Cyclic changes in plasma progestins and estrogens in squirrel monkeys

Monitoring sexual steroids and cortisol at different stages of the ovarian cycle from two capuchin monkey species: use of non- or less invasive methods than blood sampling

Endocrine monitoring of non-human primates (NHP) via faecal metabolites of steroid hormones appears as a useful non-invasive alternative to evaluate the reproductive status of free living NHP, as well as of those kept in captivity but of difficult handling. However, validation is needed with plasma values before its application in the field. The aim of the present study was to monitor the different phases of the menstrual cycle from the new world NHP Sapajus apella and S. libidinosus. For this, hormonal and faecal plasma levels of E₂, P₄ and cortisol were assessed during different days of the menstrual cycle, together with colpocitology. The mean duration of the menstrual cycle according colpocitology was of 21.7 and 21.0 days for S. apella and S. libidinosus, respectively. These values were similar to those observed via plasma analysis, i.e. 22.7 and 20.3 days for S. apella and S. libidinosus, respectively. The day of plasmatic E₂ peak was set as Day -1 and the estimated day of ovulation was set as Day 0 and occurred two days earlier in S. libidinosus than in S. apella females. In both species, it was observed a delay in faecal E₂ peak of six days for S. apella and of 11 days for S. libidinosus when compared with the plasma peak. A maximum P₄ plasma concentration was observed in the middle of luteal phase in S. apella and in S. libidinosus, both at around day 5. However, faecal P₄ peaks were detected at days 9 and 8 in S. apella and S. libidinosus, respectively. Mean plasma and faecal cortisol levels were variable during all ovulatory cycle of S. apella and S. libidinosus females. Although no exact correlation was observed between plasmatic and faecal profile of steroid hormone, faecal samples were able to indicate ovarian cycle phase, being important to assess the reproductive status of the females applying a non-invasive method.

Ancestral resurrection of anthropoid estrogen receptor β demonstrates functional consequences of positive selection

Anthropoid primates arose during the Eocene approximately 55 million years ago (mya), and extant anthropoids share a most recent common ancestor ∼40mya. Paleontology has been very successful at describing the morphological phenotypes of extinct anthropoids. Less well understood is the molecular biology of these extinct species as well as the phenotypic consequences of evolutionary variation in their genomes. Here we resurrect the most recent common ancestral anthropoid estrogen receptor β gene (ESR2) and demonstrate that the function of this ancestral estrogen receptor has been maintained during human descent but was altered during early New World monkey (NWM) evolution by becoming a more potent transcriptional activator. We tested hypotheses of adaptive evolution in the protein coding sequences of ESR2, and determined that ESR2 evolved via episodic positive selection on the NWM stem lineage. We separately co-transfected ESR2 constructs for human, NWM, and the anthropoid ancestor along with reporter gene vectors and performed hormone binding dose response experiments that measure transactivation activity. We found the transactivation potentials of the ancestral and human sequences to be significantly lower (p<0.0001 in each comparison) than that of the NWM when treated with estradiol, the most prevalent estrogen. We conclude the difference in fold activation is due to positive selection in the NWM ERβ ligand binding domain. Our study validates inferential methods for detecting adaptive evolution that predict functional consequences of nucleotide substitutions and points a way toward examining the functional consequences of positive Darwinian selection.

Population estimate and morphometry of ovarian preantral follicles from three recently recognized squirrel monkey species: a comparative study

