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Evidence for a direct effect of oxytocin on the bovine corpora lutea of early pregnancy
xvi 31
Abstracts
Control of Gestradiol Production in the Pig Follicle J. Watson and K.S. Dodson Department of Biochemistry, University of Strathclyde, The Todd Cantre, Street, Glasgow. G4 ONR. Scotlaud.
31 Taylor
The pre-ovulatory increase in osstradiol production by the maturing follicle is Previous studies in the rat and the pig have characteristic of reproductive cycles. demonstrated that follicular oestradiol production is controlled by FSH stimulation of the aromatare enzyme system, located within the granulosa cell. However the mechanism of FSH stimulation is unknown. Studiee in pig follicles have shown that FSH will also stimulate production of prortaglandin F2a and that PGFz,, but not The PGE2, stimulates oestradiol production when measured by radioimmunoassay. present study was designed to investigate the possibility that prortaglandins play a direct role in androgen aromatiaation and therefore in control of oestradiol production. Experiments were performed using halved pig follicles (0.9 - 1.0 cm diameter) and granulosa cells prepared by aspirating follicles (2 x lo6 cellr/ follicle). The effects of FSH, PGF2u, PGE2 and indomethacin, an inhibitor of prostaglandin synthesis, on conversion of [3H] testosterone (1 &i) to [5H] oestradiol were studied during 3h static incubations in Medium 199 (5 ml) at 37’C. [3H] oestradiol was isolated by partition extraction with toluene/petroleum ether and sodium hydroxide followed by T. L. C. In both follicles and granulora cells FSH and PGF2u increared the incorporation of [%-I] testosterone into oeatradiol by 100% compared to controls. PGE2 on the other hand reduced the incorporation to SO% of the control value, whilst indomethacin reduced the incorporation to 20% and completely inhibited the FSH stimulation. The results suggest that prostaglandins may be involved in the mechanism of androgen aromatization. The oppodng effects of the two prostaglandins may be an important factor in controlling oestradiol production in the prbovulatory follicle.
32 Evidence for a Direct Effect of Oxytocin on the Bovine Corpora Lutea of Early Pregnancy G. J. S. Tan, B. Tweedale and J. S. G. Biggs, Dept. Obstetrics and Gynaecology, University of Queensland, Royal Brisbane Hospital. Published studies have suggested that oxytocin may be involved in the regulation of the oestrous cycle in both the sheep and the cow. The site of action is thought to be at the uterus where oxytocin acts to sttiate the release of prostaglandins which the uterus is apparently not involved in the coninitiate luteolysis. In the Wn, trol of the menstrual cycle, and a direct effect of oxytocin on the ovary is a possibility in the hunw, as well as in other species. In view of this, the direct effect of oxytocin on bovine luteal cella was studied. Corpora lutea were obtained from cows in early pregnancy and isolated luteal cells prepared using collagenase Worthington Typa I). Aliqwts of approximately 10' cells were incubated at 37 C in 95% Or and 5* COr in 0.5 ml Ham's P 10 medium with various test substances for 3 hours. The incubations ware terminated by freezing the sasgles in dry ice and the progesterone extracted with diethyl ether prior.to radioismnosssay. Oxytocin influenced progesterone production in a&se relatedmanner. Basal progesterone productionwas stisulated to over 60% of that induoed by hCG (10 iu/ml) by a low concentration of oxytocin (4 nu/ml) whereas a high oxytooin level (BOO mu/ml) had little effect. The response of the luteal cells to hCG was inhibited by over 50% by the high oxytocin concentration but not with the low concentration. These data provide evidence for a direct effect of oxytocin on the ovary. At low concentration of oxytocin, this hormone is highly luteotrophic and gives little interference with the luteotrophic action of KG. High oxytocin ooncentration is not luteotrophic but mark.edlyinhibits the luteotrophic effect of hCG. Suppression of oxytocin release may thus be important in corpus luteum maintenance &ring early pregnancy and should be considered in studies of the human corpus luteum.
