Inhibitory effect of calcitonin on growth hormone response to growth hormone releasing hormone in acromegaly

ABSTRACT

1. A neuroendocrine role for calcitonin (CT) has been suggested by the finding of CT receptors in the hypothalamus. We have recently shown that salmon calcitonin (sCT) inhibits growth hormone releasing hormone (GHRH)-induced GH secretion in msn by a mechanism apparently independent of changes in peripheral cortisol, glucose, calcium or parathyroid levels. 2. We have further investigated the inhibitory action of sCT on GH secretion by studying the effects of sCT (100 MRC units, im) or placebo on basal and GHRH (1-29) NH2 (50µg, iv) stimulated GH secretion in 6 acromemgalic patients with active disease. 3. Basal GH lelvels were not altered by sCT administration (placebo 136 ñ 99 µg/1 vs sCT 99 ñ 53 µg/1). However, the GH response to GHRH was decreased by sCT. The area under the curve was signficantly smaller when patients were treated with sCT compared to placebo controls (placebo 77202 ñ 57036 vs sCT 64828 ñ 51909 µg min-1 1-1; P < 0.01). No changes in glucose or calcium levels were observed. 4 These results demonstrate that sCT decresases GHRH-induced GH secretion in acromegalic patients. Although the mechanism of action of sCT on GH secretion is unknown, our results indicate that the inhibitory effect of this peptide on GH secretion is also observed in patients harboring pituitary adenomas