To determine the site where Aza may be acting to prevent the advent of puberty, we first examined the competence of the ovary to respond to gonadotropins with estradiol production. We treated rats with Aza from PND 22 to 28, administered a single s.c injection of pregnant mare serum gonadotropin (PMSG, 8 IU/rat) on PND 26, and collected trunk blood for estradiol measurement on PND 28. The Aza treatment did not inhibit, and even enhanced, the estradiol response of the ovary to PMSG (Fig. 2a). This outcome suggested that the delay in puberty is due to a central or pituitary, instead of an ovarian defect. Consistent with this interpretation, basal plasma LH levels were lower in 28-day-old Aza treated rats than vehicle-treated controls (C= 1.89 ± 0.41 ng ml−1, n=19 vs Aza= 0.55 ± 0.16 ng ml−1, n=23; t=3.23, p=0.002, Student t Test), and Aza treated rats had a greatly diminished LH response to ovariectomy, performed on PND 24 and assessed on PND 28 (C=52.56 ± 6.93 ng ml−1, n=6 vs Aza=7.43 ± 2.76 ng ml−1, n=6; t=6.48, p<0.001, Student
