The Effect of Calcitonin on Growth Hormone Secretion in Man

Abstract

To determine whether human calcitonin inhibits GH secretion in man, as has been described for salmon calcitonin, the effect of an i.v. bolus of human calcitonin or saline on GH release after either insulin-induced hypoglycaemia or the administration of GH-releasing hormone (GHRH) or saline was studied. After the injection of calcitonin, no spontaneous GH surges were seen; the GH response to hypoglycaemia was diminished and the response to GHRH almost completely suppressed. Administration of calcitonin also caused a small and transient rise in plasma PRL and TSH but not LH levels, and no change in the integrated PRL or TSH response. Calcium and magnesium levels did not change. It is concluded that human calcitonin suppresses GH secretion in man, but not by suppressing GHRH and probably not by increasing somatostatin release. In addition, calcitonin has limited PRL and TSH-releasing activity.

The Effect of Calcitonin on Growth Hormone Secretion in Acromegaly

“…The results reported here demonstrate that human calcitonin suppresses GH release in patients with active acromegaly. As in normal subjects (Looij et al, 1988), the onset of action was rapid: nadir levels were reached 45 min after i.v. injection.…”

“…We have shown that calcitonin suppresses GH secretion stimulated by GHRH or hypoglycaemia in normal individuals (Looij et al, 1988). In addition, we found a small stimulatory effect on the release of both PRL and TSH.…”

“…Plasma GH and calcitonin were measured with commercially available radioimmunoassays (RIA); plasma PRL and TSH levels were determined by time-resolved fluorometric assays (TRFA) as described before (Looij et al, 1988). The variation coefficients varied from 5.5 to 7.2% (RIA) and from 3.5 to 5.0% (TRFA) for different hormone concentrations.…”

Parathyroid hormone and calcitonin may modulate hepatic IGF-I production in calves

“…Thus, stimulation of the collagenous matrix synthesis is partly dependent on the IGF-I stimulatory effect on DNA synthesis (1). The decrease in IGF-I synthesis following CT infusion might be induced by an inhibition of GH release induced by CT in calves as in man (25)(26). How¬ ever, such an inhibition of IGF-I (and collagen) synthesis induced by sCT may be pharmacological rather than physiological since CT exerts a protec¬ tive effect upon the skeleton (20-21) and does not inhibit the anabolic effect of PTH on bone (27) physiological; in a 100-kg calf, the PTH secretion rate measured from one superior parathyroid gland varied between 0.5 and 14 ng/min (30).…”

Dexamethasone suppression of the calcitonin induced ?-endorphin, ACTH and cortisol secretion

“…The fact that dexamethasone suppresses the CT induced 13-endorphin, ACTH, and cortisol secretion brings further support to the idea that the hypothalamic-pituitary-adrenal axis is involved in this stimulative effect of CT. Many data have accumulated which show that CT is able to influence the secretion of many other adenohypophyseal hormones: CT inhibits hypoglycemia induced PRL (prolactin) (Kaji et al, 1985;Lengiel et al, 1987) and GH secretion (Petralito et al, 1979;Looij et al, 1988), CT also inhibits arginine (Cantalamessa etal., 1978) and GHRH (Giustina etal., 1989;Looij etal., 1988) induced GH secretion in man. It was also found to decrease GH secretion in acromegaly (Looij et al, 1989).…”