[Comparative study of HCG receptors in rat ovary and testis]

It has been documented that there are specific human chorionic gonadotropin (HCG) receptors in cell membrane of rat ovary and testicle. In order to make a further study on the characteristics of the HCG receptors on rat ovary and testicle, we focused on comparing those two kinds of receptors. Furthermore, we contrasted the testicular cell membrane with its homogenates. Rat ovarian and testicles were homogenized and soniced under ice cold conditions. The homogenates were centrifuged at 12,100 x g for 20 min following filtration. After sucrose density gradient ultracentrifugation (78,000 x g, 2.5h) for the pellets, the interface layers between 37% and 41% were collected. The pellets were subsequently suspended in cold 1mmol/L NaHCO3 solution and recentrifuged at 27,000 x g for 25 min. The results show that the cell membrane of both the rat ovary and testicle can bind to HCG specifically. A small amount of HCG has more evident inhibitory effect on the binding in testis than ovary. Scatchard plot analysis for the binding assay yielded a bound capacity of testicle cell membrane of 4.5 x 10(-5) mol/micrograms protein, Kd of 1.6 x 10(-7) mol/L, whereas it was 0.51 x 10(-9) mol/micrograms protein, a Kd of 1.69 x 10(-6) mol/L in ovarian cell membrane. In comparison with homogenates and cell membrane, the HCG binding activity of later is more sensitive.