ENDOCRINE REGULATION OF EMBRYONIC MUSCLE DEVELOPMENT - HORMONAL CONTROL OF DNA ACCUMULATION, PENTOSE CYCLE ACTIVITY AND MYOBLAST PROLIFERATION

Chick embryos were hypophysectomized by the partial decapitation technique at 33-36 hours of incubation. Determination was made of the effects of hypophysectomy on dry weight, protein, and DNA accumulation and on the activities of phosphorylase, phosphoglucomutase, and glucose-6-phosphate dehydrogenase in leg muscle. These results were compared with those obtained from normal embryos and hypophysectomized embryos that had had anterior pituitaries transplanted to the chorioallantoic membrane on day 10 of incubation. Hypophysectomy resulted in suppressed dry weight and protein accumulation, and suppressed phosphorylase and phosphoglucomutase activities. Cell proliferation and DNA accumulation continued in hypophysectomized embryos through day 20 but stopped by day 16 in normal embryos. Glucose-6-phosphate dehydrogenase activity in normal embryonic muscle decreased to unmeasurable levels by day 18 but significant activity was found in hypophysectomized embryos through day 20. The effects of hypophysectomy on the rates of accumulation of all parameters were reversed by pituitary transplantation. The possibility of endocrine regulation of DNA synthesis and cell proliferation by hormonal control of the pentose cycle is discussed. © 1969.