[Reaction of cells in the anterior lobe of the rat pituitary after acute cooling].

The anterior hypophysis (AH) of rat exposed to total cooling at --10 degrees C for 6 min was studied histologically and autoradiographically. 3, 6, 12, 18, and 24 hours after the exposure the diurnal cycle of modifications of the functional state of the AH secretory cells, the number of mitoses and of the labeled DNA-synthesizing cells was traced. In 12 hours a considerable activation of the thyrotrops and a doubling of mitoses occurred; there was no change of the labeled cells index for twenty four hours. The data obtained showed that stress reaction to cold was characterized by the intensification of the thyrotropic function and an acceleration of mitotic process in the AH cells.