Hyperaldosteronism following total fasting in obese subjects

Effects of a 1 day fast on biohumoral variables associated with human circadian rhythmicity

1. The aim of the present study was to investigate the effects of a short (1 day) fast by testing biohumoral variables associated with the human circadian rhythm. 2. Fifteen clinically healthy male volunteers (32 +/- 8 years old) participated in the study. Subjects were fed a control diet for 7 days. The last day was a control day and the following 8th day was the fasting day. Each subject was asked to collect urine seven times over a 24 h period. Chemical and hormonal variables were measured in each fractionated urine specimen. The time- qualified urinary excretion rates were biometrically analysed using conventional and chronobiological methods. 3. During fasting, significant incremental changes were detected in the urinary excretion rates of potassium, aldosterone, 17-hydroxycorticosteroids and adrenaline and significant decremental changes were detected in the excretion rates of sodium, chloride, creatinine, urea nitrogen, uric acid, 17-ketosteroids, noradrenaline and dopamine. The circadian rhythmicity of the variables was well preserved and remained almost stable throughout the fasting phase. 4. Fasting affected the mean oscillatory levels and oscillatory amplitudes of variables, suggesting that nutrients may have played roles as tonic and phasic modulators on the mechanisms that physiologically regulate ircadian rhythmicity.

Effects of a mild and prolonged restriction in sodium or food intake on the circadian rhythm of aldosterone and related variables

The effect of a mild reduction in dietary sodium intake (-30 mEq/24 hr) and body weight (-2 kg/2 months) on circadian rhythms of urinary aldosterone (UA), sodium (UNa), potassium (UK), creatinine (UC) and volume (UV) have been investigated in nine clinically healthy subjects. The mild reduction in dietary sodium is associated with: (1) a decrease in the 24-hr excretion rate of UNa, UK and UV, and an increased mesor of UA and UC; (2) a lowered extent of the circadian variation for UNa, UK, UV and a greater amplitude for UA and UC (3) a later crest in the temporal phase for UK, UA, UC, an earlier phasic wave for UNa. The mild reduction in calorie intake resulting in a body weight loss is associated with a more pronounced decrease in the 24-hr excretion rate of UNa and UK, and in the extent of circadian fluctuation for UNa. Peculiar events are: (1) the decreased 24-hr excretion rate for UA, and the increased mesor for UV; (2) the extent variability increased for UV, decreased for UC. Such effect may have a practical resonance for heuristic physiology since the role of dietary sodium and food intake has been better clarified. Dietary sodium and food can be regarded as 'chronomodulatory agents' for the adrenal cortex since their adrenotropic influence is extended to the tonic as well as phasic secretion of aldosterone.

Sodium balance and renal tubular sensitivity to aldosterone during total fast and carbohydrate refeeding in the obese

In man the first days of fasting are characterized by enhanced natriuresis despite an increase in aldosterone secretion. Therefore the possibility of a decreased renal tubular sensitivity to this hormone was considered. The response to aldosterone infused before a fast and again on day 4 of fasting was evaluated in 12 starving obese women in terms of urinary sodium, chloride and potassium excretion. The data were compared to those obtained from 20 untreated starving obese women. In addition, salivary flow and sodium output were measured before and after aldosterone infusion in 4 out of the 12 patients treated. The involvement of aldosterone in the mechanism of fasting natriuresis and glucose-induced sodium retention was evaluated by means of spironolactone treatment (Aldactone A; 300 mg/day p.o.) on days 6 to 8 of the fast, with an oral glucose load (100 g) on day 7. Aldosterone infused on day 4 of the fast caused on average only 40% of the antinatriuretic effect it achieved before the fast. On the other hand even before aldosterone infusion, salivary sodium output was markedly reduced during the fast to levels comparable to those observed after aldosterone treatment in the pre-fast period. Furthermore, spironolactone administration on day 6 of the fast was associated with a prompt and marked increase in natriuresis. These 3 sets of facts indicate a definite biological activity of aldosterone during the initial phase of fasting with factor(s) interfering at the renal level with the normal expression of the hormonal action on sodium balance. There was still a distinct antinatiuretic effect of glucose in the presence of spironolactone, but less pronounced than when glucose was administered alone. The well-documented hyperaldosteronism of a total fast may represent a compensatory mechanism to decrease sodium loss at the end of a week-long fast. In addition a marked sodium-retaining effect of glucose can be demonstrated after aldosterone action is blocked by spironolactone. This provides another indication that glucose stimulates sodium retention through mechanism(s) which do not involve aldosterone.