Influence of the Interaction of Calcitonin and 1,25(OH)₂-Vitamin D₃ on Prolactin Secretion

Summary

Calcitonin inhibits and 1,25(OH)₂-Vitamin D₃ (1,25(OH)₂D₃) stimulates prolactin and thyrotropin secretion. During concurrent administration of calcitonin and 1,25(OH)₂D₃ the action of the two calciotropic substances on thyrotropin secretion antagonizes each other. In the submitted investigation the effect of a single dose of synthetic salmon calcitonin on the prolactin secretion at rest and TRH-induced secretion was compared in untreated healthy subjects and in subjects given for four days previously 1,25(OH)₂D₃ in doses which have a stimulating effect on prolactin secretion (3 (μg/d).

Calcitonin, 50 U, administered by the i.v. route by infusion inhibited the secretion of prolactin at rest (p < 0.05) and the TRH-stimulated secretion during the 20th, 30th, 40th and 60th minute after TRH administration (p < 0.01 at all time intervals) in untreated subjects but also the secretion at rest (p < 0.01) and TRH — stimulated secretion at times 20, 30, 40 and 60 mins following TRH administration (p < 0.01, p < 0.05, p < 0.05 and p < 0.05, respectively) in subjects pretreated with 1,25(OH)₂D₃.

Compared with the thyrotropic system, the inhibiting effect of calcitonin on the lactotropic system is not cancelled by the administration of 1,25(OH)₂D₃. It is assumed that differences in the response of the lactotropic and thyrotropic system to the concurrent administration of calcitonin and 1,25(OH)₂D₃ are conditioned by the different ratio of the number of receptors for calcitonin and 1,25(OH)₂D₃ in the lactotropic and thyrotropic cell.

Key words

Calcitonin - 1,25(OH)₂-Vitamin D₃ - Prolactin