Sexual differentiation of sexual behaviour and preovulatory LH surge in ewes

Effects of Long-Term Flutamide Treatment During Development on Sexual Behaviour and Hormone Responsiveness in Rams

Testosterone exposure during midgestation differentiates neural circuits controlling sex-specific behaviours and patterns of gonadotrophin secretion in male sheep. Testosterone acts through androgen receptors (AR) and/or after aromatisation to oestradiol and binding to oestrogen receptors. The present study assessed the role of AR activation in male sexual differentiation. We compared rams that were exposed to the AR antagonist flutamide (Flu) throughout the critical period (i.e. days 30-90 of gestation) to control rams and ewes that received no prenatal treatments. The external genitalia of all Flu rams were phenotypically female. Testes were positioned s.c. in the inguinal region of the abdomen, exhibited seasonally impaired androgen secretion and were azospermic. Flu rams displayed male-typical precopulatory and mounting behaviours but could not intromit or ejaculate because they lacked a penis. Flu rams exhibited greater mounting behaviour than control rams and, similar to controls, showed sexual partner preferences for oestrous ewes. Neither control, nor Flu rams responded to oestradiol treatments with displays of female-typical receptive behaviour or LH surge responses, whereas all control ewes responded as expected. The ovine sexually dimorphic nucleus in Flu rams was intermediate in volume between control rams and ewes and significantly different from both. These results indicate that prenatal anti-androgen exposure is not able to block male sexual differentiation in sheep and suggest that compensatory mechanisms intervene to maintain sufficient androgen stimulation during development.

Sex differences in expression of oestrogen receptor α but not androgen receptor mRNAs in the foetal lamb brain

Gonadal steroid hormones play important roles during critical periods of development to organise brain structures that control sexually dimorphic neuroendocrine responses and behaviours. Specific receptors for androgens and oestrogens must be expressed at appropriate times during development to mediate these processes. The present study was performed to test for sex differences in the relative expression of oestrogen receptor (ER)α and androgen receptor (AR) mRNA during the window of time in gestation that is critical for behavioural masculinisation and differentiation of the ovine sexually dimorphic nucleus (oSDN) in the sheep. In addition, we examined whether ERα and AR mRNA expression is localised within the nascent oSDN and could be involved in its development. Using the quantitative real-time polymerase chain reaction, we found that females expressed more ERα mRNA than males in medial preoptic area and medial basal hypothalamus during the mid-gestational critical period for brain sexual differentiation. No sex differences were found for AR mRNA in any tissue examined or for ERα in amygdala and frontal cortex. Using radioactive in situ hybridisation, we found that the distributions of ERα and AR mRNA overlapped with aromatase mRNA, which delineates the boundaries of the developing oSDN and identifies this nucleus as a target for both androgens and oestrogens. These data demonstrate that the transcriptional machinery for synthesising gonadal steroid receptors is functional in the foetal lamb brain during the critical period for sexual differentiation and suggest that possible mechanisms for establishing dimorphisms controlled by gonadal steroids may exist at the level of steroid hormone receptor expression.

Developmental programming: postnatal steroids complete prenatal steroid actions to differentially organize the GnRH surge mechanism and reproductive behavior in female sheep

In female sheep, estradiol (E2) stimulates the preovulatory GnRH/LH surge and receptive behavior, whereas progesterone blocks these effects. Prenatal exposure to testosterone disrupts both the positive feedback action of E2 and sexual behavior although the mechanisms remain unknown. The current study tested the hypothesis that both prenatal and postnatal steroids are required to organize the surge and sex differences in reproductive behavior. Our approach was to characterize the LH surge and mating behavior in prenatally untreated (Control) and testosterone-treated (T) female sheep subsequently exposed to one of three postnatal steroid manipulations: endogenous E2, excess E2 from a chronic implant, or no E2 due to neonatal ovariectomy (OVX). All females were then perfused at the time of the expected surge and brains processed for estrogen receptor and Fos immunoreactivity. None of the T females exposed postnatally to E2 exhibited an E2-induced LH surge, but a surge was produced in five of six T/OVX and all Control females. No surges were produced when progesterone was administered concomitantly with E2. All Control females were mounted by males, but significantly fewer T females were mounted by a male, including the T/OVX females that exhibited LH surges. The percentage of estrogen receptor neurons containing Fos was significantly influenced in a brain region-, developmental stage-, and steroid-specific fashion by testosterone and E2 treatments. These findings support the hypothesis that the feedback controls of the GnRH surge are sensitive to programming by prenatal and postnatal steroids in a precocial species.

