Regulation of menstrual cycle and termination of pregnancy in the monkey by estradiol and PGF2 alpha

A role for prostaglandins in estrogen growth regulation

Several lines of evidence support the theory that estrogen increases prostaglandin F2 alpha (PGF2 alpha) receptor number and amplifies the intracellular response to the uterine mitogen, PGF2 alpha, in primary cultures of rabbit endometrium. It is proposed here that estrogen induction of growth in target tissues may be mediated through prostaglandins. Determination of prostaglandin receptor status and prostaglandin levels in estrogen dependent tumors could be of importance as diagnostic tools. The use of prostaglandin synthesis inhibitors and/or antagonists in the therapy of these tumors should be considered.

Peritoneal fluid 6-keto prostaglandin F1 alpha levels in women with endometriosis

Peritoneal fluid was collected from women undergoing investigations for infertility at laparoscopy performed during the luteal phase. The volume of fluid was recorded and concentrations of 6-keto prostaglandin F1 alpha were determined by radioimmunoassay. No difference was found in either the total amount or the concentration of 6-keto prostaglandin F1 alpha in the women with or without endometriosis. Furthermore, there was no difference in the volume of peritoneal fluid between these two groups of women. We conclude that 6-keto prostaglandin F1 alpha in peritoneal fluid is not associated with macroscopically visible endometriosis.

The concentration of 13,14-dihydro-15-keto prostaglandin F2 alpha and prostaglandin E2 in peritoneal fluid of infertile patients with and without endometriosis

Prostaglandin F2 alpha (PGF2 alpha) metabolite (13,14-dihydro-15-keto PGF2 alpha) and prostaglandin E2 (PGE2) were assayed in the cul-de-sac fluid aspirated from 15 patients with endometriosis, in saline peritoneal washings of 5 patients with unexplained infertility, and in 5 control subjects. The fluid from the cul-de-sac of patients with endometriosis showed wide variations in the concentrations of PGF2 alpha metabolite and PGE2. There was no correlation between the concentration of these prostaglandins (PGs) and the stage of the cycle. Saline peritoneal washings from patients with unexplained infertility had significantly higher concentrations of PGF2 alpha metabolite than the control subjects. The concentration of PGE2 in the saline peritoneal washings was higher in the group with unexplained infertility than in the control group; however, the difference was not significant. The concentration of PGF2 alpha metabolite and PGE2 in the peritoneal saline washings from patients with unexplained infertility were no different from the concentrations of these PGs in the peritoneal fluid (PF) from patients with endometriosis. PG concentration in PF of infertile patients with or without endometriosis is a new variable for evaluation in these patients.

Surgical induction of endometriosis in the rabbit: effects on fertility and concentrations of peritoneal fluid prostaglandins

The association of endometriosis and infertility is well know. However, the exact mechanisms involved remain unclear. To study the effect of endometriosis on fertility, an experimental model was developed using New Zealand White rabbits. Endometrium obtained from one uterine horn was surgically implanted into the peritoneum, and the viability of the implants was demonstrated histologically. Adipose tissue was implanted in another group of animals which served as a control. The induction of endometriosis significantly impaired fertility rates (25%) as compared with the control group (75%). The decrease in fertility was independent of adhesion formation and primarily due to a defect in ovulation; however, a postovulatory effect cannot be excluded. Peritoneal fluid prostaglandin (PG) F concentrations increased significantly after the induction of endometriosis, whereas PGE concentrations and the PGF:PGE ratio showed no change. There was no change in PGF or PGE levels in the control group. The increased PGF in peritoneal fluid may alter follicular rupture, ovum transport, corpus luteum function, or implantation, thus representing a mechanism by which endometriosis may cause infertility.

Effects of (15S)-15-methyl prostaglandin E2 alpha methyl ester and estrogens upon the corpus luteum and conceptus of the rhesus monkey

