Rat myometrial activity in vivo: effects of oestradiol-17 beta and progesterone in relation to the concentrations of cytoplasmic progesterone receptors.
The amplitude, frequency and rate of rise of intra-uterine pressure cycles in rats (postpartum, ovariectomized) were unaffected by treatment with progesterone. Amplitude was also unaffected by a combination of treatments with progesterone and oestradiol-17 beta, which was adequate to ensure the survival of 84% of foetuses in ovariectomized pregnant rats. The failure of progesterone to influence myometerial activity could not be attributed to a lack of "true" progesterone receptors since these were present in the myometria of the test animals in concentrations exceeding those of oestrous animals. Evidence was obtained which suggested that a high-affinity binding protein, different from the "true" receptor may predominate in the myometrium of the pregnant rat. Oestradiol-17 beta in single or repeated doses of from 0.25 to 5 microgram, however, was found to reduce the frequency of pressure cycles but to increase significantly their rate of rise of pressure. There was a latency of 6--8 h in these effects of oestradiol. The possibility that inhibition of the myometrium by oestrogen may play a part in the preparation for parturition is discussed.
D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D009215:Myometrium / Q000187:drug effects*; D011247:Pregnancy; D011312:Pressure; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011980:Receptors, Progesterone / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects; D014599:Uterus / Q000187:drug effects*
D011980:Receptors, Progesterone; D011374:Progesterone; D004958:Estradiol