AJP - Endocrinology and Metabolism, Vol 242, Issue 3 206-E213, Copyright © 1982 by American Physiological Society
Calcitonin modulation of insulin and glucagon secretion in man
D. Giugliano, N. Passariello, S. Sgambato, R. Torella and F. D'Onofrio
These studies were undertaken to evaluate the effect of different doses of
calcitonin on insulin and glucagon responses to intravenous glucase loads
and to assess the mechanism/s by which calcitonin inhibits insulin
secretion in man. In our studies, even the infusion of the 1-U dose of
calcitonin was found to inhibit by 45% the acute insulin response to a
glucose (20 g) pulse. This effect was associated with a significant
decrease in glucose disappearance rates. These negative effects of
calcitonin on both insulin secretion and glucose tolerance were
dose-related. The inhibition of the acute insulin response to glucose was
65% and up to 90% with the infusion of the 4- and 8-U doses, respectively.
The suppressive effect of glucose on glucagon secretion was significantly
reduced by calcitonin. The inhibitory effect of calcitonin on insulin
responses to glucose (5 g) and glucose tolerance was reversed by both
theophylline and calcium. By contrast, infusion of lysine acetylsalicylate
to block the synthesis of endogenous prostaglandins did not diminish the
inhibitory effect of calcitonin on insulin secretion. These results
demonstrate that a) calcitonin inhibits glucose-induced insulin responses
and deteriorates glucose tolerance in normal humans in a dose-dependent
manner; b) calcitonin reduces the suppressive effect of glucose on glucagon
secretion in a dose-related fashion; and c) both theophylline and calcium
reverse the inhibitory effect of calcitonin on insulin secretion. It is
hypothesized that calcitonin effects on insulin and glucagon release are
mediated via a change in calcium redistribution in the islet cells.
