Role of testosterone in regulating the growth of mice from lines selected for low vs high plasma insulin-like growth factor-I concentrations

Abstract

A study was undertaken to investigate the role of testosterone in regulating growth and circulating levels of insulin-like growth factor-I in male mice from lines divergently selected on the basis of plasma IGF-I. Controls of each lines were sham-operated at 10 days of age and treated with peanut oil from day 14 to day 70. A second group, which was castrated at 10 days and treated with testosterone enanthate (0.5 micrograms.(g body weight)-1.day-1) from day 14 to 70, did not differ from controls in body weight but had higher plasma IGF-I concentrations. Delaying testosterone therapy until day 42 in a third group retarded growth, with body weights being significantly lower than those of other two groups from days 35 to 56. However, plasma IGF-I levels in this group were not different from those of controls. Effects of line and treatment were additive. It is concluded that the greater pubertal growth of high-line compared to low-line males is not due to greater stimulation of circulating IGF-I by testosterone. Furthermore, testosterone does not appear to influence pubertal growth by acting on circulating levels of IGF-I.