Final answer:
The primary function of interstitial endocrine cells, or Leydig cells, is the production of testosterone, an essential androgen for male reproductive health and the process of spermatogenesis.
Step-by-step explanation:
The function of interstitial endocrine cells, specifically Leydig cells, is to produce androgens, such as testosterone. These cells are found between the seminiferous tubules within the testes and have a crucial role in regulating the development and maintenance of male secondary sexual characteristics, muscle development, bone growth, and spermatogenesis. Testosterone production is regulated by luteinizing hormone (LH) which is released by the pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. Leydig cells synthesize testosterone, contributing to higher concentrations of testosterone within the testes compared to the systemic circulation, which is vital for spermatogenesis and male fertility.