Respostas hormonais ao tratamento com GnRH e estradiol e suas correlações com desenvolvimento testicular e número de células sertoli em touros angus x charolês na fase de pré-puberdade

Moura, Arlindo de Alencar Araripe; Erickson, Bert H.

doi:10.1590/S1516-35981999000100006

Resumos

O objetivo desta pesquisa foi determinar as correlações entre níveis hormonais aos 2 e 6 meses de idade e diâmetro e histologia testicular em tourinhos Angus x Charolês aos 6 meses de idade (n=15). Aos dois meses, duas amostras basais de sangue foram coletadas a intervalos de 1 hora. Após a última coleta, os animais receberam 5 mg de GnRH e 1,5 e 3,0 horas depois novas amostras foram coletadas. Aos seis meses, os tourinhos foram tratados com 1 mg de estradiol benzoato (E) e receberam 10 mg de GnRH doze horas depois. Após cinco dias, os tourinhos receberam 10 mg de GnRH, mas sem pré-tratamento com estradiol. As amostras de sangue foram coletadas 1,5 e 3,0 horas após a injeção de GnRH nas duas ocasiões. Imediatamente antes dos tratamentos com estradiol e GnRH, duas amostras basais foram coletadas. Os animais foram cirurgicamente castrados aos seis meses. Houve correlações entre níveis de FSH estimulados com GnRH aos dois meses e diâmetro testicular e número de células Sertoli e espermatogônias A1 por testículo aos seis meses de idade (r = -0,65 a -0,80). As associações entre FSH aos dois meses e número de seções de túbulos seminíferos sem células germinativas (r = 0,59) e número de túbulos com espermátides circulares (r = -0,55) também foram significativas. As correlações entre níveis de LH e esteróides e parâmetros testiculares não foram significativas. Aos 6 meses, níveis basais de FSH não alteraram 12 horas após estradiol, mas as concentrações de FSH estimuladas com GnRH foram 2,5 vezes mais elevadas, quando se usou estradiol em relação ao uso somente de GnRH. Modelos de regressão com número de células Sertoli, em função dos níveis de FSH após GnRH, mostraram que, quando se utilizaram GnRH + estradiol, obteve-se maior valor de R² (0,43) em comparação à injeção somente de GnRH (0,30). Portanto, concentrações periféricas de FSH são potenciais indicadores do desenvolvimento testicular na fase de pré-puberdade.

testículo; FSH; estradiol; célula de Sertoli; tourinhos

The objective of this research was to determine the correlation among hormone levels at 2- and 6-month of age and diameter and histology of the testis in Angus x Charolais young bulls at 6 months (n= 15). At two months, two basal blood samples were collected at 1-h intervals. After the last collection, the animals received 5 mg of GnRH and 1.5 and 3.0 h later, new samples were collected. At 6 months, the young bulls were treated with 1 mg of estradiol benzoate (E) and received 10 mg GnRH twelve hours later. After five days, the young bulls received 10 mg GnRH, but without pre-treatment with estradiol. In both cases, blood samples were collected 1.5 and 3.0 h after GnRH injection. Immediately before the GnRH and estradiol treatments, two basal samples were collected. The animals were surgically castrated at six months. Concentrations of GnRH-stimulated FSH at two months were related to testis diameter, number of Sertoli cells and A1 spermatogonia per testis (r=.65 to .80). The associations between FSH at two months and number of seminiferous tubule sections without germ cells (r=.59) and tubules with round spermatids (r= -.55) were also significant. The correlations between the basal LH and steroids and testis parameters were not significant. At 6 months, the basal levels of FSH did not alter 12 h after estradiol, but the FSH concentrations stimulated with GnRH were 2.5-fold higher when estradiol was used than when GnRH was used. Regression models with Sertoli cell numbers in function of FSH after GnRH showed that when GnRH + estradiol was used, a greater R² (.43) was obtained in comparison to GnRH injection only (.30). Thus, peripheral concentrations of FSH are potential indicators of testicular development at the prepubertal phase.

testis; FSH; estradiol; Sertoli cell; young bulls

MELHORAMENTO, GENÉTICA E REPRODUÇÃO

Respostas hormonais ao tratamento com GnRH e estradiol e suas correlações com desenvolvimento testicular e número de células sertoli em touros angus x charolês na fase de pré-puberdade^{^*} * Pesquisa financiada pelo Tenessee Institute of Agriculture e CNPq.

