Ovarian estradiol secretion during early pregnancy in monkeys: luteal versus extra-luteal secretion and effect of chorionic gonadotropin.

To determine the locus of ovarian estradiol secretion during early pregnancy, six monkeys were luteectomized (CLx) on days 22 to 24 of pregnancy. Daily peripheral serum concentrations of progesterone were maintained or slightly elevated despite removal of the corpus luteum (CL), while serum estradiol concentrations fell precipitiously (P less than 0.05). It is concluded that the CL of early pregnancy in these monkeys is the primary source of serum estradiol, but that ovarian tissues other than the primary luteal body secrete estradiol at low levels. Further, preliminary results suggest that mCG may be an important stimulus of ovarian estrogen secretion, by both luteal and extra-luteal compartments, in these primates. MCG may stimulate the CL to sustain estradiol secretion even after luteal cells are no longer responsive to this endogenous gonadotropin as regards progesterone secretion.     

Serum concentrations of deoxycorticosterone in women during the luteal phase of the ovarian cycle are not suppressed by dexamethasone treatment

We determined the serum levels of deoxycorticosterone (DOC) in plasma of six healthy, apparently ovulatory women during the mid-follicular and mid-luteal phases of their ovarian cycles; and we evaluated the effect of dexamethasone (1 mg by mouth) on the concentrations of DOC and cortisol in serum at times when plasma progesterone levels were high or low. The serum levels of DOC, unlike those of cortisol, did not vary significantly in single blood samples obtained in the morning (8-10 a.m.) and afternoon (3-5 p.m.); and serum DOC levels in women were significantly higher (P less than 0.05) during the mid-luteal phase than during the mid-follicular phase of the cycle. There were unmistakable diurnal variations in serum levels of cortisol, and cortisol concentrations were reduced to less than 20% of pretreatment levels after the ingestion of 1 mg dexamethasone during the mid-follicular or mid-luteal phase. The serum concentrations of DOC were reduced only to approx 70% of pretreatment levels after dexamethasone ingestion during the follicular phase. The serum levels of DOC did not decline significantly after administration of dexamethasone during the mid-luteal phase, when progesterone levels in serum are high (14-16 ng/ml). Blood samples also were obtained at hourly intervals during the 24 h before and after dexamethasone administration in one woman during the follicular phase and in another woman the during the early luteal phase (progesterone levels = 1-3 ng/ml) of the ovarian cycle. DOC levels (pre-dexamethasone) fluctuated in synchrony with those of cortisol in the woman studied during the follicular phase but not in the woman studied during the early luteal phase of the cycle. In the post-dexamethasone period, plasma cortisol levels were suppressed for at least 24 h in both women whereas DOC levels were decreased only partially. We conclude that plasma DOC is derived from both adrenal secretion and from extraadrenal 21-hydroxylation of progesterone--the latter source of DOC is not affected by dexamethasone suppression of ACTH secretion.     

Asymmetric secretion of principal ovarian venous steroids in the primate luteal phase

We have characterized the degree of asymmetry of ovarian steroid secretion in the luteal phase of the menstrual cycle in rhesus and cynomolgus monkeys. Femoral blood levels of FSH, LH, progesterone, estradiol and 17-hydroxyprogesterone were determined. In addition, laparotomies were performed in the early, mid or late luteal phase to facilitate localization of the corpus luteum and collection of ovarian venous blood. We conclude that: 1) the ovary bearing the active corpus luteum contributes virtually all of the progesterone entering peripheral circulation in the luteal phase; 2) the ipsilateral ovary secretes more 17-hydroxyprogesterone than the contralateral one, although both are active in the luteal phase; and 3) the asymmetrical secretion of estradiol was manifest only in the early and mid-luteal phase, with ovarian symmetry being reestablished in the late luteal phase.     