Gonadotropin-inhibitory hormone is a hypothalamic peptide that provides a molecular switch between reproduction and feeding

OBJECTIVE

Gonadotropin-inhibitory hormone (GnIH)-3 is a neuropeptide that plays a major role in the regulation of reproduction and feeding in mammals.

MATERIALS AND METHODS

We measured endocrine and behavioural parameters of reproduction in sheep, and sexual behaviour in sheep, mice and cynomolgus monkeys. In addition, GnIH gene expression (in situ hybridization) was examined in ewes, and effects of GnIH-3 on food intake and energy expenditure were measured in various species. GnIH-3 was infused (i.v.) into ewes after an i.m. injection of estradiol benzoate to determine whether the peptide blocks the surge in luteinizing hormone (LH) secretion.

RESULTS

GnIH gene expression was reduced in the preovulatory period in ewes. Infusion (i.v.) of GnIH-3 blocked the estrogen-induced LH surge (in ewes). Intracerebroventricular infusion had no effect on female or male sexual behaviour in each of the three species, but increased food intake. There were no effects on energy expenditure in sheep or rats. GnIH increased fos protein (immunohistochemistry) was seen in orexigenic neurons (in sheep and rats), but also in anorexigenic neurons (in sheep).

CONCLUSIONS

GnIH-3 reduces reproductive hormone levels and increases food intake in mammals without reducing energy expenditure. There is minimal effect on reproductive behaviour. The dual effect on reproduction and feeding suggests that GnIH-3 provides a molecular switch between these two functions. Blockade of the positive feedback effect of estrogen with parenteral infusion indicates that this peptide may have utility as a blocker of reproductive function in mammals.

Separate critical periods exist for testosterone-induced differentiation of the brain and genitals in sheep

Sheep exposed to testosterone during a critical period from gestational day (GD) 30 to GD 90 develop masculine genitals and an enlarged male-typical ovine sexually dimorphic nucleus of the preoptic area (oSDN). The present study tested the hypothesis that separate critical periods exist for masculinization of these two anatomical end points. Pregnant ewes were treated with testosterone propionate (TP) either from GD 30 to GD 60 (early TP) or GD 60 to GD 90 (late TP). Control (C) pregnant ewes were treated with corn oil. Fetuses were delivered at GD 135 and the volume of the oSDN was measured. Early TP females possessed a penis and a scrotum devoid of testes, whereas late TP and C females had normal female genitals. Neither period of TP exposure grossly affected the genitals of male fetuses. Despite masculinized genitals, the mean volume of the oSDN in early TP females (0.32 ± 0.06 mm³) was not different from C females (0.24 ± 0.02 mm³) but was significantly enlarged in late TP females (0.49 ± 0.04 mm³; P < 0.05 vs. C) when the genitals appeared normal. In contrast, the volume of the oSDN in late TP males (0.51 ± 0.02 mm³) was not different from C males (0.51 ± 0.04 mm³) but was significantly smaller in the early TP males (0.35 ± 0.04 mm³; P < 0.05 vs. C). These results demonstrate that the prenatal critical period for androgen-dependent differentiation of the oSDN occurs later than, and can be separated temporally from, the period for development of masculine genitals.

