Elevated ovarian expression and serum concentration of α inhibin in the luteal phase during follicular development in the squirrel monkey (Saimiri boliviensis) compared to the human

The goal of the present investigation was to determine in the squirrel monkey the source and pattern of inhibin, a hormone known to effect reproductive steroid levels via pituitary and ovarian mechanisms. Since this seasonally polyestrous species is known to have elevated serum levels of reproductive steroids compared to other primates, the levels of ovarian alpha subunit mRNA expression and serum total alpha inhibin, estradiol, progesterone, and luteinizing hormone were measured and compared to human levels. Expression of the alpha subunit was robust in monkey luteal tissue compared to expression in human luteal tissue. Squirrel monkey serum inhibin peaked 4 days after the luteinizing hormone surge and correlated with progesterone changes. These luteal serum levels of inhibin were greater than 12 times higher than the human levels yet bio‐LH activities were less than in the human during the luteal phase. Inhibin concentrations during the non‐breeding season were generally half the levels measured in the breeding season and undetectable in ovariectomized animals. However, exogenous FSH stimulation induced a marked rise in inhibin, which correlated with an estradiol rise. In conclusion, abundant alpha inhibin subunit expression in the luteal ovary of the squirrel monkey and loss of serum delectability in ovariectomized animals indicates that the principle source of inhibin in the squirrel monkey is the ovary. Elevated serum inhibin levels during the luteal phase concurrent with ovulatory‐size follicular development is unique among species studied thus far. Possible simultaneous inhibin production from both follicular and luteal tissue may be responsible for the exceptionally high inhibin levels. Am. J. Primatol. 47:165–179, 1999. © 1999 Wiley‐Liss, Inc.     

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.     

Ovarian hormones influence odor cues emitted by female meadow voles, Microtus pennsylvanicus.

During the spring-summer breeding season female meadow voles emit odors that are preferred by males, whereas in the autumn-winter season of reproductive quiescence females emit odors that are not preferred by males, but are attractive to females. The effects of daylength and ovarian hormones on salience of female odors were determined by assaying male responses to odors. Females housed in long and short photoperiods transmitted odors that elicited responses similar to those of spring and autumn female voles, respectively. The odor cues emitted by ovariectomized (OVX) females, irrespective of photoperiodic history, were similar to those generated by females during the nonbreeding season. In the absence of ovarian hormones, long daylengths were not sufficient to induce females to broadcast the spring odors preferred by males. Spring-type odor cues were, however, emitted by OVX voles housed in either photoperiod and treated with estradiol. Ovarian hormones appear necessary and sufficient to generate breeding season odor cues and sufficient to induce production of such cues during the nonbreeding season. We conclude that daylength affects odor cues emitted by females by altering ovarian hormone activity.     

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.     

Effect of estradiol-treated females on all-female groups of rhesus monkeys during the transition between the nonbreeding and breeding seasons

Behavior, sex steroid levels and sex skin color were monitored in 2 out-door-housed all-female groups of rhesus monkeys during the nonbreeding season and into the breeding period. Each group contained gonadally intact and ovariectomized (OVX) females. In one group, 2 OVX females were implanted with estradiol benzoate pellets. Female-to-female sexual behavior, sex skin redness and endocrine indices of ovulation (in intact females) all increased as the breeding season approached. The two groups did not differ with regard to these measures. This lack of difference suggests that the presence of males may be required to mediate socially facilitated out-of-season breeding by females. No strong relationships were detected between steroid levels of intact females and sex skin color or female-to-female sexual behavior in all-female groups.     