Prolonged lactational infertility in adolescent rhesus monkeys

The present study examined the effects of first pregnancy and nursing behavior on postpartum infertility in seasonally breeding rhesus monkeys to assess whether prolonged lactational infertility observed in adolescent mothers is due to a particular pattern of nursing or to decrements in body growth rates. After a successful first pregnancy, a significant percentage of the lactating adolescent mothers (57.1%; n = 8) failed to exhibit an ovulation with normal luteal phase during the subsequent breeding season. In contrast, the remaining lactating adolescents (42.9%, n = 6) and all of the adult mothers (100%, n = 6) exhibited ovulations with a normal luteal phase. Age alone was not the critical variable, since all nonlactating adolescents exhibited ovulations with normal luteal phase parameters in the subsequent breeding season. The luteal phase abnormalities exhibited by the subset of lactating adolescent females were characterized by an inadequate luteal phase (ILP) and by significantly lower serum levels of progesterone, estradiol, and bioactive luteinizing hormone. The occurrence of these ILP ovulations was associated with more frequent nursing bouts prior to ovulation and during the subsequent luteal phase. In contrast, nursing patterns for adult females who had ovulations with normal luteal phases were more similar to those of the infertile lactating adolescents exhibiting significantly longer and more frequent nursing bouts, suggesting that fully adult females may be less sensitive to the inhibitory aspects of a suckling stimulus. Differences in luteal phase function among lactating adolescents were not related to differential rates of ponderal or skeletal growth. A still-developing neuroendocrine system may thus render a significant proportion of adolescent females more sensitive to suckling-induced suppression of gonadotropin secretion.     

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.     

Topiramate as a Cause of False Positive in the Overnight 1-Mg Dexamethasone Suppression Test

ObjectiveTo describe that topiramate may cause a false positive in an overnight 1-mg dexamethasone suppression test (DST) for hypercortisolism screening.MethodsWe present a case in which topiramate induced dexamethasone metabolism, leading to a false positive on the DST.ResultsA 44-year-old female with an incidentally found adenoma in the right adrenal gland underwent a DST for hypercortisolism screening. The patient was taking topiramate prescribed by a psychiatrist for an affective disorder, and insufficient cortisol suppression (11.9 mcg/ dL) was observed. Her free cortisol in 24-hour urine was normal, and insufficient suppression was established in a second determination (9.3 mcg/dL). Finally, her psychiatrist switched her treatment from topiramate to bupropion, and the measurements were repeated. When she was not taking topiramate, correct suppression with 1 mg of dexamethasone was obtained (1.7 mcg/dL), and her free cortisol in 24-hour urine was again normal, thereby excluding the presence of hypercortisolism. On reviewing the literature, topiramate was not found to have been previously described as a cause of a false positive on DST, but it was proposed as a cause of hypoadrenalism in a patient taking oral corticosteroid replacement due to its capacity to induce dexamethasone metabolism.ConclusionTopiramate treatment may well be a cause of false positives in DSTs, and its presence should be taken into consideration when screening for hypercortisolism. (Endocr Pract. 2014;20:e116-e118)     

Corpus luteum function during the early postpartum interval in lactating rhesus monkeys: in vivo and in vitro response to exogenous gonadotropin.

The response of the postpartum corpus luteum to exogenous gonadotropin was studied in 12 lactating rhesus monkeys given daily injections of either human chorionic gonadotropin (HCG, n = 6) or saline (control, n = 6) for 4 days immediately following parturition. Peripheral blood samples were collected daily. On the 5th day postpartum, luteectomy was performed progesterone production by dispersed luteal cells was examined. Whereas progesterone in the peripheral circulation of control monkeys progressively declined between days 1 and 5 postpartum, progesterone levels increased significantly (p less than 0.025) with the onset of HCG treatment and remained significantly (p less than 0.025) elevated above the controls throughout the period of HCG treatment. However, despite the daily administration of HCG, circulating progesterone levels declined (p less than 0.05) between days 3 and 5 postpartum. The weight of the corpus luteum excised from HCG-treated macaques was significantly (p less than 0.005) greater than that of the controls. Dispersed cells from corpora lutea of saline-treated monkeys produced progesterone in vitro under control conditions (nutrient medium alone) and responded to the addition of high (100 ng/ml), but not low (1 ng/ml), levels of HCG with increased steroidogenesis. Although luteal cells from HCG-treated macaques tended to produce more progesterone in vitro than cells from control monkeys, they also exhibited a 50-fold reduction in sensitivity to HCG in vitro. These data suggest that the corpus luteum of lactating postpartum rhesus monkeys exhibited steroidogenic function which was stimulated by exogenous gonadotropin. However, prolonged exposure of the corpus luteum to high levels of exogenous gonadotropin appeared to produce a state of refractoriness to additional gonadotropic stimuli.     