The development of male-oriented behavior in rams

The sheep offers a unique mammalian model in which to study paradoxical same-sex sexual partner preferences. Variations in sexual partner preferences occur spontaneously with as many as 8% of rams in a population exhibiting a sexual preference for other rams (male-oriented). The current review presents an overview and update of the male-oriented ram model and discusses several theories that have been invoked to explain same-sex preferences in this species. Although our understanding of the biological determinants and underlying neural substrates of sexual attraction and mate selection are far from complete, compelling evidence is discussed that supports the idea that neural substrates regulating sexual partner preferences are organized during prenatal development. The challenge for future research will be to construct an integrated picture of how hormones, genes, and experience shape sexual partner preference.

Differential effects of prenatal testosterone timing and duration on phenotypic and behavioral masculinization and defeminization of female sheep

The process of sexual differentiation leaves genetically female individuals at risk of being masculinized by exogenous androgens. Previous research with sheep indicates that exposure to excess testosterone from Gestational Day (GD) 30 to GD 90 of the 147-day gestation masculinizes and defeminizes behavior as well as genitalia. Lower doses and shorter durations produce animals with varying degrees of genital virilization and alterations of the hypothalamic-pituitary-gonadal axis, but to our knowledge, the effects on complex behavior and its prediction by the amount of external virilization have not been explored. Previous research in rodents has suggested that sexual differentiation of the central nervous system and the external genitalia can be dissociated. Therefore, we hypothesized that the extent of virilization of external genitalia would not be predictive of the lack of female-typical, or the presence of male-typical, mating behavior. To test this hypothesis, we compared control females, females exposed to exogenous testosterone from GD 30 to GD 90 (T60 females) that have virilized genitalia, and females exposed to testosterone from GD 60 to GD 90 (T30 females) that have female-typical genitalia. Both natural behavioral estrus in the flock and hormonally controlled behavioral tests were used to explore reproductive behavior. The T60 and T30 females exhibited more masculinized reproductive behavior than the controls; however, the T30 females also exhibited feminine behavior. Neither testosterone-treated group was receptive or was mounted at rates comparable to those of controls. These data illustrate that variation in the timing or duration of exposure to prenatal testosterone during a critical period for masculinization can have variable effects on defeminization and that the effects of testosterone on genitalia are not entirely predictive of behavior.

Polycystic ovary syndrome and its developmental origins

The prenatal testosterone (T)-treated adult female rhesus monkey is one animal model of polycystic ovary syndrome (PCOS) in women, with early prenatal T excess programming a permanent PCOS-like phenotype characterized by luteinizing hormone (LH) hypersecretion from reduced hypothalamic sensitivity to steroid negative feedback and relative insulin excess from increased abdominal adiposity. These combined reproductive and metabolic abnormalities are associated with ovarian hyperandrogenism and follicular arrest in adulthood, as well as premature follicle differentiation and impaired embryo development during gonadotropin therapy for in vitro fertilization (IVF). A second animal model for PCOS, the prenatal T-treated sheep also is characterized by LH hypersecretion from reduced hypothalamic sensitivity to steroid negative feedback, persistent follicles and insulin resistance, but also is associated with intrauterine growth retardation and compensatory growth after birth. The ability of prenatal T excess in both species to alter the developmental trajectory of multiple organ systems in utero provides evidence that the hormonal environment of intrauterine life programs target tissue differentiation, raising the possibility that T excess in human fetal development promotes PCOS in adulthood. Such a hypothesis must include data from clinical studies of PCOS women to clarify the homology between these PCOS-like animal models and PCOS per se in reproductive and metabolic function. Future studies should develop new clinical strategies that improve pregnancy outcome and minimize pregnancy loss in women with disorders of insulin action, including PCOS, obesity and diabetes mellitus as well as minimize transgenerational susceptibility to adult PCOS and its metabolic derangements in male close relatives.

