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(OH2D) in the regulation ofhormone synthesis and secretion. To evaluate this problem, six children with the syndrome of resistance to 1,25(OH2D with ricketsand alopecia underwent dynamic tests of insulin, TSH, PRL, GH, and testosterone secretion. Oral glucose loading resulted in normal glucose curves, subnormal peak insulinresponses of 12–20 μU/ml in three hypocalcemic patients, and normal peak seruminsulin values of 30–40 μU/ml in two normocalcemic patients. Basal serum, TSH, PRL, T4, and T3 concentrations were normalin all patients. Peak serum TSH values after TRH were 11–17 and 16–32 μU/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 8ng/ml in all fiv...