Oxytocin and ovarian function

(1) Oxytocin is synthesized in the luteal cells of all species so far studied, including the human. Vasopressin is also synthesized, but at a much lower rate. (2) The oxytocin-neurophysin gene is expressed in granulosa cells and granulosa-derived luteal cells but not in theca cells. Ovulation or spontaneous luteinization initiates the gene expression which peaks in the early luteal phase and ceases around mid-cycle. (3) Luteal oxytocin concentrations rise with considerable delay after the peak of specific mRNA and reach maximal levels around mid-cycle. Oxytocin concentrations fall to low levels in the late luteal phase and in pregnancy. (4) Thecal tissue produces substances such as catecholamines and ascorbic acid that stimulate oxytocin secretion in granulosa cells. The adrenergic innervation of thecal tissue provides a source of catecholamines and may therefore serve a modulatory function in ovarian oxytocin secretion. (5) Oxytocin has little or no direct effect on luteal progesterone production. (6) Oxytocin inhibits LH-stimulated prostacyclin production in luteal cells of cows. Oxytocin may induce the release of PGF-2 alpha or lipo-oxygenase products from the ovary but this has not yet been documented. (7) PGF-2 alpha releases oxytocin from the ovary but does not turn off its synthesis. (8) The concept that ovarian oxytocin participates in the luteolytic process is gaining acceptance. In some species (sheep, goat) ovarian oxytocin acts as a hormone causing PGF-2 alpha release from the uterus. In others it acts in a paracrine or autocrine fashion on ovarian prostanoid production (cow, possibly primates).(ABSTRACT TRUNCATED AT 250 WORDS)