On the correlation between sexual behavior and ovarian hormone level during the menstrual cycle in captive Japanese monkeys

The amount of estradiol and progesterone in the systemic blood plasma of six adult female Japanese monkeys was measured by radioimmunoassay. Data on heterosexual pairing tests was also collected and examined for correlation with these hormones. The relationship between ovarian hormones and frequency of ejaculation varied with each female. In nine normal menstrual cycles, the frequencies of invitation and approach by the female reached peaks on the day of the estradiol surge, after which they rapidly decreased. Frequencies of male behaviors including approach, leaving, invitation, and yawning significantly decreased during the luteal phase, as compared with those at the midcycle. Grooming by both sexes of the partner reached low points during the late follicular phase. The number of ejaculations per test increased significantly at the midcycle and reached a maximum a few days after the estradiol surge. The present results suggest that female proceptivity is highly correlated with the amount of estradiol, but her attractiveness is little correlated with estradiol and is lowered by progesterone.     

Salivary progesterone for the assessment of the ovarian function in the capuchin monkey (Cebus apella)

Salivary and plasma progesterone were measured in normally cycling (n=10) and castrated (n=4) femaleCebus monkeys (Cebus apella). During the follicular phase, progesterone levels in saliva ranged between 0.05 and 1.40 ng/ml and in the luteal phase they increased to between 0.22 and 4.70 ng/ml. These values represented on average 6.5 and 3.2% of those values measured in plasma, for the follicular and luteal phases, respectively. The regression analysis of the steroid concentrations in both fluids showed a highly significant correlation (r=0.8985,n=180,P<0.0001). Ovariectomized monkeys had consistently low salivary (0.37±0.02 ng/ml) and plasma (4.70±0.25 ng/ml) progesterone, showing a low, but significnat, correlation coefficient (r=0.2592,n=58,P=0.047). The ratio of plasma/salivary progesterone was significantly higher in the luteal phase (31.09±1.65) than in the follicular phase (23.06±2.26) and in castrated monkeys (16.00±1.38). The free fraction of progesterone constituted 5.3±0.2% of the total plasma progesterone during the follicular phase and 3.3±0.1% during the luteal phase. Ovariectomized monkeys showed a significantly higher percentage of free progesterone in plasma (7.7±0.1%). In contrast, free progesterone made up 64.4 and 70.9% of the total salivary progesterone for the follicular and luteal phases, respectively. The proportion of free progesterone in castrated animals was within the range observed in cycling animals. We suggest that the levels of progesterone in the saliva of capuchin monkey follow a pattern similar to that for plasma progesterone, reflecting the free steroid fraction. Thus, the measurement of such steroid in saliva may offer a valuable alternative to plasma determinations for the assessment of the ovarian function inCebus and probably other New World monkey species.     

Intratesticular steroid levels and their hormonal control

Litter-mate adult male rats were treated with daily intramuscular injections of ACTH (10.5 micrograms), dexamethasone (2.0 mg), ethynyl estradiol (1.7 micrograms) and hCG (5 IU) for three consecutive days. The animals were sacrificed on the fourth day and the intratesticular and peripheral plasma steroid levels were analyzed. The steroids measured by radioimmunoassay included pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone, progesterone, 17-hydroxyprogesterone, androstenedione, testosterone and dihydrotestosterone. In addition, the sulphoconjugated forms of pregnenolone, dehydroepiandrosterone, testosterone and dihydrotestosterone were estimated in the peripheral blood. The administration of ACTH diminished the intratesticular levels of all steroids studied. Also dexamethasone and ethynyl estradiol treatment suppressed all intratesticular steroid levels, except that of pregnenolone (the former) and of 17-hydroxyprogesterone (the latter). The suppressive effect of ethynyl estradiol was strongest on the levels of the delta 5-steroids and that of dexamethasone on the delta 4-steroids; the latter was significantly stronger than the effect of ACTH. The stimulatory effect of hCG was limited to the metabolism of progesterone and was restricted to the sequence: 17-hydroxyprogesterone----androstenedione----testosterone---- dihydrotestosterone. Dexamethasone-suppression, and hCG-stimulation of the intratesticular levels of delta 4-steroids, was mirrored by corresponding changes in the peripheral plasma levels, with the exception of the plasma levels of androstenedione which were not influenced by any of the treatments studied. Also the suppression of intratesticular testosterone and dihydrotestosterone levels by ACTH, dexamethasone, or ethynyl estradiol was closely reflected by their plasma levels both in the unconjugated and sulphoconjugated forms. On the hand, the administration of ACTH diminished the intratesticular levels of pregnenolone and progesterone but significantly increased those in the plasma. Moreover, both ACTH and ethynyl estradiol reduced the levels of all delta 5-steroids in testicular tissue, but not in the peripheral plasma, although they decreased the circulating levels of pregnenolone sulphate and dehydroepiandrosterone sulphate. The data are interpreted as suggesting that the hormonal agents studied interfere with testicular steroidogenesis through different mechanisms.     

