Fine structure of pituitary blood vessels in embryos of the dwarf (dw) mutant mouse.

Blood vessels in the pars distalis of the embryonic pituitary gland of the dwarf (dw) mutant mouse were analyzed by means of electron microscopy. Dwarf (dw/dw) embryos ranging in age from 15 through 18 days of gestation were obtained from matings of dwarf homozygotes in which reproductivity was induced by means of hormone supplementation and grafts of normal pituitary to the kidney capsule. Endothelial cells in vessels of the dwarf pituitary were retarded in development as indicated by a retention of macrovesicles and marginal flaps beyond embryonic stages when they normally subside in normal embryos, as well as a lag in the development of endothelial cell attenuations. This retardation may be causally related to the pituitary pathology involving faulty cytodifferentiation of somatotrophs and mammotrophs.