The developmental endocrinology of the spleen in chicken embryos. II. The pars distalis and splenomegaly.

Pars distalis-extract treatment of intact or 'hypophysectomized' chicken embryos resulted in a splenomegaly, perhaps of a host-versus-graft nature, by 17 and 17-5 days of incubation. Pars distalis grafts in intact embryos reduced spleen size, encouraged white-pulp follicle formation, but 'suppressed' red-pulp development. Adult spleen extract and bovine serum albumin did not change spleen sizes or histology appreciably in intact embryos. Perhaps pars distalis hormones inhibit red-pulp development or stimulate white-pulp follicles which may compete with red-pulp proliferation but encourage splenic vasculogenesis alone or by stimulating adrenocorticoid, thyroid, and other hormone levels while other extract factors cause splenomegaly.