Abstract:
The concentration and affinity of luteinizing hormone (LH) receptors in bovineluteal tissues during the oestrous cycle and pregnancy were investigated byScatchard analysis of the binding of <emph type="7">125I-labeled humanchorionic gonadotropin. Corpora lutea (CL) were classified into five stages ofthe oestrous cycle and three stages of pregnancy. The concentration of LHreceptors sharply increased from the early I stage of the oestrous cycle (Days2-3; 3.09 fmol mg<emph type="7">-1 protein) to the early II stage(Days 5-6; 9.44 fmol mg<emph type="7">-1 protein) and thenremained constant until the late luteal stage (Days 15-17;8.14-9.56 fmol mg<emph type="7">-1 protein). The LH receptorscould not be analysed in the regressed luteal tissue due to the small amountsof binding. There was no significant difference in the concentrations of LHreceptors (5.63-9.64 fmol mg<emph type="7">-1 protein) among thethree stages of pregnancy. Moreover, the concentrations of the receptors inthe CL of pregnancy were comparable to those in the mid-cycle CL. The bindingaffinity did not change significantly during the oestrous cycle and pregnancy.Based on these results, it is assumed that the luteal function during theentire period of pregnancy might be regulated, at least in part, by LH, whichis mediated via its specific receptors, and that the luteal function duringpregnancy seems not to be regulated by changes in the binding capacity andaffinity of LH receptors. To understand the physiological roles of LH inregulating luteal function in pregnant cows, further studies are required.