Postnatal androgenization induces premature aging of rat ovaries

In the present paper, we report that ovaries of adult rats treated with testosterone propionate (TP) on a critical postnatal Day 5 exhibit histologic and immunohistochemical findings which resemble those of the anovulatory ovaries in middle-aged female rats. The sterile rat model has been long known whereas ovarian failure seems to be a reason for anovulation with normal hypothalamo-pituitary-gonadotropin background. Appropriate function of ovarian steroidogenic cells is also regulated by mesenchymal cells. To characterize the ovarian failure, we studied the histology, luteinizing hormone receptor (LHR) expression, and characterized changes of vascular pericytes, T cells, and dendritic cells in ovarian steroidogenic compartments consisting of interstitial cells (ISC) of ovarian interstitial glands, and granulosa and theca interna cells of ovarian follicles. Normal adult ovaries contained 63% of mature interstitial glands. The mature ISC exhibited moderate cytoplasmic and strong surface LHR expression and fine (<5 micrometer) cytoplasmic vacuoles (ISC of 'luteal type'). They originated from young ISC of 'thecal type,' which exhibited strong cytoplasmic LHR expression. Remaining 37% were aged interstitial glands, which consisted of aged ISC (increased cytoplasmic vacuolization, nuclear pyknosis, and reduced surface LHR expression) and regressing ISC (weak cytoplasmic and no surface LHR expression). However, no mature ISC of 'luteal type' were detected in anovulatory ovaries of adult rats (45- and 60-day-old) injected with TP (100 or 500 microgram) on postnatal Day 5 (TP rats). Their ovaries contained 96% of aged interstitial glands with aged and regressing ISC. Remaining 4% were abnormal interstitial glands with direct transition of young ISC of 'thecal type' into aged ISC (young/aged glands). Lack of mature ISC, and similar amount of aged (96%) and young/aged interstitial glands (4%) was also detected in anovulatory ovaries of untreated persistently estrous middle-aged (10-month-old) females (aging PE rats). The aging process in TP and aging PE rats was accompanied by regression of vascular pericytes, T cells, and dendritic cells within the interstitial glands. In addition, anovulatory ovaries of TP rats and aging PE females contained mature follicles exhibiting LHR overexpression by granulosa cells, and aged (cystic) follicles with reduced layers of granulosa cells lacking LHR expression. In contrast, when the rats were injected with 500 microgram of TP later, on postnatal Day 10, the adult females exhibited estrous cycles and normal ovaries with corpora lutea. These results show that injection of TP during the critical postnatal period causes a lack of mature and preponderance of aged ISC in adult ovaries, accompanied by degeneration of mesenchymal cells. We suggest that mesenchymal cells regulate qualitative aspects of tissue-specific cells, and this function of mesenchymal cells is programmed during the critical period of development.     

Reproductive hormone profiles in mares during the autumn transition as determined by collection of jugular blood at 6 h intervals throughout ovulatory and anovulatory cycles

The aim was to define precisely the FSH secretion pattern in mares during the two ovulatory cycles before, and for 24 days after, the last ovulation of the season and to compare this with the profiles of other reproductive hormones and follicular growth to identify changes which may lead to the termination of follicular cycles. Jugular blood was collected every 6 h from ten light horse mares for 6 weeks in autumn. Samples were assayed for FSH, LH, prolactin, inhibin, oestrone conjugates and progesterone. Luteolysis occurred earlier and periovulatory oestrone, but not inhibin, concentrations were significantly lower in the last than in the second to last cycles. In ovulatory and anovulatory cycles, daily mean FSH concentrations were low at the expected time of ovulation and high between days 9 and 11 (day 0 = ovulation), which were usually after luteolysis. However, the periovulatory FSH nadir was prolonged in the last compared with the second to last cycles, and the difference between peak and trough values was not significant in anovulatory cycles. Between day 5 and day 8, the FSH interpulse interval was approximately 2 days, and did not vary in successive cycles. The LH profile also showed progressive changes as mares entered acyclicity; the surge terminated sooner in the last than in the second to last cycles, and failed to occur when expected in acyclicity. Sporadic prolactin pulses occurred at luteolysis in a similar proportion of ovulatory and anovulatory cycles. These results indicate that inadequate gonadotrophin stimulation in early dioestrus may be a critical event leading to suboptimal follicular and luteal development, and eventually acyclicity. Moreover, the time relationships amongst changes in pituitary and ovarian hormones and follicular growth become increasingly disrupted during the autumn transition, which may contribute to the cessation of cyclicity.     

