Objective: To test the hypothesis that the Hpa II variant of the atrial natriuretic peptide gene (ANP), which has been reported to be more common among black hypertensives than it is among normotensive controls, is related to the response of blood pressure to salt intake in normotensive Caucasians.
Methods: One hundred and three young (aged 19-35 years) male volunteers were fed a low-salt diet (20 mmol NaCl/day) for 2 weeks and a supplement of either 200 mmol NaCl/day (slow sodium) or placebo for 1 week each in a randomized double-blind cross-over order. Salt sensitivity was defined as a significant (P < 0.05) decrease in resting mean arterial blood pressure by > 3 mmHg under the low-salt diet. The genotype was determined by amplification of genomic DNA extracted from peripheral leukocytes and subsequent digestion of the amplicon with Hpa II restriction enzyme.
Results: According to the above definition, 27 subjects were salt sensitive. There were no significant differences in age, body-mass index and waist:hip ratio between the salt-sensitive and salt-resistant groups. Only salt-sensitive subjects displayed a significantly higher blood pressure under the high-salt diet (increase in mean arterial pressure 5.6 +/- 2.4 mmHg, P < 0.001). The prevalence of the ANP-Hpa II wild-type (w) allele did not differ between the salt-sensitive (qw = 1.0, qm = 0) and the salt-resistant group (qw = 0.96, qm = 0.04). Furthermore, the salt-induced response of blood pressure did not differ between homozygotes (ww) and heterozygotes (wm).
Conclusions: Our findings do not support the hypothesis that the ANP-Hpa II polymorphism is a marker for salt sensitivity in young Caucasian normotensives.