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. 2016 Jul 27;5(8):e003858.
doi: 10.1161/JAHA.116.003858.

One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function

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Free PMC article

One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function

Xiaoyin Wang et al. J Am Heart Assoc. .
Free PMC article

Abstract

Background: Despite public awareness that tobacco secondhand smoke (SHS) is harmful, many people still assume that marijuana SHS is benign. Debates about whether smoke-free laws should include marijuana are becoming increasingly widespread as marijuana is legalized and the cannabis industry grows. Lack of evidence for marijuana SHS causing acute cardiovascular harm is frequently mistaken for evidence that it is harmless, despite chemical and physical similarity between marijuana and tobacco smoke. We investigated whether brief exposure to marijuana SHS causes acute vascular endothelial dysfunction.

Methods and results: We measured endothelial function as femoral artery flow-mediated dilation (FMD) in rats before and after exposure to marijuana SHS at levels similar to real-world tobacco SHS conditions. One minute of exposure to marijuana SHS impaired FMD to a comparable extent as impairment from equal concentrations of tobacco SHS, but recovery was considerably slower for marijuana. Exposure to marijuana SHS directly caused cannabinoid-independent vasodilation that subsided within 25 minutes, whereas FMD remained impaired for at least 90 minutes. Impairment occurred even when marijuana lacked cannabinoids and rolling paper was omitted. Endothelium-independent vasodilation by nitroglycerin administration was not impaired. FMD was not impaired by exposure to chamber air.

Conclusions: One minute of exposure to marijuana SHS substantially impairs endothelial function in rats for at least 90 minutes, considerably longer than comparable impairment by tobacco SHS. Impairment of FMD does not require cannabinoids, nicotine, or rolling paper smoke. Our findings in rats suggest that SHS can exert similar adverse cardiovascular effects regardless of whether it is from tobacco or marijuana.

Keywords: artery; cannabis; endothelium; flow‐mediated dilation; marijuana; nitric oxide synthase; secondhand smoke; smoking; vasodilation.

Figures

Figure 1
Figure 1
Experimental design for FMD measurement and smoke exposures. FMD was measured by micro‐ultrasound measurements of femoral artery diameter before and after transient (5 minutes) surgical occlusion of the common iliac artery. Anesthetized rats were exposed to SHS for varying durations and FMD was measured 3 times (before exposure, 10 minutes after end of exposure to evaluate impairment, and 30 minutes later to evaluate recovery). As described in the Results section for specific experiments, the smoke exposure was either for 30 minutes or 1 minute, and initial FMD impairment or baseline diameter changes were measured either within 10 minutes or 25 to 30 minutes after the end of exposure. In some cases, FMD recovery was assessed every 30 minutes over a total duration of 90 minutes. FMD indicates flow‐mediated vasodilation; SHS, secondhand smoke.
Figure 2
Figure 2
Impairment of FMD by exposure to marijuana SHS at declining levels over a 30‐minute period. A, RSP levels over 30 minutes for each rat. Mean starting concentration, mean concentration over time, and total exposure derived from the area under the curve (AUC) are listed for each group ±SD. 670 and 210 μg/m3 correspond roughly to high and moderate levels of tobacco SHS in restaurants that allow smoking. B, Impaired FMD and (C) unchanged baseline artery diameter. Each line corresponds to an individual rat; colors track individual animals through panels A, B, and C. See Table for mean FMD values. There were no significant differences between the extents of FMD impairment by high‐dose, low‐dose, and THC‐marijuana smoke exposure, and no significant differences between the baseline diameter levels for the different exposure groups. FMD indicates flow‐mediated vasodilation; RSP, respirable suspended particles; SHS, secondhand smoke; THC, tetrahydrocannabinol.
Figure 3
Figure 3
Rolling paper is not required for FMD impairment. A, Stainless steel mesh used for paperless cigarettes with a normal cigarette for comparison. B, FMD impairment in rats exposed to paperless THC‐free marijuana SHS. FMD indicates flow‐mediated vasodilation; SHS, secondhand smoke; THC, tetrahydrocannabinol.
Figure 4
Figure 4
Impairment of FMD by 1 minute of exposure to marijuana SHS. See Table for group mean FMD and diameter values. A, FMD and baseline artery diameter in rats exposed to chamber air (0.73±0.055 μg/m3; n=8), high‐dose marijuana SHS (584±16 μg/m3; n=10), or high‐dose THC‐free marijuana SHS (608±13 μg/m3; n=8); errors are SD. Because smoke levels did not decline substantially over 1 minute, the average concentration over time is listed. Colors track individual rats through the FMD graphs and corresponding diameter graphs. FMD in rats exposed to SHS from regular marijuana or THC‐free marijuana decreased, whereas baseline diameter increased significantly by 8.2% for regular marijuana and 9.2% for THC‐free marijuana. B, Waiting for 25 minutes post‐end of exposure before FMD measurement (562±16 μg/m3; n=7) revealed substantial impairment of FMD without concomitant baseline vasodilation. C, FMD impairment for at least 90 minutes (617±10 μg/m3; n=8) with no significant improvement. Removal of 1 potential outlier (red line) would result in a significant partial improvement at 90 minutes postexposure relative to 30 minutes (P=0.019), but all postexposure values would still be depressed relative to pre‐exposure with P<0.0005. FMD indicates flow‐mediated vasodilation; SHS, secondhand smoke; THC, tetrahydrocannabinol.
Figure 5
Figure 5
Endothelium‐independent vasodilation is not impaired by SHS. Percent vasodilation is reported for 4 time points consisting of pre‐exposure FMD, postexposure FMD (impaired), nitroglycerin‐induced endothelium‐independent dilation (NTG, not impaired), and subsequent FMD (still impaired). FMD indicates flow‐mediated vasodilation; SHS, secondhand smoke.
Figure 6
Figure 6
Impairment of FMD from 1 minute of marijuana SHS persists longer than impairment from tobacco SHS. Impairment of FMD recovered by 30 minutes after 1 minute of exposure to tobacco SHS (591±28 μg/m3), but not after 1 minute of exposure to marijuana SHS (572±32 μg/m3; n=8/group). FMD indicates flow‐mediated vasodilation; SHS, secondhand smoke.
Figure 7
Figure 7
Smoke exposure chamber showing lack of visible smoke. Yellow arrows designate the corners of the exposure chamber. Double‐headed orange arrows show depth of chamber, ≈30 cm.

Comment in

  • Secondhand Marijuana Smoke Is Not Benign.
    Wilson KM. Wilson KM. J Am Heart Assoc. 2016 Jul 27;5(8):e004004. doi: 10.1161/JAHA.116.004004. J Am Heart Assoc. 2016. PMID: 27464789 Free PMC article. No abstract available.

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