Lactation‐associated infertility in Japanese monkeys (Macaca fuscata) during the breeding season

To investigate the endocrine factors in Japanese monkeys (Macaca fuscata) responsible for the suppression of the estrous cycle during the first reproductive season after delivery (150–360 days postpartum), peripheral blood was taken to measure plasma concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol‐17β, immunoreactive (ir)‐inhibin, and cortisol. The results demonstrated that during the breeding season of lactating Japanese monkeys, circulating concentrations of FSH (1.7–2.7 ng/ml), LH (308.5–461.0 pg/ml), estradiol‐17β (<62.6 pg/ml), and progesterone (145.0–453.0 pg/ml) remained low and were similar to the nadir levels observed during both the normal menstrual cycles and the nonbreeding season. Concentrations of ir‐inhibin, which is secreted from both follicles and corpus luteum in female Japanese monkeys, were also low (300.5–585.0 pg/ml). This strongly suggests that no follicular development occurs during lactation. Serum concentrations of cortisol (261.0–519 ng/ml) were higher during lactation than during the nonbreeding season. Since babies were often seen suckling their mothers during the study, the results indicate that the increased cortisol levels were associated with suckling‐induced secretion of corticotrophin‐releasing hormone (CRH) and adrenocorticotropic hormone (ACTH). The results of this study indicate that a long period of postpartum infertility in lactating Japanese monkeys, with apparent inhibition of follicle growth and anovulation, is due to weak gonadotropin stimulation, which may occur as the result of a suckling stimulus. Zoo Biol 22:65–76, 2003. © 2003 Wiley‐Liss, Inc.     

Circadian cortisol secretion and circadian adrenal responses to ACTH are maintained in dexamethasone suppressed capuchin monkeys (Cebus apella)

We tested the hypothesis that the capuchin monkey adrenal (Cebus apella) gland has oscillatory properties that are independent of adrenocorticotropic hormone (ACTH) by exploring under ACTH suppression by dexamethasone: (i) maintenance of a circadian rhythm of plasma cortisol and (ii) clock time dependency of plasma cortisol response to exogenous ACTH. The capuchin monkey had a clear ACTH and plasma cortisol rhythm. Dexamethasone treatment resulted in low non-rhythmic ACTH levels and decreased cortisol to 1/10 of control values; nevertheless, the circadian rhythm of plasma cortisol persisted. We found that cortisol response to exogenous ACTH was clock time-dependent. The maximal response to ACTH occurred at the acrophase of the cortisol rhythm (0800 h). These results suggest that the capuchin monkey adrenal cortex may possess intrinsic oscillatory properties that participate in the circadian rhythm of adrenal cortisol secretion and in the circadian cortisol response to ACTH.     

Progesterone, but not luteal estrogen, is required for the establishment of pregnancy in the new world monkey Cebus apella

The aim of this study was to examine the requirement of luteal progesterone or luteal estrogen for the establishment of pregnancy in the Cebus monkey and to test in a primate species the synergism between RU 486 and letrozole (LTZ) found in rodents for inhibiting implantation. Exposure of target tissues to either hormone was suppressed during the mid-luteal phase of mating cycles by subcutaneous administration of the antiprogestin (RU 486), the aromatase inhibitor LTZ or the antiestrogen (ICI 182780) on days 4-7 of the luteal phase. Administration of 0.1 or 0.5 mg/kg of LTZ on days 5-7 of the luteal phase caused a profound drop in the levels of E(2) in all animals, whereas administration of ICI 182780 0.2 mg/kg on days 4-6 of the luteal phase had the opposite effect. The pregnancy rate in vehicle treated cycles of the same females was (58.3%). Treatment with RU 486, 0.8 mg/kg/day on days 5-7 of the luteal phase-induced endometrial bleeding in 3/5 mated females none of which became pregnant, whereas pregnancy was confirmed in one of the two animals that did not bled. Treatment with RU 486, 0.4 mg/kg/day alone or with LTZ on days 5-7 or ICI 182780 alone, on days 4-6 of the luteal phase failed to induce bleeding, allowing the establishment of pregnancy in 50.0-66.6% of the animals in these groups. We conclude that in Cebus monkeys, progesterone but not luteal estradiol is required for the establishment of pregnancy and that RU 486 and LTZ do not exhibit in this species the synergism found in rodents.     

