Changes of in Vivo LH-RH·I¹²⁵, HCG·I¹²⁵ and Estradiol·H³ Distribution in Tissues with Aging of Rats

Abstract

In vivo LH-RH.I¹²⁵, HCG.I¹²⁵ estradiol-H³ (E₂ H₃) distributions in tissues with aging of female rats (8-120 weeks) were studied, and the following results were obtained. The distributions were expressed as concentration ratio (cpm/mg tissue to cpm/0.1ml plasma) and organ ratio [cpm/organ (mg) to cpm/0.1ml plasma].
1) The LH-RH·I¹²⁵ concentration and organ ratio observed in mature rats, was low in the hypothalmus, cerebral cortex and cerebellum, but high only in the pituitary.
2) The LH-RH·I¹²⁵ concentration and organ ratio in the pituitary through the combined administration with LH-RH 501U was lower by 36% and 47%, respectively than those with a single LH-RH·¹²⁵ administration.
3) The LH-RH·I¹²⁵ concentration in the pituitary tended toward a decrement with aging, while the organ ratio did not change.
4) In a subcellular distribution of HCG·I¹²⁵, approximately 60% of radioactivity in the ovary was distributed in a 3,000 X G pellet, whereas a great part of radioactivity was distributed in a 10⁵ X G supernatant in other organs.
5) The HCG·I¹²⁵ concentration ratio at 2 hours after the injection was high in the following sequence : ovary, kidney, spleen, liver, etc.
6) The HCG·I¹²⁵ concentration ratio in 80 week-old ovaries was 80% lower than that of 20 week-old ovaries. However, there was no significant difference in other tissues between both groups.
7) The E₂·H³ concentration ratio was high in the pituitary, uterus, Fallopian tube and ovary, moderate in the adrenal and low in the hypothalmus, etc. However, the concentration ratio in the hypothalmus was significantly higher than that of the cerebral cortex and cerebellum.
8) The E₂ ·H³ concentration ratio in all target organs tended toward a decrement at 68 weeks. However, the organ ratio did not show any change with aging, except a decrement in the adrenal.
From these results it was revealed that the gonadotropin receptors in the ovary among hormone receptors in organs of the hypothalamic-pituitary-ovarian axis decrease most markedly in an early stage of senescence in rats.