Monitoring luteal function in the lion-tailed macaque (Macaca silenus) through urinary progesterone metabolite measurements

A direct radioimmunoassay for measuring urinary 20-hydroxyprogesterone cross-reactivity to monitor and assess luteal function and detect pregnancy in the lion-tailed macaque (Macaca silenus) is described. Urine samples were collected daily during ten nonconceptive and five conceptive ovarian cycles of five dult female lion-tailed macaques. Urine was analyzed for concentrations of 20α-hydroxypro-gesterone cross-reactivity, estrone conjugates, and creatinine. The strength of the luteal phase in normal nonconceptive cycles (n = 8) is characterized by a maximum sevenfold increase (day 9) in mean 20α-hydroxyprogesterone cross-reactivity over follicular phase levels; the duration, by a 13-day sustained elevation of mean 20α-hydroxyprogesterone cross-reactivity levels. Pregnancy is detectable from 20α-hydroxyprogesterone cross-reactivity values approximately 20 days after the periovulatory estrone conjugate peak (n = 4). Apparent anovulation (n = 1), extended follicular phase (n = 1), and early abortion (n = 1) also are detectable using 20α-hydroxyprogesterone cross-reactivity measurements.     

Ovarian activity during normal and abnormal length estrous cycles in the goat

Ovarian and behavioral cyclicity were studied during 3-5 estrous cycles in a group of 10 multiparous, Nubian does. Changes in ovarian morphology throughout the estrous cycle were identified and photographed laparoscopically. Forty-eight estrous cycles were observed during the study and of these, 21 were abnormally short in duration (mean +/- SEM, 6.5 +/- 0.5 days). Mean duration of the estrous cycle for the 27 normal length cycles was 21.5 +/- 0.8 days. Eighteen/21 (86%) of the short cycles and 6/27 (22%) of the normal cycles were initiated during early breeding season (between September 1st and October 15th). There were no differences (P greater than 0.05) in the duration of estrus for the short (mean, 2.9 +/- 0.3 days) and normal (mean, 2.8 +/- 0.8 days) cycle groups. A total of 6/11 (55%) of the short duration cycles examined laparoscopically appeared to be anovulatory, but ovulation was observed in all normal cycles examined. The number of corpora lutea (CL) observed during normal length and short estrous cycles was 3.1 +/- 0.2 and 2.2 +/- 0.2, respectively (P less than 0.01). The cumulative percentage of does that showed morphological evidence of ovulation by the first, second and fifth day after the onset of estrus was 30%, 60% and 100%, respectively. Based on distinct differences in morphology and development, 2 types of CL were identified. The maximum visible diameter of Type I and Type II CL was 9.4 +/- 0.6 mm and 5.1 +/- 0.5 mm, respectively. These data document ovarian morphology throughout the normal and abnormal duration estrous cycle of the goat and indicate that 1) short estrous cycles observed early in the breeding season are associated with prematurely regressing CL or anovulation and 2) the ovary produces 2 morphologically distinct types of CL which differ not only in size and appearance, but also potentially in postovulatory function and longevity.     

Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Male aggressive behavior is generally regulated by testosterone (T). In most temperate breeding males, aggressive behavior is only expressed during the reproductive period. At this time circulating T concentrations, brain steroid receptors, and steroid metabolic enzymes are elevated in many species relative to the nonreproductive period. Many tropical birds, however, display aggressive behavior both during the breeding and the nonbreeding season, but plasma levels of T can remain low throughout the year and show little seasonal fluctuation. Studies on the year-round territorial spotted antbird (Hylophylax n. naevioides) suggest that T nevertheless regulates aggressive behavior in both the breeding and nonbreeding season. We hypothesize that to regulate aggressive behaviors during the nonbreeding season, when T is at its minimum, male spotted antbirds increase brain sensitivity to steroids. This can be achieved by locally up-regulating androgen receptors (ARs), estrogen receptors (ERs), or the enzyme aromatase (AROM) that converts T into estradiol. We therefore compared mRNA expression of AR, ERalpha, and AROM in free- living male spotted antbirds across reproductive and nonreproductive seasons in two brain regions known to regulate both reproductive and aggressive behaviors. mRNA expression of ERalpha in the preoptic area and AR in the nucleus taeniae were elevated in male spotted antbirds during the nonbreeding season when circulating T concentrations were low. This unusual seasonal receptor regulation may represent a means for the year-round regulation of vertebrate aggressive behavior via steroids by increasing the brain's sensitivity to sex steroids during the nonbreeding season.     

