Plasma Concentrations Of Ir-inhibin Research Articles

Plasma Concentrations of Immunoreactive (ir)-Inhibin, Gonadotropins and Steroid Hormones during the Ovulatory Cycle of the Duck

The present study was undertaken to determine changes in circulating levels of immunoreactive (ir)-inhibin, FSH, LH, estradiol-17beta, progesterone, and testosterone during the ovulatory cycle of Shao ducks. Serial blood samples were taken from two groups of laying ducks for measurement of ir-inhibin, gonadotropins, and steroid hormones at 2 h intervals for 24 h. Plasma concentrations of ir-inhibin did not change significantly during the ovulatory cycle. The highest level of plasma ir-inhibin was observed 6 h prior to ovulation, which coincided with a decreased level of plasma FSH. One FSH surge was found 12 h after ovulation. Estradiol-17beta, progesterone, and testosterone were also determined during the ovulatory cycle. Two peak values were detected for estradiol-17beta 8 h before ovulation and 4 h after ovulation, while progesterone started to increase 4 h before ovulation and reached a peak at ovulation. The highest level of plasma testosterone was detected around the time of ovulation. These results suggest that inhibin may be involved in the control of FSH secretion during the ovulatory cycle. In addition, both LH and progesterone are of importance in the ovulation process of Shao ducks.

Plasma Concentrations of Ir-inhibin, Inhibin A, Inhibin pro-αC, FSH, and Estradiol-17β During Estrous Cycle in Mares and Their Relationship with Follicular Growth

The relationship among plasma levels of immunoreactive (ir)-inhibin, inhibin A, inhibin pro-alphaC, FSH, estradiol-17beta and follicular growth were investigated during the normal estrous cycle in mares. Seven mares were used for two successive normal estrous cycles. Follicular diameters and ovulation were obtained by transrectal ultrasonography, and blood samples were collected daily by jugular venipuncture for hormonal assay. The results showed that inhibin A was inversely correlated (r = -0.59, p < 0.0001) with FSH indicating its contribution to negative feedback control of FSH secretions from the pituitary gland. Estradiol-17beta increased during the follicular phase reaching a peak (37.9 +/- 3.8 pg/mL) 2 d before ovulation. Estradiol-17beta was positively correlated (r = 0.78, p < 0.0001) with inhibin A. The high levels of inhibin A and estradiol-17beta were associated with the growth of the preovulatory dominant follicle and inversely correlated with FSH suggesting that both hormones are products of the large dominant follicles and were responsible for the decline in FSH secretion during the follicular phase of estrous cycle. In conclusion, an inverse relationship between inhibin A and FSH was clearly demonstrated indicating that inhibin A has a key role in the negative feedback control of FSH from the pituitary gland. In addition, inhibin A and estra-diol-17beta secretions were associated with the growth of the preovulatory dominant follicle and were positively correlated.

Inhibin as a Possible Indicator of Follicular Development during Perinatal Period in Mares.

Plasma concentrations of immunoreactive (ir-) inhibin, FSH, LH, estradiol and progesterone were measured by RIA between -6 and 12 days after parturition in 6 mares. Follicular development was also monitored in the same animals after parturition by ultrasound scanner. Plasma concentrations of ir-inhibin were relatively low before parturition, then rose significantly after parturition, in accordance with the development of 10-30 mm follicles in diameter during the early period of postpartum estrus. In contrast, concentrations of both estradiol and progesterone remained high before parturition, then dropped significantly 1 day after parturition. The present study demonstrated that inhibin is more likely to be secreted from maternal ovaries into maternal circulation than the feto-placental unit during the prenatal period. This suggests that inhibin could be used as a potential indicator of follicular development around parturition in mares.

Roles of Basal Levels of Circulating Luteinizing Hormone on Follicular Maturation in the Pregnant Golden Hamster (Mesocricetus auratus).

To investigate physiological roles of basal levels of circulating LH on follicular development during the second half of pregnancy in golden hamsters, we treated animals with anti-luteinizing hormone (A/LH) or normal horse serum (control serum) at 1100 h on day 12 of pregnancy (day 0 of pregnancy=sperm positive in vaginal smear). Thereafter, changes in plasma concentrations of immunoreactive (ir)-inhibin, estradiol-17β, progesterone and testosterone were determined until 48 h after the treatment; ovaries were also examined immunohistochemically. Furthermore, pregnant golden hamsters were injected with human chorionic gonadotropin (hCG) to determine the effects of immunoneutralization of LH on follicular activity. Plasma concentrations of ir-inhibin and estradiol-17β decreased significantly within 24 h after A/LH treatment, while plasma concentrations of progesterone and testosterone were unchanged. The number of follicles ovulating in response to hCG in the A/LH treated groups (7.0 ± 3.4, n=3) was significantly lower than in the control serum treated group (34.6 ± 4.8, n=5) at 24 h after the treatment. Immunostaining of inhibin α subunit was observed in granulosa cells of healthy and atretic large follicles at 24 h after A/LH treatment, whereas immunopositive reaction of aromatase was not observed in atretic follicles. Positive immunoreaction of 17α-hydroxylase/C17, 20-lyase (CYP17) was observed in theca cells of healthy follicles but not in atretic follicles. These results clearly demonstrate that basal levels of circulating LH are important for maturation of antral follicles and secretion of ir-inhibin and estradiol-17β, but not for progesterone during the second half of pregnancy in the golden hamster.

