Comparison of gonadotroph, thyrotroph and mammotroph development in situ, in transplants and in organ culture.

This study was conducted to examine the role of the hypothalamus in development of gonadotrophs, thyrotrophs, and mammotrophs up to the time of birth in the rat. The development of the in situ newborn pituitary (22 days post-coitus; dpc) was compared with the development of 12 and 15 dpc pituitary anlagen grown under the kidney capsule of an adult host or in organ culture for a time period equivalent to 22 days of gestation. Morphological development was evaluated by light microscopic histology and gonadotrophin immunocytochemistry. Functional development was analyzed by radioimmunoassay determination of luteinizing hormone, thyrotrophin, and prolactin content of the in situ, kidney capsule grafted, and organ-cultured pituitary. The results provide evidence that factors, perhaps blood-borne, play a significant role in pituitary development but that direct hypothalamic influences are of minimal importance in the development of gonadotrophs and mammotrophs. The fetal hypothalamus may play a significant role in stimulating high storage levels of thyrotrophin in the prenatal pituitary.