the tail (174 +/- 22, 2001 +/- 396) and body (165 +/- 22, 2850 +/- 600) than in the head (91 +/- 17, 668 +/- 156) of pancreas. Glucagon concentration (micrograms per g) and total mass (micrograms) were 17 +/- 2, 178 +/- 17 in the tail; 9.5 +/- 2, 158 +/- 32 in the body, and negligible (0.78 +/- 0.32, 7 +/- 3) in the head, whereas somatostatin concentration (micrograms per g) and total mass (micrograms) were 0.58 +/- 0.26, 4.20 +/- 1.5 in the T, 0.23 +/- 0.10, 3.9 +/- 1.6 in the B, and 0.22 +/- 0.05, 1.8 +/- 0.6 in the H. The striking finding was that adrenalectomy caused large increases in somatostatin in all three regions of pancreas in both Adx I and Adx II. The total mass of somatostatin in Adx I and Adx II increased 4-fold in the tail (P less than 0.02-0.005), 5-fold in the body (P less than 0.01-0.001), and 7-9-fold in the head (P less than 0.05-0.005) and concentration increased 6-fold in the body (P less than 0.005) and 7- to 8-fold in the head (P less than 0.01-0.001). There were no significant changes in the content of insulin and glucagon after adrenalectomy. Plasma concentration of glucagon increased by 50% in Adx I (P less than 0.005) and 70% in Adx II (P less than 0.02), insulin decreased by 39% (P less than 0.005), 23% (NS), respectively, and somatostatin increased by 258% (P less than 0.001) in Adx II. Thus the adrenal glands appear to play an important role in regulation of the content of somatostatin in pancreatic islets.