Fig. 6.

Estimated relationships between near-maximal modal GnRH concentrations (nm) calculated at near-zero suppression (low feedback) by free T and age in 21 subjects. Free T is viewed as repressing GnRH secretion noncompetitively. Degree of inhibition of GnRH secretion was defined by multiplying T's inhibitory efficacy by a percentage between zero (complete suppression) and 100 (no suppression). Each GnRH mode (y-axis value) was calculated at four designated values of 70, 80, 90, and 95% of GnRH efficacy. Resultant modal GnRH values in the 21 subjects were then regressed against age, yielding the four panels. None of the four slopes is significantly different from zero (P values are two sided), indicating that the level of GnRH resulting from near-zero free-T suppression is independent of age.