Effects of Calcitonin on Basal and Thyrotropin-Releasing Hormone-Stimulated Prolactin Secretion in Man*

Plasma PRL fell in nine healthy subjects and four patients with hyperprolactinemia after iv administration of salmon calcitonin (CT). The maximum fall was observed 30--60 min after the infusion. There was no change in the plasma concentrations of the other anterior pituitary hormones tested (GH, FSH, LH, and TSH). In five healthy subjects, TRH was injected 60 min after the CT infusion. This protocol was repeated in the same subjects at 3-day intervals, except CT was not administered. Plasma PRL before TRH injection was clearly lower when CT had been administered. Plasma concentrations of the other anterior pituitary hormones did not change. PRL and TSH responses to TRH were markedly inhibited when CT had been previously infused. These observations are in agreement with preceeding studies showing a similar effect of CT on the plasma concentration of various other polypeptide hormones. This general effect of CT could be attributed to a change in intracellular calcium of the secreting cells.