Sexual behavior in ewes and other domestic ruminants

Similarities as well as differences across species in the control of sexual behavior are helping to fully understand the subtle relations between physiology and eco-ethological constraints and how the brain integrates such information. We will illustrate this with sexual behavior in domestic ruminants and especially ewes. Females of these species like humans, but unlike rodents, have a long luteal phase. A prolonged exposure to progesterone (Pg) before the preovulatory estradiol rise is necessary for estrous behavior to be displayed. Estradiol action and receptor localization is very similar to that observed in other species. But not too surprisingly, the role of Pg is rather different with a priming effect not observed in rodents. However, as in rodents, Pg also has an inhibitory effect, is necessary for the display of proceptivity and is responsible for the timing of the different periovulatory events. These steroids act on the central nervous system in similar areas across mammalian species to regulate estrous behavior. Steroid fluctuations during the estrous cycle cause changes in catecholaminergic activity in the hypothalamus. Interestingly, these neurotransmitters seem to have very similar effects in ewes and rats as illustrated by the norepinephrine rise after male-female interactions observed in both species. Similar comparisons can be made regarding the action of some neuropeptides, including oxytocin and GnRH, and more integrative processes like sexual differentiation and modulation of reproduction by social interactions. Data on sheep, goats and cows will be compared with those of rodents.

Developmental programming in sheep: administration of testosterone during 60-90 days of pregnancy reduces breeding success and pregnancy outcome

Evidence suggests that exposure to excess steroids during critical periods of fetal development leads to reproductive disorders. Exposure of female lambs to excess testosterone (T) from Days 60 to 90 of gestation (T60-90; term, 147 days) delayed onset of the LH surge and resulted in to male-typical reproductive behavior. The objectives of this study were to test the ability of T60-90 ewes to mate, conceive and lamb during the first three breeding seasons (Years 1, 2 and 3). Pregnant Suffolk ewes were injected with T propionate in cottonseed oil (100mg, im twice weekly) or vehicle (control; C) from Days 60 to 90 of gestation. In Year 1, ewes (C=12, T60-90=12) were kept with a vasectomized ram for 3 months and markings/visual observation of copulations were recorded. Rams had paint applied to their chest to facilitate detection of estrus and mating. All C but only three T60-90 ewes were marked (P<0.001). All ewes were then estrus-synchronized with two injections of prostaglandin F2alpha (20mg, im) given 11 days apart and allowed to mate with a painted, fertile ram. Nine of 12 C and 4 of 12 T60-90 ewes (P=0.1) were mated. Based on estrus and long-term monitoring of progesterone, more C than T60-90 became pregnant (82 and 18%, respectively; P<0.01). In Year 2, to maximize ram exposure, two C and two T60-90 estrus-synchronized ewes were placed with a painted, fertile ram at a time and mated ewes were removed to a nearby pen to force mating with others. Twenty-four hour video monitoring revealed the rams mated more C than T60-90 ewes (83 and 25%, respectively; P=0.01). In both Years 1 and 2, the rams preferred C over T60-90 ewes; therefore in Year 3 rams were given access only to T60-90 ewes. Only four T60-90 estrus-synchronized ewes were placed with a painted ram at a time. Not given an option, 91% of the T60-90 ewes were marked resulting in 4 of 11 (36%; first-service pregnancy rate in the breeding herd was 91%) ewes becoming pregnant to the synchronized estrus. Collectively these studies showed that fertility in T60-90 females was severely compromised, even after overcoming ram preference for controls.

The effect of aromatase inhibition on the sexual differentiation of the sheep brain

