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Department of Physiology (T.P., L.N. M.P., I.H.), University of Turku, Fin-20500 Turku, Finland; Department of Physiology (F-P.Z.), University of Helsinki, Biomedicum, Fin-00014 Helsinki, Finland; and Institute of Reproductive and Developmental Biology (I.H.), Imperial College London, London W12 0NN, United Kingdom
Address all correspondence and requests for reprints to: Professor Ilpo Huhtaniemi, Institute of Reproductive and Developmental Biology, Imperial College London, Du Cane Road, London W12 0NN, United Kingdom. E-mail: ilpo.huhtaniemi{at}imperial.ac.uk.
It is considered a dogma that a secretory peak of LH is indispensable as the trigger of ovulation. However, earlier studies on hypophysectomized rodents have shown that stimulation with recombinant FSH, devoid of any LH activity, is able to boost the final stages of follicular maturation and trigger ovulation. As the expression of ovarian LH receptors (LHRs) still persists after hypophysectomy, such studies cannot totally exclude the possibility that LHR activation is involved in the apparently pure FSH effects. To revisit this question, we analyzed in LHR knockout (LuRKO) mice the progression of folliculogenesis and induction of ovulation by human chorionic gonadotropin and human recombinant FSH treatments. The results provide clear evidence that follicular development and ovulation could not be induced by high doses of FSH in the absence of LHR expression. Ovarian histology and oocyte analyses indicated that follicular maturation did not advance in LuRKO mice beyond the antral follicle stage. Neither were ovulations detected in LuRKO ovaries after any of the gonadotropin treatments. The ovarian resistance to FSH treatment in the absence of LHR was confirmed by real-time RT-PCR and immunohistochemical analyses of a number of gonadotropin-dependent genes, which only responded to the treatments in wild-type control mice. Negative findings were not altered by estradiol priming preceding the gonadotropin stimulations. Hence, the present study shows that, in addition to ovulation, the expression of LHR is essential for follicular maturation in the progression from antral to preovulatory stage.
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