Role of progesterone and oestradiol in the regulation of uterine oxytocin receptors in ewes

Abstract

Summary. The interaction between oestrogen and progesterone in the regulation of the uterine oxytocin receptor in sheep was evaluated by measuring the binding of oxytocin to membrane preparations of caruncular and intercaruncular endometrium and myometrium. Ovariectomized ewes were assigned in groups of five to each cell of a 4 \m=x\2 factorial design. The four treatments were (a) vehicle (maize oil) for 12 days, (b) progesterone (10 mg day\m=-\1) for 9 days, (c) progesterone for 9 days followed by maize oil until day 12 and (d) progesterone for 12 days. The two oestradiol treatments consisted of the administration of implants in the presence or absence of oestradiol. The ewes were killed on day 10 (group b) or day 13 (groups a, c and d) for collection of uterine tissues. The response of the caruncular and intercaruncular endometrium to the treatments was similar. In the absence of oestradiol, treatment with progesterone continuously for either 9 or 12 days reduced the concentration of the oxytocin receptor in comparison with both the control and the progesterone withdrawal group (in which values were similar). The presence of oestradiol reduced the receptor concentrations in control and both 9-and 12-day continuous progesterone treatment groups, but enhanced the concentration in the progesterone withdrawal group. The myometrial oxytocin receptors responded in a similar way to those in the endometrium to progesterone treatment alone, but the addition of oestradiol produced no further effect. In conclusion, progesterone and oestradiol caused downregulation of the endometrial oxytocin receptor. On the other hand, progesterone withdrawal, similar to that which occurs during luteolysis, increased receptor density in the presence of oestradiol. Progesterone may influence the response of the myometrium to oxytocin by causing a reduction in receptor density.

Cigarette smoke extract enhances oxytocin-induced rhythmic contractions of rat and human preterm myometrium

“…However, it remains unclear whether the inhalation of cigarette smoke directly enhances the expression of OTR mRNA in the myometrium. Since OTR levels are known to be upregulated through progesterone regression, which occurs during luteolysis in the ewe (Hixon & Flint 1987, Zhang et al 1992, the increased expression of OTR mRNA in the pregnant rat myometrium, in the smoking group, may be caused indirectly through progesterone regression via luteolysis. Thus, inhalation of cigarette smoke may damage the function of the corpus luteum in the pregnant rat.…”

“…This uncertainty is based upon the findings that progesterone decreases the levels of uterine OTR mRNA and protein in pregnant rats (Soloff et al 1983), and estrogen increases the levels of OTR in the rat uterus and in human-cultured myometrial cells (Soloff 1975, Adachi & Oku 1995. Additionally, it has been reported that OTR levels are upregulated through progesterone regression, which occurs during luteolysis in the ewe (Hixon & Flint 1987, Zhang et al 1992. Therefore, the increased expression of OTR mRNA in the pregnant rat myometrium in the smoking group may be caused indirectly through progesterone regression via luteolysis.…”

Efeito do tratamento com progesterona e do diâmetro folicular nas características histológicas e moleculares uterinas em vacas Nelore em anestro pós-parto

“…Alguns experimentos indicaram inclusive um possível efeito inibitório do E2 nos OTR na ausência de pré-exposição à P4 (VALLET et al, 1990;ZHANG et al, 1992), enquanto o E2 após exposição à P4, causa grande estímulo à expressão de OTR e à secreção de PGF2α estimulada pela OT em bovinos e ovinos (LAU et al, 1993;KAMINSKI et al, 1997;WALKER et al, 1997). É possível, portanto, que a pré-exposição à P4 seja necessária para que o E2 exerça seus efeitos clássicos mais relevantes sobre o endométrio.…”

“…Estudos em ovelhas demonstraram que apenas a queda na concentração circulante de P4 foi suficiente para iniciar a expressão de OTR, mas a administração de E2 no momento da retirada da P4 maximizou o estímulo à expressão gênica de OTR (LEAVITT et al, 1985;VALLET et al, 1990;ZHANG et al, 1992). Além disso, diversos estudos in vivo demonstraram que o E2 estimula a expressão endometrial de OTR (HIXON & FLINT, 1987;BEARD & LAMMING, 1994;SPENCER et al, 1995) e um estudo in vitro confirmou o efeito do E2 em acelerar a expressão gênica de OTR sem, no entanto, alterar a concentração final de mRNA de OTR (LEUNG & WATHES, 1999).…”

“…Estudos em ovelhas demonstraram que apenas a queda na concentração circulante de P4 foi suficiente para iniciar a expressão de OTR, mas a administração de E2 no momento da retirada da P4 maximizou o estímulo à expressão gênica de OTR (LEAVITT et al, 1985;VALLET et al, 1990;ZHANG et al, 1992), pois o E2 acelera a expressão gênica de OTR (LEUNG & WATHES, 1999) e possivelmente ativa OTR pré-existentes (HIXON & FLINT, 1987;PARKINSON et al, 1990).…”