EFFECT OF ADMINISTRATION FREQUENCY OF GROWTH HORMONE ON LONGITUDINAL BONE GROWTH IN THE HYPOPHYSECTOMIZED RAT

Abstract

The effect of the administration frequency of growth hormone [GH] on longitudinal bone growth was investigated with tetracycline as an intravital marker of the bone growth of the proximal tibia in hypophysectomized rats. The total dose of GH (NIH[National Institutes of Health]-GH-B16) and the administration period were the same in all compared experiments. It was possible to achieve an optimum growth response for a certain total dose of growth hormone by increasing injection frequency. The period of hormone administration was 10 or 5 days followed by a 10 day withdrawal period. When the GH was administered alone or in association with L-thyroxine [L-T4] for 10 days, the optimum injection [inj.] frequency for GH was 1 inj./day in hypophysectomized rats and 2 inj./day in T4 [thyroxine] treated hypophysectomized rats. When the administration period was 5 days for GH given in association with L-T4, the growth stimulation induced by 1 daily GH inj. was the same as that induced by 2 or 4 daily inj. of the same total dose. An increase in the administration frequency for a total daily dose of T4 from 1-2 inj./day did not increase the longitudinal bone growth either when T4 was given alone or in association with GH.