A MORE EXTENSIVE STUDY ON THE UPTAKE OF LABELLED PROGESTERONE BY THE HYPOTHALAMUS AND PITUITARY GLAND OF RATS

Abstract Short-term experiments (Seiki, Higashida, Imanishi, Miyamoto, Kitagawa & Kotani, 1968; Seiki, Miyamoto, Yamashita & Kotani, 1969) have failed to show any specific progesterone-binding receptors in the hypothalamus and pituitary gland. These sites do not show selective uptake of progesterone compared with other parts of the brain after i.v. administration of [3H]progesterone to rats in various experimental conditions. To investigate more extensively the existence of specific receptor sites in the hypothalamus and pituitary gland, a long-term experiment was carried out. Female Wistar rats, weighing about 230 g, were used. Ovariectomy was carried out only on animals in dioestrus, as determined by vaginal smears. Two to three weeks after the operation, the animals were given an i.v. injection of 50 μCi [7α-3H]progesterone/100 g body weight (sp. act. 18·1 Ci/μmol) in 0·2 ml 0·9% NaCl solution containing 5% (v/v) ethanol. The animals were killed by decapitation at varying intervals of