This study tested the hypothesis that aromatization of testosterone to estradiol is necessary for sexual differentiation of the sheep brain. Pregnant ewes (n = 10) were treated with the aromatase inhibitor 1,4,6- androstatriene-3,17-dione (ATD) during the period of gestation when the sheep brain is maximally sensitive to the behavior-modifying effects of exogenous testosterone (embryonic d 50-80; 147 d is term). Control (n = 10) ewes received vehicle injections. Fifteen control lambs (7 males and 8 females) and 17 ATD-exposed lambs (7 males and 10 females) were evaluated for sexually dimorphic behavioral and neuroendocrine traits as adults. Prenatal ATD exposure had no significant effect on serum concentrations of androgen at birth, growth rates, expression of juvenile play behaviors, or the onset of puberty in male and female lambs. Rams exposed to ATD prenatally exhibited a modest, but significant, decrease in mounting behavior at 18 mo of age. However, prenatal ATD exposure did not interfere with defeminization of adult sexual partner preferences, receptive behavior, or the LH surge mechanism. In summary, our results indicate that aromatization is necessary for complete behavioral masculinization in sheep. However, before we can conclude that aromatization does not play a role in defeminization of the sheep brain, it will be necessary to evaluate whether intrauterine exposure of male fetuses to higher doses of ATD for a more extended period of time can disrupt normal neuroendocrine and behavioral development.

Fetal programming: prenatal testosterone treatment leads to follicular persistence/luteal defects; partial restoration of ovarian function by cyclic progesterone treatment

Prenatal testosterone (T) excess during midgestation leads to estrous cycle defects and polycystic ovaries in sheep. We hypothesized that follicular persistence causes polycystic ovaries and that cyclic progesterone (P) treatment would overcome follicular persistence and restore cyclicity. Twice-weekly blood samples for P measurements were taken from control (C; n = 16) and prenatally T-treated (T60; n = 14; 100 mg T, im, twice weekly from d 30-90 of gestation) Suffolk sheep starting before the onset of puberty and continuing through the second breeding season. A subset of C and T60 sheep were treated cyclically with a modified controlled internal drug-releasing device for 13-14 d every 17 d during the first anestrus (CP, 7; TP, 6). Transrectal ovarian ultrasonography was performed for 8 d in the first and 21 d in the second breeding season. Prenatal T excess reduced the number, but increased the duration of progestogenic cycles, reduced the proportion of ewes with normal cycles, increased the proportion of ewes with subluteal cycles, decreased the proportion of ewes with ovulatory cycles, induced the occurrence of persistent follicles, and reduced the number of corpora lutea in those that cycled. Cyclic P treatment in anestrus, which produced one third the P concentration seen during luteal phase of cycle, did not reduce the number of persistent follicles, but increased the number of progestogenic cycles while reducing their duration. These findings suggested that follicular persistence might contribute to the polycystic ovarian morphology. Cyclic P treatment was able to only partially restore follicular dynamics, but this may be related to the low replacement concentrations of P achieved.

Fetal Programming: Testosterone Exposure of the Female Sheep During Midgestation Disrupts the Dynamics of Its Adult Gonadotropin Secretion During the Periovulatory Period1

Prenatal exposure of the female sheep to excess testosterone (T) leads to hypergonadotropism, multifollicular ovaries, and progressive loss of reproductive cycles. We have determined that prenatal T treatment delays the latency of the estradiol (E2)-induced LH surge. To extend this finding into a natural physiological context, the present study was conducted to determine if the malprogrammed surge mechanism alters the reproductive cycle. Specifically, we wished to determine if prenatal T treatment 1) delays the onset of the preovulatory gonadotropin surge during the natural follicular phase rise in E2, 2) alters pulsatile LH secretion and the dynamics of the secondary FSH surge, and 3) compromises the ensuing luteal function. Females prenatally T-treated from Day 60 to Day 90 of gestation (147 days is term) and control females were studied when they were approximately 2.5 yr of age. Reproductive cycles of control and prenatally T-treated females were synchronized with PGF2alpha, and peripheral blood samples were collected every 2 h for 120 h to characterize cyclic changes in E2, LH, and FSH and then daily for 14 days to monitor changes in luteal progesterone. To assess LH pulse patterns, blood samples were also collected frequently (each 5 min for 6 h) during the follicular and luteal phases of the cycle. The results revealed that, in prenatally T-treated females, 1) the preovulatory increase in E2 was normal; 2) the latencies between the preovulatory increase in E2 and the peaks of the primary LH and FSH surges were longer, but the magnitudes similar; 3) follicular-phase LH pulse frequency was increased; 4) the interval between the primary and secondary FSH surges was reduced but there was a tendency for an increase in duration of the secondary FSH surge; but 5) luteal progesterone patterns were in general unaltered. Thus, exposure of the female to excess T before birth produces perturbances and maltiming in periovulatory gonadotropin secretory dynamics, but these do not produce apparent defects in cycle regularity or luteal function. To reveal the pathologies that lead to the eventual subfertility arising from excess T exposure during midgestation, studies at older ages must be conducted to assess if there is progressive disruption of neuroendocrine and ovarian function.