We describe morphological and morphometrical characteristics of preantral ovarian follicles from three recently recognized Saimiri species: S. macrodon, S. cassiquiarensis and S. vanzolinii; the last one a threatened species. Ovaries from four adult monkeys were evaluated: one pair from a pregnant S. macrodon, two ovarian pairs from S. cassiquiarensis females (one of them pregnant), and one left ovary from a senile S. vanzolinii, applying classical histology. Follicular preantral population was quantified and morphology and morphometry of primordial, primary and secondary follicles were evaluated. Follicular preantral population varied among species, being 347,153 in the ovaries of the S. macrodon, 270,342 and 278,376 in the ovaries of both adult non-pregnant and pregnant S. cassiquiarensis females, and 28,149 in the ovary from a senile S. vanzolinii. Most follicles were at primordial or transition stages, except for the senile S. vanzolinii female, which presented the lowest percentages of primordial and transition follicles when compared with primary and secondary ones. Most preantral follicles (>70%) were morphologically normal in the ovaries from all studied S. macrodon and S. cassiquiarensis females, but the ovary of the senile S. vanzolinii female presented a significant decrease in the percentage of normal follicles (primordial: 61%, transition: 52%, primary: 54%, and secondary: 48%). In general, follicular diameter increased significantly from primordial to transition, and subsequently from primary to secondary follicles.

Ovarian aging in squirrel monkeys (Saimiri sciureus)

In female squirrel monkeys (Saimiri sciureus), the reproductive period normally extends from approximately 2.5 years to the mid-teens. In the present study, we examined the age-associated cytological changes in the ovaries of 24 squirrel monkeys ranging in age from newborn to approximately 20 years. We found a significant, age-related decline in the number of primordial follicles, with the most pronounced loss occurring between birth and 5 years. After approximately 8 years of age, relatively few primordial follicles were evident in the ovarian sections examined. An unusual feature of the aging squirrel monkey ovary is the emergence of highly differentiated, encapsulated clusters of granulosa cells that increase in size and number, particularly after the age of 8 years. Many of these cells express anti-Müllerian hormone, and, histologically, the clusters resemble granulosa cell tumors in humans. However, granulosa cell clusters (GCCs) are present in both ovaries of all older squirrel monkeys, and they display no obvious signs of malignancy, suggesting that they are a normal feature of ovarian aging in this species. Our findings indicate that reproductive senescence in female squirrel monkeys, as in other primates, involves the inexorable depletion of ovarian follicles. In addition, the consistent appearance of abundant, well-differentiated clusters of granulosa cells in older squirrel monkeys, prior to the cessation of reproduction, suggests that these structures may influence the later stages of reproductive potential in this species. Analysis of GCCs in older squirrel monkeys also could yield insights into the pathophysiology of granulosa cell tumors in humans.

Elevated ovarian expression and serum concentration of alpha 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 nonbreeding 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.

Urinary progesterone in free-ranging red howler monkeys (Alouatta seniculus): preliminary observations of the estrous cycle and gestation

The goals of this study were to develop and validate a radioimmunoassay (RIA) for measurement of unconjugated progesterone (P) concentrations in the urine of red howler monkeys (Alouatta seniculus) and to use urinary P profiles to characterize the reproductive cycle of this species. Analysis of P profiles from two females provided a preliminary estimate of the length of the estrous cycle (mean days +/- S.E.M. = 29.5 +/- 1.5; n = 2), and indicated that one female red howler copulated throughout two apparent estrous cycles. Urinary P concentrations during two confirmed pregnancies (211.8 +/- 29.7 ng P/ml) were higher (P < 0.05) than during the luteal phase (77.4 +/- 10.6 ng P/ml; n = 4) of the cycle.

Incorporation of a GnRH agonist, leuprolide acetate, into regimens with exogenous gonadotropins to produce ovarian stimulation and ovulation in the nonpregnant squirrel monkey

