A model for the evaluation of estrogens: withdrawal bleeding in ovariectomized rhesus monkeys

Use of the progestin challenge test in nonhuman primates (Macaca fascicularis)

OBJECTIVE

To determine whether the progestin challenge test (PCT) would provide a reliable, noninvasive indicator of endometrial stimulation in nonhuman primates. DESIGN; Randomized, 2x2, crossover study. SETTING; Nonhuman primates (Macaca fascicularis) in an academic research environment.

PATIENT(S)

Adult, surgically postmenopausal, female cynomolgous macaques (n = 27) were studied.

INTERVENTION(S)

Females were randomly assigned to receive estradiol (n = 14; 0.028 mg/kg body weight) or vehicle (n = 13) daily. All animals were administered two PCTs in a crossover study design using two doses (0.28 mg/kg or 0.56 mg/kg body weight) of medroxyprogesterone acetate (MPA).

MAIN OUTCOME MEASURE(S)

Incidence and severity of withdrawal bleeding and serum estradiol (E(2)) and progesterone (P(4)) levels were evaluated.

RESULT(S)

Estradiol treatment resulted in endometrial "withdrawal" bleeding in all but one instance. Females receiving daily doses of E(2) exhibited a significantly greater (P<.01) incidence, severity, and duration of withdrawal bleeding compared to control animals. Of the five positive responses observed in the control females, four occurred when the higher dose of MPA was administered.

CONCLUSION(S)

These results indicate that the PCT is a useful, noninvasive method for determining the presence of endometrial stimulation in nonhuman primates.

Assessment of hormonally active agents in the reproductive tract of female nonhuman primates

Using the ovariectomized macaque model of postmenopausal women's health, we investigated the effects of long-term treatments (5 weeks-3 years) with estradiol, conjugated equine estrogens (CEE), esterified estrogens, progestins such as medroxyprogesterone acetate (MPA) and nomegestrol acetate, CEE + MPA, tamoxifen, soybean phytoestrogens (SPEs), a variety of putative selective estrogen receptor modulators (SERMs), and androgens. Agents tested were selected on the basis of beneficial effects on arteries and/or bone. Doses were scaled on a caloric or serum-concentration basis to approximate human clinical doses. We evaluated endometrial and mammary gland histopathology and morphometry and used immunohistochemistry to evaluate cell proliferation and expression of estrogen receptor alpha and progesterone receptor (PR). Both estradiol and CEE induced endometrial hyperplasia. MPA antagonized epithelial proliferation induced by CEE in endometrium and induced pseudodecidual stromal hyperplasia in some animals. Tamoxifen induced endometrial polyps, cystic hyperplasia, stromal fibrosis, and PR expression but not Ki-67 expression. SPEs were not estrogenic at dietary doses and antagonized estrogen-induced proliferation in the endometrium and breast. Nandrolone induced mucometra and an adenomyosis-like change. The potential SERM 17 alpha dihydroequilenin did not have uterotrophic or mammotrophic effects. In general, experimental findings in macaques have been predictive of outcomes in human clinical trials of the same agents.

Comparative studies of the ethynyl estrogens used in oral contraceptives. I. Endometrial response

Reproductive-age women were given identically prepared mestranol or ethynylestradiol orally for two consecutive 21 day cycles in doses ranging from 50 to 100 mug per day. Endometrial biopsies were obtained at the end of the second cycle and assessed for estrogenic effect. At these dose levels and with this treatment regimen, no differences could be detected between doses or between drugs, indicating that a plateau in endometrial response was reached.