Minor age difference substantially affects renal function in conscious and anaesthetized rats*

In this study we re-examined the postulate that in the rat age-related body metabolism and kidney function changes progress only slowly. Thus we checked whether a moderate between-animal age distance may cause any marked difference, which could affect interpretation of experimental results. Food and water consumption, renal sodium and potassium excretion and haemodynamics were lower in rats aged 15 versus 9 weeks. In turn, hematocrit, mean arterial pressure, and renal vascular resistance were significantly higher in older animals, whereas renal excretion of NO3-/NO2- and vascular endothelial growth factor A and in situ renal tissue NO signal did not differ. Evidently, an age older by 6 weeks was associated with decreased hydration, tone of systemic and renal blood vessels, and renal excretion. In conclusion, since the actual age is an important determinant of the animal’s functional status, accurate age-matching of experimental groups is a necessary pre-condition for correct data interpretation.