Reduction in FSH receptors in the rat testis by injection of homologous hormone.

Intratesticular injection of 25 microgram rat FSH into rats under continuous urethane anaesthesia resulted 24 h later in a 50% reduction in binding sites for FSH in testicular homogenates. By 48 h after injection, receptor number usually returned to control values. Intratesticular injection of 125I-labelled rat RSH showed less than 1% remaining in the testis 24 h later, suggesting that the reduction in receptor numbers at 24 h is not due to occupancy by the FSH. Experiments did not suggest that the injection of FSH induced FSH-degrading enzymes or inhibitors of binding.