Circannual renal function and plasma electrolytes of the marmot

Studies with unanesthetized active (non-lethargic) marmots demonstrated circannual rhythms of renal function (clearances of p-aminohippurate, creatinine, and inulin), plasma osmolality, and plasma sodium and potassium concentrations. Effective renal plasma flow, glomerular filtration rate, the clearance of creatinine, and plasma potassium were highest in spring and lowest in the fall and winter. Plasma osmolality and plasma sodium concentrations tended to be highest during the winter months and lowest in the spring and summer. p-Aminohippurate excretion was shown to be a Tm-limited system.