Primate Cycle Research Articles

Understanding the links between social ties and fitness over the life cycle in primates

Abstract Many studies highlight the correlation between social ties and fitness, yet often cannot reveal how ties influence fitness. This review is aimed to facilitate the formulation and testing of hypotheses in this area on non-human primates. I outline fitness-relevant measures of social ties and 6 potential pathways from ties to fitness. Pathways include communal care; group level cooperation for resources; monopolizing resources within groups; attaining social status; reducing risk and allostatic load; and developing behavioural competence. Hypotheses for further evaluation include (1) fitness increases sociality, not vice versa; (2) early life experience influences both ties and fitness, (3) ties are actually costly; (4) short term costs of ties are outweighed by long term benefits. With the advance of theoretical and methodological approaches to evaluate the costs and benefits of social ties, and monitor them at multi-generational field sites, primate behavioural ecologists are poised to test several of these hypotheses.

Testing socially mediated estrous synchrony or asynchrony in wild baboons

Social structure of animal groups is affected by the spatial and temporal distribution of females. In particular, the extent to which fertile periods of females are temporally overlapped has been deemed as a crucial factor to determine the structure of social groups in primate species. Dominant males are less able to monopolize fertile females when there are more females being in estrous simultaneously. This provides a potential opportunity for females to manipulate their defensibility by dominant males by modifying the level of estrous overlap. Previous studies that have attempted to detect socially mediated synchrony or asynchrony of estrous cycles have produced mixed results, some of which have been questioned on methodological grounds. Here, we address this issue using an exceptionally large dataset of daily reproductive states in four troops of wild anubis baboons (Papio anubis) over 14 to 24 years (77 troop-years). We compare observed levels of estrous synchrony with null distributions obtained by a randomization procedure under the assumption that estrous cycles are mutually independent among females in the same troop. We do not find any evidence supporting synchrony or asynchrony of estrous cycles. Based on our result and those of previous studies in other species of baboons, we conclude that socially mediated synchrony or asynchrony is unlikely to play a significant role in structuring social groups in baboons. In addition, our analysis points out that care should be taken when applying randomization procedures to a dataset with missing observations. Females in some animal species have been suggested to synchronize or desynchronize their estrus cycles. This phenomenon may have a significant impact on the structure of animal societies because when there are more females simultaneously in estrus, even a dominant male is less able to defend them from other males. Previous attempts to detect non-random estrous cycles in primates have produced mixed results, and some of them have been criticized on the methodological grounds. We investigate whether wild female anubis baboons exhibit non-random estrous cycles using a larger dataset than previous studies. For a statistical analysis, we use a randomization procedure, taking a biasing effect of missing observations into consideration. Consistent with earlier studies on other species of baboons, our analysis does not find any evidence supporting estrous synchrony or asynchrony in anubis baboons.

Effects of steroid ablation and progestin replacement on the transcriptome of the primate corpus luteum during simulated early pregnancy

Previous microarray analyses indicated that a portion of the transcriptome in the macaque corpus luteum (CL) of the menstrual cycle was regulated indirectly by luteinizing hormone via the local actions of steroid hormones, notably progesterone (P). The current study was designed to investigate this concept in the CL of early pregnancy by analyzing chorionic gonadotrophin (CG)-regulated genes that are dependent versus independent of local steroid action. Exogenous human chorionic gonadotropin treatment simulating early pregnancy (SEP) began on Day 9 of the luteal phase in female rhesus monkeys with and without concurrent administration of the 3-β-hydroxysteroid dehydrogenase inhibitor trilostane (TRL) with or without the synthetic progestin R5020. Compared with SEP treatment alone, TRL altered 50 mRNA transcripts on Day 10, rising to 95 on Day 15 (P<0.05, ≥2-fold change in gene expression). Steroid-sensitive genes were validated; notably effects of steroid ablation and P replacement varied by day. Expression of some genes previously identified as P-regulated in the macaque CL during the menstrual cycle were not significantly altered by steroid ablation and P replacement during CG exposure in SEP. These data indicate that the majority of CG-regulated luteal transcripts are differentially expressed independently of local steroid actions. However, the steroid-regulated genes in the macaque CL may be essential during early pregnancy, based on previous reports that TRL treatment initiates premature structural regression of the CL during SEP. These data reinforce the concept that the structure, function and regulation of the rescued CL in early pregnancy differs from the CL of the menstrual cycle in primates.

