Circulating activin A during equine gestation and immunolocalization of its receptors system in utero-placental tissues and fetal gonads.

Although equine gestation is unique from the standpoint of fetal gonadal enlargement and regression, the activator of this process is still unknown. The present study aimed to show a possible role of activin during equine gestation. In the first experiment, weekly plasma samples from six pregnant mares were used to measure activin A. In the second experiment, eight pregnant mares carrying female (gestational days 110, 140, 180, and 270) and male fetuses (gestational days 120, 180, 225, and 314) were used for immunohistochemistry of activin receptors (IA, IB, IIA, IIB), and their intracellular mediators (Smad2, Smad3, Smad4). Activin A levels in maternal circulation remained low until fourth weeks of gestation, thereafter, started to increase, and peaked first at 11 weeks of gestation. The second significant peak was observed on the day of parturition. Activin receptors type IA, IB, IIA, and IIB were immunostained in interstitial and germ cells of fetal ovaries and testes along with utero-placental tissues. Smad2, Smad3, and Smad4 were also immunolocalized in all these organs. These results demonstrated the activin-producing capacity of utero-placental tissues, and also evidenced the existence of activin receptors and functional signaling molecules in these organs. The first increment in circulating activin A in maternal circulation coinciding with the timing of initiation of fetal gonadal enlargement suggests that activin from the utero-placental tissues may have a stimulatory role in fetal gonad enlargement and utero-placental development in mares, whereas the second peak could be important to follicular development in the maternal ovary for foal heat.

Influence of exercise and emotional stresses on secretion of prolactin and growth hormone in Thoroughbred horses.

The secretion of prolactin and growth hormone in response to exercise and emotional stresses was investigated in Thoroughbreds. Two experiments were performed: one with loading of only exercise stress and one with simultaneous loading of exercise and emotional stresses. Exercise stress was loaded in 4 steps using a treadmill for horses: pre-exercise period (5 min), walking period (6.5 min), galloping period (3 min), and cooling down period (10 min). Emotional stress was loaded by showing a loud video of an audience at a racetrack during the walking period. The results clearly demonstrated that exercise stress rapidly increased the secretion of prolactin and growth hormone and that secretion of them persisted for a specific period after the exercise. In addition, emotional stress promoted prolactin secretion.

Evaluation of the chemiluminescent enzyme immunoassay system for the measurement of testosterone in the serum and whole blood of stallions.

Testosterone (T) concentration is a useful indicator of reproductive function in male animals. However, T concentration is not usually measured in veterinary clinics, partly due to the unavailability of reliable and rapid assays for animal samples. In this study, a rapid chemiluminescent enzyme immunoassay system (CLEIA system) that was developed for the measurement of T concentration in humans use was validated for stallion blood samples. First, serum T concentrations were measured using the CLEIA system and compared with those measured by a fluoroimmunoassay that has been validated for use in stallions. The serum T concentrations measured by the two methods were highly correlated (r = 0.9865, n = 56). Second, to validate the use of whole blood as assay samples, T concentrations in whole blood and in the serum were measured by the CLEIA system. T concentrations in both samples were highly correlated (r = 0.9665, n = 64). Finally, to evaluate the practical value of the CLEIA system in clinical settings, T concentrations were measured in three stallions with reproductive abnormalities after the administration of human chorionic gonadotropin (hCG). Two stallions with small or absent testes in the scrotum showed an increase in T production in response to hCG administration and one stallion with seminoma did not. In conclusion, the CLEIA system was found to be a rapid and reliable tool for measuring T concentrations in stallions and may improve reproductive management in clinical settings and in breeding studs.

Expression of activin receptors in the equine uteroplacental tissue: an immunohistochemical analysis.

