Calcitonin inhibition of prolactin secretion in isolated rat pituitary cells.

Salmon calcitonin inhibited TRH-stimulated release of prolactin in isolated pituitary cells from untreated female rats. These cells were still capable of responding to the fresh addition of TRH after the removal of calcitonin. Calcitonin gene-related peptide had only a weak effect in inhibiting prolactin release in these cells. Pituitary cells isolated from female rats which had been treated with weekly s.c. injections of 1 mg oestradiol dipropionate for 4 weeks, exhibited a marked increase in the magnitude of the inhibition of prolactin release by salmon calcitonin. Both basal and TRH-stimulated release of prolactin were inhibited by concentrations of 0.1 nmol salmon calcitonin/l or higher. Prolactin release from these cells was also inhibited at somewhat higher concentrations by calcitonin gene-related peptide. Our results demonstrate that calcitonin can directly inhibit basal as well as TRH-stimulated prolactin release by acting directly at the pituitary. The results strongly suggest that the peptide may be involved in the regulation of prolactin release in certain physiological conditions.