THE EFFECT OF ESTERIFICATION ON THE RELEASE OF TESTOSTERONE AND ESTRADIOL FROM SILICONE IMPLANTS

Four experiments were conducted to determine the effect of esterificat ion on the release of testosterone and estradiol from capsule-type sil icone implants. In castrated male rats testosterone propionate and, te stosterone enanthate implants increased (P < .05) blood testosterone c oncentrations and seminal vesicle weights move than empty and testoste rone implants. Testosterone propionate and testosterone enanthate impl ants released 4 times and 10 times, respectively, more equivalent test osterone per cm(2) per day than testosterone implants. The increase in blood testosterone concentrations was proportional to the increase in implant release rate for testosterone propionate, but not for testost erone enanthate. Although estradiol-17 beta implants increased (P < .0 5) uterine weights of ovariectomized rats, uterine weights in estradio l benzoate implanted ovariectomized rats were 1.3 times greater than i n estradiol-17 beta implanted rats. Estradiol benzoate implants releas ed less than 0.5 times the amount of equivalent estradiol per cm(2) pe r day than estradiol-17 beta implants.