The Yanomamo Indians are an unacculturated tribe inhabiting the tropical equatorial rain forest of northern Brazil and southern Venezuela who do not use salt in their diet. The group therefore presented an unusual opportunity to study the hormonal regulation of sodium metabolism in a culture with life-long extreme restriction of dietary sodium, with parallel observations on blood pressure. Blood pressures increased from the first to second decade but, in constrast to civilized populations, do not systematically increase during subsequent years of life. In twenty-four hour urine collections on adult male Indians, excretion of sodium averaged only 1 plus or minus 1.5 (SD) mEq. Simultaneous plasma renin activities were elevated and comparable to those of civilized subjects placed for brief periods on 10 mEq sodium diets. Similarly, excretion rates of aldosterone equaled those of acculturated subjects on low sodium diets. The findings suggest that the hormonal adjustments to life-long low sodium intakes are similar to those achieved in acute sodium restriction of civilized man. Parenthetically, these elevated levels of aldosterone and renin were probably the norm for man during much of human evolution and suggest that the values observed in civilized controls are depressed by an excessive salt intake in contemporary diets.

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SUMMARY The Yanomama Indians of northern Brazil and southern Venezuela have been identified as a "'no-salt" culture. In this study, data were obtained to determine in this population the adjustments of sodiumrelated hormones to the stresses imposed upon sodium balance by pregnancy and prolonged lactation. Controls against the possibility that findings in the Yanomama were ethnic rather than dietary were provided by similar observations in the Guaymi Indians of Panama, who have free access to salt. Urinary concentrations of sodium were approximately 1 mEq/l in male and female Yanomama, with 24-hour excretion rates in the males averaging 1 mEq, similar to our prior observations. The pregnant Yanomama had exceeding high urinary concentrations of aldosterone. These were associated with higher plasma renin activities and serum aldosterone concentrations than in all other subjects. Although pregnant Guaymi had elevations of serum and urinary aldosterone, these were significantly lower (p < 0.001) than those of the Yanomama. Prolonged lactation in the Yanomama was associated with elevation of plasma renin activity and serum and urinary aldosterone concentration compared with the Guaymi, but were not higher than those in nonlactating Yanomama females. The findings suggest that pregnancy in a salt-poor environment is associated with an exaggerated augmentation of hormonal responses that enhance positive sodium balance.DURING PREGNANCY, there are marked increases in maternal peripheral blood of renin substrate, renin concentration, renin activity, angiotensin and angiotensinase.'-' Simultaneously, secretion and excretion of aldosterone increase.6`This interlocking hormonal system of renin-angiotensin-aldosterone has a major influence on sodium retention. The possible importance of these hormonal responses is emphasized by the fact that the products of normal pregnancy -fetus, placenta, associated membranes, and amniotic fluid, plus growth of breasts and uterus -have been estimated to require an accumulative retention of 500-700 mEq of sodium.8 9 The subsequent lactation, often extending over 2-3 years in unacculturated societies, results in a daily loss of 5-7 mEq of sodium/I of breast milk. We previously reported our observations on blood pressure and hormonal adjustments in male Yanomama Indians of northern Brazil and southern Venezuela, a group with no added dietary salt.'`In this follow-up, we present the results of an attempt to study in this same group From the

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