Uptake and binding of androgens by the anterior pituitary gland, hypothalamus, preoptic area and brain cortex of rats.

Abstract

ABSTRACT [1,2-3H] testosterone was given intramuscularly to castrated adult male and female rats. The concentration of radioactivity in the anterior pituitary gland, hypothalamus, preoptic area, brain cortex, ventral prostate and muscle tissue was measured at different time intervals. In the ventral prostate a preferential concentration and retention of radioactivity was recorded. In the anterior pituitary, hypothalamus, preoptic area and brain cortex, however, the maximum uptake was observed 7½ min after the injection of the hormone. Thereafter the radioactivity rapidly declined. Non-labelled testosterone was found to compete with the radioactive testosterone for the binding sites in the anterior pituitary, hypothalamus and preoptic area. High doses of non-labelled testosterone caused a slight, and statistically insignificant reduction of the radioactivity in the brain cortex. The concentration of radioactivity in the muscle tissue was not affected by any of the doses of non-radioactive testosterone given. Filtration of serum on Sephadex G-25 columns showed that considerable amounts of radioactivity were associated with macromolecules. Therefore in order to get a valid record of the binding of androgens to the specific molecules of the target cells, perfusion of the vascular system was essential. In vivo and in vitro experiments revealed that considerable amounts of radioactive material were bound to macromolecules in the cytosol fractions of the anterior pituitary gland, hypothalamus, preoptic area and brain cortex. Thus for the first time a binding of androgens by macromolecules in the cytosol fraction of the preoptic area and brain cortex has been found. Since association of androgens with plasma constituents can be excluded, the radioactive material is most likely bound to specific binding molecules present in the target cells of the anterior pituitary gland, hypothalamus, preoptic area and the brain cortex.