Hormonal responses to GnRH and estradiol treatments and their correlation with testicular development and number of sertoli cells in prepubertal angus x charolais bulls

Arlindo de Alencar Araripe Moura^I; Bert H. Erickson^II

^IUniversidade Federal do Ceará - Departamento de Zootecnia, Av. Mister Hull, s/n - Campus do Pici - Caixa Postal, 12.168 - Fortaleza - Ceará - Brasil - 60021-970; Fone: (085) 288 - 9703; Fax: 288 - 9701; E-mail: amoura@ufc.br ^IIProfessor Emeritus, Department of Animal Science, The University of Tennessee, USA Knoxville, TN 37901-1071

RESUMO

O objetivo desta pesquisa foi determinar as correlações entre níveis hormonais aos 2 e 6 meses de idade e diâmetro e histologia testicular em tourinhos Angus x Charolês aos 6 meses de idade (n=15). Aos dois meses, duas amostras basais de sangue foram coletadas a intervalos de 1 hora. Após a última coleta, os animais receberam 5 mg de GnRH e 1,5 e 3,0 horas depois novas amostras foram coletadas. Aos seis meses, os tourinhos foram tratados com 1 mg de estradiol benzoato (E) e receberam 10 mg de GnRH doze horas depois. Após cinco dias, os tourinhos receberam 10 mg de GnRH, mas sem pré-tratamento com estradiol. As amostras de sangue foram coletadas 1,5 e 3,0 horas após a injeção de GnRH nas duas ocasiões. Imediatamente antes dos tratamentos com estradiol e GnRH, duas amostras basais foram coletadas. Os animais foram cirurgicamente castrados aos seis meses. Houve correlações entre níveis de FSH estimulados com GnRH aos dois meses e diâmetro testicular e número de células Sertoli e espermatogônias A1 por testículo aos seis meses de idade (r = -0,65 a -0,80). As associações entre FSH aos dois meses e número de seções de túbulos seminíferos sem células germinativas (r = 0,59) e número de túbulos com espermátides circulares (r = -0,55) também foram significativas. As correlações entre níveis de LH e esteróides e parâmetros testiculares não foram significativas. Aos 6 meses, níveis basais de FSH não alteraram 12 horas após estradiol, mas as concentrações de FSH estimuladas com GnRH foram 2,5 vezes mais elevadas, quando se usou estradiol em relação ao uso somente de GnRH. Modelos de regressão com número de células Sertoli, em função dos níveis de FSH após GnRH, mostraram que, quando se utilizaram GnRH + estradiol, obteve-se maior valor de R²(0,43) em comparação à injeção somente de GnRH (0,30). Portanto, concentrações periféricas de FSH são potenciais indicadores do desenvolvimento testicular na fase de pré-puberdade.

Palavras-chave: testículo, FSH, estradiol, célula de Sertoli, tourinhos.

ABSTRACT

The objective of this research was to determine the correlation among hormone levels at 2- and 6-month of age and diameter and histology of the testis in Angus x Charolais young bulls at 6 months (n= 15). At two months, two basal blood samples were collected at 1-h intervals. After the last collection, the animals received 5 mg of GnRH and 1.5 and 3.0 h later, new samples were collected. At 6 months, the young bulls were treated with 1 mg of estradiol benzoate (E) and received 10 mg GnRH twelve hours later. After five days, the young bulls received 10 mg GnRH, but without pre-treatment with estradiol. In both cases, blood samples were collected 1.5 and 3.0 h after GnRH injection. Immediately before the GnRH and estradiol treatments, two basal samples were collected. The animals were surgically castrated at six months. Concentrations of GnRH-stimulated FSH at two months were related to testis diameter, number of Sertoli cells and A1 spermatogonia per testis (r=.65 to .80). The associations between FSH at two months and number of seminiferous tubule sections without germ cells (r=.59) and tubules with round spermatids (r= -.55) were also significant. The correlations between the basal LH and steroids and testis parameters were not significant. At 6 months, the basal levels of FSH did not alter 12 h after estradiol, but the FSH concentrations stimulated with GnRH were 2.5-fold higher when estradiol was used than when GnRH was used. Regression models with Sertoli cell numbers in function of FSH after GnRH showed that when GnRH + estradiol was used, a greater R² (.43) was obtained in comparison to GnRH injection only (.30). Thus, peripheral concentrations of FSH are potential indicators of testicular development at the prepubertal phase.

