Serum Somatomedin and Fibroblast Proliferative Activity with Growth Hormone Injection in Hypophysectomized and Sham-Operated Rats

Publisher Website
Google Scholar
Abstract
Twenty hypophysectomized and 20 sham-operated male Sprague-Dawley rats averaging 150 g body wt were maintained for 7 days without treatment to verify health and effectiveness of hypophysectomy. Water of hypophysectomized rats contained appropriate amounts of glucose and electrolytes. Half of the rats of each group then received s.c. injections of either 0.23 IU (0.58 mg) porcine growth hormone [GH] in 0.2 ml saline or 0.2 ml saline 3 times daily for 9 days. On day 10, rats were sacrificed to obtain serum. The serum fibroblast proliferative activity [FPA] assay was based on uptake of 3H-methyl-thymidine by human lung fibroblasts (WI-38). The serum somatomedin [SM] assay was based on uptake of 35SO4 by excised cartilage from 3-5 wk old chicks. Comparison with pooled human serum established that 1 U [unit] of rat SM activity was equivalent to 0.75 U human SM activity as measured by this system. Parallelism of SM curves was compared by F-test and SM treatment means compared by analysis of covariance and Duncan''s least significant difference (DLSD) test. Body weight gains and FPA were compared with 1 way analysis of variance and DLSD. GH injection partially restored weight gains of hypophysectomized rats but did not affect gain of sham rats compared to the saline control. FPA was higher in serum of hypophysectomized rats than in shams, but GH treatment did not change FPA in either group. SM was restored to normal by GH in the hypophysectomized rats with no change in FPA. FPA was not related directly to SM in this system. The increase in FPA with hypophysectomy could have been due to an increase in a non-SM growth factor or to a decrease in an inhibitory factor such as corticosteroids. Hypophysectomy eliminates secretion of ACTH which controls corticosteroid secretion. Cortisol inhibited fibroblast growth. Further studies are aimed at determining possible relationships between SM, FPA and GH in overall control of growth.