Activin is secreted from equine uterine glands and plays important roles in establishment and maintenance of pregnancy in mares. This study aimed to localize activin receptors (ActRs) IA/B and IIA/B using immunohistochemistry in the uteroplacental tissues of seven pregnant Thoroughbred mares. At the time of tissue collection, the mares were at the following days of pregnancy: 88, 120, 161, 269, 290, 313, and 335 days. We fixed the uteroplacental tissues in 4% paraformaldehyde and obtained serial sections that were subsequently stained for analysis. All four isoforms of ActR were expressed in the uteroplacental tissues, including the endometrial epithelium, uterine glands, trophoblasts, and myometrium, throughout pregnancy. Our results suggested the potential role of activin in the uteroplacental tissues.

Seasonal expression of P450arom and estrogen receptors in scented glands of muskrats (Ondatra zibethicus).

Male muskrats have one pair of scented glands that grow and involute annually. To investigate the annual changes in the scented gland, we measured the expressions of aromatase cytochrome P-450 (P450arom) and estrogen receptors (ERs) in the scented glands. P450arom was expressed in glandular cells and epithelial cells in the scented glands during the breeding season, and only in glandular cells during the nonbreeding season. ERα and ERß were also detected in different types of cells in the scented gland during the breeding and nonbreeding seasons. Both mRNA and protein levels of P450arom, ERα, and ERß were higher in the scented glandular tissues during the breeding season than those during the nonbreeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed microRNAs might be the genes encoding P450arom and ERs. In conclusion, the seasonal changes in the expression of P450arom and ERs may be involved in the regulation of scented gland functions.

Seasonal expressions of follicle-stimulating hormone receptor and luteinizing hormone receptor in the scented gland of the male muskrat (Ondatra zibethicus).

Accumulating evidence has shown that follicle-stimulating hormone (FSH) and luteinizing hormone (LH) may influence the functions of nongonadal tissues in addition to their classic target gonads. Our previous studies revealed that the scented glands of male muskrats expressed prolactin receptor, steroidogenic enzymes, and inhibin/activin subunits. To further seek the evidence of the activities of pituitary gonadotropins in scented glands, we investigated the seasonal expression patterns of FSH receptor (FSHR) and LH/choriogonadotropin receptor (LHCGR). The weight and size of scented glands during the breeding season were significantly higher than those during the nonbreeding season. Immunohistochemical studies showed that FSHR was present in the serous cells of scented glands, whereas LHCGR was present in the interstitial cells. The protein and mRNA expression levels of FSHR and LHCGR were significantly higher in the scented glands during the breeding season than those during the nonbreeding season. Importantly, the levels of circulating FSH and LH were remarkably higher during the breeding season. Taken together, these results suggested that gonadotropins may affect the function of muskrat scented gland via the locally expressed receptors in a season-dependent manner.

4-Nitrophenol exposure alters the AhR signaling pathway and related gene expression in the rat liver.

4-Nitrophenol (PNP) is well known as an environmental endocrine disruptor. The aim of this study was to clarify the mechanism of PNP-induced liver damage and determine the regulatory involvement of the aryl hydrocarbon receptor (AhR) signaling pathway and associated gene expression. Immature male Wistar-Imamichi rats (28 days old) were randomly divided into control and PNP groups, which consisted of 1- and 3-day exposure (1 DE and 3 DE, respectively) and 3-day exposure followed by 3-day recovery (3 DE + 3 DR), groups. Each group was administered the vehicle or PNP (200 mg kg-1 body weight). The body and liver weight were significantly decreased in the 3 DE group. The mRNA expression levels of estrogen receptor-α (ERα), glutathione S-transferase (GST) and AhR exhibited a significant increase in the 1 DE group whereas, in contrast, that of cytochrome P450 (CYP) 1A1 decreased significantly in the 3 DE +3 DR group. AhR and CYP1A1 proteins were detected in the cytoplasm of hepatocytes of the 1 DE and 3 DE +3 DR groups whereas the ERα protein was found in the hepatocyte nuclei of the 1 DE and 3 DE groups. The present study demonstrates that PNP activated the AhR signaling pathway and regulated related CYP1A1 and GST gene expression in the liver. Copyright © 2016 John Wiley & Sons, Ltd.

