Direct involvement of luteinizing hormone in uterine function

The effect of bovine LH on bovine uterine tissue from three phases of the oestrous cycle was studied. It was found that in the luteal phase the endometrium, myometrium and cervix contain a LH receptor (LH-R) mRNA transcript and the 93 kDa receptor protein. Both LH-R protein and its mRNA were also found in the uterine vein but mainly at pre-oestus/oestrus. Incubation of cervical minces from the luteal phase with LH significantly increased (p < 0.05) the intracellular cAMP, inositol phosphate and cyclooxygenase as well as the production of PGE₂ but not PGF(2α). Induction of endometrial cyclooxygenase by LH is associated with release of PGF(2α) in the late luteal phase and 2 to 4 days postovulation. In contrast, in the pre-oestrous/oestrous uterine vein, the signal for the transcript for LH-R and the LH-R protein was significantly higher than at other stages of the cycle. Incubation of uterine vein minces from pre-oestrus/oestrus with LH significantly increased intracellular concentration of cyclooxygenase as well as production of both PGE₂ and PGF(2α). The presence of physiologically active LH-R in the uterine tissue suggests a direct involvement of LH in uterine function, i.e. uterine relaxation by cAMP and PGE₂ and regression of the corpus luteum by uterine PGF(2α).