Dynamic Expression of the SLIT-ROBO Pathway in the Periovulatory Follicle and Corpus Luteum in Primates.

The Slit-Robo pathway was initially identified in Drosophila and plays a critical role in axon guidance during development of the nervous system. Recently, three Slit (1-3) ligands and four Robo (1-4) receptor isoforms were identified in mammals, in both non-neuronal and neuronal systems where they may function in tissue growth, remodeling, and development. Members of the SLIT-ROBO system were detected in human and nonprimate ovary, but their regulation and functions are unclear. As an initial step in considering its importance in the primate ovary, experiments were designed to investigate the expression of SLIT-ROBO family members in the pre- and peri-ovulatory follicle and corpus luteum (CL) of rhesus monkeys during the menstrual cycle. Using our previously reported Controlled Ovulation (COv) model, the dominant follicle (n=4/interval) was collected at 0, 12, 24, and 36 (ruptured, or unruptured) hours after injection of an ovulatory dose (1000 IU) of hCG. CL (n>4/stage) were collected at early, mid, mid-late, late, or very late (days 3-5, 6-8, 10-12, 14-16 post-LH surge, and menses respectively) luteal phase. These stages encompass the entire lifespan of the CL, from development (early luteal phase) through functional (late) and structural (very late) regression. Total RNAs were extracted from individual tissues, real-time PCR performed, and mRNA levels analyzed by Sigma Stat software using 18S rRNA as an internal control. The mRNAs for all three SLIT ligands and four ROBO receptors were detected in each tissue sample. Appreciable mRNA levels for SLIT1 were present in the preovulatory follicle at 0 hour before hCG injection, followed by a transient decline (p<0.05) at 12 hours post-hCG. Elevated levels returned at 24-36 hours post-hCG prior to follicle rupture, but then declined (p<0.05) to low-levels in the ruptured follicle, which remained invariant in the CL from early to very late luteal phase. The mRNA levels for SLIT2 were appreciable, but unchanging within the periovulatory follicle or CL, until increasing (p<0.05) in the very late luteal phase. Levels of SLIT3 mRNA were low and not significantly different during the periovulatory interval or luteal phase. In contrast, ROBO1 mRNA levels increased (p<0.05) in the preovulatory follicle within 12 hours post-hCG, and remained elevated through follicle rupture, as well as in CL throughout the luteal phase. The levels of ROBO2 or ROBO4 mRNA did not change in the periovulatory follicle or CL during the menstrual cycle, except for a modest, transient increase (p<0.05) in ROBO4 transcript at mid luteal phase. Remarkably, ROBO3 mRNA levels increased from 12 to 36 hours post-hCG in the periovulatory follicle, and again throughout the CL lifespan to peak at late to very late luteal phase (p<0.05). Thus, the presence and dynamic expression of several members of the SLIT-ROBO family in the preovulatory follicle and corpus luteum suggests that this ligand-receptor system plays a role in ovulatory processes and/or luteal development and regression during the ovarian cycle in primates. Supported by NICHD HD18185 (Proj 3), HD053648, RR00163 (poster)

Environmental factors influencing the seasonality of estrus in chimpanzees

Although the energetics of the estrous cycle in primates is not well understood, evidence suggests that energy and nutrient acquisition influence ovulation and the timing of conception. Energy for estrus has to compete with energy allocated for cellular maintenance, thermoregulation, movement for food, and predation avoidance. While some chimpanzee (Pan troglodytes) populations do not have a seasonal birth period, evidence suggests that there is seasonality in the number of estrous females. Similarly, the onset of postpartum cycles has been reported to be seasonal. We used 33 months of data from the Taï National Park, Côte d'Ivoire, to examine how the number of estrous females in a given month was influenced by the abundance and distribution of food, diet, rainfall and temperature. In a second analysis, we examined if there was a seasonal effect on first estrous swellings in adolescent females and postpartum adult females. Results demonstrated that the number of females in estrous in a given month was positively related to food abundance and percent foraging time spent eating insects, and negatively related to mean rainfall in the two preceding months and the mean high temperature. The timing of first estrous swellings of postpartum females and prepartum young females was positively related to the food abundance, and negatively related to mean high temperature. These results showed that environmental conditions can seasonally limit the energetically demanding estrus cycle. The presence of estrous females increases gregariousness in chimpanzee communities, and this study identified environmental factors that affect estrus directly and hence social grouping indirectly.