Estrogenic Compounds Impair Primordial Follicle Formation by Inhibiting the Expression of Proapoptotic Hrk in Neonatal Rat Ovary.

Exposure to endocrine-disrupting chemicals (EDCs) during fetal and neonatal periods can have toxic effects that are irreversible and last a lifetime. However, the mechanism underlying this phenomenon is still unknown. Here, we show the effect of 17alpha-ethynyl estradiol (EE) on the development of the primordial follicle during early ovarian development in female rats. Microarray analysis revealed the down-regulation of Hrk, an activator of apoptosis, in neonatal ovaries exposed to EE. Real-time PCR analysis also showed a decrease of Hrk mRNA expression in ovaries treated with EE both in vitro and in neonatal rats. An immunostaining assay showed that HRK protein and cleaved caspase 3 colocalize in the oocytes at Postnatal Day 1 (PND1). The EE-exposed ovaries had a reduced number of oocytes positive for TUNEL staining compared to control ovaries at PND1. Abnormal follicle formation of EE-exposed ovaries was observed at PND7 and PND21. A TUNEL staining assay revealed that Hrk depletion reduced the number of apoptotic oocytes. In addition, down-regulation of Hrk mRNA expression was observed in ovaries treated with other estrogenic chemicals. We propose a model in which EE inhibits oocyte apoptosis in the neonatal ovary by suppressing the expression of Hrk, thereby disrupting follicle formation and ovary function.

Effects of Daily Exposure to Saccharin and Sucrose on Testicular Biologic Functions in Mice.

Saccharin sodium consumption is considered safe and beneficial, owing to its very intense sweetness without any associated calories, but supporting scientific data remain sparse and controversial. Herein, we demonstrate that dose-response relationships existed with regard to administration of saccharin or sucrose to mice for 35 days, and this association involved testis-expressed sweet-tasting molecules (taste receptor type 1 subunit 3 [T1R3]; G protein alpha-gustducin [Galpha]). Mouse body weights and testis weights in middle- and low-dose saccharin-treated groups were increased with up-expressions of molecules involved in testicular sweet taste and steroidogenic (middle saccharin: steroidogenic acute regulatory protein [StAR]; P450 cholesterol side-chain cleavage enzyme [CYP11A1]; 17-alpha-hydroxylase/C17,20-lyase [CYP17A1]; low saccharin: StAR). Moreover, a high-dose saccharin-related decline in reproductive hormone levels and injuries to testis and sperm were observed to be associated with suppression of testicular T1R3 and Galpha, as well as steroidogenic-related factors (StAR; 3-beta-hydroxysteroid dehydrogenase [3-beta-HSD]; CYP11A1; CYP17A1; 17-beta-hydroxysteroid dehydrogenase [17-beta-HSD]), and activation of cleaved caspase-3. However, abnormalities of the testis and sperm in high- and middle-dose sucrose-exposed mice were related to the increased-cleaved caspase-3, but independent of T1R3 and/or Galpha. Collectively, our results clearly suggest that saccharin-induced physiologic effects on testis are associated with testicular T1R3 and Galpha, which differed from sucrose. We hence call for a reassessment of the excessive use of sweeteners in daily life, especially artificial ones, considering their potential side effects.

Evidence for a PGF2α auto-amplification system in the endometrium in mares.

