Circaseptan rhythm in sodium and potassium excretion in salt-sensitive and salt-resistant Dahl rats

Six salt-sensitive (S) and six salt-resistant (R) male Dahl rats were housed in metabolic cages under LD 12:12 (L 0600-1800). High-salt (8%) and low-salt (0.4%) diets were available to half the S and R rats, respectively for 4 hr during a 24-hr span (feeding 1800-2200). Urine was collected at 4-hr intervals for 30 days. Sodium and potassium were determined by ion-specific electrode. Apart from circadian rhythmicity, a circaseptan rhythm in sodium and potassium excretion came to the fore in the rats on the high-salt diet only, with a phase difference of about 180 degrees between sodium and potassium. These rhythms were not detectable in the animals eating their usual-low salt diet. The ability to induce circaseptan variations in renal function may lend itself to the chronotherapeutic utilization of such cycles in achieving optimal therapeutic effects or minimizing undesirable side effects of different forms of treatment.