Figure 2: Comparison of estradiol levels produced by two steroid replacement systems. Bars show weekly estradiol (E) levels achieved by Silastic implants (S) and commercial pellets (P). Plasma estradiol of rats implanted with an estradiol-filled Silastic tubing decreased gradually with time, being the highest values at 7 days versus the concentrations observed at 28 days (at least *p<0.02), according to FISHER multiple comparison test. Plasma estradiol of rats implanted with commercially available pellets showed a wavelike pattern with estradiol levels fluctuating between the time-points studied. Statistical analysis demonstrated that the levels of estradiol were significantly higher at 14 days relative to day 7 (at least #p<0.05), but returned to a similar level by day 21. All values are significantly different from that of intact rats at day 0 (with ovaries: white bar). Intact n=29; OVX+S3 n=10; OVX+S4 n=11; OVX ± S5 n=5; OVX+P3 n=8; OVX+P4 n=7. Data are expressed as mean ± S.E.M.