This study was designed to measure the effects of variations in the length of pretreatment with a GnRH agonist, leuprolide acetate (LA), on subsequent follicular development and ovulation. The hypothesis was that the duration of LA suppression of pituitary function does not adversely affect ovarian response to standardized ovulation induction protocols in squirrel monkeys. The first phase determined the dose and duration of LA needed to achieve a hypogonadal state. One of two groups received daily subcutaneous injections of 50 microg of LA. The other received a single injection of 175 microg of a depot suspension of LA. Sera were assayed for estradiol (E2) and progesterone (P). E2 and P levels increased 2- to 5-fold with peak levels on days 4 and 7, respectively. Suppression of steroid levels took 10 to 15 days in the LA-treated group. Depot-LA did not effectively suppress steroid production. After suppression, females receiving daily LA received five daily injections of hMG to stimulate follicular development. E2 and P increased in these animals. These results suggest that cycling squirrel monkeys have P-secreting capacity throughout the cycle. This may explain how the squirrel monkey is able to accommodate both a short (4-5 day) luteal phase of their 9 day cycle and implantation from 5 to 7 days after ovulation. A second study compared exogenous follicle stimulating hormone (FSH) to endogenous gonadotropins released as a response to LA in ovulation induction. Steroid production and hCG-induced ovulation were assessed. LA treatment was compared to a standard ovulation induction protocol by using a randomized cross-over measures design. There were no differences in E2 and P levels in response to dosages of either LA or hMG. The ovulatory response following LA treatment was not significantly greater than that using FSH. The number of animals with unovulated, large follicles was greater on the FSH protocol (12/18) compared to the LA protocol (3/18). Thus, a single injection of a depot preparation of LA is sufficient to stimulate follicular development and ovulation when followed by an hCG injection. Based on this observation and the data on unovulated large follicles, it is suggested that the ovary responds more readily to endogenous gonadotropins released by LA than to exogenous FSH.

New method for in vivo recording of myometrial activity in the squirrel monkey, Saimiri sciureus

Videolaparoscopy was used to visualize the reproductive tract contractility of the squirrel monkey, Saimiri sciureus. This technique gives information on the nature, direction of propagation, duration, and frequency of contractions. At the times of ovulation, and embryo entry to the uterus, contractile activity was observed in both the uterus and oviduct, with the latter being more frequent. The dominant direction of propagation was towards the utero-tubal junction, and simultaneous contractions were frequently observed in both uterus and oviduct. © 1992 Wiley-Liss, Inc.

Breeding readiness in squirrel monkeys: female-primed females are triggered by males

The South American squirrel monkey (Saimiri) shows pronounced annual variations in reproductive activity. We investigated the contribution of social stimulation to breeding readiness, as reflected in behavior and gonadal hormones. A previous study indicated that formation of new heterosexual pairs can induce breeding readiness in males, but not in females. In the present study we examined the response of individually housed females to the formation of triads of unacquainted females and, subsequently, the response of these triads to the introduction of a single male. The formation of the all-female group was accompanied by a marked reduction in basal cortisol levels. Introduction of a male to such a group promptly induced breeding readiness in the females, as indicated by increased gonadal hormone production and cyclic variation in estrogen and progesterone levels. The contrasting responses of group-living or single females to a new male suggest that at least two processes are involved in the induction of breeding readiness by group formation in females. One is a "priming" effect resulting from interfemale stimulation: the other is a "triggering" effect resulting from the presence of a male.

Behavioral and endocrine consequences of heterosexual pair formation in squirrel monkeys

The South American squirrel monkey (Saimiri sciureus) typically lives in large social groups containing several individuals of all age/sex categories. When living in established heterosexual pairs, reproduction in this seasonally breeding primate is poor. We attempted to induce breeding activity in pair-housed monkeys by forming new heterosexual pairs just prior to the breeding season. Breeding readiness, as reflected in behavior and gonadal hormones, was induced in males, but not in females. Males also showed persistent increases in cortisol levels following formation of new heterosexual pairs; females did not. The results indicate that social stimulation provided by a single novel female is sufficient to enhance breeding readiness in male squirrel monkeys. Females, on the other hand, are apparently unresponsive to a single male whether novel or familiar; this may account for the poor reproductive success in squirrel monkeys housed in heterosexual pairs.