Social suppression of female reproductive maturation and infanticidal behavior in cooperatively breeding Mongolian gerbils

In several cooperatively breeding species, reproductively suppressed, nonbreeding females are attracted to infants and routinely provide alloparental care, while breeding females may attack or kill other females' infants. The mechanisms underlying the transition from alloparental to infanticidal behavior are unknown. In this study, we tested the hypothesis that this transition is associated with cessation of reproductive suppression and onset of ovarian activity in the Mongolian gerbil (Meriones unguiculatus), a cooperatively breeding rodent. Young female gerbils were housed with their natal family (FH), with a female pairmate (PH) or singly (SH). When females were either 11-13 or 16-18 weeks of age, we characterized their behavioral responses to an unfamiliar pup, reproductive development, and plasma progesterone, cortisol, and prolactin concentrations. In both age groups, FH females were significantly less likely to attack pups than PH or SH females and in fact never did so. FH females also had smaller ovaries and uteri, less developed scent glands, and lower progesterone levels, and were more likely to be anovulatory than PH or SH females, especially in the 11- to 13-week-old age group. Prolactin concentrations did not differ with reproductive status but were significantly higher in females that did not attack pups than in those that did. We found no other significant associations, however, between reproductive or endocrine measures and behavioral responses to pups. These results suggest that cohabitation with the natal family inhibits both infanticidal behavior and reproductive maturation in young female gerbils but that these two effects may not be causally related.     

Lack of pubertal influences on female dispersal in muriqui monkeys, Brachyteles arachnoides

The hormonal mediation of dispersal in female mammals is poorly understood, in part because of the difficulties of detecting the onset of ovarian cycling and puberty in dispersing individuals. We used noninvasive methods of faecal steroid assays to determine the timing of dispersal relative to puberty and ovarian cycling in wild female muriqui monkeys, a species in which males are philopatric and nearly all females transfer from their natal groups. Natal females had a mean+/-SE age of 73.4+/-7.2 months (N=18) at the time of their transfers. Intergroup transfers occurred when one or more sexually active adult females were present, but did not show any seasonal patterns. Faecal progesterone and oestradiol profiles from nine natal females prior to transfer and four non-natal females that transferred into our study group demonstrate unequivocally that dispersal occurs prior to puberty in this species. All females showed baseline oestradiol levels and low progesterone levels compared with cycling adult females. Immigrants were first observed to copulate at 11.2+/-2.2 months of age (N=4), prior to the onset of normal ovarian cycles, and gave birth to their first offspring at 33.8+/-7.3 months (N=4) after transferring. Mean cortisol levels did not differ between natal emigrants or recent immigrants, and were within the range of those of adult males during the nonbreeding season in 10 of the 11 prepubertal females sampled. These results indicate that female dispersal is not triggered by activational hormones associated with puberty or escape from reproductive suppression in this species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Suppressed copulatory behavior and ovarian function in lactating Japanese monkeys (Macaca fuscata fuscata) during the mating season

The influence of lactation on copulatory behaviors and ovarian functions was studied in Japanese monkeys (Macaca fuscata fuscata) during the mating season. Three lactating females were housed in an outdoor group cage with their infants, and three nonlactating females were housed in an adjacent outdoor cage. They were mated by introduction of one of four rotationally chosen males into the females' cage, for two hours three times a week; the occurrence of ejaculatory copulations was recorded. Blood samples were collected on each observation day, and plasma levels of estradiol, progesterone, and luteinizing hormone (LH) were measured by specific radioimmunoassays. In nonlactating females, plasma estradiol increased during the transition into the mating season, and rose to levels over 90 pg/ml for the first time on about 50 days before the first ovulation. Shortly after plasma estradiol exceeded 90 pg/ml in the nonlactating females, the onset of ejaculatory copulations occurred. They received ejaculations continuously up to the early ovarian luteal phase. On the other hand, in lactating females, there were lower levels of plasma estradiol (below 90 pg/ml) during the transition into the mating season, and they received no ejaculation during that period. Two of the three lactating females ovulated only once, and they received ejaculations only during the periovulatory period, coinciding with the rise of their plasma estradiol levels over 90 pg/ml. The remaining lactating female remained anovulatory and received no ejaculation throughout the entire mating season. These results have demonstrated that the low sexual activity of lactating females is clearly correlated with low levels of plasma estradiol due to suppressed ovarian function.     