Controlled ovulation of the dominant follicle: a critical role for LH in the late follicular phase of the menstrual cycle.

A method was sought to control ovulation of the dominant follicle and to test the importance of LH during the late follicular phase of the menstrual cycle. Menstrual cycles of rhesus monkeys were monitored, and treatment initiated at the late follicular phase (after dominant follicle selection, before ovulation). The 2-day treatment consisted of GnRH antagonist plus either r-hFSH and r-hLH (1:1 or 2:1 dose ratio) or r-hFSH alone. In addition, half of the females received an ovulatory bolus of hCG. When treatment was initiated at estradiol levels >120 pg/ml, neither the endogenous LH surge, ovulation nor luteal function were controlled. However, when treatment was initiated at estradiol levels 80-120 pg/ml using either 1:1 or 2:1 dose ratios of FSH:LH, the LH surge was prevented, and ovulation occurred following hCG treatment. FSH-only treatment also prevented the LH surge, but follicle development appeared abnormal, and hCG failed to stimulate ovulation. Control over the naturally dominant follicle is possible during the late follicular phase using an abbreviated GnRH antagonist, FSH+LH protocol. This method offers a model to investigate periovulatory events and their regulation by gonadotrophins/local factors during the natural menstrual cycle in primates.

Cell type-specific expression and regulation of neuropilin-1 and -2 in the rhesus macaque endometrium suggests roles for VEGF-Neuropilin in endometrial remodeling during the menstrual cycle in primates

Objective: Neuropilin-1 and -2 (NP-1/NP-2) are transmembrane receptors that play a role in axonal guidance by binding class III semaphorins, and in angiogenesis by binding vascular endothelial growth factor (VEGF). Although much is known about the biology of VEGF and its cognate receptors, VEGFR1 and VEGFR2, the roles of NP-1 and NP-2 in the primate endometrium are unknown. The goal of this study was to investigate the temporal and spatial expression of NP-1 and NP-2 in the rhesus macaque endometrium during the menstrual cycle. Design: We used in situ hybridization to investigate the cellular localization of NP-1 and NP-2 mRNA in the endometrium of ovarectomized, artificially cycled rhesus macaques. Materials and Methods: Twenty-four ovariectomized rhesus macaques were sequentially treated with estradiol (E) for 14 days and E plus progesterone (P) for 14 days. Then P was withdrawn from all animals to induce menstruation, and E was maintained. Uteri were obtained from one set of animals on days 5–6 (early-proliferative, n = 4), 8-10 (mid-proliferative, n = 3) and on day 14 (late-proliferative, n = 4) after P withdrawal. In the rest of the animals, P was added back after 14 days E treatment and tissue was sampled 3 (early-secretory, n = 4), 7/8 (mid-secretory, n = 4), and 14 (late-secretory, n = 3) days later. In situ hybridization was performed using self-designed probes by RT-PCR and cloning into GEM-T /Teasy vector systems to evaluate the expression and localization of NP-1 and -2 mRNA. Results: NP-1 mRNA was highly expressed in the endothelium of both arteries and veins, but there were no marked changes in its expression during the cycle. However, the luminal epithelium, which also expressed NP-1 mRNA, showed increased expression during the mid- to late-proliferative phase followed by a substantial decrease in expression of this receptor during the luteal phase. NP-1 mRNA was also abundantly expressed in the endometrial stromal cells (but not the glands) with a marked gradient of expression from the surface to the lower-functionalis. Stromal cell NP-1 mRNA changed little during the cycle except for a slight down-regulation during the mid- to late-secretory phase. NP-2 mRNA expression was strictly localized to the endothelium of the veins, was very low during the proliferative phase, and became substantially elevated during the secretory phase. Conclusion: This is the first report in the primate endometrium showing dynamic cell-specific expression and regulation of NP-1 and -2 mRNA during the menstrual cycle. The cyclic expression of NP-1 in the luminal epithelium suggests that VEGF-NP-1 interactions may influence the cyclic changes in the surface properties of this epithelium. In the vascular endothelium, VEGF-neuropilin interactions may result in proliferative effects when only NP-1 is present, and other effects (perhaps related to permeability) when both NP-1 and NP-2 are present during the secretory phase. Stromal NP-1 may mediate other, nonendothelial effects of VEGF through paracrine or autocrine routes. Supported by:German Research Foundation GE 1173/1-1 (AG) and Mellon Foundation (NRN).

