Age-dependent pattern of androgen-binding protein secretion from rat Sertoli cells in primary culture

The pattern and hormonal control of rat androgen-binding protein (rABP) secretion in vitro was investigated using animals of different ages to initiate primary cultures of Sertoli cells. Sertoli cells were isolated from testes of 7- to 31-day-old rats and cultured for periods of up to 30 days in serum-free medium, medium supplemented with insulin, transferrin, and epidermal growth factor (3F), or 3F plus FSH, testosterone, progesterone, hydrocortisone, and vitamin E (8F). The amount of rABP secreted by Sertoli cells during the first 24 h in culture (initial rate) exhibited an age-dependent pattern which reflected the apparent in vivo activity of these cells. Between 7 and 25 days of age, the initial rate of rABP secretion per Sertoli cell increased 20-fold; a further 2-fold increase occurred between 25 and 35 days of age. The pattern of rABP secretion exhibited by Sertoli cells cultured for several weeks was dependent not only on added factors (3F or 8F), but also on Sertoli cell age, expressed as the total of animal age plus time in culture (total age). In cultures of Sertoli cells isolated from very young animals (7-10 days old), the rate of rABP secretion increased until 20 days (total age), but declined thereafter. This early increase in rABP secretion was augmented by, but not dependent on, hormone additions. In contrast, Sertoli cells isolated from older animals always showed decreasing rates of secretion with time in culture. Furthermore, Sertoli cells from very young animals retained the capacity to respond to hormones in vitro with increased secretion of rABP and maintenance of cell viability. This responsiveness decreased with age, similar to the loss of hormone response seen in vivo after puberty. In conclusion, culture conditions were established which permitted the study of FSH-dependent and independent regulation of rABP secretion and of the acquisition of hormone resistance at the time of puberty. The initial rate of rABP secretion in culture (first 24 h) correlates with the age of the animal from which the cultures are obtained. The pattern of rABP secretion during subsequent long term culture is determined by the total age (animal and culture age), with increasing rates of secretion up to 20 days and decreasing rates thereafter. This inherent pattern of rABP secretion as well as loss of responsiveness of the Sertoli cell to hormonal stimulation appear to be programmed early in development.