Dietary and behavioral factors have been implicated in the development of primary hypertension through epidemiological studies, but the pathophysiological mechanisms by which these factors, either independently or synergistically, affect long-term blood pressure regulation remain to be clarified. Animal studies have shown that high sodium intake engenders sustained hypertension if, and only if, the subject is concurrently exposed to recurrent behavioral stress. The present project addresses the hypothesis that neuroendocrine factors, which alter sodium regulation are activated under conditions of behavioral stress and, when combined with a high sodium intake, result in elevated blood pressure. In the first study, medical students consumed either sodium chloride or placebo tablets daily for two weeks immediately preceding examinations and for two weeks during the summer. The high sodium intake during the exam preparation period was associated with greater increases in systolic and mean blood pressure than the high sodium intake during the summer and the usual sodium intake during the preparation period. State anxiety was significantly related to the changes in blood pressure observed in the high sodium group. A second study has been designed to replicate the systolic and mean pressure effects of the high sodium intake under conditions of exam preparation. Urinary excretion data were obtained and indicate compliance with the sodium manipulation. Analysis for circulating inhibitors of the sodium pump in serum collected during the exam preparation period is in progress. The results are consistent with the hypothesis that behavioral stress and sodium intake have synergistic effects on long-term blood pressure regulation.