Prenatal programming of reproductive neuroendocrine function: the effect of prenatal androgens on the development of estrogen positive feedback and ovarian cycles in the ewe

Exposure of the female ovine fetus to male hormones during a sensitive window of in utero life causes disruption to reproductive function. In some animals, androgen exposure completely abolishes reproductive cycles, but in others, cycles are progressively lost with age. The present study tested two predictions: that noncycling, androgenized animals are unable to respond to estrogen with a preovulatory-like surge of LH (estrogen positive feedback), and that the androgenized animals that exhibit a progressive loss of cycles also show a progressive loss of estrogen positive feedback. Androgenized ewes were generated by injection of their mothers with testosterone propionate twice per week from Day 30 to Day 90 of pregnancy (term, 147 days). Control ewes received no injections. Whether ewes could exhibit estrogen positive feedback was tested on five occasions before puberty (30 wk) and once during the anestrous period. All control animals had repeated reproductive cycles in both the first and second breeding season, and all showed robust LH surges during test periods. Despite the fact that 64% of androgenized animals showed reproductive cycles, estrogen positive feedback could be demonstrated in only 6.1% of trials. Subsequent experiments revealed that the lack of response to estrogen in androgenized animals was not because of pituitary insensitivity to GnRH, a requirement for higher concentrations of estrogen, or a surge that was delayed relative to the time of estrogen administration. The mechanisms by which some androgenized ewes can produce normal reproductive cycles in the apparent absence of estrogen positive feedback are currently unknown.

Prenatal programming of reproductive neuroendocrine function: fetal androgen exposure produces progressive disruption of reproductive cycles in sheep

In the agonadal, androgenized ewe testosterone before birth produces a precocious pubertal rise in circulating LH and abolishes the LH surge mechanism. The present study tested two predictions from this model in the ovary-intact female: 1) prenatal androgen exposure produces early ovarian stimulation; and 2) despite early ovarian stimulation, progestogenic cycles would not occur because of the abolition or disruption of the LH surge. Pregnant ewes were injected with testosterone propionate twice per week from either d 30-90 (T60 group; 100 mg/injection) or d 60-90 (T30 group; 80 mg/injection) of gestation (term, 147 d). Control ewes received no injections. At birth, the androgenized and control lambs were divided into two groups: ovary-intact to determine the effects of prenatal androgen on the timing of puberty and subsequent ovarian function, and ovariectomized to assess the timing of the pubertal decrease in sensitivity to estrogen negative feedback and the subsequent increase in LH. Neonatally orchidectomized, estrogen-treated males were included for comparison of the timing of this pubertal rise in LH secretion. Neuroendocrine puberty (determined on the basis of LH increase) was advanced in the androgenized females to a similar age as in males. Repeated progesterone cycles of the same duration and number occurred in the ovary-intact ewes, and they began at the same time as for control females, thus negating both predictions. Differences appeared during the second breeding season, when reproductive cycles were either absent (T60) or disrupted (T30 group). Our findings reveal that exposure to androgens in utero causes a progressive loss of cyclic function in adulthood.