In mares, prostaglandin F2α (PGF2α) secreted from the endometrium is a major luteolysin. Some domestic animals have an auto-amplification system in which PGF2α can stimulate its own production. Here, we investigated whether this is also the case in mares. In an in vivo study, mares at the mid-luteal phase (days 6-8 of estrous cycle) were injected i.m. with cloprostenol (250 µg) and blood samples were collected at fixed intervals until 72 h after treatment. Progesterone (P4) concentrations started decreasing 45 min after the injection and continued to decrease up to 24 h (P < 0.05). In turn, 13,14-dihydro-15-keto-PGF2α (PGFM) metabolite started to increase 4h after an injection and continued to increase up to 72 h (P < 0.05). PGF receptor (PTGFR) mRNA expression in the endometrium was significantly higher in the late luteal phase than in the early and regressed luteal phases (P < 0.05). In vitro, PGF2α significantly stimulated (P < 0.05) PGF2α production by endometrial tissues and endometrial epithelial and stromal cells and significantly increased (P < 0.05) the mRNA expression of prostaglandin-endoperoxide synthase-2 (PTGS2), an enzyme involved in PGF2α synthesis in endometrial cell. These findings strongly suggest the existence of an endometrial PGF2α auto-amplification system in mares.

PATHFAST, a novel chemiluminescent enzyme immunoassay for measuring estradiol in equine whole blood and serum.

A novel chemiluminescent enzyme immunoassay system, PATHFAST, for the measurement of estradiol in horses was evaluated. The concentrations of estradiol in the whole blood and serum of mares were measured using PATHFAST and the estradiol concentrations measured by PATHFAST were compared with those measured by a time-resolved fluoro-immunoassay (FIA). To monitor physiological changes, serum estradiol concentrations in mares were measured using PATHFAST throughout the gestation period. The serum estradiol concentrations correlated highly with those in whole blood samples. The serum concentrations of estradiol measured by PATHFAST also correlated well with FIA. Circulating estradiol increased during mid-gestation and high levels of serum estradiol were maintained in late gestation, followed by an abrupt decline to term. These results demonstrate the utility of PATHFAST in equine clinics as an accurate diagnostic tool for the rapid assay of estradiol within 26 min using unextracted whole blood.

Effects of sulpiride and ethylene glycol monomethyl ether on endometrial carcinogenicity in Donryu rats.

Sulpiride and ethylene glycol monomethyl ether (EGME) are known ovarian toxicants that stimulate prolactin (PRL) secretion, resulting in hypertrophy of the corpora lutea and increased progesterone (P4) production. The purpose of the present study was to investigate how the PRL stimulatory agents affected uterine carcinogenesis and to clarify the effects of PRL on endometrial adenocarcinoma progression in rats. Ten-week-old female Donryu rats were treated once with N-ethyl-N'-nitro-N-nitrosoguanidine (20 mg kg(-1) ), followed by treatment with sulpiride (200 ppm) or EGME (1250 ppm) from 11 weeks of age to 12 months of age. Sulpiride treatment inhibited the incidence of uterine adenocarcinoma and precancerous lesions of atypical endometrial hyperplasia, whereas EGME had no effect on uterine carcinogenesis. Sulpiride markedly prevented the onset of persistent estrus throughout the study period, and EGME delayed and inhibited the onset of persistent estrus. Moreover, sulpiride-treated animals showed high PRL and P4 serum levels without changes in the levels of estradiol-17ß, low uterine weights and histological luteal cell hypertrophy. EGME did not affect serum PRL and P4 levels. These results suggest that the prolonged low estradiol-17ß to P4 ratio accompanied by persistent estrous cycle abnormalities secondary to the luteal stimulatory effects of PRL may explain the inhibitory effects of sulpiride on uterine carcinogenesis in rats. Copyright © 2015 John Wiley & Sons, Ltd.

IMMUNOLOCALIZATION OF INHIBIN/ACTIVIN SUBUNITS AND STEROIDOGENIC ENZYMES IN THE TESTES OF AN ADULT AFRICAN ELEPHANT (LOXODONTA AFRICANA).