Abstracts
Control of Gestradiol Production in the Pig Follicle J. Watson and K.S. Dodson Department of Biochemistry, University of Strathclyde, The Todd Cantre, Street, Glasgow. G4 ONR. Scotlaud.
31 Taylor
The pre-ovulatory increase in osstradiol production by the maturing follicle is Previous studies in the rat and the pig have characteristic of reproductive cycles. demonstrated that follicular oestradiol production is controlled by FSH stimulation of the aromatare enzyme system, located within the granulosa cell. However the mechanism of FSH stimulation is unknown. Studiee in pig follicles have shown that FSH will also stimulate production of prortaglandin F2a and that PGFz,, but not The PGE2, stimulates oestradiol production when measured by radioimmunoassay. present study was designed to investigate the possibility that prortaglandins play a direct role in androgen aromatiaation and therefore in control of oestradiol production. Experiments were performed using halved pig follicles (0.9 - 1.0 cm diameter) and granulosa cells prepared by aspirating follicles (2 x lo6 cellr/ follicle). The effects of FSH, PGF2u, PGE2 and indomethacin, an inhibitor of prostaglandin synthesis, on conversion of [3H] testosterone (1 &i) to [5H] oestradiol were studied during 3h static incubations in Medium 199 (5 ml) at 37’C. [3H] oestradiol was isolated by partition extraction with toluene/petroleum ether and sodium hydroxide followed by T. L. C. In both follicles and granulora cells FSH and PGF2u increared the incorporation of [%-I] testosterone into oeatradiol by 100% compared to controls. PGE2 on the other hand reduced the incorporation to SO% of the control value, whilst indomethacin reduced the incorporation to 20% and completely inhibited the FSH stimulation. The results suggest that prostaglandins may be involved in the mechanism of androgen aromatization. The oppodng effects of the two prostaglandins may be an important factor in controlling oestradiol production in the prbovulatory follicle.
32 Evidence for a Direct Effect of Oxytocin on the Bovine Corpora Lutea of Early Pregnancy G. J. S. Tan, B. Tweedale and J. S. G. Biggs, Dept. Obstetrics and Gynaecology, University of Queensland, Royal Brisbane Hospital. Published studies have suggested that oxytocin may be involved in the regulation of the oestrous cycle in both the sheep and the cow. The site of action is thought to be at the uterus where oxytocin acts to sttiate the release of prostaglandins which the uterus is apparently not involved in the coninitiate luteolysis. In the Wn, trol of the menstrual cycle, and a direct effect of oxytocin on the ovary is a possibility in the hunw, as well as in other species. In view of this, the direct effect of oxytocin on bovine luteal cella was studied. Corpora lutea were obtained from cows in early pregnancy and isolated luteal cells prepared using collagenase Worthington Typa I). Aliqwts of approximately 10' cells were incubated at 37 C in 95% Or and 5* COr in 0.5 ml Ham's P 10 medium with various test substances for 3 hours. The incubations ware terminated by freezing the sasgles in dry ice and the progesterone extracted with diethyl ether prior.to radioismnosssay. Oxytocin influenced progesterone production in a&se relatedmanner. Basal progesterone productionwas stisulated to over 60% of that induoed by hCG (10 iu/ml) by a low concentration of oxytocin (4 nu/ml) whereas a high oxytooin level (BOO mu/ml) had little effect. The response of the luteal cells to hCG was inhibited by over 50% by the high oxytocin concentration but not with the low concentration. These data provide evidence for a direct effect of oxytocin on the ovary. At low concentration of oxytocin, this hormone is highly luteotrophic and gives little interference with the luteotrophic action of KG. High oxytocin ooncentration is not luteotrophic but mark.edlyinhibits the luteotrophic effect of hCG. Suppression of oxytocin release may thus be important in corpus luteum maintenance &ring early pregnancy and should be considered in studies of the human corpus luteum.