Tetrahydrobiopterin improves endothelial function and decreases arterial stiffness in estrogen-deficient postmenopausal women

Moreau KL, Meditz A, Deane KD, Kohrt WM. Tetrahydrobiopterin improves endothelial function and decreases arterial stiffness in estrogen-deficient postmenopausal women. Am J Physiol Heart Circ Physiol 302: H1211-H1218, 2012. First published January 13, 2012; doi:10.1152/ajpheart.01065.2011.-The mechanisms mediating arterial stiffening with aging and menopause are not completely understood. We determined whether administration of tetrahydrobiopterin (BH4), a critical cofactor for endothelial nitric oxide synthase to produce nitric oxide, would increase vascular endothelial-dependent vasodilatory tone and decrease arterial stiffness in estrogen-deficient postmenopausal women. Additionally, we examined whether the beneficial effects of estrogen on vascular function were possibly related to BH4. Arterial stiffness (carotid artery compliance) and endothelial-dependent vasodilation [brachial artery flow-mediated dilation (FMD)] were measured in postmenopausal (n = 24; 57 +/- 1 yr, mean +/- SE) and eumenorrheic premenopausal (n = 9; 33 +/- 2 yr) women before and 3 h after the oral administration of BH4. Subsequently, in postmenopausal women, vascular testing (before and after BH4) was repeated following randomization to either 2 days of transdermal estradiol or placebo. Baseline carotid artery compliance and brachial artery FMD were lower in postmenopausal than in premenopausal women (P < 0.0001). BH4 administration increased carotid artery compliance (0.61 +/- 0.05 to 0.73 +/- 0.04 mm(2).mmHg(-1).10(-1) vs. baseline, P < 0.0001) and brachial artery FMD (P < 0.001) in postmenopausal women but had no effect in premenopausal women (P = 0.62). Carotid artery compliance (0.59 +/- 0.05 to 0.78 +/- 0.06 mm(2).mmHg(-1).10(-1), P < 0.001) and FMD increased in postmenopausal women in response to estradiol (P = 0.02) but were not further improved with the coadministration of BH4, possibly because estrogen increased BH4 bioavailability. Carotid artery compliance and FMD increased with BH4 in the placebo group (P = 0.02). Although speculative, these results suggest that reduced vascular BH4 may be an important contributor to arterial stiffening in estrogen-deficient postmenopausal women, related in part to reduced endothelial-dependent vasodilatory tone.