SA2: To determine whether the decrease in EDD in response to acute ovarian suppression in pre- and early perimenopausal women is related to reduced BH4 bioavailability and elevated markers of oxidative stress. This will be assessed by comparing EDD and plasma markers of oxidative stress after acute oral supplementation of BH4 (or PL) following either acute ovarian suppression with (GnRHant+E2) or without (GnRHant+PL) E2 add-back. Additionally, endothelial cell protein expression of markers of BH4 biosynthesis and oxidative stress will be measured before and after the suppression/add-back paradigm.