Gonadotropin versus steroid regulation of the corpus luteum of the rhesus monkey during simulated early pregnancy.

During the nonconceptive cycle in primates, progesterone is a likely intermediary for several LH-dependent events in the ovary including ovulation, luteinization of the follicle wall, and maintenance of the developed corpus luteum. To determine whether progesterone is an important local factor in the ability of chorionic gonadotropin (CG) to enhance luteal structure and function in early pregnancy, rhesus monkeys received hCG in a dose-escalating regimen (15-2880 IU twice daily) beginning on Day 9 of the luteal phase of the natural menstrual cycle to simulate the rapid rise in serum CG levels associated with early pregnancy. Some animals were concomitantly treated with the 3beta-hydroxysteroid dehydrogenase (3beta-HSD) inhibitor trilostane (500 mg twice daily) to suppress progesterone production during gonadotropin stimulation. Corpora lutea were removed after 1, 3, 6, and 9 days of treatment (n = 3-4 per group); time-matched control tissues were obtained from untreated animals (n = 3 per group). Treatment with hCG prevented both the decrease in luteal wet weight (p < 0.05) and the histologic indices of luteal regression seen in controls during the menstrual cycle. However, coadministration of the progesterone synthesis inhibitor led to early declines in luteal wet weight (p < 0.05) and luteal cell size compared to treatment with hCG alone. Luteal progesterone receptor (PR) mRNA content increased (p < 0.05), but the percentage of cells staining positive for immunoreactive PR declined (p < 0.05) over the treatment interval in all groups. CG administration alone and in combination with trilostane increased PR staining intensity in some luteal cells within 1 day of treatment; intensely staining cells persisted around vascular elements after 9 days of treatment with hCG+trilostane but not with hCG alone. These data suggest that some, but not all, actions of CG to maintain the primate corpus luteum in early pregnancy are mediated by progesterone via a receptor-mediated pathway.

Recombinant human inhibin-A administered early in the menstrual cycle alters concurrent pituitary and follicular, plus subsequent luteal, function in rhesus monkeys.

Inhibin, a suppressor of pituitary FSH secretion in nonprimate species, may also act in the ovary to regulate follicular development. To examine whether inhibin has similar actions in primates, female rhesus monkeys (n = 3/treatment), exhibiting regular menstrual cycles, received sc injections of either vehicle or 60 micrograms/kg recombinant human inhibin-A at 0800 and 1600 h for 5 days beginning at menses. The vehicle-treated monkeys displayed menstrual cycles of normal length, with the follicular (11.3 +/- 2.5 days, mean +/- SE) and luteal (16.3 +/- 2.5 days) phases demarcated by midcycle peaks in serum estradiol (E) and bioactive LH. After the first inhibin injection, levels of immunoreactive inhibin A peaked at 10 ng/mL within 1 h and returned to baseline (< 0.1 ng/mL) before the second injection 8 h later. Although serum E and LH did not change, bioactive FSH decreased (to 66% of pretreatment levels, P < 0.05) within 8 h. Within 1 day, circulating bioactive FSH was less (P < 0.05) in inhibin-treated monkeys, compared with controls. By 2-3 days, serum E levels were also markedly (P < 0.05) reduced in inhibin-treated animals, whereas bioactive LH rose 3-fold (P < 0.05). After inhibin treatment, the midcycle rises in serum E and LH were delayed; hence, the follicular phase was prolonged (15.0 +/- 2.6 days, P < 0.05), compared with controls. Although the patterns and levels of serum LH circulating during the subsequent luteal phase seemed comparable in both groups, mean progesterone levels were suppressed to 2-3 ng/mL (P < 0.05) during the midluteal phase in inhibin-treated monkeys. However, the length of the luteal phase in inhibin-treated cycles (13.0 +/- 2.6 days) was not significantly altered. We conclude that exogenous inhibin rapidly diminishes pituitary FSH secretion in female monkeys during the early follicular phase of the menstrual cycle. This action, and/or other actions directly on the ovary, leads to subsequent effects on follicular steroidogenesis and pituitary LH secretion that culminate in an aberrant ovarian cycle characterized by an insufficient luteal phase. The study identifies, for the first time, possible activities and roles of inhibin during the ovarian cycle in primates.

