Technical Note: Vaginal Absorption of 1,25(OH)2D3 in Cattle

Abstract Although exogenous 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] administered via intravenous, intramuscular, and oral routes has been tested for efficacy in preventing parturient hypocalcemia in dairy cows, there are few reports concerning intravaginal administration. For this study, 1,25(OH) 2 D 3 was administered via the bovine vaginal lumen, and subsequent changes in blood chemistry, including levels of 1,25(OH) 2 D 3 and several minerals, were measured to confirm vaginal absorption. Each of 5 heifers received a single intravaginal dose of 1 μ g of 1,25(OH) 2 D 3 /kg body weight; a single control heifer received the ethanol carrier alone. In heifers receiving 1,25(OH) 2 D 3 , the plasma 1,25(OH) 2 D 3 levels increased markedly from baseline (88.3±20.3 pg/mL) within 2h and reached a peak at 6h after treatment (1967.4±1139.6 pg/mL). Plasma Ca levels increased from baseline (10.4±0.4 mg/dL) to a peak of 11.96±0.7 mg/dL at 24h. The levels of inorganic phosphate in plasma increased over time from 7.3±0.5 to 8.1±0.8 mg/dL by 6h and were maintained at a plateau level (9.1±0.7 to 8.6±0.6 mg/dL) from 24 to 96h after treatment. Plasma magnesium decreased from a baseline level of 2.1±0.1 mg/dL to a plateau level of 1.8±0.1 mg/dL, which was sustained from 24 to 48h after treatment. The present study provides evidence of the absorption of exogenous 1,25(OH) 2 D 3 from the bovine vaginal wall, as shown by the marked elevation of plasma 1,25(OH) 2 D 3 levels by 2h after administration, and indicates the possible utility of intravaginal administration of 1,25(OH) 2 D 3 for prophylaxis of hypocalcemia.