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Institut für Nutztierwissenschaften

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    Steuerungsmechanismen der Spermatogenese beim Eber: Auswirkungen einer GnRH-Immunisierung und anschließender Estradiolinfusion
    (2005) Wagner, Anna; Claus, Rolf
    Whereas the regulation of spermatogenesis is well known in various species, specific differences, however, exist for the boar, which require species-specific investigation. High concentrations of estrogens are synthesized in the boar testis. It is known, that they play a synergistic role for male behaviour and function of accessory sex glands. Additionally, estrogens in the ejaculate reach the female genital tract and contribute to sperm transport and ovulation in the sow. A possible involvement of estrogens in spermatogenesis, however, was not investigated so far. Similarly, high concentrations of glucocorticoids occur in the tubuli of mature boars. Their regulatory function in spermatogenesis so far is unknown. For clarification, boars were actively immunized against GnRH. GnRH stimulates gonadotropin-release from the pituitary. The evaluation of hormone concentrations in blood plasma after GnRH immunization showed unexpectedly, that the gonadotropin FSH is not influenced, whereas LH- and in consequence steroid- (androgen and estrogen) concentrations were abolished. This offers the possiblity to characterize the selecitve function of estrogens in the presence of FSH. Three groups were evaluated: intact boars (n=5), immunized boars (n=5), 17ß-estradiol infused, immunized boars (n=6). All animals were fitted with indwelling cephalic vein catheters on both sides. One of them was reserved for infusion, the other one for uncontaminated blood sampling. All animals were infused with physiological saline over 7 weeks. For the 17ßEstradiol infused, immunized boars, a defined concentration of estradiol was added to the solution. Blood samples were collected over the whole 7-week period for LH, FSH, testosterone and estradiol. Blood samples were later analysed by established radioimmunological procedures. At the end of the 7-week period, all animals were killed. Tissue samples were fixed for histological examination. Morphological criteria included e.g. tubular diameter, seminiferous epithelial height and number of Leydig cells. Imunocytochemical evaluation was performed for mitosis (Ki-67), apoptosis (TUNEL) and the glucocorticoid receptor. The number of germ cell in the tubuli was reduced by 60% in immunized boars compared to the intact controls. These changes were explained by a more pronounced expression of the glucocorticoid receptor in spermatogonia, followed by the appearance of apoptosis in spermatogonia and primary spermatocytes. In consequence these findings demonstrate for the first time an involvment of glucocorticoids in the quantitative regulation of spermatogenesis. They counteract tubular mitosis by reducing the number of germ cells by apoptosis. In the 17ßestradiol infused group of immunized boars, the infusion led to the restoration of physiological estradiol concentrations (230 pg/ml) in peripheral blood plasma. As expected, androgen concentrations were minimal, so that the specific role of estrogens for spermatogenesis could be clarified. Data from the histological evaluation showed, that the expression of the estrogen receptor alpha occured in spermatogonia, selectively in the mitotic active stage of the seminiferous epithelial cycle leading to a 41-50% rise of germ cell numbers compared to immunized boars. The apoptotic rate in the tubuli of the estradiol infused boars however was not changed compared to immunized boars, so that physiological sperm numbers as they are characteristic for intact boars, were not reached. This study shows for the first time that both glucocorticoids and estrogens play an essential role for spermatogenesis in the boar. They are involved in the regulation of sperm yield by influencing the mitosis-apoptosis equilibrium in the tubuli of boars.