Autoradiographical localization of oxytocin-binding sites in the guinea-pig ovary at different stages of the oestrous cycle

Abstract

The discovery that oxytocin is synthesized and stored in corpora lutea of ruminants has fostered a renewed interest in the possible roles of oxytocin in ovarian function. In the present study we describe the distribution of binding sites for oxytocin in the guinea-pig ovary. Sections were reacted with a radioiodinated oxytocin antagonist (125I-labelled OTA) to yield autoradiograms on film. Specific binding sites for oxytocin were defined as those which bound 0.05 nmol 125I-labelled OTA/l and where 1 mumol non-radioactive oxytocin/l displaced the radioactivity. 125I-Labelled OTA consistently labelled the ovarian stroma and the theca interna, but not the corpora lutea, the granulosa cells or the theca externa. The amount of 125I-labelled OTA bound to ovarian stroma and theca interna was high in animals killed during dioestrus, and low during and shortly after oestrus. These data suggest that the binding sites are regulated by steroid hormone levels and that in the guinea-pig ovary oxytocin could exert a role in follicular steroidogenesis, maturation or ovulation rather than in luteal function. Oxytocin-binding sites were also shown in the uterus but their numbers varied only slightly during the cycle.

G protein expression and second messenger formation in human granulosa cells

“…The oxytocin receptor is thought to be coupled to PLC activation via n and, when the cells were challenged with oxytocin, there was rapid accumulation of inositol phosphates and an increase in intra¬ cellular calcium, demonstrating an active PLC-InsP3 pathway. Oxytocin is produced by granulosa/luteal cells in ruminants (Jones and Flint, 1988;Camier et al, 1991) and humans (Guillou et al, 1992), and the oxytocin receptor is expressed in the ovary (Fuchs et al, 1990;Zhang et al, 1991;Kimura et al, 1993). This component may represent a¡ stimulation of PLC.…”

Effect of Intravenous Treatment with the Oxytocin Antagonist Atosiban on Circulating Progesterone in the Ewe

“…In nonpregnant women, oxytocin-binding sites (Fuchs et al, 1990) and oxytocin receptor mRNA were at the highest concentration in late luteal phase. Oxytocin positive staining in the ovarian stroma and theca interna was maximal during diestrus (Zhang et al, 1991). In the cow ovary, oxytocin staining was found in the stroma and CL with peak concentrations around the time of luteolysis (Fuchs et al, 1990).…”