The effect of testosterone withdrawal and subsequent germ cell depletion on transferrin and sulfated glycoprotein-2 messenger ribonucleic acid levels in the adult rat testis.

We have examined the effects of decreasing intratesticular testosterone concentration and of decreasing germ cell number on levels of transferrin mRNA and sulfated glycoprotein (SGP)-2 mRNA in the adult rat testis. Intact rats received implants of testosterone- and estradiol-filled capsules to suppress LH secretion from the pituitary, thereby suppressing Leydig cell testosterone production. The levels of intratesticular testosterone declined 70% to 20 ng/ml within 3 days, were reduced further to approximately 15 ng/ml by 14 days, and subsequently reached a minimum of about 10 ng/ml. In contrast, the number of elongated spermatids per testis remained unchanged through 14 days, then declined to fewer than 20% of normal between 14 and 28 days, and reached zero by 56 days postimplantation. Likewise, both pachytene spermatocytes and round spermatids declined only after 14 days postimplantation. Northern blots of testicular RNA showed that Sertoli cell transferrin mRNA per testis decreased markedly between 14 and 28 days postimplantation. However, SGP-2 mRNA per testis was unchanged over the time course of the experiment. The decrease in transferrin mRNA, concomitant with germ cell loss, suggests that this mRNA is regulated by the number of germ cells in the testis and not directly by testosterone. In contrast, the constant level of SGP-2 mRNA in the face of reduced intratesticular testosterone and the subsequent loss of germ cells suggests that this mRNA is constitutively maintained in the adult rat testis.