Bovine cyclic endometrium contains high-affinity luteinizing hormone/human chorionic gonadotropin binding sites

Area of Science:

• Reproductive Biology
• Endocrinology
• Molecular Endocrinology

Background:

• High-affinity luteinizing hormone/human chorionic gonadotropin (LH/hCG) binding sites are known in several species' uteri.
• Understanding these sites in cattle is crucial for reproductive research.

Purpose of the Study:

• To characterize LH/hCG binding sites in bovine endometrium.
• To determine the presence and concentration of these sites throughout the bovine estrous cycle.
• To compare endometrial LH/hCG binding with that of luteal cells.

Main Methods:

• Radioreceptor assays using endometrial membrane homogenates.
• Specificity testing with various hormones (FSH, prolactin, eCG).
• Western blot analysis for cyclooxygenase (COX) expression.

Main Results:

• LH/hCG binding sites were found in bovine endometrium, with specificity for hCG and some cross-reactivity with eCG.
• Receptor concentrations varied during the estrous cycle, with higher levels on Days 2-4 and 15-17.
• Endometrial binding capacity was lower than that of luteal cells, but affinity constants were similar.
• Cyclooxygenase (COX) expression was strongest at Days 15-17 of the estrous cycle.

Conclusions:

• Bovine endometrium possesses specific LH/hCG binding sites whose concentration fluctuates during the estrous cycle.
• These endometrial sites may play a role in bovine reproduction, distinct from luteal cell binding.
• The temporal expression of COX aligns with periods of high endometrial LH/hCG receptor concentration.