Hypothalamus and cytodifferentiation of the foetal pituitary gland. Study in vivo.

To investigate whether the hypothalamus is involved in the cytodifferentiation of the anterior pituitary gland, rat foetuses were encephalectomized in utero on day 16 of pregnancy. Pituitary sections from encephalectomized and normal littermate foetuses were studied on day 21 with the immunofluorescence technique using antibodies anti alpha-MSH, anti beta-MSH, anti alpha-(17-39) ACTH and anti beta-(1-24) ACTH. On day 16, only the anti beta-MSH revealed a few cells in the pars distalis but not in the pars intermedia. On the other hand, on day 21, the pituitary cells reacting with antibodies anti alpha-MSH, anti beta-MSH and anti alpha-(17-39) ACTH were as numerous in the encephalectomized foetuses as in the normal littermate foetuses. The cells revealed with the antibody anti beta-(1-24) ACTH were less numerous and less fluorescent in the pars distalis and intermedia of the hypophysis of the encephalectomized foetuses. On day 21, the adrenals of the encephalectomized foetuses were atrophied in comparison with those of the normal littermate foetuses but they were larger than on day 16. These data suggest that the cytodifferentiation of the corticotroph and melanotroph cells of the hypophysis occurs without the influence of the hypothalamus which is necessary for the normal release of ACTH.