Postnatal development of renal function in piglets: changes in excretory pattern of sulphachlorpyridazine

The renal excretion of sulphachlorpyridazine (SCP) was measured in 34 unanaesthetized piglets 5-74 days of age. The renal handling of SCP was found to include: glomerular filtration, active tubular secretion and passive reabsorption. During the age period studied the clearance of ultrafiltrable SCP increased several times more than GFR (inulin clearance) indicating that the balance between filtration, secretion and reabsorption is changed during postnatal maturation. The age-related change in clearance ratio possibly reflects both a greater increase in tubular secretory capacity than in glomerular filtration and a relative decrease in the passive reabsorption.