Menstrual cycle characteristics of seasonally breeding rhesus monkeys

Rhesus monkeys in seminatural environments exhibit a distinct seasonal mating cycle with conceptions restricted to the fall and winter months. In the present study, the characteristics of menstrual cycles were examined during a 1-year period in twelve rhesus monkeys in whom pregnancy was prevented. Menses occurred throughout the year, but ovulations were observed only in the fall and winter months. Menses in the spring and summer months occurred irregularly and were associated exclusively with anovulatory cycles. The total number of ovulations exhibited by these females during the breeding season ranged from two to six and was positively related to body weight, mean luteal phase progesterone (P) levels of normal cycles and social dominance rank. Ovulations with a short luteal phase were exhibited by four females (seven cycles), with the likelihood of occurrence increasing as the breeding season progressed. The incidence of abnormal cycles was predicted from the linear combination of parity, body weight and luteal phase P of normal ovulatory cycles. These results suggest that during the seasonally delimited period of ovulation, females exhibit a range in the quality and quantity of ovulations which may be predicted by certain idiosyncratic physical and behavioral traits.     

Ovarian stimulation of squirrel monkeys (Saimiri boliviensis boliviensis) using pregnant mare serum gonadotropin

The application of assisted reproductive technologies (ART) to nonhuman primates has created opportunities for improving reproductive management in breeding colonies, and for creation of new animal models by genetic modification. One impediment to the application of ART in Saimiri spp. has been the lack of an effective gonadotropin preparation for ovarian stimulation. Pregnant mare serum gonadotropin (PMSG) is inexpensive and readily available, but its repeated use in rhesus monkeys has been associated with induction of a refractory state. We have compared PMSG to recombinant human follicle stimulating hormone (rhFSH) for controlled ovarian stimulation in Bolivian squirrel monkeys. Groups of mature squirrel monkeys received rhFSH (75 IU daily) or PMSG (250 IU twice daily) by subcutaneous injection for 4 d during the breeding season (November to January) or nonbreeding season (March to September). Serum estradiol (E2) was measured daily. Follicular growth was monitored by abdominal ultrasound. During the breeding season, PMSG induced a higher E2 response than did rhFSH, with mean E2 levels being significantly higher within 3 d of stimulation. Superior follicular development in PMSG animals was confirmed by abdominal ultrasonography. During the nonbreeding season, PMSG elicited a similar increase in serum E2 levels despite the fact that basal serum E2 is typically low during the nonbreeding season. Repeated use of PMSG (< or = 3 cycles of administration) produced no attenuation of the E2 response. We conclude that PMSG is highly effective for repeated cycles of controlled ovulation stimulation in the squirrel monkey.     

Seasonal changes in reproductive behavior in two ovariectomized female rhesus monkeys treated year-round with estradiol

Two ovariectomized female rhesus monkeys treated year-round with estradiol-filled capsules were used in hour-long behavioral tests with male rhesus monkeys both in and out of the normal breeding season. The study was designed primarily to test male hormonal responses to copulatory behavior and it was expected that behavior of the females would be essentially the same under both seasonal conditions. Several behaviors of the female, however, were found to fluctuate on a seasonal basis, namely (1) proximity to the male, (2) grooming of the male, (3) sexual presentations, and (4) threatening away (a form of sexual invitation). All of these behaviors, except proximity, were found to be positively correlated with the male partner's testosterone levels before and after the behavior test in the only test condition in which most males ejaculated. The preliminary suggestion is made that these females responded to some cue, either from the environment or from the males, that caused a change in their behavior between breeding and nonbreeding seasons despite the constant hormonal environment provided by the estradiol capsules. Since the same behaviors which were sensitive to seasonal effects were positively correlated with male testosterone levels, it is possible that the male's hormonal status affects affects female behavior.     

Dynamics of messenger RNAs encoding inhibin/activin subunits and follistatin in the ovary during the rat estrous cycle