Elevated levels of inhibin-A and immunoreactive inhibin in aged male Wistar rats with testicular Leydig cell tumor.

This study was undertaken to investigate the endocrine changes that occur in male Tig:Wistar rats with Leydig cell tumors, with special reference to immunoreactive inhibin (ir-inhibin) and its dimeric forms. Adult male rats from 2 to 28 months of age were used. Blood samples were taken to measure plasma concentrations of ir-inhibin, inhibin-A, inhibin-B, 17beta-estradiol (E2), testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Inhibin bioactivity in both peripheral plasma and testicular extracts was also measured. Rats aged 18 months and older had testicular Leydig cell tumor. Testicular tissue sections from 27-month-old rats examined immunohistochemically showed strong positive staining for all 3 inhibin subunits, in particular inhibin alpha and betaA subunits, in the tumor cells. Plasma concentrations of ir-inhibin began to rise significantly (P < .05) at 18 months of age. High bioactivity of inhibin was detected not only in testicular extracts but also in peripheral plasma of aged rats. Thus, plasma concentrations of bioactive inhibin-A, but not inhibin-B, were significantly elevated with increasing age. The concentrations were significantly higher than those in normal male (P < .01) or normal female (P < .05) rats. Plasma concentrations of E2 were significantly (P < .05) elevated only at 23-24 months of age. A marked reduction (P < .05 to .001) in plasma LH and FSH concentrations was observed at 18 months of age and older. Plasma concentrations of testosterone were highest at 2 months of age and then decreased gradually and significantly (P < .05 to .001) afterward. Significant (P < .05 to .001) positive (testosterone vs LH) and negative (ir-inhibin vs FSH, ir-inhibin vs LH, and E2 vs FSH) correlations were observed. It is suggested that plasma inhibin-A levels are elevated in male Tig:Wistar rats with Leydig cell tumor, and thus inhibin-A may be used as a specific marker of testicular Leydig cell tumors. The present results also suggest that the age-related decline in plasma gonadotropins and thus testosterone levels in Tig:Wistar rats may be due to the development of tumors of the Leydig cells rather than to aging per se.

Inhibin secretion in the mare: localization of inhibin alpha, betaA, and betaB subunits in the ovary.

To determine the source of circulating inhibin and estradiol-17beta during the estrous cycle in mares, the cellular localization of the inhibin alpha, betaA, and betaB subunits and aromatase in the ovary was determined by immunohistochemistry. Concentrations of immunoreactive (ir-) inhibin, estradiol-17beta, progesterone, LH, and FSH in peripheral blood were also measured during the estrous cycle in mares. Immunohistochemically, inhibin alpha subunits were localized in the granulosa cells of small and large follicles and in the theca interna cells of large follicles, whereas inhibin betaA and betaB subunits were localized in the granulosa cells and in the theca interna cells of large follicles. On the other hand, aromatase was restricted to only the granulosa cells of large follicles. Plasma ir-inhibin concentrations began to increase 9 days before ovulation; they remained high until 2 days before ovulation, after which they decreased when the LH surge was initiated. Thereafter, a further sharp rise in circulating ir-inhibin concentrations occurred during the process of ovulation, followed by a second abrupt decline. After the decline, plasma concentrations of ir-inhibin remained low during the luteal phase. Plasma estradiol-17beta concentrations followed a profile similar to that of ir-inhibin, except during ovulation, and these two hormones were positively correlated throughout the estrous cycle. Plasma FSH concentrations were inversely related to ir-inhibin and estradiol-17beta. These findings suggest that the dimeric inhibin is mainly secreted by the granulosa cells and the theca cells of large follicles; granulosa cells of small follicles may secrete inhibin alpha subunit, and estradiol-17beta is secreted by the granulosa cells of only large follicles in mares.

Effects of age, season, and fertility status on plasma and intratesticular immunoreactive (IR) inhibin concentrations in stallions

