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

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 man by a mechanism apparently independent of changes in peripheral cortisol, glucose, calcium or parathyroid hormone 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 (50 micrograms, iv) stimulated GH secretion in 6 acromegalic patients with active disease. 3. Basal GH levels were not altered by sCT administration (placebo: 136 +/- 99 micrograms/l vs sCT: 99 +/- 53 micrograms/l). However, the GH response to GHRH was decreased by sCT. The area under the curve was significantly smaller when patients were treated with sCT compared to placebo controls (placebo: 77202 +/- 57036 vs sCT: 64828 +/- 51909 micrograms min-1 l-1; P less than 0.02). No changes in glucose or calcium levels were observed. 4. These results demonstrate that sCT decreases 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.