The researchers suggest smoking appears to lower a key enzyme in the lungs which regulates blood pressure. The researchers used a chemical tracer and sophisticated scans to estimate levels of the enzyme monoamine oxidase were 50% lower in the smokers’ lungs.

Lead researcher Dr Joanna Fowler said: “The effects of smoking on human health are enormous; yet, little is known about the pharmacologic effects of smoking on the human body apart from the effects of nicotine.” The scientists examined monoamine oxidase rates in 9 smokers and 9 non-smokers. The scans showed that rates of the enzyme were similar in all of the peripheral organs of both groups, except the lungs. Examination also showed that the lungs of smokers held onto the tracer chemical much longer than non-smokers, and the delivery of tracer into the arterial blood supply was lower for smokers, for the first few minutes after being injected.

Non-smokers and smokers respond differently to other substances that enter the body via the blood including anesthetics, therapeutic drugs and abused substances. Dr Fowler said: “The role played by MAO in other conditions associated with smoking may also be significant and deserves further investigation, considering the differences observed in the enzyme level between smokers and non-smokers.”

Dr John Moore-Gillon, president of the British Lung Foundation, added: “It is a very interesting piece of research, which provides another piece in the jigsaw. We already know that smoking is enormously harmful to many different body systems, and this might help to show how it is damaging to blood pressure. It was already known that nicotine constricted the blood vessels – and thus tended to raise blood pressure. Smoking is also known to damage the balance of different enzymes responsible for maintaining the tissues of the lung in a healthy state. It also damages the lining of the lungs, causing them to secrete excessive amounts of mucus which could lead to chronic bronchitis. In addition, damage to the ability of cells to multiply and repair themselves could lead to lung cancer.”

Judy O’Sullivan, a cardiac nurse at the British Heart Foundation said: “While this study is small in size, it adds weight to the existing and overwhelming evidence that smokers are risking their health and even their lives by continuing with their deadly habit. We cannot emphasize enough the need for smokers to stop smoking to protect themselves from premature death and disability.”