Cross-sexual Effects of Testosterone on Mesenteric Arterial Reactivity in Ovariectomized Female Rats

The number of transgender individuals is on the rise in the United States. Although there are studies on the effects of sex hormones on cardiovascular function of cisgender male and female, still much is not known about the effects of cross-sex hormone therapy (CSHT) on cardiovascular function in transgender individuals. It has been shown that the risk factors of cardiovascular diseases (CVD) are increased in transgenders after they undergo CSHT. Epidemiological studies suggest that transgender females (male to female, MtF) on estrogen therapy develop higher risk of CVD compared to transgender males (female to male, FtM) taking testosterone. This study investigates the effects of testosterone or estrogen treatment on the third branch of mesenteric arterial reactivity in ovariectomized female rats. Briefly, 8-10 weeks old female Sprague Dawley (SD) rats were ovariectomized (OVX) and subcutaneously implanted with placebo (OVX + PL) or testosterone (OVX + T, 7.5 mg) or 17β- estradiol (OVX + E 2 , 1.5 mg) pellets for about 35 days. Age matched intact female SD rats were also included in the experimental groups. Endothelium-dependent vasorelaxation (EDV) to acetylcholine (ACh) was measured in the precontracted mesenteric arteries with phenylephrine (PE), using wire myography. Responses to sodium nitroprusside (SNP)-induced vasorelaxation, and PE- and endothelin-1 (ET-1) induced vasocontraction were also determined. We demonstrated that the responses to ACh in rat mesenteric arteries were not altered by either ovariectomy or estrogen treatment. However, testosterone treatment of OVX female rats significantly enhanced the sensitivity to ACh-induced vasorelaxation compared with those in other experimental groups. Moreover, the mesenteric arteries of OVX + T exhibited a trend of reduced sensitivity to PE responses compared to other groups. Furthermore, the maximum tension to ET-1 was significantly reduced in mesenteric arteries of OVX + T compared to OVX+E 2 and OVX+PL groups. The vasorelaxation responses to SNP were not altered in any of experimental groups studied. These data suggest that elevated sensitivity to ACh in testosterone-treated ovariectomized female rats might be, in part, due to reduced vessel responses to contractile agents, but not altered sensitivity of smooth muscle to nitric oxide (NO) in this group. Additional studies are needed to investigate the underlying mechanisms and document the consequences for the improvement of EDV observed in OVX + T rats. NIDA/NIGMS, 1SC1DA052120-01 to MF, Bridge Grant from University of the Pacific to RR. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.