Quantitative changes in ovarian inhibin/activin subunit and follistatin mRNAs during the rat estrous cycle were examined by ribonuclease protection assay using digoxygenin-labeled RNA probes. Levels of ovarian inhibin alpha subunit mRNA remained low throughout estrus, metestrus, and diestrus; abruptly increased on the morning of proestrus; then rapidly decreased when the primary gonadotropin surge occurred. A similar changing pattern was observed in inhibin/activin beta(A) subunit mRNA. On the other hand, inhibin/activin beta(B) subunit mRNA showed a different changing pattern. Levels of beta(B) subunit mRNA remained constant during metestrus and diestrus, abruptly decreased on the afternoon of proestrus, then quickly recovered from the nadir by 1100 h on estrus. Throughout the rat estrous cycle, especially during the periovulatory period, alpha subunit mRNA levels were considerably higher than beta(A) and beta(B) subunit mRNA levels. In addition, changes in plasma concentrations of inhibin A and inhibin B were very similar to that in ovarian beta(A) and beta(B) subunit mRNA levels, respectively, with several-hour delays. These results suggest that levels of beta subunit mRNAs restrict secretion of dimeric inhibins. Levels of follistatin mRNA remained low from the midnight of metestrus to the midnight of diestrus, then increased until initiation of the primary gonadotropin surge. Thereafter, follistatin mRNA decreased, reached the nadir at 0200 h on estrus, then increased abruptly at 1100 h on estrus. Afterward, follistatin mRNA levels remained high until the morning of metestrus. The changing pattern of ovarian follistatin mRNA was similar to, and preceded, the changes in plasma concentrations of progesterone, suggesting that ovarian follistatin may modulate progesterone secretion during the rat estrous cycle.     

Maternal Responsiveness Increases during Pregnancy and after Estrogen Treatment in Macaques

Maternal responsiveness in primates has long been considered emancipated from endocrine factors and entirely dependent on experience and cognition. Here we report that group-living pigtail macaque females increased their rate of interaction with infants in the last weeks of pregnancy in correspondence with an increase in plasma levels of estradiol and progesterone. Estrogen treatment increased the rate at which ovariectomized rhesus females interacted with infants. This is the first evidence that steroid hormones influence maternal responsiveness in anthropoid primates. All untreated ovariectomized females and nonpregnant females interacted with infants, indicating that although estrogen can enhance responsiveness to infants, ovarian or pregnancy hormones are not necessary for the expression of infant-directed behavior in female macaques. The findings of this study suggest fundamental similarities, rather than differences, in the endocrine modulation of maternal responsiveness in primates and other mammals.     

Age-dependent changes in fecal 17β-estradiol and progesterone concentrations in female spider monkeys (Ateles geoffroyi)

The objective of this study was to investigate whether sex steroids decreased with age in female black-handed spider monkeys (Ateles geoffroyi). Fecal concentrations of 17β-estradiol and progesterone (five samples/wk) and the number of ovulatory and anovulatory cycles were compared between adult (n = 3) and aged females (n = 2). All animals (regardless of age) had higher 17β-estradiol concentrations during the fertile than the nonfertile phases. However, during the fertile phase, concentrations of this hormone were significantly higher in adult females. Conversely, progesterone concentrations varied normally throughout the menstrual cycle in both adult and aged animals, with no significant difference between age classes. Similarly, there was no significant effect of age on the number of ovulatory and anovulatory cycles. In conclusion, we inferred that the aged female spider monkeys did not reach menopause, instead they remained in a perimenopausal period characterized by changes in fecal concentrations of ovarian steroids and hypothalamus-hypophysis-ovary axis activity, as well as irregular menstrual flows, for prolonged intervals.     

Concentrations of inhibin,progesterone and oestradiol in fluid from dominant and subordinate follicles from mares during spring transition and the breeding season

Dominant and subordinate follicles were collected from mares on the day after the dominant follicle reached 30 mm in diameter, to investigate regulation of folliculogenesis during spring transition and the breeding season. Concentrations of oestradiol-17beta, progesterone and inhibin A, but not inhibin isoforms with pro- and alpha C-immunoreactivity, were significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. Steroidogenic activity was regained gradually in the dominant follicles of successive anovulatory waves through spring transition. The dominant follicles, during both spring transition and cyclicity, contained higher concentrations of oestradiol, progesterone and inhibin A, but not inhibin pro- and alpha C-isoforms, than subordinate follicles. The results indicate that high follicular levels of oestradiol, progesterone and inhibin A are associated with continued follicle growth and ovulation. The low concentrations of oestradiol and progesterone in transitional follicles indicate that the deficiency in steroidogenesis exists early in the steroidogenic pathway. The similarity in patterns of follicular hormones in spring transition and during cyclicity strongly suggests that the mechanism of dominance is the same in both types of follicle.