Differential effects of depot formulations of GnRH agonist leuprorelin and antagonist degarelix on the seminiferous epithelium of the rat testis

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Despite their pharmacologically opposite actions, long-acting depot formulations of both GnRH agonists and antagonists have been clinically applied for treatment of androgen-sensitive prostate cancer. Sustained treatment with GnRH analogues commonly suppresses both the synthesis and release of gonadotropins, leading to depletion of testicular testosterone. To clarify the underlying differences in the effects of GnRH agonists and antagonists on spermatogenesis, we compared histological changes in the seminiferous epithelium after administration of depot formulations of GnRH agonist leuprorelin and antagonist degarelix to male rats. Testicular weight had markedly declined by 28 days after administration of both GnRH analogues, although the testicular weight was decreased more promptly by leuprorelin compared with degarelix. Shortly after administration, massive exfoliation of premature spermatids and anomalous multinucleated giant cells was observed in seminiferous tubules of leuprorelin-treated rats, probably via the initial hyperstimulatory effects on the hypothalamic-pituitary-testicular axis, whereas no discernible changes were found in those of degarelix-treated rats. Long term treatment with both types of GnRH analogues similarly induced a marked reduction in the height of the epithelium and deformation of apical cytoplasm in Sertoli cells, resulting in premature detachment of spermatids from the epithelium. Lipid droplets had accumulated progressively in Sertoli cells, especially in those of degarelix-treated rats. These findings clearly demonstrate the differences in the effects of GnRH agonists and antagonists on the spermatogenic process. This study suggests that an appropriate choice of GnRH analogues is necessary to minimize their adverse effects on spermatogenesis when reproductive functions should be preserved in patients.