Human Growth Hormone Increases Intestinal Vitamin D-Dependent Calcium-Binding Protein in Hypophysectomized Rats*

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Abstract
The effects were examined of hypophysectomy and pituitary hormone replacement on vitamin D-dependent calcium-binding protein (CaBP) in rat small intestine. The concentration of immunoreactive CaBP per mg intestinal protein was decreased by at least 56% in hypophysectomized rats compared to that in intact pair-fed controls. Alkaline phosphatase and total protein also were reduced by hypophysectomy, but pair-feeding produced comparable decreases. Daily injections of 2, 10, or 50 .mu.g human growth hormone (hGH) for 9 days produced a dose-dependent increase in CaBP. At the highest hGH dose (50 .mu.g), the content of CaBP was increased 2- to 4-fold to intact levels. By comparison, the increases in total protein and alkaline phosphatase were small (25 to 40% and 80 to 90%, respectively). The induction of CaBP preceded the other protein responses; half-maximal increases in CaBP occurred after 2 days of hGH (50 .mu.g/day) treatment before statistically significant changes in total protein or alkaline phosphatase activity. hGH was the most potent pituitary hormone tested; ovine TSH (25 mU/day) had no effect on CaBP, and ovine prolactin (10 or 50 .mu.g/day) increased CaBP by only 25-27% (P = 0.014). The vitamin D-dependent intestinal CaBP in hypophysectomized rats apparently is regulated by GH. The pituitary may be involved in regulating vitamin D-dependent intestinal adaptations.