Involvement of glucocorticoids in testicular involution after active immunization of boars against GnRH

Abstract

Active GnRH immunization of boars inhibits LH and testicular steroids but the consequences for spermatogenesis are unknown. Six boars were immunized three times against GnRH at 20, 24 and 28 weeks. Another six boars served as controls. Plasma LH and FSH were determined at 28 and 31 weeks. Testosterone and cortisol were determined before killing the pigs at 32 weeks. Tissue samples were taken for histology and fluid from the seminiferous tubuli for steroid determination. Individual germ cells were counted in histological sections. The glucocorticoid receptor (GCR), mitosis of spermatogonia and apoptosis were characterized by immunocytochemistry. Immunization reduced LH and testosterone to base levels whereas FSH was not changed. Testis weight was reduced by 64% due to a loss of Leydig cell cytoplasm (90.3%) and a decrease of tubule diameters (60.6%). Except for A-spermatogonia, all other spermatogenic cells were reduced by about 60%. Mitosis was reduced in immunized boars. Expression of GCRs was limited to spermatogonia and differed between immunized boars (8% of spermatogonia) and controls (2%). In the controls, androgen concentrations in tubular fluid were tenfold higher compared with immunized boars. Cortisol concentrations were of the order of 40 nmol/l both in the tubular fluid and blood plasma. These concentrations did not differ between groups. Apoptosis occurred only in spermatogonia and pachytene spermatocytes and was twofold higher in immunized boars compared with controls. Thus the availability of glucocorticoids in the tubuli and the expression of GCRs initiate apoptosis, which in turn reduces sperm yield. Testosterone is known to be an inhibitor of GCR expression, thus increasing the efficiency of spermatogenesis.

Expression of 11β-hydroxysteroid-dehydrogenase 2 in Sertoli cells of boar testes

“…In the pig, an effect of cortisol on testicular steroidogenesis was not substantiated so far and the GR does not occur in Leydig cells (Wagner and Claus, 2004). However, we demonstrated GR expression in spermatogonia of boar testes which is linked with a considerable degree of apoptosis limiting overall sperm yield.…”

“…However, we demonstrated GR expression in spermatogonia of boar testes which is linked with a considerable degree of apoptosis limiting overall sperm yield. Moreover, inhibition of LH and thus testicular steroid formation by active immunization against GnRH led to an increased expression of GR by spermatogonia and thus an increase of apoptosis (Wagner and Claus, 2004). By determination of 11ß-HSD enzyme activity we could demonstrate the presence of high amounts of 11ß-HSD2 activity but not of 11ß-HSD1 activity in the testes of boars.…”

Return of testicular function after vaccination of boars against GnRH: consequences on testes histology

“…In addition, seminiferous tubule diameter was reduced by 30%. Mitosis was reduced, but except for type A spermatogonia, the spermatogenic cells were reduced by about 60% (Wagner and Claus, 2004).…”

“…It was shown that the second dose of vaccine leads to maximal GnRH antibody titre and the concurrent drop of LH within one week . Surprisingly, FSH is not altered by vaccination of boars (Awoniyi et al, 1988a and1988b;Wagner and Claus, 2004) and it was concluded that it is regulated either by a separate releasing hormone, or by the hypothalamic secretion of activin (Padmanabhan and McNeilly, 2001).…”

“…Testosterone analysis Measurements were performed every third day after extraction with tert-butyl methyl ether (Wagner and Claus, 2004) from blood plasma samples. The antiserum had been raised against testosterone-3-CMO-BSA as an antigen and was specific.…”