DEVELOPMENTAL-CHANGES IN TESTICULAR LUTEINIZING-HORMONE RECEPTORS ANDANDROGENS IN THE DOG

The changes with age in the levels of testicular luteinising hormone ( LH) receptors in dogs, were correlated with plasma androgen concentrat ions and the effects of stimulation with human chorionic gonadotrophin (hcc). The presence of high-affinity binding sites for LH was demonst rated in the testes of all the animals studied, and the apparent affin ity of the LH receptors did not change significantly with age. The tot al number of LH receptor sites per testis increased continuously with age and the growth of the testis. The major rise in the number of LH r eceptors occurred between six and 10 months of age, and coincided with the phase of rapid testicular growth. The concentrations of androsten edione, testosterone and 5 alpha-dihydrotestosterone in plasma increas ed gradually until six months of age, and then increased rapidly with the increase in the number of testicular LH receptors. An increase in the concentrations of androgens in plasma was observed in response to stimulation with hCG after the number of testicular LH receptors began to increase progressively. The increase in the sensitivity of the dog s' gonads to LH could be responsible for the marked increase in the se cretion of androgens which occurs during puberty in the male dog.