Manipulation of inhibin during the luteal-follicular phase transition of the primate menstrual cycle fails to affect FSH secretion

The pattern of inhibin concentrations in blood during the menstrual cycle in primates has suggested an endocrine role of inhibin in the negative feedback control of FSH secretion during the luteal phase. Conversely, the fall in inhibin during the late luteal phase may play a role in the rise in serum FSH during the luteal-follicular phase transition. This hypothesis was examined by determining the effects of manipulation of inhibin on FSH secretion in stumptailed macaques. During the mid-luteal phase the putative inhibin feedback was inhibited by i.v. administration of 20 ml of ovine antiserum to human recombinant inhibin in 4 macaques. FSH secretion was unaffected during the initial 24 h period post-treatment and the timing of the rise in FSH which occurred during the subsequent luteal-follicular phase transition was normal. To determine whether the elevated serum concentrations of FSH observed during the early follicular phase could be reduced by administration of inhibin, 5 cyclic macaques were treated with 200 micrograms of recombinant human inhibin i.v. Serum FSH concentrations were unaltered. These results suggest that inhibin does not play a major role in modulating FSH secretion during the luteal-follicular phase transition.

The impact of subchronic hypercortisolemia on progesterone metabolism and the luteinizing hormone-progesterone axis in the cynomolgus monkey.

The purpose of the study was to assess the impact of subchronic hypercortisolemia on progesterone (P) metabolism and production and on peripheral LH levels in a nonhuman primate using a repeated measures experimental design. Osmotic pumps that released hydrocortisone phosphate (HP) at a dose of 15 mg/day were implanted sc in seven cynomolgus monkeys for two menstrual cycles. The pumps were filled with saline for the two control cycles, which either preceded (three animals) or followed (four animals) HP infusion. P metabolism, P production, and episodic secretion of LH were determined 8 +/- 1 days after the serum estradiol peak in the second control cycle and in the second cycle of HP infusion in each monkey, after iv bolus administration of 50 microCi [3H]P, followed by a 6-h blood sampling period. HP infusion elevated serum cortisol levels 1.6-fold. Serum P levels were decreased throughout the luteal phase by 58% (P < 0.01). The MCR of P and the volume of distribution at steady state of P were increased by 200% during HP infusion (both P < 0.005). The production rate of P was increased by HP treatment in five of seven monkeys. HP infusion increased the ratio of 20 alpha-[3H]dihydroprogesterone to [3H]P in serum from 0.5 to 1.0 (P < 0.05) while decreasing the fraction of [3H]P and its metabolites excreted in urine from 20% to 11% (P < 0.05). Serum LH levels, determined over a 5.25-h period in the luteal phase, were elevated by 200% during HP treatment (P < 0.05). Episodic secretion of LH during treatment was characterized by a 660% increase in the pulse amplitude (P < 0.05) and an apparent decrease in the pulse frequency. The results of this study provide evidence that moderate elevation of serum cortisol levels for two menstrual cycles in primates 1) increases the MCR of P, which may be the cause of the observed decrease in serum P levels; and 2) elevates serum LH levels by amplifying its pulse amplitude, which may result in a compensatory rise in the production rate of P.

Effects of subchronic implantation of hydrocortisone phosphate-releasing osmotic pumps on peripheral gonadotropin levels and estradiol feedback to gonadotropin secretion in the cynomolgus monkey.