Fetal programming: prenatal androgen disrupts positive feedback actions of estradiol but does not affect timing of puberty in female sheep

We studied the impact of prenatal androgen exposure on the timing of onset of puberty, maintenance of cyclicity in the first breeding season, and the LH surge mechanism in female sheep. Pregnant sheep were injected with testosterone propionate (100 mg i.m.) twice each week from Day 30 to Day 90 (D30-90) or from Day 60 to Day 90 (D60-90) of gestation (term = 147 days). Concentrations of plasma progesterone and gonadotropins were measured in blood samples collected twice each week from control (n = 10), D60-90 (n = 13), and D30-90 (n = 3) animals. Rate of weight gain and initiation of estrous behavior were also monitored. After the first breeding season, when the animals entered anestrus, competency of the gonadotropin surge system to respond to estradiol positive feedback was tested in the absence or presence of progesterone priming for 12 days. Prenatally androgenized females had similar body weight gain and achieved puberty (start of first progestogenic cycle) at the same time as controls. Duration of the breeding season and the number of cycles that occurred during the first breeding season were similar between control and prenatally androgenized sheep. In contrast, prenatal exposure to androgens compromised the positive feedback effects of estradiol. Onset of LH/FSH surges following the estradiol stimulus was delayed in both groups of androgenized ewes compared with the controls in both the absence and presence of progesterone priming. In addition, the magnitude of LH and FSH surges in the two animals that surged in the D30-90 group were only one third and one half, respectively, of the magnitudes observed in the control and D60-90 groups. The present findings indicate that disruption of the surge system can account for the fertility problems that occur during adulthood in prenatally androgenized sheep.

In utero exposure of female lambs to testosterone reduces the sensitivity of the gonadotropin-releasing hormone neuronal network to inhibition by progesterone

Exposure of the female ovine fetus to exogenous androgens during early gestation permanently masculinizes the reproductive anatomy, physiology, and behavior of the adult ewe. In utero testosterone exposure has been shown to act centrally on the GnRH neuronal network to alter the response to both the stimulatory and inhibitory actions of estrogen. It is currently unknown whether fetal androgens alter other mechanisms that are critical for the regulation of GnRH release and, specifically, other important regulatory steroid feedback loops. Three studies were performed on gonadectomized postpubertal sheep to determine whether the inhibitory actions of progesterone on episodic LH release are also sex-specific and engendered by early in utero exposure to testosterone. In each study, the pulsatile pattern of LH release was determined both before and after the sc implantation of a progesterone releasing CIDR device. The studies involved 7 female, 7 male, and 12 androgenized female sheep (T60 (n = 7) and T30 (n = 5) groups; 200 mg testosterone propionate/week im to the mother for 60 or 30 days, respectively, from day 30-90 or 60-90 of pregnancy). The first two studies were performed in the anestrous season in the presence (Exp 1) or absence (Exp 2) of a low circulating concentration of estradiol. Exp 3 was carried out in the breeding season in the absence of exogenous estrogen. In all three studies progesterone inhibited LH pulse frequency only in the females. Progesterone had no action on mean LH concentrations or the frequency or amplitude of LH pulses in the males or either group of androgenized ewes. We conclude that the inhibition of episodic LH release by progesterone is sexually differentiated in the sheep, males being less responsive than females to steroid negative feedback. Further, these sex differences are a consequence of in utero exposure to androgens for a period as short as 30 days between days 60 and 90 of a 147-day pregnancy.

Sexual play behavior in lambs androgenized in utero

In lambs, play behavior, mainly including male-like sexual behavior patterns, is observed during weeks 4-8 following birth. The higher frequency of this behavior in male lambs has no obvious relationships with secretions of testosterone during infancy. In our experiment, pregnant ewes received subcutaneous implants of testosterone on gestation day 50. The frequency of male-like sexual patterns did not differ reliably between female lambs born to treated ewes and male lambs born to treated or control ewes. However, the frequency was lower for female control lambs. These results suggest that sexually dimorphic social play in lambs is dependent on prenatal exposure, which seems to have a masculinized effect.