Opioids Cause Vascular Dysfunction in a Sex‐Specific Manner

Abstract

Recent studies have shown that indices of vascular age and arterial stiffness are increased in opioid dependent patients in comparison with opioid naïve controls, and the effects are more marked in women. It has also been shown that chronic use of prescription opioids leads to an increased risk of a cardiovascular event, which was higher among women than men. Despite the growing evidence that implicates opioid use as an unconventional risk factor for cardiovascular disease, the precise mechanisms involved remain unknown. We hypothesized that exposure to exogenous opioids causes sex-specific (1) vascular stiffness via suppression of actin depolymerization, leading to changes in smooth muscle contractility, and (2) vascular smooth muscle cell proliferation. To test our first hypothesis, we performed continuous intraluminal infusion of morphine in pressurized mesenteric resistance arteries (MRA, 5th order) from male and female mice (C57BL/6NTac, 10 weeks old; n=4) using culture pressure myographs. We observed that morphine reduced the lumen diameter by 23% (without morphine: 185.8 ± 25.4µm vs. morphine: 143.2 ± 36.7µm*, *p<0.05) in MRA from female mice, with an average change of -40µm from baseline values (Figure 1). In contrast, there was little to no change in the luminal diameter of male arteries (without morphine: 174.0 ± 23.7µm vs. morphine: 169.2 ± 19.4µm*, *p<0.05). We also observed that treatment with morphine caused a left shift in the stress-strain curve of MRA from female mice compared to control arteries, which implies decreased elasticity and increased stiffness. On the other hand, morphine caused a right shift in the stress-strain curve of male MRA, indicating opposite effects of increased elasticity and decreased stiffness. To address our second hypothesis, we cultured and treated aortic vascular smooth muscle cells from male and female rats (Dahl R, 11-13 weeks old, n=4) with morphine (10nM, 10µM) and hydrocodone (10nM, 10µM). Proliferation was measured continuously until 120 hours. Our results showed that chronic treatment with morphine induced vascular smooth muscle cell proliferation in both male [confluence (%): DMSO vehicle 20.4 ± 4.8, 10nM 32.6 ± 9.0, and 10µM 33.3 ± 10.2*; * p<0.05] and female cells [confluence (%): DMSO vehicle 49.9 ± 16.1, 10nM 81.4 ± 13.3, and 10µM 80.1 ± 12.7*; * p<0.05] in a dose independent manner, but the rate of proliferation was markedly increased in female cells (Figure 2). Chronic treatment with hydrocodone also induced vascular smooth muscle cell proliferation in both male [confluence (%): DMSO vehicle 20.4 ± 4.8, 10nM 19.4 ± 12.1, and 10µM 34.4 ± 10.3*; * p<0.05] and female cells [confluence (%): DMSO vehicle 49.9 ± 16.1, 10nM 80.7 ± 11.7, and 10µM 71.3 ± 23.5*; * p<0.05] seen in a dose dependent manner, with an increased proliferation rate in female cells. Collectively, these results have significant implications for the previously unexplored role of exogenous opioids as a modifiable cardiovascular risk factor, especially in women.