The final process in the development of a mature, fertilizable oocyte is the release of the oocyte from within the follicle wall enclosure (= Ovulation). While many studies have been directed at the hormonal regulation of ovulation, none have been able to successfully delineate this control and virtually nothing is known about the mechanism of action of putative ovulatory hormones. A better understanding of the hormonal regulation of ovulation could ultimately contribute to 1) the development of different and possibly more effective contraceptives and 2) an increase in the ability to artificially stimulate oocyte production for the control of fertility. The long-term goals are to understand the mechanism by which ovulation is controlled at the follicle level, the hormones that are involved, and how these hormones act. On the basis of recent published research a new model is advanced in this proposal. In this model, ovulatory agonists stimulate the phosphatidylinositol (PI) cycle and through secondary messenger of the PI cycle, subsequently stimulate protein kinase C (PKC). In turn, PKC acts on ovulation in part, through the production of a lipoxygenase product(s). In this proposal, new investigations are presented that will look at 1) the effects of cyclooxygenase products, such as PGE2 and PGF2alpha on the stimulation of the PI cycle in the follicle, 2) the stimulation of ovulation by various lipoxygenase products such as leukotrienes and hydroxyeicosatetraenoic acids, and 3) the mechanism by which PKC stimulates lipoxygenase synthesis in the follicle. Effects of cyclooxygenase products on PI cycling will be studied using radiolabeled myoinositol incorporation. PKC control of lipoxygenase will be completed using radiolabeled arachidonic acid release from phospholipids and labeled arachidonic acid incorporation, and the effects of lipoxygenase products on ovulation will be investigated using an in vitro incubation system. The experiments will be conducted using established fish model systems. In the study of ovulation, lower vertebrate models have a particular advantage over mammalian models in that 1) there are thousands of synchronously developing oocytes/female with which to experiment, 2) the follicles of fish ar large relative to many popular mammalian models, 3) the individual follicles of fish are extremely easy to incubate for long periods of time in simple in vitro systems and 4) fish are easier and less costly to procure and maintain. Though phylogenetic differences may exist between fish and mammals in the higher level control of reproduction, published research suggests that follicular processes at the cellular level for the control of ovulation may be very similar between these vertebrates.
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|Goetz, F W; Bradley, J A (1994) Stimulation of in vitro ovulation and contraction of brook trout (Salvelinus fontinalis) follicles by adrenaline through alpha-adrenoreceptors. J Reprod Fertil 100:381-5|
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|Hsu, S Y; Goetz, F W (1992) Oxoanions stimulate in vitro ovulation and signal transduction pathways in goldfish (Carassius auratus) follicles. Am J Physiol 263:E943-9|