In this case report, the authors investigated immunolocalization of inhibin α and inhibin/activin ßA and ßB subunits, as well as steroidogenic enzymes, in the testes of an African elephant. Testes were collected from a reproductively active male African elephant (24 yr old) at autopsy. Histologically, all types of spermatogenic cells including mature-phase spermatozoa were found in the seminiferous tubules. Positive immunostaining for inhibin α and inhibin/activin ßA and ßB subunits was observed in Sertoli and Leydig cells. In addition, P450scc, 3ßHSD, P450c17, and P450arom were also detected in the cytoplasm of Leydig cells. These results suggested that Leydig cells of adult African elephant testes have the ability to synthesize progestin, androgen, and estrogen, whereas both Sertoli and Leydig cells appear as a major source of inhibin secretion in the male African elephant.

Effects of a single use of the GnRH analog buserelin on the induction of ovulation and endocrine profiles in heavy draft mares.

We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus were monitored using transrectal ultrasound imaging and measurement of blood levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and estradiol-17ß. The ovulation rates within 48 hr was significantly higher in the treated group (100%, 8/8) than in the control group (57.1%, 8/14; P=0.051). The mean ± SEM time before confirmation of ovulation was 29 ± 9 hr for the treated group and 59 ± 7 hr for the control group. There were no significant differences in mating frequency, double ovulation rate, or fertility rate between the two groups. One to two days after administering buserelin, LH and FSH temporarily increased, and in the control group, LH was high during ovulation, whereas FSH temporarily increased with the growth of the follicle. These results indicate that a single injection of 40 µg buserelin when follicles are at least 45 mm in diameter and uterine edema is decreased is effective for inducing ovulation.

Embryonic sex steroid hormones accumulate in the eggshell of loggerhead sea turtle (Caretta caretta).

Steroids hormones such as estradiol-17ß (E2) and testosterone (T) are involved in gonadal differentiation of oviparous animals with temperature-dependent sex determination (TSD), and are greatly distributed. This hypothesizes that these embryonic steroid hormones probably accumulate in the eggshell throughout blood or/and chorioallantoic fluid in sea turtle species with TSD, producing females at higher temperature. To demonstrate this hypothesis, concentrations of E2 and T in the blood plasma from the hatchling loggerhead sea turtle (Caretta caretta) and in their eggshells were measured by radioimmunoassay. In the present study we propose that both concentrations of E2 and T in the blood plasma are correlated with amounts of these sex steroids in the eggshell. Moreover, contents of E2 in the eggshell showed a significant positive correlation with mean incubation temperatures during a thermosensitive period in the experimental nests, whereas T contents in the eggshell did not. Taken together, these findings indicated that embryonic E2 and T that accumulated in the eggshell can be extracted and measured. Furthermore, the present study suggested that contents of E2 in the eggshell may differ between male and female, and monitoring of these steroids is a useful method to identify the sex of loggerhead sea turtle hatchling.

4-Nitro-3-phenylphenol has both androgenic and anti-androgenic-like effects in rats.

To investigate the effect of endocrine disruption of 4-nitro-3-phenylphenol (PNMPP) on immature male Wistar-Imamichi rats, the rat pituitary was exposed to PNMPP (10(-5)-10(-9) M) for 24 h with or without gonadotropin-releasing hormone (GnRH) in experiment I. In addition, the Leydig cells (10(-5)-10(-9) M) were exposed to PNMPP for 24 h with or without human chronic gonadotropin (hCG) in experiment II. Our results showed that the PNMPP at 10(-5)-10(-7) M suppressed follicle-stimulating hormone (FSH) and luteinizing hormone (LH) productions from GnRH-stimulated pituitary cells. At the same time, PNMPP 10(-5)-10(-7) M induced an increase in testosterone production from the Leydig cells treated with or without hCG. Based on our results, it can be concluded that that PNMPP might have both androgen agonist action by decreasing FSH and LH production in the pituitary and anti-androgenic action by increasing testosterone production in the Leydig cell.

Declining semen quality and steadying seminal plasma ions in heat-stressed boar model.

