Hormone replacement therapy and cardiovascular function: Evidence for dual and opposite effects of estrogen on vascular reactivity

Richard E. White, Guichun Han, Scott A. Barman

Research output: Contribution to journalReview article

1 Scopus citations

Abstract

Hormone replacement therapy (HRT) remains one of the most controversial topics in cardiovascular pharmacology. Although earlier studies demonstrated that exogenous estrogen lowered a woman's risk of cardiovascular disease, the more recent Woman's Health Initiative (WHI) trial indicates that HRT actually increases the risk of coronary heart disease or stroke. However, there is no clear explanation for this discrepancy. Is estrogen a helpful or a harmful hormone in terms of cardiovascular function? This review discusses some recent findings that propose a novel mechanism which may shed significant light upon this controversy. We propose that nitric oxide synthase (NOS) expressed within the vascular wall is a target of estrogen action. Under normal conditions in younger women, the primary product of estrogen action is NO, which produces a number of beneficial effects on vascular biology. As a woman ages, however, there is evidence for loss of important molecules essential for NO production (e.g., tetrahydrobiopterin, L-arginine). As these molecules are depleted, NOS becomes increasing "uncoupled" from NO production, and instead produces superoxide, a dangerous reactive oxygen species. Therefore, we propose that estrogen is neither "good" nor "bad", but simply stimulates NOS activity. It is the biochemical environment around NOS that will determine whether estrogen produces a beneficial (NO) or deleterious (superoxide) product, and can account for this dual and opposite nature of estrogen pharmacology. Further, this molecular mechanism is consistent with recent analyses revealing that HRT produces salutary effects in younger women, but mainly increases the risk of cardiovascular dysfunction in older postmenopausal women.

Original languageEnglish (US)
Pages (from-to)17-26
Number of pages10
JournalCurrent Topics in Pharmacology
Volume11
Issue number2
StatePublished - Dec 1 2007

Keywords

  • Coronary
  • Estrogen
  • Hormone replacement therapy
  • Nitric oxide
  • Superoxide

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)

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