Figure 2

Serum estradiol concentrations depends on administration mode. The three most commonly-used methods for administrating 17β-estradiol to rats were tested in a previous study [23]: slow-release pellets (0.25 mg 60 day-release pellets, 0.10 mg 90 day-release pellets) and silastic capsules (silastic laboratory tubing, inner/outer diameter: 1.575/3.175 mm, filled with 20 mm columns of 180 μg 17β-estradiol/mL sesame oil). Blood samples were obtained at days 2, 7, 14, 21, 28, 35 and 42 after administration, and hormone levels were analyzed. As can be observed in the graph, silastic capsules produced 17β-estradiol concentrations that were within the physiological range for at least 4 weeks, while the pellets resulted in early supraphysiological peaks followed by a substantial decrease.