Temporal Serum Concentrations of Growth Hormone, Thyrotropin, Insulin, and Glucagon in Sheep Immunized against Somatostatin*

Abstract

Six ram lambs were immunized with somatostatin conjugated to egg albumin, and six control lambs were immunized with egg albumin to examine the physiological role of somatostatin in regulating GH, TSH, insulin, and glucagon secretion. The influence of treatment on hormonal (GH, insulin, and glucagon) response to arginine stimulation was also tested. Baseline and overall serum GH concentrations were higher in antisomatostatin lambs (Anti-S) than in controls (C). The amplitude of GH secretory spikes was also higher, but the difference was not statistically significant. None of the variables of insulin secretion was statistically different between treatments. Serum TSH and plasma glucagon were not different between treatment groups. Arginine infusion stimulated an increase in serum GH, insulin, and plasma glucagon in both treatment groups. Serum GH concentrations responded to arginine infusion to a greater extent in Anti-S lambs than in C lambs. Conversely, serum insulin increased after arginine infusion to a greater extent in C lambs than in Anti-S lambs. No statistical differences were observed between treatment groups and glucagon concentrations. Despite the observed elevation in serum GH, and the exaggerated GH response to arginine stimulation, the Anti-S lambs gained significantly less weight over the treatment period than did C lambs. Anti-S titer and weight gained were negatively correlated (r = −0.75). Furthermore, the amplitude of GH secretory spikes and weight gained over the treatment period were also negatively correlated (r = −0.72), while Anti-S titer and overall GH concentration were positively correlated (r = 0.99). Cause and effect relationships, however, can only be postulated from these data. These data suggest that endogenous circulating somatostatin is involved in the tonic suppression of GH secretion, while circulating somatostatin does not appear to be involved in the regulation of insulin, glucagon, or TSH secretion in the sheep. It was not possible to stimulate an increase in growth by increasing serum GH concentrations via a blockade of endogenous circulating somatostatin activity. (Endocrinology106: 1027, 1980)