The corpus luteum inhibiting activity of (15S)-15-methyl prostaglandin F2 alpha methyl ester (15M-PGF2 alpha) was determined when given in combination with estrogens. Administration of 15M-PGF2 alpha alone (3 injections of 500 microgram each) to monkeys concomitantly receiving hCG reduced serum progesterone concentrations to 50% of values observed in control animals. Ethinyl estradiol or mestranol alone did not inhibit the corpus luteum of the hCG-treated, nonpregnant monkey. Serum progesterone values for nonpregnant monkeys treated with 15M-PGF2 alpha plus estradiol-17 beta, ethinyl estradiol or mestranol did not differ statistically from those observed in monkeys treated with 15M-PGF2 alpha alone. The dose of 15M-PGF2 alpha (3 x 500 microgram) which only partially inhibited the corpus luteum of the hCG-treated, nonpregnant monkey promptly terminated gestation when given on Day 28 od fertile menstrual cycles. Pregnancy terminated in two of three treated monkeys when the dose of 15M-PGF2 alpha was reduced ten-fold (3 x 50 microgram). Mestranol alone reduced serum progesterone and estradiol-17 beta concentrations to one-half and one-third of pretreatment values, but did not interrupt pregnancy. Pregnancy terminated in only two of five monkeys when mestranol was administered with the low dose of 15M-PGF2 alpha. It is concluded that: 1) estrogens do not enhance the corpus luteum inhibiting of 15M-PGF2 alpha in the nonpregnant monkey; 2) the primary action of 15M-PGF2 alpha during early pregnancy is upon the conceptus and not the corpus luteum; 3) concomitant treatment with mestranol and 15M-PGF2 alpha offers no advantage of 15M-PGF2 alpha alone for the termination of early pregnancy; and 4) mestranol alone can impair the steroidogenic potential of the corpus luteum of early pregnancy, but is not sufficiently active to terminate gestation.

Pharmacologic induction of luteolysis in cynomolgus monkeys (Macaca fascicularis)

Earlier studies reported from this laboratory demonstrated the luteolytic effect of a 5-day sequential regimen of 3 days of estrogen overlapped with 3 days of PGF2 alpha administered during the midluteal phase to cynomolgus monkeys. In this study, a different regimen, containing estrogen, lower doses of PGF2 alpha, and methylergonovine maleate (MEM), was used. Individual components of this modified sequential regimen were not effective as luteolytic agents. When 3 days of estrogen (40 micrograms of depoestradiol cypionate [DEC] on the first day and 40 micrograms of estradiol benzoate [EB] on second and third day) was followed by 3 days of MEM (400 micrograms, twice daily) overlapping 1 day of estrogen treatment, there was a significant shortening of the length of the menstrual cycle (less than 26 days) in eight of 10 animals, with a concomitant decline in plasma levels of progesterone. When a low dose of MEM (100 micrograms, twice daily), which was completely ineffective in shortening cycle lengths with the same estrogen treatment, was administered alternately with PGF2 alpha (5 mg twice daily, 11 of 14 animals had shortened cycles, with an associated decline in levels of progesterone. PGF2 alpha and MEM without the estrogen pretreatment did not have a significant effect on cycle lengths or blood levels of progesterone, thus demonstrating a synergism between estrogen and the other compounds in inducing luteolysis. Since the agents used in these sequential regimens have potent effects on the uterus, the treatments were repeated in hysterectomized monkeys to determine whether the uterus was involved in the mediation of luteolysis. These treatments caused a significant drop in plasma levels of progesterone by the tenth day after the preovulatory estrogen peak, thus demonstrating that the uterus is not essential to the luteolytic action.

Anti-implantation effect of prostaglandins in the rat

PGF2alpha and PGE2 have been instilled in small amounts (5mug) into the uterine horns of pregnant rats at different intervals following mating. Unilateral as well as bilateral injections have been used. Three parameters have been taken into consideration at laparotomy performed on the 13th day of pregnancy: a) the number of implantation sites; b) the number of viable fetuses; and c) the number of corpora lutea present on the ovarian surface. Both PGs proved able to inhibit implantation, to affect the development of embryos and to exert some luteolytic activity when given between D-1 and D-6 of pregnancy.

Luteolysis induced in pigtail monkeys (Macaca nemestrina) with prostaglandin f 2 alpha, ICI 80996 and ICI 81008

Non-pregnant pigtail monkeys (M. nemestrina) were given ICI 80996 subcutaneously and ICI 81008 and PGF2alpha subcutaneously or intravaginally, once daily on days 20-30 inclusive, or two or three times on days 24 or 26 only. Doses of 50 mug/kg of ICI 80996, 100 mug/kg of ICI 81008 and approx. 1 mg/kg of PGF2alpha were used. In the majority of monkeys treated subcutaneously a rapid fall in circulating progesterone concentrations and earlier than normal menstrual bleeding occurred. When given per vaginam, ICI 81008 was as effective as when given subcutaneously, though PGF2alpha was less effective intravaginally than by the subcutaneous route.