Developmental changes in testicular luteinising hormone receptors and androgens in the dog

The changes with age in the levels of testicular luteinising hormone (LH) receptors in dogs, were correlated with plasma androgen concentrations and the effects of stimulation with human chorionic gonadotrophin (hCG). The presence of high-affinity binding sites for lh was demonstrated in the testes of all the animals studied, and the apparent affinity of the LH receptors did not change significantly with age. The total 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 receptors occurred between six and 10 months of age, and coincided with the phase of rapid testicular growth. The concentrations of androstenedione, testosterone and 5α-dihydrotestosterone in plasma increased 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 dogs' gonads to LH could be responsible for the marked increase in the secretion of androgens which occurs during puberty in the male dog.