The nature of the relationship between inhibin and reproductive function in the stallion is yet to be elucidated. Blood and testes from 51 light horse stallions ranging in age from 2 mo to 25 years were collected during the breeding and nonbreeding seasons to study the effects of testicular maturation, aging, season, and fertility status on peripheral and intratesticular concentrations of Ir inhibin and other reproductive hormones. Of the 51 stallions, 12 age-matched stallions (6 fertile, 3 subfertile, and 3 infertile) were used in the fertility study. Blood samples were taken before castration and plasma stored at −20°C for analysis of Ir inhibin, luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), estradiol (E 2), and estrogen conjugates (EC) by radioimmunoassay (RIA). Testes were homogenized and testicular extracts prepared and frozen at −70°C for analysis of Ir inhibin, T, E 2, and EC by RIA. Plasma concentrations of Ir inhibin, LH, FSH, T, E 2, and EC and intratesticular concentrations of Ir inhibin, T, E 2, and EC increased with age (P < 0.01). The most dramatic effect appeared to be during testicular maturation. An aging effect was not observed in adult stallions. A seasonal effect was not detected for any of the plasma hormones, whereas for the intratesticular hormones the only change noted was an increase in T in the nonbreeding season (P < 0.05). Plasma Ir inhibin, E 2, and EC were lower (P < 0.01) and gonadotropins higher (P < 0.05) in infertile stallions. Plasma T levels did not change. Intratesticular Ir inhibin concentrations tended to be lower (P < 0.1) in subfertile stallions and significantly lower (P < 0.01) in infertile stallions, whereas intratesticular steroid levels were not different among the three groups. In conclusion, plasma and intratesticular Ir inhibin concentrations seem to be affected by testicular maturation and fertility status.

Inhibin secretion in the stallion.

To examine the physiological role of inhibin in the stallion, a heterologous radioimmunoassay (RIA) based on a bovine RIA was validated and used to measure immunoreactive (ir)-inhibin concentrations in plasma and testicular homogenates. The bioactivity of equine testicular inhibin was also examined using an assay for suppression of FSH secretion from rat anterior pituitary cells. In addition, to identify the cell responsible for secreting testicular inhibin, the localisation of inhibin in the testis was investigated by an immunohistochemical method using a polyclonal antibody against (Tyr30)-porcine inhibin alpha(1-30) NH2. In the RIA, parallel dose response curves were obtained for the bovine inhibin standard and serial dilutions of stallion plasma and equine testicular homogenates. Parallel FSH inhibition curves were also observed for the bovine inhibin standard and serial dilutions of equine testicular homogenates in the bioassay. The inhibition of FSH secretion from rat pituitary cells by equine testicular homogenates was neutralised by an antiserum against bovine inhibin in vitro. Plasma concentrations of ir-inhibin, testosterone and oestradiol-17beta in stallions decreased abruptly after bilateral gonadectomy and FSH and LH concentrations in the plasma subsequently increased. Therefore, circulating inhibin in the stallion appeared to be largely of testicular origin. The histochemical results showed for the first time that strong immunopositive staining for inhibin occurred in the Leydig cells of the testes. Sertoli cells were also stained by the inhibin antibody but the reaction was weaker than that in Leydig cells. These results indicate clearly that both Leydig and Sertoli cells are potential sources of testicular inhibin in the stallion. A clear increase in plasma ir-inhibin concentrations was observed during the natural breeding season. Similar seasonal changes in the plasma concentrations of testicular steroid hormones and pituitary gonadotrophins occurred throughout the year. In conclusion, the testes appear to be the main source of inhibin, and testicular inhibin is secreted by Leydig and Sertoli cells in stallions. The positive correlations between plasma ir-inhibin and testicular activity during both the breeding and nonbreeding seasons indicate that plasma ir-inhibin is a useful indicator of reproductive activity in the stallion.

High concentrations of immunoreactive inhibin in the plasma of mares and fetal gonads during the second half of pregnancy.

Plasma concentrations of immunoreactive (ir)-inhibin were measured in seven pregnant mares from around Day 140 of gestation to Day 2 after parturition using a heterologous bovine-based radioimmunoassay (RIA). Concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), oestradiol-17 beta, progesterone and relaxin were also measured in the same samples. A marked increase in plasma concentrations of ir-inhibin, FSH and LH occurred between Day 220 and Day 300 of gestation but the concentrations of all three hormones returned to baseline by about Day 320 (three weeks before parturition). In contrast, circulating concentrations of the three placental hormones, oestradiol-17 beta, progesterone and relaxin, increased during the final weeks of pregnancy and then decreased markedly to basal values within two days of parturition. There was a positive correlation between circulating concentrations of ir-inhibin and FSH (r = 0.75, P < 0.01) rather than the expected negative correlation. ir-inhibin was not detected in homogenates obtained at Day 190 of pregnancy and form term placenta, but high concentrations of ir-inhibin were present in homogenates of fetal and newborn gonads. Despite the high concentrations of ir-inhibin in these homogenates, they failed to exert any suppressive bioactivity on FSH secretion by rat pituitary cells cultured in vitro. Furthermore, immunohistochemical staining revealed the presence of inhibin in the interstitial cells of equine fetal gonads at Day 190 of gestation. These findings demonstrate for the first time that high concentrations of ir-inhibin, LH and FSH are secreted into the peripheral circulation of the mare during the second half of pregnancy. However, ir-inhibin present in the plasma of pregnant mares appears to be biologically inactive. This hormone is not presumed to be of placental origin but it is proposed that either the enlarged fetal gonads or the maternal ovaries, or both of these organs, may be a source of inhibin in response to the coincident increase in circulating concentrations of LH and FSH.