Key Words: testis, FSH, estradiol, Sertoli cell, young bulls.

Texto completo disponível apenas em PDF.

Full text available only in PDF format.

Recebido em: 27/03/98

Aceito em: 28/08/98

ABERCROMBIE, M. 1946. Estimation of nuclear population from microtome sections. Anat. Rec, 94:239-251.
BARDIN, C.W., CHENG, C.Y., MUSTOW, N.A. et al. 1994. The Sertoli cell. In: E. KNOBIL, J. D. NEIL (Ed.), The Physiology of Reproduction, p. 1291. Raven Press, New York.
BERNDTSON, W.E., IGBOELI, G., PICKETT, B.W. 1987a. Relationship of absolute numbers of Sertoli cells to testicular size and spermatogenesis in younf beef bulls. J. Anim. Sci. 64:241.
BERNDTSON, W.E., IGBOELI, G., PARKER, W.G. 1987b. The numbers of Sertoli cells in mature Holstein bulls and their relationship to quantitative aspects of spermatogenesis. Biol. Reprod., 37:60-72.
BERNDTSON, W.E., DESJARDINS, C. 1974. The cycle of the seminiferous epithelium and spermatogenesis in the bovine testis. Am. J. Anat, 140:167-178.
BAME, J., DALTOM, J.C., DEGELOS, S.D. et al. Immunization against inhibin enhances sperm production in dairy bulls. In: ANNUAL MEETING OF THE SOCIETY FOR THE STUDY OF REPRODUCTION, 29, 1996, London, Ontarion, Canada. 54:138 (abstract).
BOLT, D.J. 1981. Development of homologous radioimmunoassay for ovine follicle stimulating hormone: Studies of estrous, ovariectomy, estradiol and releasing hormone. J. Anim. Sci., 53:730-738.
BOLT, D.J., ROLLINS, R. 1983. Development and application of a radioimmunoassay for bovine follicle stimulating hormone. J. Anim. Sci., 56:146-153.
CARATY, A.A., LOCATELLI, A., MARTIN, G.B. 1989. Biphasic response in the secretion of gonadotropin-releasing hormone in ovariectomized ewes injected with estradiol. J. Endocrinol, 123:375-386.
CHALKLEY, H. W. 1943. Method for the quantitative morphologic analysis of tissue. Journal of the National Cancer Institute, 4:47-55.
COX, N. M., RAMIREZ, J.L., MATAMOROS, I.A. 1987. Influence of season on estrous and luteinizing hormone responses to estradiol benzoate in ovarioectomized sows. Theriogenology, 27:395-404.
CURTIS, S.K., AMANN, R.P. 1981. Testicular development and establishment of spermatogenesis in Holstein bulls. J. Anim. Sci., 53:1645-1654.
D'OCCHIO, M.J., KINDER, J.E., SCHANBACHER, B.D. 1982. Patterns of LH secretion in castrated bulls (steers) during intravenous infusion of androgenic and estrogenic steroids: pituitary response to exogenous luteinizing hormone-releasing hormone. Biol. Reprod., 26:249-257.
ERICKSON, B. H., BLEND, W.J. Response of the Sertoli cell and stem cell to ⁶⁰Co g-radiation (dose and dose rate) in testes of immature rats. Biol. Reprod., 14:641-652, 1976.
HOCHEREAU-DE RIVIERS, M. T., MONET-KUNTZ, C., COUROT, M. 1987. Spermatogenesis and Sertoli cell numbers and function in rams and bulls. J. Reprod. Fert., 34:101-110.
JÉGOU, B., SHARPE, R. 1993. Paracrine mechanisms in testicular control. In: D. de Kretser (Ed.), Molecular Biology of the Male Reproductive System. p. 271. Academic Press, San Diego.
JOHNSON, L., NEAVES, W.B. 1981. Age-related changes in the Leydig cell population, seminiferous tubules, and sperm production in stallions. Biol. Reprod., 24:703-712.
KESNER, J.S. 1988. Site of action for the estradiol-induced luteinizing hormone surge in farm animals and primates. Dom. Anim. Endocr, 5(4):265-281.
