Does 1,25-dihydroxyvitamin D participate in the regulation of hormone release from endocrine glands?

The presence of receptors for 1,25-dihydroxyvitamin D3 in the pituitary, pancreas, testis, and ovary has raised the question of a possible direct role for 1,25-dihydroxyvitamin D (1,25(OH)2D) in the regulation of hormone synthesis and secretion. To evaluate this problem, six children with the syndrome of resistance to 1,25(OH)2D with rickets and alopecia underwent dynamic tests of insulin, TSH, PRL, GH, and testosterone secretion. Oral glucose loading resulted in normal glucose curves, subnormal peak insulin responses of 12-20 microU/ml in three hypocalcemic patients, and normal peak serum insulin values of 30-40 microU/ml in two normocalcemic patients. Basal serum, TSH, PRL, T4, and T3 concentrations were normal in all patients. Peak serum TSH values after TRH were 11-17 and 16-32 microU/ml in the hypo- and normocalcemic patients, respectively. The PRL response to TRH stimulation in either hypocalcemic or normocalcemic patients was normal [mean 26.2 +/- 5.1 (SD) ng/ml]. Peak serum GH levels were greater than 8 ng/ml in all five patients studied after one or more of the various stimuli. Serum testosterone concentrations after hCG stimulation were normal in the three patients studied (4.1-8.0 ng/ml). Thus, in children with resistance to 1,25(OH)2D, we could find no significant abnormalities in hormone secretion from the pituitary, pancreas, and testis apart from those presumably due to the hypocalcemia itself.