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Circulating relaxin concentrations in the human rise in the late luteal phase and increase further in response to increasing circulating CG concentrations immediately after implantation. Similar events have not been documented in the laboratory macaque because of the lack of sensitivity of heterologous assay systems. A homologous enzyme-linked immunosorbent assay for authentic macaque relaxin was developed and validated. Using this enzyme-linked immunosorbent assay, relaxin concentrations were measured in peripheral and ovarian venous blood collected from cynomolgus and rhesus macaques. Relaxin concentrations rose in the late luteal phase of nonconceptive menstrual cycles in cynomolgus macaques, but it was not detected at other times in the cycle. In conceptive cycles, relaxin concentrations rose rapidly in close association with the appearance of mCG 13-14 days after mating. Pregnant rhesus macaques also had elevated relaxin concentrations in blood samples collected on days 15-17 postbreeding. Relaxin concentrations disappeared immediately after luteectomy or ablation of the trophoblast by either surgery or administration of methotrexate. The rise of relaxin paralleled the rise of mCG until 20-25 days postbreeding, while progesterone concentrations declined during this same time period. The lack of correlation between relaxin and progesterone secretion profiles suggests that either the cellular origins or the intracellular mechanisms promoting the secretion of these hormones are different. The periimplantational profile of serum relaxin in macaques was similar to the profile of relaxin observed during early human pregnancy.

Dexamethasone (8 mg/day im) has been administered to rhesus monkeys (Macaca mulatto) from days 146–156 of pregnancy, until term. This treatment was ineffective in precipitating premature delivery, and the monkeys delivered spontaneously at the expected time (day 166–176). Maternal peripheral plasma progesterone concentrations were unaffected by the dexamethasone treatment. However, administration of the synthetic glucocorticoid resulted in a marked suppression of the maternal plasma estrone and estradiol-17β concentrations in all animals. In the 4 monkeys in which injections of dexamethasone were initiated earliest (days 146–150), the plasma unconjugated estrogen levels at term were 15–40% of those found prior to the start of treatment. At autopsy, the adrenal glands from the fetuses of dexamethasone-treated monkeys had markedly atrophied, and showed appreciable regression of the fetal zone. It is suggested that dexamethasone crosses the placenta and inhibits fetal ACTH release, resulting in regression of...

The secretory response of the primate corpus luteum (CL) to CG after implantation suggests that gonadotropin receptors are not depleted despite increasing CG production and continuous elevated tropic stimulation. Such continuous stimulation is known to cause down-regulation of receptors in other tissues. To determine if CG secretion is intermittent during the initial stages of CL rescue, we assessed the secretory pattern of CG during the periimplantation period by collecting frequent (4/h) blood samples in two studies (for 4 h on 3 separate days between days 8-13, or for 2 separate 13-h sequences between days 10-15 postovulation) in 13 chair-adapted females. Day 0 of gestation was defined as the day of ovulation, as estimated by peak urinary estrone conjugate excretion in females mated on days 9, 11, and 13 of the menstrual cycle. Hormone concentrations were measured by either RIA [irFSH; estradiol and progesterone (P)] or Leydig cell bioassay (bioLH or bioCG). In the first study, 4 of 6 females conceived, and the mean for bioLH was not significantly elevated until days 12-13. In the second study, 5 of 7 females conceived, and the episodic secretory pattern of circulating pituitary bioLH typically observed in cycling females (2.7 +/- 0.3 peaks/13 h) was replaced by a relatively nonpulsatile, but steadily increasing profile during days 12-15 of gestation (1.5 +/- 0.4 peaks/13 h). Although occasional large fluctuations in bioLH/CG and P were noted, the bioLH/P peaks were less congruent than those in nonfertile cycles, and there was no diurnal pattern in the secretion of either hormone. In contrast, irFSH concentrations did not fluctuate and were similar in the two groups of females [2.93 +/- 0.28 vs. 2.34 +/- 1.7 ng/ml (mean +/- SEM)]. These data demonstrate that 1) a steady, gradually increasing secretory pattern of CG is associated with rescue of the CL; 2) the circulating profile of CG during the periimplantation interval is not consistently episodic and does not support the hypothesis that intermittent CG release prevents LH/CG receptor down-regulation in the CL during early pregnancy; 3) increased bioLH/CG levels during conceptive cycles in rhesus monkeys are not detected until days 12-13 after the midcycle bioLH peak; 4) irFSH patterns on pooled aliquots appear to be uninformative with regard to gonadotropin dynamics in early pregnancy; and 5) urinary estrone conjugate measurements provide a practical method for the precise timing of infrequent events, such as implantation, in the laboratory macaque.

The concentrations of progesterone, estrone and estradiol-17β have been measured by radioimmunoassay in serial samples of peripheral plasma from rhesus monkeys (Macaca mulatto) during the final third of normal pregnancy, and during the induction of abortion with prostaglandin F2α (PGF2α). In 3 out of 5 animals, the plasma progesterone concentration increased during the 5–10 days preceding spontaneous labor. In no animal did the progesterone concentration decrease before parturition. The concentration of estradiol-17β was greater than that of estrone in most plasma samples. The levels of both estrogens in maternal plasma increased within 5 days before parturition, but decreased rapidly after the fetus had been delivered. Daily maternal injections of PGF2α (10–15 mg/day) administered around day 150 of pregnancy reliably induced premature delivery. The concomitant steroid hormone changes were variable, although most monkeys showed a decline in the plasma progesterone and estrogen levels during the final 24 h...

Progesterone (P) levels in the peripheral blood of parous bonnet monkeys (Macaca radiata) were studied by a competitive protein-binding radioassay method during the menstrual cycle and in pregnancy. During the menstrual cycle P levels averaged less than .5 ng/ml during the first 9 days and then began to rise considerably between Days 9-11 reaching maximal levels on Day 18. P levels then showed a considerable decline by Day 24 of the cycle when compared with levels during Days 15-23. 2-3 days prior to menstruation P levels were less than 1 ng/ml. P levels during the first 12 days postbreeding were higher than during the luteal phase but presented a similar pattern. A definite divergence of P levels in pregnancy compared with nonpregnant animals occurred at Day 15 of pregnancy or Day 24 of the menstrual cycle when levels in pregnant animals were maintained and levels in nonpregnant animals significantly declined. This devergence suggests that there is a well-defined period in which the corpus luteum regresses if the animal is not pregnant. P concentrations began to decline on Day 35 postbreeding and continued until Days 45-50. Until Days 145-150 P levels varied and thereafter began to increase. The greatest increase in P levels was observed during the last 6 days before delivery. P levels which averaged 20 ng/ml about 12 hours before delivery declined to 2 ng/ml at 12 hours postpartum.

Plasma progesterone levels were determined in the crab—eating macaque (Macaca fascicularis) during the menstrual cycle and pregnancy, including parturition. Menstrual cycles averaged 31 days in duration. Progesterone levels rose above 1 ng/ml plasma about 15 days prior to the onset of menstruation with peak values (7.8 ng/ml) observed on day 7 prior to menstruation. Progesterone levels declined to > 1 ng/ml 1–4 days before menstruation. Two animals studied daily for the first 30 days postbreeding, and then 2 times weekly, had 2 distinct progesterone peaks, one about IS days postbreeding and another at about 34 days with a low point in progesterone levels observed between these peaks at about days 23 to 25. The progesterone decline which followed the second peak reached minimal levels (1 to 2 ng/ml) by about day 45 of gestation. Progesterone levels increased gradually throughout the rest of gestation with average values of about 4 ng/ml observed the last 2 weeks prior to parturition. No significant changes...