The functional differentiation of the embryonic chick duodenum has previously been shown to be dependent on grafted anterior pituitary glands in hypophysectomized embryos. Precocious duodenal differentiation can be produced in normal chick embryos by the administration of extracts of avian anterior pituitary glands. Five daily treatments prior to day 17.5 of incubation results in a 2-4 fold increase over control levels in the specific activity of alkaline phosphatase in duodenal homogenates. Some aspects of villus morphogenesis are accelerated in extract treated embryos, and the degree of precocious differentiation corresponds to the amount of alkaline phosphatase increase in individual samples. Other aspects of duodenal development are unique to the extract-stimulated condition. Growth is reduced with higher levels of extract, and the endocrine end organs show indications of hyperstimulation.
Hypophysectomized embryos respond to extract treatment with improved duodenal development, growth, end organ weight and histology, and reduced mortality. Repair of the hypophysectomized condition, however, is incomplete.
Extract treatment of hypophysectomized and intact embryos produces splenomegaly. This appears to be a host versus graft type of response to the non-hormonal components of the extract. Hormonal components appear to suppress spleen red pulp development, and may also stimulate white pulp development and vascularization.
Response of the embryonic chick to the saline-extractable contents of pituitary cells confirms that the system is not maximally stimulated, and minimizes the possibility that membrane-graft interactions or redifferentiation is prerequisite for the effects of grafted glands. Pars distalis grafts produce an effect similar to extract treatment in intact embryos, suggesting that the embryonic negative feedback system does not repress the hormonal output of grafts. The high survival rate of treated embryos provides an indication that data obtained in hypophysectomy experiments (in which there is only 6% survival) is not atypical of the population. The pattern of variability in the response of embryos to extract or pars distalis grafts suggests a differential sensitivity to pituitary hormones which may be indicative of a variable threshold or a differential dependence on pituitary hormones in the population.