Growth hormone suppression of pancreatic polypeptide secretion

Abstract

Effects of GH treatment on human pancreatic polypeptide (hPP) secretion and glucose homeostasis were evaluated in seven GH-deficient children with chronological ages of 7-15 yr and bone ages of 5-13 yr. Both before and after long term GH therapy, blood samples were obtained for measurement of serum hPP, insulin, and glucose concentrations throughout a 24-h period during which meals were taken. In addition, serum glucose and hPP responses to insulin tolerance tests (ITT) were determined on four occasions: 1) before GH treatment, 2) 2 h after the last of three daily injections of GH, 3) 2 h after the last injection of GH (0.1 IU/kg, im), three times each week for 8 weeks), and 4) 72 h after withdrawal of GH. Fasting serum hPP concentrations were also obtained in 15 short-normal children. Mean fasting hPP concentrations were slightly but not significantly greater in the seven GH-deficient children than in the short-normal children with equivalent bone ages. In the GHdeficient children, long term GH therapy significantly decreased the 24-h secretion (integrated plasma values) of hPP and increased the concentrations of glucose and insulin compared tothe tests before GH treatment. Short and long term GH therapy also significantly decreased the hPP responses to ITT; plasma glucose concentrations of the latter ITT were not different from those of the ITT before GH therapy. Seventy-two hours after discontinuation of long term treatment, hPP responses to ITT returned toward pretreatment values even though the concomitant hypoglycemic response to insulin was significantly enhanced compared to the pretreatment response. These results suggest the following. 1) GH treatment suppresses stimulated hPP release. This may relate in part to the effect of GH to increase serum glucose levels, but GH treatment also suppresses hPP release through a mechanism not dependent on any GH-induced increase in serum glucose. 2) GH treatment increased plasma insulin and glucose concentrations, but the cumulative effects on glucose homeostasis after short term treatment are different from the cumulative effects after chronic GH treatment. These observations demonstrate that the readjustment of glucose control mechanisms to GH treatment is complex and time dependent. © 1981 by The Endocrine Society.