Purpose: There are increasing concerns about infertility of male exposure to high environmental temperatures. Nevertheless, the relationship between heat and accessory sex gland secretion underlying the high ambient temperature-induced poor semen quality has not yet been addressed. Methods: In the present study, five boars were used as an animal model to evaluate semen quality and the secretory function of accessory sex glands. After the boars received 3 days of heat exposure, semen collection was standardized to 18 continual times with a 3-day interval to determine the semen variables of semen volume, semen concentration, abnormal spermatozoa, seminal plasma composition, and testosterone level in the seminal plasma and serum. Results: The total sperm count was lowest by the end of week 2. The higher abnormal spermatozoa percentage were observed by the end of week 2 and persisted until week 6 after heat exposure. Additionally, there was no significant change in semen volume, testosterone level, and concentrations of ions and total protein in the seminal plasma before and after heat exposure. Conclusions: A single 3-day heat exposure caused poor semen quality, but did not disturb accessory sex gland secretion in boars. Declining semen quality might be mainly due to the damaged germ cells, which were sensitive to elevated temperature in hot summer months.

Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings.

The effects of an extended photoperiod (EP) treatment (14.5 hr light, 9.5 hr dark) on Thoroughbred colts and fillies from December 25 at 7-9 months old to the following May at 12-14 months old on coat condition and gonadal functions were investigated. Coat condition was evaluated in April. The colts and fillies in the EP treatment group changed from winter to summer coats (molting of winter coats), whereas those in the control group did not. To determine the day of first ovulation, the plasma concentrations of progesterone were measured once a month in fillies. The day of first ovulation was advanced in the EP treatment fillies compared with the control fillies. The present study clearly demonstrated that the EP treatment advanced the molting of winter coats and advanced ovulation in fillies, even in weanlings.

Comparison of growth and endocrine changes in Thoroughbred colts and fillies reared under different climate conditions.

Development and endocrine changes in Thoroughbreds colts and fillies were compared between those reared at two facilities of the Japan Racing Association, the Hidaka Training and Research Center (Hidaka) and Miyazaki Yearling Training Farm (Miyazaki). Thoroughbred colts and fillies born in Japan between 2003 and 2010 were used. Each colt group and filly group was divided into 2 groups, respectively, and raised in Hidaka or Miyazaki for 7 months from September at 1 year old to April at 2 years old. For the growth parameters, the body weight, height at withers, and girth and cannon circumferences were measured once a month. For parameters of endocrine function, circulating prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin-like growth factor-1 (IGF-1), testosterone, progesterone, and estradiol-17ß levels were measured. Regarding growth, the rate of increase over the 7-month period was significantly higher in both colts and fillies raised in Miyazaki than in Hidaka in all 4 parameters: body weight, height at withers, and girth and cannon circumferences. The endocrine changes of the colts and fillies born in 2007 were as follows. In colts, although circulating prolactin tended to be higher in colts reared in Hidaka from October to April, circulating LH, FSH, testosterone, estradiol-17ß and IGF-1 tended to be higher in colts reared in Miyazaki than in Hidaka, suggesting that the gonadotropin-releasing hormone-LH/FSH system and the growth hormone-IGF-1 system were more active in colts reared in Miyazaki as compared with those reared in Hidaka. In fillies, circulating prolactin tended to be higher in fillies reared in Hidaka in February and March, but no significant difference was noted in the serum LH, FSH, IGF-1, or progesterone level between the 2 groups. Circulating estradiol-17ß tended to be higher in fillies reared in Miyazaki than in Hidaka in October and November. Regarding ovarian function, the initial ovulation occurred by the end of March in 2 (16.7%) of 12 fillies reared in Hidaka and 7 (38.9%) of 18 fillies reared in Miyazaki, suggesting that the ovarian function was more active in fillies reared in Miyazaki as compared with those reared in Hidaka. Based on these findings, it was clarified that development of the body and gonads was faster in Miyazaki compared with Hidaka in both colts and fillies.

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies.

The effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17ß and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17ß and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.