EFFECT OF DOSE AND ADMINISTRATION PERIOD OF GROWTH HORMONE ON LONGITUDINAL BONE GROWTH IN THE HYPOPHYSECTOMIZED RAT

Abstract

ABSTRACT The effect of bovine growth hormone (NIH-GH-B15) on the growth in length of the proximal growth plate of the tibia in hypophysectomized female Sprague-Dawley rats was studied by the tetracycline method. The width of the growth plate was also determined and the weight of the body and heart was registered. The completeness of the hypophysectomy was determined microscopically. The daily sc injection of 25 μg NIH-GH-B15 for 10, 20 or 30 days resulted in an increasing growth in length with increasing administration period. When various doses (5, 25, 100 or 400 μg) NIH-GH-B15 were administered daily for 20 days, the growth in length increased with the dose. A single injection of 45 mg/kg cortisone acetate given at hypophysectomy depressed the growth stimulation of growth hormone. The age at hypophysectomy also influenced the growth hormone-induced growth stimulation. Animals hypophysectomized at 40 days of age had a higher growth in length for the same doses and administration periods of growth hormone than those operated at 60 days of age. The width of the growth plate of the proximal tibia and the weight of the body and heart responded in a similar manner as the longitudinal bone growth to various doses and administration periods of growth hormone, but the changes were less obvious. The dose-response relation after the administration of various doses of growth hormone for 20 days was tested for different growth parameters by the index of precision (λ). Of the growth parameters in this investigation, the accumulated growth in length in animals hypophysectomized at 60 days of age without cortisone at operation was found to be most suitable for dose-response determination of growth hormone. The intention is to develop a bio-assay for growth hormone.