Conversion of androgens to estrogens in the male squirrel monkey (Saimiri sciureas)

Many New World primates such as the squirrel monkey have extraordinarily high plasma levels of steroid hormones including cortisol, testosterone, progesterone and vitamin D3. While plasma estrogen levels in female squirrel monkeys apparently are approximately the same as those found in other species no information is available for males. The present results indicate that the plasma levels of estrone (E1), estradiol (E2), and E1 sulfate are approximately 10-fold higher than those found in men. Comparative in vitro studies of androgen metabolism in genital skin fibroblasts indicate that squirrel monkey cells have higher aromatase and lower 5-alpha-reductase activity than human cells. Estimation of aromatase activity in vivo by a radiometric assay indicates that the high plasma estrogens are derived by peripheral conversion from testicular and/or adrenal androgens.

The new world primates as animal models of glucocorticoid resistance

Many New World primate species have greatly increased plasma cortisol concentrations, decreased plasma cortisol binding globulin capacity and affinity, marked resistance of the hypothalamic-pituitary-adrenal axis to suppression by dexamethasone, and no biological evidence of glucocorticoid excess. These primates also have high levels of circulating progesterone, estrogen, mineralocorticoid, androgen and vitamin D. The glucocorticoid target tissues that have been examined (circulating mononuclear lymphocytes and cultured skin fibroblasts) have normal concentrations of glucocorticoid receptors with decreased affinity for dexamethasone. Transformation of B-lymphocytes with the Epstein-Barr virus leads to glucocorticoid receptor induction that is less than that observed with cells from Old World primates. The receptor in these cells has a low affinity for dexamethasone. The low affinity leads to an increased loss of specific bound ligand during thermal activation. Meroreceptor generation is normal. The molecular weight of the receptor, determined by SDS-PAGE, is similar to that of Old World primates (approximately 92,000) and the activation pattern per se, examined in vitro by heating cytosol and performing phosphocellulose chromatography, appears similar to that of human controls. The ratios of nuclear to cytosolic hormone-receptor-complexes and of cytosolic activated to unactivated receptor complexes in intact cells are similar to Old World primates. Results from mixing studies do not support the hypothesis that a binding inhibitor(s) or a deficient cytosolic positive modifier(s) of binding underlies the findings in these primates. The New World primates, unlike men with the syndrome of primary cortisol resistance, have compensated for their condition with intra-adrenal and mineralocorticoid receptor adaptations. Thus, unlike Old World primates, cortisol in New World primates has only weak sodium-retaining potency because the aldosterone receptor has a low affinity for cortisol. The common element that would explain the apparent resistance to six steroid hormones in New World primates remains unknown.

The mechanism of end-organ resistance to 1 alpha,25-dihydroxycholecalciferol in the common marmoset

The common marmoset, a New World monkey, requires a large amount of cholecalciferol (110 i.u./day per 100g body wt.) to maintain its normal growth. In a previous report, we demonstrated that the circulating levels of 1 alpha, 25-dihydroxycholecalciferol [1 alpha,25(OH)2D3] in the marmosets are much higher than those in rhesus monkeys and humans, but the marmosets are not hypercalcaemic [Shinki, Shiina, Takahashi, Tanioka, Koizumi & Suda (1983) Biochem. Biophys. Res. Commun. 14, 452-457]. To compare the effect of the daily intake of cholecalciferol, two rhesus monkeys were given a large amount of cholecalciferol (900 i.u./day per 100g body wt). Their serum levels of calcium, 25-hydroxycholecalciferol and 24R,25-dihydroxycholecalciferol were markedly elevated, but the serum 1 alpha,25(OH)2D3 levels remained within a range similar to those in the rhesus monkeys fed the normal diet (intake of cholecalciferol 5 i.u./day per 100g body wt). Intestinal cytosols prepared from both monkeys contained similar 3.5 S macromolecules to which 1 alpha,25(OH)2D3 was bound specifically. However, the cytosols from the marmosets contained only one-sixth as many 1 alpha,25(OH)2D3 receptors as those from the rhesus monkeys. Furthermore, the activity of the 1 alpha,25(OH)2D3-receptor complex in binding to DNA-cellulose was very low in the marmosets. These results suggest that the marmoset possesses an end-organ resistance to 1 alpha,25(OH)2D3 and is a useful animal model for studying the mechanism of vitamin D-dependent rickets, type II.