MATURATION OF 17-BETA-ESTRADIOL BINDING-PROTEIN IN HYPOTHALAMUS AND ANTERIOR-PITUITARY OF MALE RATS

  • 1 January 1978
    • journal article
    • research article
    • Vol. 12  (2) , 89-101
Abstract
Levels of estrogen binding proteins in the cytosol of hypothalamic and pituitary tissue of male rats at different ages were estimated. Two classes of estrogen binding sites were detected in 13 and 20 day old animals. The number of high affinity estrogen binding sites (K .apprxeq. 2 .times. 10-10 mol) of the hypothalamus was slightly larger in 13 day old animals, then decreased to constant levels at the age of 20 days and no changes were observed thereafter. Levels of low affinity binding sites of the hypothalamus (K .apprxeq. 5 .times. 10-9 mol) decreased with age and were no longer detectable in 30 day old animals. A decrease of low affinity estrogen binding sites with age was recorded for pituitary cytosol samples and this class of receptor sites was no longer observable in 30 day old male rats. At 13 days high levels of high affinity 17.beta.-estradiol binding protein was registered and minimal numbers of binding sites were found at 20, 30 and 40 days. Thereafter, the levels remained constant until 100 days and were similar to values observed in the 13 day old male animals. Apparent affinity constants of 2 classes of binding sites in hypothalamus and pituitary were similar. The numbers of high affinity binding sites in the pituitary were approximately 10-fold higher than in the hypothalamus throughout all ages studied. These results suggest the great importance of the pituitary in the estrogen feedback control system of hypothalamo-pituitary axis. Ontogeny of the estrogen feedback control system of hypothalamo-pituitary axis. Ontogeny of the estrogen binding sites reflects the maturation of the hypothalamo-pituitary unit. Histological examinations of testicular tissues corroborate these data. Spermatogonia and spermatocytes of the leptotene stage as well as spermatids in the acrosomic phase were found in 40 day old animals. This coincides with the disappearance of the low affinity binding protein which was classified as a 4-5 S moiety upon sucrose gradient ultracentrifugation. This class of binding sites seems to be of extracellular origin and may be involved in protecting the hypothalamo-pituitary unit from the high estrogen levels at early ages. The high affinity estrogen binding protein was found to sediment in the 8 S region. The data combine to suggest that the estrogen binding protein is involved in the 17.beta.-estradiol feedback control of the hypothalamo-pituitary axis.