Identification of specific FSH binding sites in the testes of adult monkeys of different species

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Abstract
The interaction of 125I-labeled h[human]FSH with primate testicular tissue from 4 spp. of adult monkeys (Macaca mulatta, M. nemestrina, M. fascicularis and Papio cynocephalus) was investigated. 125I-labeled hFSH binding to a particulate fraction (P1, 40,000 g) of frozen testes was highly specific and saturable. Displacement curves generated using the P1 fraction of testes from the 4 spp. and 125I-labeled hFSH and unlabeled FSH were very similar. The binding of FSH to the monkey testicular receptor was not species-specific because purified FSH from heterologous species such as horse, sheep, pig and rat were very effective in competing with 125I-labeled hFSH for binding. The equine FSH was about 10 times more active than hFSH in this respect. 125I-labeled ovine FSH bound as well as labeled hFSH to the testes fractions of all 4 monkey species. In marked contrast to the high binding of 125I-labeled hFSH, binding of 125I-labeled hCG with rhesus monkey testis homogenates and P1 fractions was very low. The FSH receptor in the adult rhesus monkey testis was present in much larger quantity than the LH [luteinizing hormone] receptor and was more readily detectable. Frozen primate testis can be utilized for investigating testicular-FSH interactions.