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A. of angiogenesis occur during the luteal transition in the absence of prolactin signaling. These modifications lead to the decrease of LH receptor expression and consequently to a loss of the enzymatic cascades necessary to produce adequate levels of progesterone which are required for the maintenance of pregnancy. strong class=”kwd-title” Keywords: ovary, fertility, physiology, prolactin receptor, mice Background Prolactin (PRL) is a multifunctional hormone involved in diverse processes such as luteal function and thus maintenance of the pregnancy [1], and has long been known for its luteotropic actions in rodents [2-5]. Hormonal responsiveness in the mammalian ovary involves complex cellular processes that are essential for organ function and which can be deleterious if inappropriately orchestrated. After ovulation, subsequent luteinization leads to the formation of the corpus luteum, which is an endocrine gland of limited lifespan. This resulting corpus luteum is a highly vascularized endocrine organ producing progesterone, essential for uterine preparation SC-144 and maintenance of pregnancy. The granulosa cells remaining in the postovulatory follicle undergo luteinization, which involves exit of the cells from the cell cycle, cellular hypertrophy, acquisition of steroidogenic morphology, and expression of cytochrome P450 cholesterol side chain cleavage. We previously demonstrated that female mice homozygous for a disruption SC-144 of PRL receptor (PRLR) gene are infertile due to a failure of implantation [6]. PRL SC-144 mediates its action via a single receptor, which is present in the corpus luteum during pregnancy and is also expressed in the uterus later in the pregnancy [7]. The PRL receptor is thus a key component regulating ovarian function and governing the regulation of progesterone secretion and, in fact PRL may trigger an early signal to induce the maintenance of the corpus luteum. In rodents, semi-circadian surges of PRL secretion are SC-144 induced by cervical stimuli, which are believed to be responsible for the conversion of the corpus luteum of pregnancy (CLP) from the corpus luteum (CL) of the cycle. The CLP secretes a sufficient progesterone amount to maintain pregnancy [8,9]. The factors SC-144 affecting sterility of PRLR-/- mice were attributed to multiple causes, in particular to the absence of sufficient progesterone to support implantation and subsequent placental development and maintenance [6]. Since the corpus luteum is the unique source of progesterone production in rodents, progesterone administration is able to rescue preimplantation egg development and embryo implantation in PRLR-/- female [10]. To better understand PRL receptor deficiency, we analyzed in detail follicular development, the ovulation process and the subsequent expression of specific mRNAs of enzymes involved in steroid production using RT-PCR and em in situ /em hybridization, in a time-dependent manner, during the first stages of early pregnancy of PRLR-/- females. The present study provides new evidence to support the importance of prolactin for survival of the luteal cells in pregnant mice. Materials and Methods Experimental animals Wild type and PRLR-/- female mice (129/Sv) were generated by intercrosses of heterozygous mice (PRLR+/-). Offspring were genotyped by PCR analysis as described previously [10]. The morning of finding a vaginal plug was designated day 0.5 of pregnancy. Animals were housed in a 12-hour day/night cycle Rabbit Polyclonal to NMDAR1 at 22C and relative humidity 50% with food and water ad libitum. Experimental designs and procedures are in agreement with the guidelines of the animal ethics committee of the Ministre de l’Agriculture. Analysis of estrous cycle Vaginal smears from 12 PRLR+/+ and 15 PRLR-/- 11-week-old females were collected every day for a 21-day period. Smears were streaked on slides and estrous cycle stages were determined. Egg collection and tissue preparation Eggs were recovered from the oviduct or uterus of the mice as previously described [6]. Wild type and PRLR-/- ovaries were collected on days 0.5, 1.5, 2.5 and 3.5 after observation of a vaginal plug, pregnancy was confirmed by recovery of eggs from the ampulla, the oviducts or from the uterine lumen. Ovaries were removed and fixed in Bouin’s fixative, embedded in paraffin and serially sectioned at 5 m, sections were stained with hematoxylin-eosin-safran. Ovarian tissues were fixed in 10% paraformaldehyde to perform immunohistochemistry of frozen sections. Hormone treatment To examine the response to gonadotropins and induction of sexual receptivity, female mice aged 4 weeks, were injected i.p. with 5 UI of Folligon? (PMSg: Pregnant Mare’s Serum gonadotropin, Intervet Inc., Millsboro, DE) to stimulate follicular growth. They were injected 48 h later with 5 UI of Chorulon? (hCG: human Chorionic Gonadotropin, Intervet, Millsboro, DE) to trigger ovulation and luteinization. After ovulation, oocytes were collected from the ampulla and counted after enzymatic dissociation.