Reprod Dom Anim 24\ 052Ð055 "1999# Þ 1999 Blackwell Wissenschafts!Verlag\ Berlin ISSN 9825!5657 Direct Involvement of Luteinizing Hormone in Uterine Function M Shemesh 0\2 \ D Mizrachi 0 \ M Gurevich 0 \ Y Stram 1 \ LS Shore 0 and MJ Fields 3 0 Departments of Hormone Research and 1 Virolo`y\ Kimron Veterinary Institute and 2 Koret School of Veterinary Medicine\ Bet Da`an\ Israel^ 3 Animal Science Department\ University of Florida\ Gainesville\ FL\ USA Contents The e}ect 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 82 kDa receptor protein[ Both LH!R protein and its mRNA were also found in the uterine vein but mainly at pre!oes! tus:oestrus[ Incubation of cervical minces from the luteal phase with LH signi_cantly increased "p ³ 9[94# the intracellular cAMP\ inositol phosphate and cyclooxygenase as well as the production of PGE 1 but not PGF 1a [ Induction of endometrial cyclooxygenase by LH is associated with release of PGF 1a in the late luteal phase and 1 to 3 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 signi_cantly higher than at other stages of the cycle[ Incubation of uterine vein minces from pre!oestrus:oestrus with LH signi_cantly increased intracellular concentration of cyclooxygenase as well as production of both PGE 1 and PGF 1a [ The presence of physio! logically active LH!R in the uterine tissue suggests a direct involvement of LH in uterine function\ i[e[ uterine relaxation by cAMP and PGE 1 and regression of the corpus luteum by uterine PGF 1a [ Introduction It is widely believed that prostaglandin F 1a "PGF 1a # released from the uterus under the in~uence of oxytocin of ovarian "corpus luteum# origin is responsible for regression of the cyclic corpus luteum in cattle[ PGF 1a leaving the uterus via the common utero!ovarian vein\ is thought to be transferred by a counter!current mech! anism to the closely opposed ovarian artery and then be transported directly to the corpus luteum\ thus avoiding rapid metabolism in the pulmonary circulation[ Fur! thermore PGF 1a of uterine origin is thought to stimulate the release of additional oxytocin from the corpus luteum[ However\ endometrial cyclooxygenase is regulated by several hormones "e[g[ estradiol 06b\ progesterone\ LH\ FSH# and oxytocin is only a single player in a complex interplay of factors "Shemesh et al[ 0883\ 0885\ 0886b\ 1999^ Freidman et al[ 0884^ Fuchs et al[ 0884\ 0885^ Izhar et al[ 0881^ Mizrachi and Shemesh 0888a\b#[ The current paper summarizes the results on the role of LH in the control of cyclooxygenase and prostanoid synthesis in the reproductive tractÐendometrium\ myometrium\ cervix and uterine vein "Shemesh et al[ 0883\ 0885\ 0886b\ 1999^ Freidman et al[ 0884^ Mizrachi and Shemesh 0888a#[ Using these tissues\ de_nitions were proposed for the following] "0# the expression of LH receptor "LH!R# and its mRNA during the oestrous cycle^ U[ S[ Copyright Clearance Center Code Statement] 9825Ð5657:1999:2492Ð9052,04[99:9 "1# the e}ect of LH on cyclooxygenase levels and pro! duction of uterine prostanoids^ and "2# the mechanism of action of the LH signal to increase uterine prostanoid synthesis[ LH receptor in cervix\ myometrium\ endometrium and uterine vein The presence of high!a.nity receptors in the bovine uter! ine tract was initially demonstrated in the bovine endo! metrium "Freidman et al[ 0884#[ It was shown that bovine endometrium contains LH:hCG binding sites that peaked on days 04Ð06 after oestrus "The oestrous cycle in the cows is 19 days#[ Thereafter the LH:hCG binding sites dropped to nondetectable level during the follicular stage "days 07Ð19^ oestrus and ovulation#[ Further stud! ies\ using the cervix and myometrium "Mizrachi and Shemesh 0888a^ Shemesh et al[ 0883\ 0885\ 0886b#\ dem! onstrated that the receptor concentrations\ as measured by Western blot analysis\ were comparable to LH recep! tor mRNA signal strength\ indicating that the receptor protein formation is probably regulated at the tran! scriptional level[ In the cervix and myometrium\ the maxi! mal receptor concentration was during the late luteal phase "days 01Ð05#[ The cervix\ myometrium and uterine vein "but not uterine artery# were found to have a LH receptor mRNA transcript essentially identical to that found in the bovine corpus luteum[ These tissues also contained a 82 kDa immunoreactive receptor protein that bound to rat anti!LH receptor antibody in Western blots[ However\ in contrast to uterine tissues\ the LH receptor mRNA and LH receptor were maximally expressed in the uterine vein from cows in pre!oestrus:oestrus com! pared to cows in luteal or postovulatory phases[ The temporal relationship between the LH receptor con! centration and the phase of the cycle are illustrated in Fig[ 0 for endometrium and uterine vein[ Effect of LH on uterine cyclooxygenase To determine the physiological signi_cance of LH!R in the reproductive tissue\ in vitro incubations of uterine tissues were carried out in the absence or presence of LH "09 ng:ml#[ The level of cyclooxygenase was determined by Western blot using an antibody to ram seminal vesicle cyclooxygenase[ In the uterine vein\ induction of cycloox! ygenase by LH "three!fold increase# was maximal in pre! oestrus:oestrus cows[ In contrast\ LH induction of cyclooxygenase in the endometrium "two!fold increase# and cervix "79) increase# was maximal during the luteal