Growth Factors in Leydig Cell Function

Leydig cell function is predominantly controlled by gonadotropins. However, a number of intratesticular factors are known to influence Leydig cell steroidogenic function. The presence of growth factors within the testis, their effects on androgen release by the isolated Leydig cells, subnormal reproductive function in animals with disrupted growth hormone/insulin-like growth factor-I secretion, and in acromegalics as well as in Laron syndrome patients clearly indicate that growth factors play an important role in reproduction. It is possible that there might be a concerted effect of intratesticularly produced factors on testosterone secretion. Evidence presented in this chapter indicates that pituitary luteinizing hormone is absolutely essential for Leydig cell endocrine function, but growth factors are required for the full effect of luteinizing hormone on androgen secretion. Also, there are indications that a number of growth factors modify gonadotropin synthesis and release from the pituitary gland. Thus, growth factors can exert endocrine as well as paracrine/autocrine effects in controlling the pituitary and testicular functions in mammals.