H2: a) The expected decrease in EDD and increase in plasma oxidative stress markers following acute ovarian suppression will be mitigated in the groups treated with oral BH4 (GnRHant+PL+BH4); there will be little or no effect of the addition of BH4 to the E2 add-back group. b) Ovarian suppression alone will reduce endothelial protein markers of BH4 biosynthesis and will increase markers of oxidative stress. These changes will not be observed following ovarian suppression with E2 add-back and oral BH4. These sets of experiments will provide evidence that the oxidative stress-related decrease in EDD in response to E2 suppression is in part, related to decreased BH4 bioavailability.