Effect of an oxytocin receptor antagonist on ovarian and uterine synthesis and release of prostaglandin F2α in pseudopregnant rats

MOTTA, ALICIA BEATRIZ; FRANCHI, ANA MARIA; FALETTI ALICA; FRANCHI ANA MARIA

PROSTAGLANDINS LEUKOTRIENES AND ESSENTIAL FATTY ACIDS

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 1996 vol. 54 p. 95 - 100

0952-3278

There is substantial experimental evidence suggesting that oxytocin has a role in luteolysis in ruminates.Endogenous pulses of uterine prostaglandin (PG) F2~ occur synchronously with pulses of oxytocin during luteolysis;leading us to propose a possible feedback loop between uterine PGF2~ and luteal oxytocin. In rats, the mechanismwhereby oxytocin acts has not been well elucidated.In the present report, the effects of an oxytocin receptor antagonist in pseudopregnant rats were investigated.Pseudopregnancy was induced in immature female rats by gonadotrophin treatment; this resulted in the formation ofcorpus luteum that remained functional for 9 + 1 days. The pseudopregnant rats were assigned to one of the followingfour groups. In the first group the relationship between the release of ovarian and uterine PGF2~ was tested. We alsostudied the serum progesterone during the pseudopregnancy. We found that PGF2~ released into the incubationmedium from ovaries of pseudopregnant rats increased (p < 0.05) and was maximal on day 9 of pseudopregnancy.This concentration remained high until day 10 of pseudopregnancy and then decreased. The PGF2~ released from theuterus to the incubation medium rose (p < 0.05) on day 8 of pseudopregnancy and reached the peak value on day 10.The serum progesterone was increased (p < 0.001) on day 2 of pseudopregnancy and was greater on day 5(p < 0.001).The second and third group received a specific oxytocin receptor antagonist (1-deamino-2-O-methyltyrosine) in twodifferent concentrations (0.05 or 0.2 gmol/I) before the peak of PG release. Both doses employed decreased(p < 0.001) the release into the incubating medium of PGF2~ from ovaries and uterus. Indeed, after the treatment, theprogesterone levels were higher (p < 0.001 ) than control on day 10 of pseudopregnancy. In the fourth group, a potentinhibitor of cyclooxygenase activity was administered on day 8 of pseudopregnancy into the ovarian bursa. The serumprogesterone levels increased (p < 0.01) compared to control suggesting a possible role of ovarian PG in the luteolyticphase of the corpus luteum regression. Thus, our findings show that oxytocin is luteolytic in pseudopregnant rats andthis action is mediated by oxytocin receptors, as it was blocked by a specific oxytocin receptor antagonist.