title: Hypervitaminosis A and calcium-regulating hormones in the rat.
abstract: The effect of vitamin A on calcium-regulating hormones was studied in rats. A single oral dose of 30 mg retinol equivalents (RE) given to adult rats caused no change to serum biologically active parathyroid hormone (bioactive-PTH) concentrations. Bioactive-PTH secretion from rat thyroparathyroid gland complexes was not significantly altered after in vitro incubation with 1.18 X 10(-6) M retinol. Chronically intoxicated rats given 15 mg RE 3 times a week for 6 wk, showed higher osteoclast numbers and lower osteoid than controls. Serum bioactive-PTH was not detectable and serum 25-hydroxyvitamin D (25-OHD) (25.2 +/- 12.5 nmol/L) was significantly (P less than 0.03) lower than controls (43.3 +/- 3.1). In acutely intoxicated rats (60 mg RE/d for 2 d), serum bioactive-PTH levels were significantly lower (0.02 +/- 0.05 ng/ml, P less than 0.03) than in control animals (0.14 +/- 0.08). Lower doses of vitamin A, 7.5 mg RE 3 times a week for 3 wk, suppressed serum bioactive-PTH to undetectable levels but had no significant effect on serum 25-OHD. Serum calcium and 25-OHD levels were significantly lower in vitamin D-intoxicated rats given 7.5 mg RE 3 times a week (ca. 3.16 +/- 0.19 mmol/L; 25-OHD 599.7 +/- 110.6 nmol/L) than vitamin D-intoxicated controls (3.42 +/- 0.17; 789.3 +/- 17.7). These results suggest that hypervitaminosis A can alter the metabolism of calcium-regulating hormones.
mesh_terms: D000208:Acute Disease; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D001842:Bone and Bones / Q000187:drug effects; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D002908:Chronic Disease; D006986:Hypervitaminosis A; D066298:In Vitro Techniques; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains; D014807:Vitamin D / Q000378:metabolism / Q000506:poisoning
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; D010758:Phosphorus; D002118:Calcium