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Effects of Continuous Administration of 1,25-Dihydroxyvitamin D₃ on Plasma Minerals and Unoccupied Colon Mucosal 1,25-Dihydroxyvitamin D₃ Receptor Concentrations

Iwate University, Morioka 020, Japan

J. P. Goff, R. L. Horst and T. A. Reinhardt

National Animal Disease Center, USDA, Agricultural Research Service, PO Box 70, Ames, IA 50010

ABSTRACT

Six mature nonlactating, nonpregnant Jersey cows were implanted with Alzet mini-osmotic pumps, which delivered 50 µg of 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃] each day for 7 d in an effort to mimic plasma concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)₂D] observed in cows at parturition. Plasma samples were obtained daily beginning 6 d prior to implantation and ending 8 d after removal of the implants. Six biopsies of the descending colon mucosa were obtained per rectum before and after implantation and assayed for unoccupied 1,25-(OH)₂D₃ receptor concentration. Plasma concentration of 1,25-(OH)₂D increased from 37 pg/ml pretreatment to 294 pg/ml with the pumps implanted. Plasma Ca concentration increased within 2 d after implantation and remained elevated for 7 d after the pumps were removed. Unoccupied colon mucosa 1,25-(OH)₂D₃ receptor mean concentration prior to treatment was 14.6 fmol/mg protein and increased within 2 d following implantation to 30.5 fmol/mg protein. These data suggest that 1,25-(OH)₂D₃ upregulates its own receptor in the intestine of the cow.