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With the use of "isotopic method" a study was made of the main parameters of functional activity of serotoninergic elements of hypothalamus--the specific uptake and release of 5-OT. The animals used were sexually mature rats castrated on the first postnatal day. In sexually mature intact males the specific uptake of 3H-5-OT by serotoninergic structures of the anterior hypothalamus was significantly lower than in females. Castration of animals on the first day of life resulted in the increase of specific 5-OT uptake in sexually mature males up to that observed in females. There were no differences between the sexes in the rate of spontaneous release of 5-OT. However, response to K(+)-depolarization in the anterior hypothalamus of intact males was significantly lower than that in females. In the hypothalamus of males castrated neonatally the amplitude of the response to the effect of the depolarizing agent was increase up to the level observed in females. By the results obtained it is indicated that elimination of the effect of male hormones on the first postnatal day results in the increase of 5-OT uptake and release in the hypothalamus of sexually mature rat males.

Concentration of thyroxin and triiodothyronine in the thyroid gland of encephalectomized and intact fetuses of rats with normal and prolonged gestation period was determined by means of isotope methods. Encephalectomy of 19-day old fetuses did not produce any significant effect on the concentration of thyroid hormones in the gland 2 and 4 days after the operation. The results obtained pointed to the absence of the hypothalamic control over the thyroid function in prenatal development of rats.

The activity of 3beta-OH-steroid dehydrogenase in the adrenal cortex of 21-day fetuses in control and 3 days after decapitation in utero was estimated quantitatively by microspectrophotometry. The enzyme activity calculated as per conditioned cell in the fascicular zone exceeded that in the forming glomerular zone. After hypophysectomy the activity of the 3beta-OH-steroid dehydrogenase decreased in both the fascicular and glomerular zones.

To specify the time of setting in of the hypothalamic control over testicular androgenous function in the prenatal development of rats, the brain hypothalamic area of 18.5-day-old fetuses was excised by encephalectomy in utero. Three days after the operation, i. e. on day 21.5 of the development, testosterone concentration in the testes was measured by radioimmunoassay. Testosterone concentration in the testes of encephalectomized fetuses was significantly decreased as compared with intact fetuses. Administration of LH-RH into the encephalectomized fetuses 2 hours prior to fixation removed the effect of encephalectomy on testosterone concentration in the testicular tissue. The data evidence the establishment of the hypothalamic control over androgenous function of the testes in rat fetuses at the end of the prenatal development.

Triiodothyronine (T3) and thyroxin (T4) were detected by radioimmunoassay in the thyroid gland and serum of encephalectomized and intact rabbit fetuses. Encephalectomy performed on the 22-23d day of development did not produce any effect on thyroid hormone concentrations in 29-day-old fetuses. However, on the 30th day the concentrations of T2 and T4 in the thyroid gland were significantly lower in the encephalectomized fetuses than in the intact ones. These findings were consistent with changes in the morphological structure of the thyroid gland. The results obtained indicate that the hypothalamus begins to control thyroid function in the rabbit fetuses apparently from the 30th day of prenatal life.

Changes in the functional state of the hypophysial-adrenal system after the removal of the hypothalamus (encephalectomy in utero) were studied in rat fetuses. The hormonal activity of the adrenal glands was evaluated by the direct fluorimetric determination of corticosterone in this organ. Removal of the hypothalamus in 18.5--19.5-day fetuses brought about a significant decrease of corticosterone in the adrenal glands. Injection of the hypothalamus homogenate to fetuses immediately after the encephalectomy prevented this decrease. The results obtained supported the existence of functional relationship between the hypothalamus and the hypophysial-adrenal system in rat fetuses.

Brain hypothalamus region was removed by encephalectomy in utero in 21-23-day-old rabbit fetuses to find out when hypothalamic control over testicular androgenous function was set up during rabbit prenatal development. Testosterone concentration in testicular tissue was measured by radioimmunoassay at different terms after the operation. Encephalectomy resulted in a reliable decrease of testosterone concentration in 29- and 25-day-old fetuses, however, no significant changes were observed in 23-day-old fetuses. The greatest reduction in hormone gland concentration was noted in 25-day-old fetuses, encephalectomized on day 23 of their development. Introduction of LH-RH to 25-day-old encephalectomized fetuses 30 min before fixation significantly increased androgen concentration in the gland. The data obtained indicate that hypothalamic control over testicular androgenous function is set up on days 23-25 of prenatal development.