Promoting Homeostasis and Heart Health
Cardiovascular disease and its associated symptoms – such as hypertension and angina pectoris – are new areas where there is mounting evidence for using acupuncture as a treatment component. For instance, accumulating data in patients and animal models shows that acupuncture decreases sympathetic outflow, including reducing renal sympathetic activity and attendant decreases in plasma hormones renin, angiotensin and aldosterone, leading to a long-lasting lowering of blood pressure. Dr Longhurst emphasises however that such hormonal changes that likely underlie acupuncture’s cardiovascular actions in hypertension require confirmation and further investigation. This increasing evidence provides a strong rationale for achieving a greater understanding of the clinical actions of acupuncture at organ, cellular and subcellular levels.
Experimental studies by Drs Longhurst, Tjen-A-Looi and Li suggest that stimulation of certain acupoints located on the arm and the leg can lower systolic blood pressure by 8 to 12 mmHg and diastolic pressure by 3 to 5 mmHg in 70% of patients. Although the reduction in blood pressure is slow in onset (a course of treatment over several weeks was required), the duration of the effect extended for as long as one month after treatment had ended. Therefore, it is likely that acupuncture can be safely used to treat patients with mild to moderate hypertension and it may be especially useful in patients with sustained vascular constriction – the excessive contraction of smooth muscle in arterial walls that can elevate blood pressure.
Another study by the team looked at the effect of acupuncture on myocardial ischaemia. A feline model of demand-induced myocardial ischaemia was induced by partially ligating a coronary artery, resulting in insufficient blood flow and transient ischaemia. They found that a course of acupuncture lowered elevated blood pressure and also reduced the rate-pressure product during exercise. The rate-pressure product is a measure of the energy demand in the heart. Together this indicated lower myocardial oxygen demand, thus reducing ischaemia. A follow-up study showed these outcomes could be reversed with naloxone (an opiate blocking drug), implicating the endogenous opioid system as the underlying mechanism for acupuncture’s action.
Further Studies into Blood Pressure
The team are also exploring the effect of acupuncture on hypotension and bradycardia (low heart rate). In experimental studies, the team found that electroacupuncture significantly reversed bradycardia and hypotension. They used two models to investigate brain regions and neurotransmitter systems involved in acupuncture’s capability to raise blood pressure. In the first model, researchers used an IV infusion of a chemical to evoke bradycardia and hypotension in order to mimic vasovagal syncope – a sudden drop in heart rate and blood pressure, often leading to fainting. They found that the preganglionic cholinergic neurons in the nucleus ambiguous in the brain stem – part of the parasympathetic nervous system – were located in close proximity to axons containing enkephalin – an opioid neurotransmitter that modulates or reduces parasympathetic neural outflow from the brain to the heart. These neurons were activated by 30 minutes of electroacupuncture, during which both enkephalin and GABA modulated the vasovagal reaction.
The second model of reflex hypertension involved gastric distension in hypercapnia induced acidosis, which involves increased acidity in the blood and body tissue triggered by elevated carbon dioxide levels. Spinal and vagal pathways are stimulated by gastric distension to lower blood pressure through a combination of sympathetic withdrawal and increased parasympathetic outflow. The team found that electroacupuncture inhibited this increase in parasympathetic outflow and limited sympathetic withdrawal, thus reducing reflex hypotension and bradycardia.
Expanding the Evidence Base
In a recent review of the evidence, Dr Longhurst confirmed the need for further research in this area. If acupuncture is to take a place within conventional western medicine, more well designed unbiased prospective studies are required. Experimental animal models can provide additional clues about how best to apply acupuncture clinically and properly constructed clinical trials on acupuncture’s effects on smoking, cholesterol reduction and weight loss are needed. Further investigation into how acupuncture can modulate cardiovascular risk is also warranted. For example, recent experimental studies examining the potential for electroacupuncture to be used in treating myocardial infarction, arrhythmias, heart failure, stroke and peripheral vascular disease either have shown mixed results or have not been conducted at all, so further experimental and clinical studies will be needed to determine acupuncture’s role in treating these diseases.
Another area of importance is research into how acupuncture effectiveness can be improved. A number of studies have indicated that only 70% of patients respond to acupuncture. Recent investigations by the team suggest that non-responders can be converted to responders by administering into the hypothalamus an antagonist to the octapeptide (a protein molecule that consists of eight amino acids linked in a chain) of the hormone cholecystokinin. This octapeptide exerts an anti-opioid effect in the brain, leading to opioid tolerance. Initial research suggests that the octapeptide in the rVLM contributes to the absence of electroacupuncture actions on hypertension in rats. This may be the beginnings of how to convert non-responders.
Finally, more experimental and clinical studies are needed to determine how acupuncture treatment can be reinforced to provide prolonged suppression of hypertension. Although a single 30-minute application of acupuncture stimulates an enkephalin response lasting 90 minutes, repeated acupuncture over several days leads to longer elevations of neurotransmitter messenger RNA, called preproenkephalin and the protein neurotransmitter enkephalin expression, which can last hours and days after acupuncture treatment is terminated. Repeated acupuncture can therefore exert a very prolonged action on blood pressure, but further research is required to guide physicians on how to best incorporate this into a care plan.