Inhibitory effects of active vitamin D preparations on PTH secretion in rats.
To study the effects of various vitamin D preparations on PTH secretion, serum calcium and urinary excretion of cAMP were monitored in conscious perfused rats, and the influences of a bolus iv injection of the preparations on these parameters were examined. Three hours after the administration of 0.25 microgram/kg (0.6 nmol/kg) of 1 alpha, 24(R)-dihydroxycholecalciferol [1 alpha, 24(OH)2D3], the urinary excretion of cAMP decreased to a level compatible with that of parathyroidectomized (PTX) rats (50% of initial value; p less than 0.05) with no change in the concentration of serum calcium (total and ionized). In PTX rats supplemented with bovine PTH (1 U/h), the vitamin D preparation showed no significant effects either on the urinary excretion of cAMP or on serum calcium. These effects were rather specific for active vitamin D preparations, i.e. 1 alpha, 25(OH)2D3 (0.25 micrograms/kg) and 1 alpha OHD3 (1.25-6.25 micrograms/kg). However, 24,25(OH)2D3 (up to 25 micrograms/kg) had no significant effect on these parameters. These results suggest that, in rats, active vitamin D preparations specifically inhibit PTH secretion without causing a significant increase in the serum calcium concentration, reflecting a direct feedback mechanism between active vitamin D metabolite and the parathyroid glands.
D015650:24,25-Dihydroxyvitamin D 3; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000097:blood; D000242:Cyclic AMP / Q000652:urine; D004100:Dihydroxycholecalciferols / Q000494:pharmacology; D006887:Hydroxycholecalciferols / Q000494:pharmacology; D008297:Male; D010280:Parathyroid Glands / Q000502:physiology; D010281:Parathyroid Hormone / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014807:Vitamin D / Q000494:pharmacology*
D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone; D014807:Vitamin D; D015650:24,25-Dihydroxyvitamin D 3; D000242:Cyclic AMP; D002117:Calcitriol; D002118:Calcium; C008088:alfacalcidol