Continued copulation of ovariectomized adrenal-suppressed stumptail macaques (Macaca arctoides).

Female stumptail macaques continue to copulate at moderate to high levels for years after gonadectomy. This study examined the extent to which sexual behavior of ovariectomized stumptail females was maintained by steroids of adrenal origin, and second, considered the possibility that ovarian fragments might have been left in situ following surgery. Daily injections of 0.1 mg of dexamethasone sodium phosphate suppressed serum cortisol, estradiol, and testosterone by at least 85% in three of four ovariectomized females, but dihydrotestosterone was suppressed by only 50 to 70%. The fourth female showed maximal suppression of cortisol but maintained much higher levels of the other steroids, in particular estradiol, and therefore it was strongly suspected that this animal had an ovarian fragment.Within the limits to which sex steroids were depressed with dexamethasone, no correlation was found between steroid levels and sexual performance. Ejaculatory frequencies and measures of attractivity, proceptivity, and receptivity collected during heterosexual pair tests remained unaffected in all four females during 4 weeks of dexamethasone treatment. Thus it was concluded that the maintenance of copulatory activity after ovariectomy in this species was largely due to nonsteroidal mechanisms.     

Evidence for a systemic role for ovarian oxytocin in luteal regression in sheep

Jugular venous concentrations of oxytocin and progesterone changed in parallel during the oestrous cycle in the ewe, falling at luteal regression and rising with formation of the new corpus luteum. These fluctuations in the circulating concentration of oxytocin were not caused by changes in its metabolic clearance rate. On Days 6-9 of the cycle circulating oxytocin concentrations exhibited a diurnal rhythm, peaking at 09:00 h; this rhythm was absent on Days 11-14. Although there was no evidence for increased production of oxytocin at or preceding luteal regression in samples taken daily, more frequent sampling revealed that two thirds of detected surges of uterine secretion of prostaglandin (PG) F-2 alpha were accompanied by raised levels of oxytocin. This oxytocin was not of pituitary origin. Luteal regression induced with cloprostenol on Day 8 after oestrus caused a decrease in circulating progesterone level followed after 24 h by a fall in oxytocin. Measurements of oxytocin in the ovary and other organs before and after treatment with cloprostenol identified the corpora lutea as a major potential source of oxytocin, and suggested that 98% of luteal oxytocin was available for secretion in response to prostaglandin stimulation. The data are consistent with a role for ovarian secretion of oxytocin in response to uterine release of PGF-2 alpha in the control of luteal regression.     

The relationship between aggressive behavior and menstrual cycle stage in female rhesus monkeys (Macaca mulatta)

The aggressive behavior of eight adult female rhesus monkeys, living in a captive social group, was studied prior to and during a breeding season extended by vasectomizing all the adult males in the group. Female reproductive status was ascertained by: recording all adult female-adult male copulations, detecting menstruation by vaginal swabbing, and analyzing serum progesterone levels by radioimmunoassay. Females were more aggressive during the follicular stage of their menstrual cycle than the luteal stage or during the period prior to the onset of seasonal ovarian activity. Increases in aggression were limited to increases in the milder forms of agonistic behavior, primarily threatening gestures. Although the females showed their highest rates of noncontact aggressive response categories during the follicular stage, several showed highest rates of contact aggressive response categories in the precycling period.     

Maternal glucocorticoid treatment programs HPA regulation in adult offspring: sex-specific effects

Pregnant guinea pigs were treated with dexamethasone (1 mg/kg) or vehicle on days 40--41, days 50--51, and days 60--61 of gestation. Adult offspring were split into two groups. Group 1 guinea pigs were catheterized, and the hypothalamo-pituitary-adrenal (HPA) axis was tested in basal and activated states. Group 2 guinea pigs were euthanized with no further manipulation. In male offspring, prenatal dexamethasone exposure resulted in a significant reduction in brain-to-body weight ratio. Dexamethasone-exposed male offspring exhibited reduced basal and activated plasma cortisol levels, which was associated with elevated hippocampal mineralocorticoid receptor (MR) mRNA and increased plasma testosterone. In females exposed to glucocorticoids in utero, basal and stimulated plasma cortisol levels were higher in the follicular and early luteal phases of the cycle, but this effect was reversed in the late luteal phase, indicating a significant interaction of sex steroids. In female offspring (at estrus), glucocorticoid receptor mRNA levels were lower in the paraventricular nucleus and pars distalis but higher in the hippocampus in animals exposed to dexamethasone in utero. Hippocampal MR mRNA levels were significantly lower (approximately 50%) than in controls. In conclusion, repeated antenatal glucocorticoid treatment programs HPA function in a sex-specific manner, and these changes are associated with modification of corticosteroid receptor expression in the adult brain and pituitary.     

