[125I]hCG binding to bovine thecal tissue from healthy and atretic antral follicles.
[125I]hCG binding to thecal tissue from healthy bovine follicles was examined and compared to [125I]hCG binding to other bovine ovarian tissues. [125I]hCG bound specifically to theca interna but not to theca externa. Binding to theca interna was a time- and temperature-dependent process, the rate of association obeying second-order kinetics with calculated rate constants of 1.97 +/- 0.13 X 10(5) and 0.85 +/- 0.04 X 10(5) 1 M-1 sec-1 at 37 and 22 degrees C, respectively. The dissociation of [125I]hCG from theca interna was a slow biphasic process with only 40% of specifically bound [125I]hCG being liberated after 8 h at 37 degrees C. Unlabelled hCG and LH, but not FSH, prolactin, GH, TSH or GnRH, inhibited [125I]hCG binding to theca interna. The specific binding of [125I]hCG to theca interna was saturable and equilibrium binding data produced a linear plot when fitted to the Woolf equation. The equilibrium dissociation constant (Kd) and maximum binding capacity (Bmax) calculated from Woolf plots were 0.21 +/- 0.02 nM (mean +/- SEM) and 34 +/- 4 fmoles/mg protein, respectively. Constants for [125I]hCG binding to granulosa cells and luteal tissue, respectively, were 0.29 +/- 0.02 and 0.31 +/- 0.04 nM for the Kd values and 32 +/- 6 and 116 +/- 13 fmoles/mg protein for the Bmax values. [125I]hCG binding constants for small (less than 8 mm dia.) and large (greater than or equal to 8 mm dia.) follicles (healthy or atretic) were not significantly different. In addition, there was no difference in the [125I]hCG binding constants of healthy and atretic follicles (large or small).(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D006063:Chorionic Gonadotropin / Q000378:metabolism*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D009928:Organ Specificity; D006080:Ovarian Follicle / Q000378:metabolism*; D010053:Ovary / Q000378:metabolism; D010477:Perfusion; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011974:Receptors, LH; D013799:Theca Cells / Q000378:metabolism*
D006063:Chorionic Gonadotropin; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D011974:Receptors, LH; C041222:iodo-chorionic gonadotropin