The purpose of our study was to investigate subchronic effects of moderate hypercortisolemia on serum gonadotropin and estradiol (E2) levels in the primate using a repeated-measures experimental design. Osmotic pumps which released hydrocortisone 21-phosphate (HP) at a dose of 5 mg/day were implanted subcutaneously (s.c.) in each of five cynomolgus monkeys for one menstrual cycle. The pumps were filled with saline for the two control cycles, one of which preceded and one of which followed hormone infusion. Subsequently, osmotic pumps which released HP at a higher dose of 15 mg/day were implanted s.c. in four of the initial five monkeys for the longer period of two menstrual cycles. The pumps were filled with saline for the two additional control cycles, one of which preceded and one of which followed HP infusion at 15 mg/day. The control cycle which followed HP infusion at 5 mg/day and the control cycle which preceded HP infusion at 15 mg/day were separated by at least one menstrual cycle. Administration of HP at the lower dose elevated serum cortisol levels 1.4-fold and decreased serum adrenal androgens to 0.6 of the pretreatment baseline. The higher dose of HP elevated serum cortisol levels 1.7-fold and suppressed serum adrenal androgens to 0.4 of the baseline. In the menstrual cycle following HP infusion serum cortisol levels were depressed to 0.8 and 0.6 of the pretreatment levels after the lower and the higher dose of HP, respectively. Serum levels of adrenal androgens returned to the baseline after the lower dose of HP, but were still suppressed to 0.5 of the baseline after the higher treatment dose. Implantation of pumps which released 5 mg/day of HP did not affect gonadotropin levels in the serum, either in the follicular phase (FP) or the luteal phase (LP) of the menstrual cycle. Serum E2 levels were increased by 77% in the FP during HP infusion at 5 mg/day (p < 0.001), but returned to control values in the LP. Implantation of pumps which released 15 mg/day of HP raised serum luteinizing hormone (LH) levels throughout the two menstrual cycles of treatment, by 111 and 96% in FPs (p < 0.001), and by 84 and 70% in LPs (p < 0.001). Conversely, serum follicle-stimulating hormone (FSH) levels were decreased by 45 and 50% in FPs (p < 0.05), and by 54 and 50% in LPs (p < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

β-Endorphin-Tagesrhythmik in Abhängigkeit von der Zyklusphase

Beta-endorphin (beta-EP) concentrations in hypophyseal portal blood are related to the menstrual cycle in primates. In women, changes in peripheral plasma beta-EP-concentrations were detected throughout the menstrual cycle. A similar circadian rhythm of beta-EP and ACTH was observed in males, suggesting a common mechanism of secretion at the pituitary level. We examined beta-EP, cortisol (F) and prolactin (PRL) levels in peripheral blood of regularly menstruating women. Samples were taken every 2 hours between 6 p.m. and 10 a.m. on days 3 and 4 of the menstrual cycle and 6 and 7 days after the rise of the basal body temperature. A diurnal rhythm of beta-EP could be seen between 6 p.m. and 10 a.m. in the luteal phase, but not in the follicular phase. An early morning rise of beta-EP was accompanied by increasing F-concentrations, suggesting a concomitant secretion of beta-EP and ACTH by the cells of the anterior pituitary. We therefore conclude, that ovarian steroids may influence beta-EP secretion at the pituitary level as well.

Anovulatory luteal cycles in primates

The short-term therapy with gonadotropins and inhibitors of prostaglandin synthesis was administered to 12 adult cycling cynomolgus monkeys to study morphology and functions of anovulatory luteinized follicles. In Group 1, five monkeys (6 cycles) received human menopausal gonadotropin (hMG 10 I.U. FSH/10 I.U. LH per 1 kg) on cycle day (c.d.) 5 and 6. Human chorionic gonadotropin (hCG 50 I.U. per 1 kg) and hMG (5 I.U. LH and 5 I.U. FSH per 1 kg) were given at 12:00 on c.d. 7. Indomethacin (15 mg/kg) was injected at 16:30 on c.d. 7 and 08:30 on c.d. 8. Ovarian biopsy was obtained in 2 cycles. In Group 2, 7 monkeys (33 cycles) received single injection of hCG (50 I.U./ kg) and hMG (5 I.U. FSH/5 I.U. LH/kg) four to one days before the expected ovulation. Two doses of Naproxen-sodium were given orally 4 and 20 hours later. After treatment, females were kept with males for 5 to 7 days. Laparotomy was performed one week after treatment. Ovarian biopsy was obtained in 5 cycles. Treatment in the midfollicular phase caused premature luteinization of the follicles and suppression of ovulation in all cycles. Histological studies revealed presence of luteinized follicles. Serum progesterone was elevated. Luteal phase averaged 13.6 days (vs. 15.8 days in ovulatory cycles). Treatment in the late follicular phase resulted in luteinization of the dominant follicle and inhibition of ovulation in 20 (61%) cycles. Luteal phase lasted 17.1 days. Serum progesterone was elevated to low or midluteal values. Gross evidence of ovulation was present in 13 (39%) cycles. One pregnancy occurred. All monkeys returned to regular, ovulatory cycles after the experiments were terminated.