KESNER, J.S., RIEBOLD T.W., CONVEY, E..M. 1982. Effect of dosage and frequency of injection of luteinizing hormone releasing hormone on release of luteinizing hormone and follicle stimulating hormone in estradiol-treated steers. J. Anim. Sci., 54(5):1023-1029.
MACDONALD, R.D., DEAVER, D.R., SCHANBACHER, B.D. 1990. Prepubertal changes in plasma FSH and inhibin in Holstein bull calves: responses to castration and (or) estradiol. J. Anim. Sci., 69:276-287.
MALAK, G. A., THIBIER, M. 1985. Individual variations in FSH release after a GnRH challenge and relationship with semen output in young bulls. J. Reprod. Fert, 75:345-357.
MARTIN, T. L., WILLIAMS, G. L., LUNSTRA, D. D. et al. 1991. Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls. Biol. Reprod., 45:73-77.
MATSCHKE, G. H., ERICKSON, B.H. 1969. Development and radioresponse of the prenatal bovine testis. Biol. Reprod., 1:207-215.
MILLER, W.L. 1993. Regulation of pituitary gonadotropins by gonadotropin-releasing hormone, estradiol, progesterone, inhibin and activin. In: R. B. L. Gwatkin (Ed.), Genes in Mammalian Reproduction. p. 247. Wiley-Liss, Inc.
MONGKONPUNYA, K., HAFS, H.D., CONVEY, E.M. et al. 1975. Serum luteinizing hormone, testosterone and androstenedione in pubertal and prepubertal bulls after gonadotropin releasing hormone. J. Anim. Sci., 40:682-695.
MOURA, A.A., ERICKSON, B.H. 1997. Age-related changes in peripheral hormonal concentrations and their relationships with testis size and number of Sertoli and germ cells in yearling beef bulls. J. Reprod. Fert , 111:183-190.
NETT, T. 1990. Regulation of genes controlling gonadotropin secretion. J. Anim. Sci. 68 (Suppl. 2):3.
NISWENDER, G.D., RICHERT, JR. L.E, MIDGLEY, JR., A.R 1969. Radioimmunoassay for bovine and ovine luteinizing hormone. Endocrinology, v. 84, p. 1166-1177.
ORTAVANT, R., COUROT, M., HOCHEREAU-DE-REVIERS, M.T. 1977. Spermatogenesis in domestic animals. In: COLE, H. H., CUPPS, P.T. (Ed.), Reproduction in Domestic Animals. p. 203. Academic Press, New York.
ORTH, J.M., GUNSALUS, G.M, LAMPERTI, A.A. 1988. Evidence from Sertoli cell-depleted rats indicates that spermatids numbers in adults depends on Sertoli cells produced during perinatal development. Endocrinology, 122:787-798.
PRICE, C.A. 1991. The control of FSH in the large domestic species. J. Endocr, 131:177-188.
SAS INSTITUTE INC., SAS/STAT® User's Guide, Version 6, Fourth Edition, Volume 2, Cary, NC: SAS Institute Inc. , 1989. 846 pp.
SCHANBACHER, B.D. 1990. Pituitary and testicular responses of beef bulls to active immunization against inhibin alpha. J. Anim. Sci., 69:252-261.
SHARPE, R.M. 1994. Regulation of spermatogenesis. In: E. Knobil and J. D. Neil (Ed.), The Physiology of Reproduction, p. 1363. Raven Press, New York.
SINOWATZ, F., AMSELGRUBER, W. Postnatal development of bovine Sertoli cells. Anat. Embryol, v. 174, p. 413-422. 1986.
SWANSON, L. V., WETTEMANN, R.P., RAWLINGS, N.C. et al. 1971. Pubertal relationships of some endocrine and reproductive criteria in Hereford bulls. J. Anim. Sci., 33:823-835.
TILBROOK, A. J., DEKETSER, D.M., CLARKE, I.J. 1993. Human recombinant Inhibin A suppress plasma follicle-stimulating hormone to intact levels but has no effect on luteining hormone in castrated rams. Biol. Reprod., 49: 779-788.
WILDEUS, S., RANDEL, R.D., HUMPHREY, W.D. 1988. Age-related changes in the supression of serum luteinizing hormone by estradiol-17b in developing steers. Theriogenology, 29(5):1065-1073.

^*

Pesquisa financiada pelo Tenessee Institute of Agriculture e CNPq.

