Comment on "Effects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans".

Letter to the EditorComment on “Effects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans”Abigail T. Colburn and Nina S. StachenfeldAbigail T. ColburnJohn B. Pierce Laboratory, New Haven, Connecticut, United StatesDepartment of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, Connecticut, United States and Nina S. StachenfeldJohn B. Pierce Laboratory, New Haven, Connecticut, United StatesDepartment of Obstetrics, Gynecology and Reproductive Sciences, Yale School of Medicine, New Haven, Connecticut, United StatesPublished Online:04 Aug 2023https://doi.org/10.1152/japplphysiol.00335.2023MoreSectionsPDF (209 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat to the editor: A recent paper by Turner et al. (1) provided insight into the effects of sex and reproductive hormone exposure on endothelium- and nitric oxide (NO)-dependent vasodilation. In addition to important findings, these investigators demonstrated a unique willingness to account for the complexities introduced by reproductive hormone exposures when studying sex differences. Their methodology improved upon previous work through the isolation of NO-dependent vasodilation (heating at 39°C + Nω-nitro-L-arginine methyl ester) from endothelial-dependent vasodilation (heating at 39°C only) as well as comparisons between men, naturally cycling (NC) women in the early follicular phase, and women taking oral contraceptive pills (OCP, during placebo pill phase). Using this novel design, these investigators found that endothelium-dependent vasodilation was greater whereas NO-dependent vasodilation was lower in men compared with women, regardless of hormone exposure. Subanalyses determined that NO-dependent vasodilation was greater within women taking OCP compared with NC women and men. In contrast, previous investigations observed no sex differences in NO-dependent vasodilation (2) or greater NO-dependent vasodilation in men compared with women (3). Interestingly, Patik et al. (2) included both NC and women taking OCP in the same group, whereas Stanhewicz et al. (3) included only NC women, suggesting the variability across these studies is likely due to different hormonal exposures between NC and the placebo phase of OCP administration. These findings are key, as they contradict previous assumptions that the placebo phase of OCP is equivalent to the low hormone phase of the menstrual cycle. This is supported by previous observations that endogenous hormone levels during the placebo week are variable and depend on hormone level in the OCP and length of exposure (4, 5). These findings by Turner et al. (1) also indicate that mechanisms underlying sex differences in NO-dependent vasodilation may be related to OCP hormone exposure, even in the placebo phase.For testing of women in physiological research, methodology should include baseline testing before OCP use (or a washout period of longer than the placebo week), control of contraceptive type/dose (e.g., stratification of subjects based on type/dose or inclusion only of subjects on the same contraceptive type/dose), and measurement of endogenous hormone levels. In addition, testing women taking OCP on days 3–5 of the placebo pills may be preferable to days 1–2, because endogenous hormones are still low and metabolites are no longer present (4, 5). Finally, the effects of race, ethnicity, and health status on sex differences and hormonal exposure require further study (6).Women continue to be understudied in research despite comprising more than half the world population. There continues to be little consensus regarding methodology to account for known hormonal effects on physiological outcomes when testing women, so inconsistent methodology hinders interpretation of results. The hormonal milieu should be considered a prominent confounding variable that is accounted for in all investigations. Through their creatively designed and carefully conducted investigation, Turner et al. (1) have accounted for the complexity that comes with evaluating the impact of sex differences and hormone exposure within women on endothelial function and mechanisms contributing to endothelial function.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the authors. AUTHOR CONTRIBUTIONSA.T.C. and N.S.S. drafted manuscript; edited and revised manuscript; approved final version of manuscript. REFERENCES1. Turner CG, Stanhewicz AE, Nielsen KE, Otis JS, Feresin RG, Wong BJ. Effects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans. J Appl Physiol (1985) 134: 858–867, 2023. doi:10.1152/japplphysiol.00586.2022. Link | ISI | Google Scholar2. Patik JC, Curtis BM, Nasirian A, Vranish JR, Fadel PJ, Brothers RM. Sex differences in the mechanisms mediating blunted cutaneous microvascular function in young black men and women. Am J Physiol Heart Circ Physiol 315: H1063–H1071, 2018. doi:10.1152/ajpheart.00142.2018. Link | ISI | Google Scholar3. Stanhewicz AE, Greaney JL, Kenney WL, Alexander LM. Sex- and limb-specific differences in the nitric oxide-dependent cutaneous vasodilation in response to local heating. Am J Physiol Regul Integr Comp Physiol 307: R914–R919, 2014. doi:10.1152/ajpregu.00269.2014. Link | ISI | Google Scholar4. Creinin MD, Lippman JS, Eder SE, Godwin AM, Olson W. The effect of extending the pill-free interval on follicular activity: triphasic norgestimate/35 µg ethinyl estradiol versus monophasic levonorgestrel/20 µg ethinyl estradiol. Contraception 66: 147–152, 2002. doi:10.1016/s0010-7824(02)00344-x. Crossref | PubMed | ISI | Google Scholar5. Schlaff WD, Lynch AM, Hughes HD, Cedars MI, Smith DL. Manipulation of the pill-free interval in oral conceptive pill users: the effect on follicular suppression. Am J Obstet Gynecol 190: 943–951, 2004. doi:10.1016/j.ajog.2004.02.012. Crossref | PubMed | ISI | Google Scholar6. Brothers RM, Stephens BY, Akins JD, Fadel PJ. Influence of sex on heightened vasoconstrictor mechanisms in the non-Hispanic black population. FASEB J 34: 14073–14082, 2020. doi:10.1096/fj.202001405R. Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESCorrespondence: A. T. Colburn (abigail.colburn@yale.edu). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Related ArticlesEffects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans 21 Mar 2023Journal of Applied PhysiologyReply to Colburn and Stachenfeld 04 Aug 2023Journal of Applied PhysiologyCited ByReply to Colburn and StachenfeldCasey G. Turner, Anna E. Stanhewicz, Karen E. Nielsen, Jeffrey S. Otis, Rafaela G. Feresin, and Brett J. Wong4 August 2023 | Journal of Applied Physiology, Vol. 135, No. 2 More from this issue > Volume 135Issue 2August 2023Pages 485-486 Crossmark Copyright & PermissionsCopyright © 2023 the American Physiological Society.https://doi.org/10.1152/japplphysiol.00335.2023PubMed37541850History Received 23 May 2023 Accepted 26 June 2023 Published online 4 August 2023 Published in print 1 August 2023 Keywordsendotheliummicrodialysisnitric oxidewomen Metrics