Effect of Inhibition of Estrogen Synthesis During the Luteal Phase on Function of the Corpus Luteum in Rhesus Monkeys 1

It has been hypothesized that estrogen synthesized by the corpus luteum initiates luteal regression during the nonfertile menstrual cycle in primates. To study the role of endogenous estrogens in functional regression of the monkey corpus luteum, we administered the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) to rhesus monkeys during the luteal phase of the menstrual cycle. Twice-daily oral administration of ATD suppressed systemic and intraluteal estrogen levels by 80-90%. The midluteal phase rise in estradiol concentrations that occurs in rhesus monkeys was completely abolished by ATD treatment. Despite suppression of estrogen synthesis during the luteal phase, mean menstrual cycle length and length of the luteal phase were not different than in control monkeys treated with vehicle only. Progesterone levels were lower in the ATD-treated group on the second and third day of treatment, but did not differ from control levels during the remainder of the cycle. These data suggest that elevated estrogen synthesis during the luteal phase of the menstrual cycle is not a prerequisite for spontaneous luteolysis in rhesus monkeys.

A comparison of primate ovarian cycles

In an attempt to relate sexual behavior to gonadal steroid production in an array of primate species, urinary estrogen and behavior were correlated in both estrous and menstrual-cycle-type species. Small daily urine samples were collected each morning from ruffed lemur, lion-tailed macaque, and gorilla. These were evaluated for total immunoreactive estrogen to monitor ovarian follicular growth and the time of ovulation in all species. Broadly comparative, selected behavioral observations were sampled daily, immediately following urine collection. The resulting data provided a description of a methodological approach to evaluate species-specific behavioral changes and relate them in time to the physiologic events of folliculogenesis and ovulation. When analyzed in this manner, characteristics of both the estrous and menstrual cycles are observed occurring throughout the order Primates and within single species. Estrogen can be directly correlated to attractiveness but not to receptivity or copulation. Furthermore, qualitative differences between primate cycle types are found to be largely due to the kinds of observations used to describe them.

Menstrual cycle and ovarian hormone effects on plasma and platelet monoamine oxidase (MAO) and plasma dopamine-beta-hydroxylase (DBH) activities in the rhesus monkey.

Dopamine-B-hydroxylase (DBH) and monoamine oxidase (MAO) in plasma and platelets were studied in six female rhesus monkeys during three complete menstrual cycles. The same monoamine enzymes of seven bilaterally ovariectomized females were compared with a group of controls. A difference was found in platelet MAO between a mid-menstrual-cycle peak and a perimenstrual trough in these animals, while plasma MAO was unchanged. DBH showed an inverted cyclical variation to that demonstrated by platelet MAO. The ovariectomized females showed significant differences from the controls, confirming the effects of the ovarian sex steroid hormones on platelet MAO and plasma DBH. The variation in these peripheral enzymes may be reflective of changes in brain monoamine systems, which may play some role in the behavioral changes observed during the menstrual cycle in primates.

Menstural and sexual cycle of primates

Menstural and sexual cycle of primates

25. The Duration and Phases of the Menstrual Cycle in Primates

Summary.Data regarding the menstrual cycle of various Primates are summarized in Table II.In animals which undergo a sexual‐skin cycle the phase of swelling (folli‐cular phase) is generally longer and more variable than the phase of quiescence (luteal phase). This finding is related to the well‐established view that the luteal phase in the human menstrual cycle is generally less variable than the pre‐ovulation phase.Various issues concerning the sexual skin, including the sexual coloration of some male monkeys, are considered.