Immunoreactive inhibin levels in peripheral blood during the breeding season in the female Japanese monkey

Serum levels of immunoreactive inhibin as well as FSH, LH, estradiol-17 beta, and progesterone were measured by RIA in four mature female Japanese monkeys (Macaca fuscata fuscata) during the breeding season and subsequent transition into the nonbreeding season. During the breeding season, each monkey showed 2-6 ovulations, which were inferred from underlying endocrine events. The concentrations of serum inhibin increased during the luteal phase, but were low during the follicular phase. Such changes in serum inhibin levels correlated positively with those in serum progesterone levels. Basal levels of serum inhibin also increased during the breeding season, decreased during transition from the breeding season, and were low during the nonbreeding season. The parallel change in serum levels of inhibin and progesterone together with the increased basal levels of serum inhibin during this period suggests that both the CL and antral follicles are sources of circulating inhibin. Decreases in serum FSH levels during the luteal phase suggest that secretion of FSH is controlled by an inhibitory action of ovarian inhibin in addition to steroid hormones.     

Cyclic changes in the circulating and urinary levels of ovarian steroids in the adult female owl monkey (Aotus trivirgatus).

Circulating levels of oestrone and progesterone were measured by radioimmunoassays in plasma samles from 5 female owl monkeys on 60 consecutive days. Both steroids exhibited cyclic fluctuations and based on nadir to nadir intervals the ovarian cycle was estimated to be 15.92 +/- 0.26 days. Levels of oestrone and pregnanediol-3 alpha-glucuronide were also measured in daily urine samples. The fluctuations of urinary steroids reflected those observed in plasma. Ketamine sedation had no effect on the length of the cycle. Peak values of plasma progesterone and oestrone were 250.48 +/- 11.37 and 3.59 +/- 0.066 ng/ml respectively. There was no clear hormonal distinction between the follicular and luteal phase of the cycle in these owl monkeys.     

Estradiol induces and progesterone inhibits the preovulatory surges of luteinizing hormone and follicle-stimulating hormone in heifers

Objectives were to determine: 1) whether estradiol, given via implants in amounts to stimulate a proestrus increase, induces preovulatory-like luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges; and 2) whether progesterone, given via infusion in amounts to simulate concentrations found in blood during the luteal phase of the estrous cycle, inhibits gonadotropin surges. All heifers were in the luteal phase of an estrous cycle when ovariectomized. Replacement therapy with estradiol and progesterone was started immediately after ovariectomy to mimic luteal phase concentrations of these steroids. Average estradiol (pg/ml) and progesterone (ng/ml) resulting from this replacement were 2.5 and 6.2 respectively; these values were similar (P greater than 0.05) to those on the day before ovariectomy (2.3 and 7.2, respectively). Nevertheless, basal concentrations of LH and FSH increased from 0.7 and 43 ng/ml before ovariectomy to 2.6 and 96 ng/ml, respectively, 24 h after ovariectomy. This may indicate that other ovarian factors are required to maintain low baselines of LH and FSH. Beginning 24 h after ovariectomy, replacement of steroids were adjusted as follows: 1) progesterone infusion was terminated and 2 additional estradiol implants were given every 12 h for 36 h (n = 5); 2) progesterone infusion was maintained and 2 additional estradiol implants were given every 12 h for 36 h (n = 3); or 3) progesterone infusion was terminated and 2 additional empty implants were given every 12 h for 36 h (n = 6). When estradiol implants were given every 12 h for 36 h, estradiol levels increased in plasma to 5 to 7 pg/ml, which resembles the increase in estradiol that occurs at proestrus. After ending progesterone infusion, levels of progesterone in plasma decreased to less than 1 ng/ml by 8 h. Preovulatory-like LH and FSH surges were induced only when progesterone infusion was stopped and additional estradiol implants were given. These surges were synchronous, occurring 61.8 +/- 0.4 h (mean +/- SE) after ending infusion of progesterone. We conclude that estradiol, at concentrations which simulate those found during proestrus, induces preovulatory-like LH and FSH surges in heifers and that progesterone, at concentrations found during the luteal phase of the estrous cycle, inhibits estradiol-induced gonadotropin surges. Furthermore, ovarian factors other than estradiol and progesterone may be required to maintain basal concentrations of LH and FSH in heifers.