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Prostaglandin F2α (PGF2α) has regulatory (mainly luteolytic) effects in the ovary but the mechanism of action is not completely understood. Reverse transcriptase–polymerase chain reaction (RT–PCR) techniques were used to demonstrate the presence of mRNA encoding the PGF2α receptor (FP receptor) in human granulosa–lutein cells. Specific primers for the amplification of cDNA were designed and yielded a single product of 696 bp corresponding to the FP receptor. The identity of this product was verified by sequencing. Fluprostenol, a selective FP receptor agonist, activated phospholipase C (PLC) and increased intracellular free calcium concentration, confirming the functional activation of the receptor. We have demonstrated by Western blotting that granulosa cells express PLC-β and PLC-γ isoforms. The cells responded to pervanadate with increased PLC activity and increased tyrosine phosphorylation, demonstrating a functional PLC-γ tyrosine kinase pathway. However, fluprostenol did not provoke any detectable tyrosine phosphorylation. Moreover, the effect of fluprostenol was inhibited through protein kinase C stimulation by phorbol 12,13-dibutyrate, and was not affected when cells were treated with phenylarsine oxide, which blocks tyrosine phosphorylation. These results suggest that the FP receptor activates PLC-β rather than PLC-γ isoforms. Fluprostenol-induced activation was pertussis toxin resistant. Granulosa cells express G proteins of the Gq family (resistant to pertussis toxin) and mRNA for both Gαq and Gα11 has been identified by RT–PCR. In conclusion, human granulosa cells have a functional FP receptor the effects of which are mediated through PLC-β activation probably via Gq/11.
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In brief
Seminal nerve growth factor induces ovulation in camelids by influencing the secretion of gonadotrophin-releasing hormone (GnRH) into the portal vessels of the pituitary gland. We show that the nerve growth factor-induced release of GnRH is not mediated directly through interaction with hypothalamic neurons.
Abstract
Ovulation in camelids is triggered by seminal nerve growth factor (NGF). The mechanism of action of NGF appears to occur via the central nervous system. In this study, we tested the hypothesis that NGF acts in the hypothalamus to induce GnRH release. To determine if NGF-induced ovulation is associated with a rise in NGF concentrations in the cerebrospinal fluid (CSF), llamas were i) mated with an urethrostomized male, ii) mated with intact male, or given intrauterine iii) seminal plasma or i.v.) saline (Experiment 1). To characterize the luteinizing hormone (LH) response after central vs peripheral administration, llamas were treated with saline (negative control) or NGF either by i.v. or intracerebroventricular (ICV) administration (Experiment 2). To determine the role of kisspeptin, the effect of ICV infusion of a kisspeptin receptor antagonist on NGF-induced LH secretion and ovulation was tested in llamas (Experiment 3). In Experiment 1, a surge in circulating concentrations of LH was detected only in llamas mated with an intact male and those given intrauterine seminal plasma, but no changes in CSF concentrations of NGF were detected. In Experiment 2, peripheral administration (i.v.) of NGF induced an LH surge and ovulation, whereas no response was detected after central (ICV) administration. In Experiment 3, the kisspeptin receptor antagonist had no effect on the LH response to NGF. In conclusion, results did not support the hypothesis that NGF-induced ovulation is mediated via a trans-synaptic pathway within the hypothalamus, but rather through a releasing effect on tanycytes at the median eminence.
