EFFECTS OF GROWTH-HORMONE ADMINISTRATION ON VITAMIN-D METABOLISM AND VITAMIN-D RECEPTORS IN THE PIG

Twelve 36-kg pigs were given either 100 μg/kg porcine pituitary growth hormone (pGH) or placebo injections daily for 33 days. Serum was obtained weekly for analysis of minerals and vitamin D metabolites. On day 34, the pigs were sacrificed and renal and duodenal tissue were obtained for analysis of vitamin D receptor content (VDR). Animals treated with pGH grew faster and had a higher rate of bone accretion than did control animals. Serum concentrations of 1,25-dihydroxyvitamin D (1,25-(OH)2D) were significantly higher in pGH-treated pigs than in control pigs at all time points following initiation of treatment, with the greatest difference observed at day 28 (42.4 ± 4.9 pg/ml in controls vs. 65.4 ± 4.7 pg/ml in pGH-treated pigs). Serum 24,25-dihydroxy-vitamin D tended to be lower in pGH-treated pigs than in control pigs, being significantly lower on day 21 of the experiment (3.22 ± .52 vs. 6.73 ± 1.22 ng/ml, respectively). Serum concentrations of 25-hydroxyvitamin D and calcium were unaffected by pGH treatment. Kidneys of control pigs contained significantly more unoccupied vitamin D receptors than did kidneys from pGH-treated pigs (73.3 ± 4.3 vs. 58.3 ± 4.1 fmoles/mg protein). Duodenal tissue unoccupied vitamin D receptor content was similar in both pGH-treated (245 ± 17.9 fmoles/mg protein) and control (263 ± 21.8 fmoles/mg protein) pigs. Duodenal occupied vitamin D receptor concentration was similar in both pGH-treated (6.8 ± .75 fmoles/mg protein) and control pigs (5.32 ± .77 fmoles/mg protein). These data indicate that pGH treatment increases circulating levels of 1,25-(OH)2D and increases small intestinal mass; thereby increasing intestinal calcium absorption capabilities necessary to support a higher rate of bone accretion. © 1990.