Datas de Publicação

Publicação nesta coleção
02 Out 2013
Data do Fascículo
Fev 1999

Histórico

Recebido
27 Mar 1998
Aceito
28 Ago 1998

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

[1] ABERCROMBIE, M. 1946. Estimation of nuclear population from microtome sections. Anat. Rec, 94:239-251.

[2] BARDIN, C.W., CHENG, C.Y., MUSTOW, N.A. et al. 1994. The Sertoli cell. In: E. KNOBIL, J. D. NEIL (Ed.), The Physiology of Reproduction, p. 1291. Raven Press, New York.

[3] BERNDTSON, W.E., IGBOELI, G., PICKETT, B.W. 1987a. Relationship of absolute numbers of Sertoli cells to testicular size and spermatogenesis in younf beef bulls. J. Anim. Sci. 64:241.

[4] BERNDTSON, W.E., IGBOELI, G., PARKER, W.G. 1987b. The numbers of Sertoli cells in mature Holstein bulls and their relationship to quantitative aspects of spermatogenesis. Biol. Reprod., 37:60-72.

[5] BERNDTSON, W.E., DESJARDINS, C. 1974. The cycle of the seminiferous epithelium and spermatogenesis in the bovine testis. Am. J. Anat, 140:167-178.

[6] BAME, J., DALTOM, J.C., DEGELOS, S.D. et al. Immunization against inhibin enhances sperm production in dairy bulls. In: ANNUAL MEETING OF THE SOCIETY FOR THE STUDY OF REPRODUCTION, 29, 1996, London, Ontarion, Canada. 54:138 (abstract).

[7] BOLT, D.J. 1981. Development of homologous radioimmunoassay for ovine follicle stimulating hormone: Studies of estrous, ovariectomy, estradiol and releasing hormone. J. Anim. Sci., 53:730-738.

[8] BOLT, D.J., ROLLINS, R. 1983. Development and application of a radioimmunoassay for bovine follicle stimulating hormone. J. Anim. Sci., 56:146-153.

[9] CARATY, A.A., LOCATELLI, A., MARTIN, G.B. 1989. Biphasic response in the secretion of gonadotropin-releasing hormone in ovariectomized ewes injected with estradiol. J. Endocrinol, 123:375-386.

[10] CHALKLEY, H. W. 1943. Method for the quantitative morphologic analysis of tissue. Journal of the National Cancer Institute, 4:47-55.

[11] COX, N. M., RAMIREZ, J.L., MATAMOROS, I.A. 1987. Influence of season on estrous and luteinizing hormone responses to estradiol benzoate in ovarioectomized sows. Theriogenology, 27:395-404.

[12] CURTIS, S.K., AMANN, R.P. 1981. Testicular development and establishment of spermatogenesis in Holstein bulls. J. Anim. Sci., 53:1645-1654.

[13] D'OCCHIO, M.J., KINDER, J.E., SCHANBACHER, B.D. 1982. Patterns of LH secretion in castrated bulls (steers) during intravenous infusion of androgenic and estrogenic steroids: pituitary response to exogenous luteinizing hormone-releasing hormone. Biol. Reprod., 26:249-257.

[14] ERICKSON, B. H., BLEND, W.J. Response of the Sertoli cell and stem cell to ⁶⁰Co g-radiation (dose and dose rate) in testes of immature rats. Biol. Reprod., 14:641-652, 1976.

[15] HOCHEREAU-DE RIVIERS, M. T., MONET-KUNTZ, C., COUROT, M. 1987. Spermatogenesis and Sertoli cell numbers and function in rams and bulls. J. Reprod. Fert., 34:101-110.

[16] JÉGOU, B., SHARPE, R. 1993. Paracrine mechanisms in testicular control. In: D. de Kretser (Ed.), Molecular Biology of the Male Reproductive System. p. 271. Academic Press, San Diego.

[17] JOHNSON, L., NEAVES, W.B. 1981. Age-related changes in the Leydig cell population, seminiferous tubules, and sperm production in stallions. Biol. Reprod., 24:703-712.

[18] KESNER, J.S. 1988. Site of action for the estradiol-induced luteinizing hormone surge in farm animals and primates. Dom. Anim. Endocr, 5(4):265-281.

