Intrauterine pressure was monitored in vivo in oestrogen-treated ovariectomized ewes before, during and after treatment with progesterone (50 mg s.c./day for 3 days). Progesterone reversibly reduced the frequency and amplitude of myometrial activity and abolished uterine reactivity to oxytocin (i.v.) and PGF-2alpha (intrauterine infusion). The rate of rise of intrauterine pressure during active pressure cycles was significantly reduced. These results confirm that the action of progesterone on the ovine myometrium is comparable to the classic progesterone 'block'. The intrauterine infusion of PGF-2alpha (10 microgram/min), which elicited a marked mechanical response in the control animals, failed to stimulate the progesterone-'blocked' uterus, suggesting that the inhibition produced by progesterone is due to a direct action of the hormone on the uterine muscle and not to an indirect mechanism operating through endometrial prostaglandin output.
PMID 621702 621702 DOI 10.1530/jrf.0.0520087 10.1530/jrf.0.0520087
Cite this article
Lye, S. J., & Porter, D. G. (1978). Demonstration that progesterone 'blocks' uterine activity in the ewe in vivo by a direct action on the myometrium. Journal of reproduction and fertility, 52(1), 87-94. https://doi.org/10.1530/jrf.0.0520087
Lye SJ, Porter DG. Demonstration that progesterone 'blocks' uterine activity in the ewe in vivo by a direct action on the myometrium. J Reprod Fertil. 1978;52(1):87-94. doi:10.1530/jrf.0.0520087
Lye, Stephen J., and D. G. Porter. "Demonstration that progesterone 'blocks' uterine activity in the ewe in vivo by a direct action on the myometrium." Journal of reproduction and fertility, vol. 52, no. 1, 1978, pp. 87-94.
Forty-eight uterine strips were excised from 24 New Zealand white rabbits and studied in vitro. Sixteen strips were examined when eight animals were 25 days pregnant, 24 strips when 12 animals were about 12 hours postpartum, and eight strips about 12 hours after four animals received a single dose of 5 mg. progesterone (P) at spontaneous delivery. When after repeated exposures to electric fields (60 cycles per second, alternating current, of optimum strength, four seconds' duration at intervals of 30 seconds) the approximately 0.5 Gm. strips developed approximately 40-50g wall tension (WT) in steady state, the field strength was reduced in graded steps from 12 v per 5 cm. to 10, 8, 6, 4 and 3 v per 5 cm. and WT recorded. By measuring the effect on WT of "decreasing electric field stimulation" (DEFS), myometrical excitably and threshold were characterized and quantitated. The technique is based on the relationship between the fraction of myometrial cells activated in the total cell population and WT. As the stimulus is decreased in graded steps from optimal to increasingly suboptimal, DEFS activates fewer and fewer cells reflected by the decrease in WT. Threshold is defined by the strength of the minimum electric field which provokes WT and subthreshold by the field strength which fails to excite. Thus fractional WT averages the excitability of cells in the tissue and thus DEFS characterizes this important parameter of uterine function and quantitates threshold under a variety of regulatory conditions. The comparative study of excised uteri in three different endocrine states showed that the regulatory conditions of normal pregnancy (P levels 9 ng. per milliliter) suppressed excitability and increased threshold (to 6 v per 5 cm.). Post partum (P levels 1 ng. per milliliter) excitability increased and threshold decreased (to 4 v per 5 cm.), unless P treatment prevented this characteristic change by suppressing excitability and increasing threshold (to 6 v per 5 cm.). Both regulatory agents, prostaglandin F2alpha (PGF2alpha) and its analogue ICI 81008, increased excitability and decreased threshold significantly in picogram per milliliter concentrations. However, this effect was observed only when the P levels were low. These compounds had little effect, even in manogram per milliliter concentrations, when the P levels were high. The studies also revealed a close relationship between threshold and spontaneous uterine activity. Low threshold promoted while high threshold suppressed spontaneous activity. In similar concentrations the oxytocic actions of PGF2alpha and ICI 81008 were similar but the effect of ICI 81008 was prolonged through strong binding at myometrical sites.
PROSTAGLANDINS (PGs) are being used increasingly as abortifacients although their precise mechanism of action is uncertain. One of the compounds frequently used is PGF2α, which has been shown to stimulate the myometrium in vitro1 and in vivo2. Whether or not the direct action of this agent on the uterine muscle alone is responsible for the interruption of pregnancy is not clear, but the long interval between infusion and abortion3 suggests that other mechanisms might be involved; for example, a luteolytic effect4–6. The prompt increase in uterine activity after treatment with prostaglandin, however, argues that the direct effect plays some part in the abortifacient action. Little is known of the influence of other myometrial regulatory agents such as the ovarian steroids on the uterine response to PGs. Accordingly we examined the influence of progesterone on myometrial responses to prostaglandin F2α in the rabbit, a species in which progesterone is known to have a blocking action on the uterine muscle7.
Samples of semen and cervical mucus were provided by 18 couples. Cervical mucus was obtained for each day possible and stored at 4 degrees C until all the samples were collected. Flat capillary tubes were loaded with the mucous samples and spermatozoa from the husband's semen sample were allowed to migrate through the cervical mucus (3 cm column) into culture medium. The spermatozoa recovered after migration through cervical mucus were assayed in vitro with zona-free hamster oocytes. Control experiments were carried out using spermatozoa from the same semen sample but prepared by the swimming-up technique. Altogether, 557 eggs in the control group and 1236 eggs in the experimental group were analysed, and the results demonstrated that the % of sperm penetration, the mean number of sperm decondensations per penetrated egg and the mean number of spermatozoa adhering per egg all had higher values (P less than 0.05) for the control samples than for the experimental samples. We suggest that cervical mucus modifies human spermatozoa, as measured by their interaction with zona-free hamster oocytes.
Reproductive EndocrinologyConception Cycle ProfilesConceiving vs Non-ConceivingProgesterone Markers
Hormonal profiles were obtained throughout 26 conception cycles and 27 non-conception control cycles. The pregnancies followed treatment (clomiphene or bromocriptine) in 12 women but were spontaneous in the remaining 14. No sustained significant difference between the various types of conception cycle was found for LH, FSH, oestradiol or progesterone concentrations. Prolactin concentrations varied widely, suggesting that mean cycle prolactin concentrations ranging from 45 to 760 mi.u./l are compatible with conception. Although there were no significant differences in progesterone secretion within the conception cycles, there were highly significant differences between the conception cycles and the non-pregnant control cycles. Mean progesterone concentrations in the conception group were higher (P less than 0.005) than those in the control women over Days 3-8 following the LH peak. This difference could only be partly accounted for by heterogeneity within the control group (15-20% of the control cycles had low progesterone concentrations and were probably subfertile. It is suggested that the higher conception cycle progesterone concentrations during the early part of the luteal phase may constitute a preimplantation component of the maternal recognition of pregnancy in women.