On the pars distalis hormonal activities involved in duodenal development in chick embryos

Duodenal development was studied in five groups of chick embryos: (1) normal, (2) hypophysectomized by partial decapitation, (3) hypophysectomized plus one chorioallantoic 19-day cephalic region pars distalis homograft added at 10.5 days, (4) hypophysectomized plus one middle region graft, and (5) hypophysectomized plus one caudal region graft. Embryos from groups one and two were killed daily from 15.5 to 20.5 days of incubation; in grafted groups (3–5) from 17.5 to 20.5 days. Levels of duodenal development were assessed by changes in mean weight and protein content (relative to body and duodenal weight, respectively), alkaline phosphatase specific activity of homogenates, and morphogenesis. Duodenal development in hypophysectomized embryos was normal with cephalic and middle region pars distalis grafts (except for the kinetics), but not with caudal grafts. Cephalic and middle grafts probably produced enough ACTH and TSH to stimulate the levels of adrenocorticoids and thyroid hormone sufficiently to correct duodenal development. These may be the only hormones controlling normal duodenal development in chick embryos. This suggests that STH is not involved. Failure of caudal grafts to correct faulty duodenal development may reinforce this conclusion.