[19] KESNER, J.S., RIEBOLD T.W., CONVEY, E..M. 1982. Effect of dosage and frequency of injection of luteinizing hormone releasing hormone on release of luteinizing hormone and follicle stimulating hormone in estradiol-treated steers. J. Anim. Sci., 54(5):1023-1029.

[20] MACDONALD, R.D., DEAVER, D.R., SCHANBACHER, B.D. 1990. Prepubertal changes in plasma FSH and inhibin in Holstein bull calves: responses to castration and (or) estradiol. J. Anim. Sci., 69:276-287.

[21] MALAK, G. A., THIBIER, M. 1985. Individual variations in FSH release after a GnRH challenge and relationship with semen output in young bulls. J. Reprod. Fert, 75:345-357.

[22] MARTIN, T. L., WILLIAMS, G. L., LUNSTRA, D. D. et al. 1991. Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls. Biol. Reprod., 45:73-77.

[23] MATSCHKE, G. H., ERICKSON, B.H. 1969. Development and radioresponse of the prenatal bovine testis. Biol. Reprod., 1:207-215.

[24] MILLER, W.L. 1993. Regulation of pituitary gonadotropins by gonadotropin-releasing hormone, estradiol, progesterone, inhibin and activin. In: R. B. L. Gwatkin (Ed.), Genes in Mammalian Reproduction. p. 247. Wiley-Liss, Inc.

[25] MONGKONPUNYA, K., HAFS, H.D., CONVEY, E.M. et al. 1975. Serum luteinizing hormone, testosterone and androstenedione in pubertal and prepubertal bulls after gonadotropin releasing hormone. J. Anim. Sci., 40:682-695.

[26] MOURA, A.A., ERICKSON, B.H. 1997. Age-related changes in peripheral hormonal concentrations and their relationships with testis size and number of Sertoli and germ cells in yearling beef bulls. J. Reprod. Fert , 111:183-190.

[27] NETT, T. 1990. Regulation of genes controlling gonadotropin secretion. J. Anim. Sci. 68 (Suppl. 2):3.

[28] NISWENDER, G.D., RICHERT, JR. L.E, MIDGLEY, JR., A.R 1969. Radioimmunoassay for bovine and ovine luteinizing hormone. Endocrinology, v. 84, p. 1166-1177.

[29] ORTAVANT, R., COUROT, M., HOCHEREAU-DE-REVIERS, M.T. 1977. Spermatogenesis in domestic animals. In: COLE, H. H., CUPPS, P.T. (Ed.), Reproduction in Domestic Animals. p. 203. Academic Press, New York.

[30] ORTH, J.M., GUNSALUS, G.M, LAMPERTI, A.A. 1988. Evidence from Sertoli cell-depleted rats indicates that spermatids numbers in adults depends on Sertoli cells produced during perinatal development. Endocrinology, 122:787-798.

[31] PRICE, C.A. 1991. The control of FSH in the large domestic species. J. Endocr, 131:177-188.

[32] SAS INSTITUTE INC., SAS/STAT® User's Guide, Version 6, Fourth Edition, Volume 2, Cary, NC: SAS Institute Inc. , 1989. 846 pp.

[33] SCHANBACHER, B.D. 1990. Pituitary and testicular responses of beef bulls to active immunization against inhibin alpha. J. Anim. Sci., 69:252-261.

[34] SHARPE, R.M. 1994. Regulation of spermatogenesis. In: E. Knobil and J. D. Neil (Ed.), The Physiology of Reproduction, p. 1363. Raven Press, New York.

[35] SINOWATZ, F., AMSELGRUBER, W. Postnatal development of bovine Sertoli cells. Anat. Embryol, v. 174, p. 413-422. 1986.

[36] SWANSON, L. V., WETTEMANN, R.P., RAWLINGS, N.C. et al. 1971. Pubertal relationships of some endocrine and reproductive criteria in Hereford bulls. J. Anim. Sci., 33:823-835.

[37] TILBROOK, A. J., DEKETSER, D.M., CLARKE, I.J. 1993. Human recombinant Inhibin A suppress plasma follicle-stimulating hormone to intact levels but has no effect on luteining hormone in castrated rams. Biol. Reprod., 49: 779-788.

[38] WILDEUS, S., RANDEL, R.D., HUMPHREY, W.D. 1988. Age-related changes in the supression of serum luteinizing hormone by estradiol-17b in developing steers. Theriogenology, 29(5):1065-1073.