Cannabis
The pharmacological modulation of CB-2 receptors by CB-2 receptor agonists and antagonists therefore appears to be a promising strategy in the treatment of diseases such as stroke, atherosclerosis, restenosis, MI and heart failure. A thorough understanding of the endocannabinoid receptor system in humans would be paramount to the discovery of molecules that exert the therapeutic effects of cannabis and cannabinoids, with minimal adverse effects.
We provide a review of the endocannabinoid system (ECS) followed by examining the effects of cannabis on the cardiovascular system, including the occurrence of arrhythmias and myocardial infarction (MI) and its effects on the peripheral vasculature and the cerebrovascular system. We conducted literature search from January 1964 to October 2016 from PubMed. We also briefly examine some of the important considerations related to anaesthesia in cannabis users.
Endocannabinoid receptors in cardiovascular system
The discovery of Δ9-tetrahydrocannabinol (THC) as the main active ingredient of Cannabis sativa (9) led to the subsequent discovery of specific receptors for THC in the human body, namely cannabinoid receptors type 1 (CB-1) and type 2 (CB-2). CB-1 receptors are expressed in the liver, muscle, fat, and brain, while CB-2 receptors are expressed in large numbers in the spleen and immune cells as well as in peripheral tissues, albeit at low levels
The ECS comprises the cannabinoid receptors (CB-1 and CB-2) as well the endogenous counterparts of THC and endogenous ligands for both cannabinoid receptors, known as N-arachidonoyl-ethanolamine (anandamide) and 2-arachidonoyl-glycerol (2-AG).
The ECS has been found to be involved in a number of processes, including cell fate and proliferation and differentiation of progenitors
Endocannabinoids were detected in heart tissues and current evidences suggest that the ECS is involved in the regulation of heart rate (HR) and blood pressure in addition to being involved in various other pathological processes (12)
Cumulative evidence seems to suggest that CB-1 and CB-2 receptors may play contributory roles in modulating cardiometabolic risk, and atherogenesis, and can also have protective roles in limiting cardiomyocyte damage
ECS have been found to exert vasorelaxing effects in cardiovascular system which appears to be mediated by numerous pathways. Activation of CB1 receptors in mice have been shown to produce prolonged hypotension.
ECS have been found to exert vasorelaxing effects in cardiovascular system which appears to be mediated by numerous pathways. Activation of CB1 receptors in mice have been shown to produce prolonged hypotension.
expression of CB-2 receptors in cellular components of the cardiovascular system as well as infiltrating immune cells such as leukocytes and macrophages was possibly involved in controlling the extent of tissue inflammation and injury occurring in various cardiovascular conditions, thereby suggesting that these receptors may play a cardioprotective role.
Arrhythmogenic properties of cannabis
A study from Norway, on apprehended drivers, demonstrated that THC- positive drivers had higher mean pulse rate than THC-negative drivers and surprisingly, the magnitude of tachycardia was independent of blood THC concentration
One of the most consistent effects of cannabis smoking on heart is 20% to 100% increase in HR which can last up to 2–3 hours, often accompanied by a slight increase in supine blood pressure. This effect of cannabis on HR is thought to be due to cannabis induced vasodilation causing reflex tachycardia (15,16). Consumption of higher doses of cannabis can cause postural hypotension associated with dizziness or fainting (17,18). However, tolerance to the effects of cannabis develops rapidly after only a day or two of repeated exposure. Chronic marijuana use is associated with a decrease in HR, disappearance of orthostatic hypotension, increase in blood volume, and decrease in the circulatory responses to exercise which are consistent with reduced sympathetic and increased parasympathetic activity (18).
This is an important consideration in youth who use marijuana in social entertainment settings since physical activity such as dancing may be common in such circumstances, which can increase the risk of precipitating acute coronary events
acute myocardial infarction (AMI)
.
Further research and studies are needed to determine the impact of acute and especially the chronic regular use of cannabis on various organ systems, particularly the cardiovascular system.
Cannabis leaves burn at higher temperature than similar quantity of tobacco causing increased direct airway irritation. Excessive respiratory burden of carbon monoxide and tar can occur with cannabis smoking when compared to smoking (91).
recent use of cannabis can cause decrease blood pressure due to vasodilatation along with tachycardia leading to increased oxygen myocardial demand (99), therefore drugs which are likely to increase HR, such as ketamine, atropine, and epinephrine should also be avoided
While the majority of published data suggest a harmful effect of cannabis and cannabinoids on the cardiovascular system, a few suggest possible beneficial effects.
cannabis or marijuana use attenuates or modulates common cardiovascular disease risk factors
reliminary data from a small double blinded placebo controlled study carried out in the U.K. examining the effects of cannabidiol delivered through an inhaler on cigarette consumption among smokers wishing to quit smoking, suggests a 40% smoking reduction in the treatment group compared to placebo (102)
Additionally, a number of epidemiologic studies have shown lower prevalence of obesity and diabetes mellitus among marijuana users compared with those who never used marijuana, suggesting a relationship between cannabinoids and metabolic processes.
A study done on 4657 adult Americans from the National Health and Nutrition Examination Survey showed that marijuana use was associated with lower levels of fasting insulin and HOMA-IR, and smaller waist circumference (103).
