Nocturnal natriuresis in hyperthyroidism

We measured urine flow and the renal excretion of total solute, sodium, potassium and calcium in eleven patients with hyperthyroidism before and after treatment. Mean nocturnal sodium excretion was significantly greater (P less than 0.05) during hyperthyroidism and was unaccompanied by any significant alterations in day time or 24-h values. As a result of this nocturnal natriuresis in hyperthyroidism significant changes were noted in the ratios of day/night sodium excretion (P less than 0.005) and urinary flow (P less than 0.05). The change in ratio of day/night sodium excretion resulting from treatment of hyperthyroidism was shown to correlate significantly with the change in plasma total triiodothyronine (r=0.73, P less than 0.01). Twenty-four hour urinary calcium output was significantly greater (P less than 0.02) in hyperthyroidism but there was no significant alteration in the day/night pattern of excretion.