Effects of Dietary Sodium on Circadian Rhythm and Physiological Responses of 18-Hydroxycorticosterone

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Abstract
The effects of dietary Na intake on plasma 18-hydroxycorticosterone (18-OHB) responses to physiological stimuli and recumbent 24-h-plasma 18-OHB levels were examined in 9 normal male subjects. Basal supine levels of 18-OHB during a 40 mmol of Na intake period (62.5 .+-. 6.0 ng/dl) were considerably greater (P < 0.0001) than the levels during a 200 mmol of Na intake period (9.8 .+-. 1.2 ng/dl). Further incremental and percentage changes of 18-OHB in response to graded dose infusions of angiotensin II and ACTH were greater during the 40 mmol of Na intake period. Although the mean 24-h levels of plasma 18-OHB during the 40 mmol of Na intake period (43.9 .+-. 4.0 ng/dl) were greater (P < 0.001) than those during the 200 mmol of Na intake period (9.4 .+-. 1.2 ng/dl), the circadian rhythm of 18-OHB secretion was similar under the 2 extremes of Na intake. Factors which increase angiotensin II levels, such as Na restriction, isometric exercise and angiotensin infusion, selectively increase 18-OHB and aldosterone, suggesting that angiotensin II increases 18-OHB and aldosterone secretion, in part, by modulation of the 18-hydroxylation reaction involved in conversion of corticosterone into 18-OHB.

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