Salt and asthmaBMJ 1994; 308 doi: https://doi.org/10.1136/bmj.308.6927.537 (Published 19 February 1994) Cite this as: BMJ 1994;308:537
- P KotankoF Skrabal
- Department of Internal Medicine, Krankenhaus Barmherzige Bruder (Marschallgasse), A-8020 Graz, Austria.
EDITOR, - Alan J Knox has reviewed evidence suggesting a relation between a high salt intake and worsening of asthma in men1 and discussed two hypothesis to explain this - namely, Blaustein's hypothesis and the hypothesis that the deterioration in asthma is due to the fall in circulating catecholamine concentrations that occurs during salt loading. We and colleagues have published findings that may provide a much simpler explanation.
We have shown that a reduction in salt intake from 200 mmol/day to 50 mmol/day over two weeks causes up regulation of Beta(sub2) adrenoceptors on lymphocytes (as well as concomitant down regulation of Alpha(sub2) adrenergic receptors on platelets).2,3 These changes in the densities of adrenoceptors are reversible: a subsequent high salt diet (200 mmol/day over two weeks) causes a decrease in Beta(sub2) adrenoceptors and an increase in Alpha(sub2) adrenoceptors. Receptor affinities remain unchanged. These changes in adrenoceptors are more pronounced in subjects whose blood pressure falls when they have a low salt intake (that is, those who are sensitive to salt). In a subsequent study we showed that subjects who are sensitive to salt have a decreased expression of Beta(sub2) adrenoceptors on cultured fibroblasts, which presumably is determined genetically.4
If our findings also apply to airway smooth muscle cells a high salt intake would lead to reduced bronchodilatation mediated by Beta(sub2) receptors. A body of literature exists in favour of the so called Beta adrenergic theory of asthma, which postulates disturbed Beta(sub2) adrenergic function as a cause of asthma.5 It would be interesting to measure beta sub2 adrenoceptors on cultured fibroblasts of patients with asthma as this might give evidence for a possible genetic background. It would also be interesting to test our findings regarding adrenoceptors on lymphocytes in patients with asthma during high and low salt diets.