Impairment of spermatogonial development and spermiation after testosterone-induced gonadotropin suppression in adult monkeys (Macaca fascicularis)

Human male hormonal contraceptive regimens do not consistently induce azoos permia, and the basis of this variable response is unclear. This study used nine adult macaque monkeys (Macaca fascicularis) given testosterone (T) im plants for 20 weeks to study changes in germ cell populations in relation t o sperm output. Germ cell numbers were determined using the optical disecto r stereological method. Four animals achieved consistent azoospermia (azoo group), whereas five animals did not (nonazoo group). T-induced gonadotropi n suppression in all animals decreased A pale (Ap) spermatogonia to 45% of baseline within 2 weeks, leading to decreased B spermatogonia (32-38%) and later germ cells (20-30%) after 14 and 20 weeks. Though the reduction in la ter germ cell types could be primarily attributed to the loss of spermatogo nia, the data suggested that some cells were lost during the spermatocyte a nd spermatid phase of development. B spermatogonial number was more markedl y suppressed in azoospermic animals, compared with the nonazoo group, as wa s the conversion ratio between Ap and B spermatogonia. Abnormal retention o f elongated spermatids (failed spermiation) was also prominent in some anim als after long-term T administration. We conclude that: 1) the variable sup pression of sperm output is attributed to the degree of inhibition of germ cell development from type B spermatogonia onwards, and this is related to the degree of FSH suppression; and 2) inhibition of Ap and B spermatogonial development and of spermiation are the major defects caused by long-term T administration to monkeys.