Study of new heart hormone

Press, 26 February 1986, Page 17

Study of new heart hormone

Major new work on a recently discovered hormone system based in the heart has been produced by doctors in the departments of endocrinology and cardiology at The Princess Margaret Hospital, assisted by the hospital’s dietary, nursing and biochemistry departments. With generous financial assistance from the National Heart Foundation, Drs M.G. Nicholls, H. Ikram, E.A. Espiner, A.M. Richards and T.G. Yandle have published the first studies on the effects on man of this powerful new hormone, atrial natriuretic factor (A.N.F.). A.N.F. is now the subject of international medical congresses at which these Christchurch doctors have been guest speakers.

Since the 1950’s electron microscopists have known that the atrial muscle of the heart of mammals contains small granules. Little attention was given to these observations until 1979 when Canadian scientists isolated the granules and injected them into rats. They reported a dramatic increase in urine volume and urine sodium (salt) output, rather like that seen with some potent drugs (diuretics) used to treat heart problems or high blood pressure. Subsequent studies demonstrated that atrial granules contain a number of peptides and scientists were able to reproduce some of these as synthetic substances.

Princess Margaret Hospital

staff were able to obtain some synthetic human A.N.F. at the very beginning and are now able to measure the amount of A.N.F. in human blood in healthy people and in patients with disorders of heart function or blood pressure.

Using themselves as experimental subjects, they also did the first experiments on human beings of this hormonal substance. A.N.F. was injected intravenously under standardised conditions. Urine sodium excretion increased six-fold in the first 30 minutes, there was smaller increases in urine volume and in calcium, magnesium and phosphorus excretion. Arterial pressure fell within two minutes of injection, then returned to normal after 10 minutes. Heart rate increased rapidly and remained high for three hours. “A.N.F. would appear to be the heart’s own defence mechanism against overload of fluid,” says Dr Nicholls. He explains that the atria are ideally sited to act as detectors of fluid overload or sensors of early heart failure. Fluid overload or damage to the left ventricle of the heart will increase pressure in the atrium, and stretching of the atrial walls may release A.N.F. into the circulation. The resulting opening of the arteries should reduce the burden of the failing left ventricle. Also A.N.F. might inhibit the release of other hormones which would cause fluid retention and arterial constriction.

Apart from emergency circumstances such as acute heart failure, it seems that A.N.F. is released slowly and continously from the heart. It may therefore contribute to the normal balance of sodium and water in the body. Internationally, the small trickle of publications on A.N.F. is rapidly becoming a torrent and the precise role of the hormone should become apparent over the next few years.

Dr Nicholls sees two particularly exciting areas to pursue — the importance of A.N.F. in physiology and the possibility of its being the basis of a new drug to be used in the treatment of high blood pressure and of heart failure.

Denis Dwyer, Canterbury Hospital

Board.