Effect of magnesium sulfate on kidney function in the newborn rabbit

The aim of this study was to investigate the acute, short-term effects of the intravenous (i.v.) administration of magnesium (Mg) sulfate on renal function in the newborn rabbit. Eight anesthetized and mechanically ventilated, normoxemic, newborn New Zealand white rabbits were studied. We measured mean arterial blood pressure (MAP), urine volume (V), glomerular filtration rate (GFR), rectal plasma flow (RPF) and calculated renal blood flow, filtration fraction (FF) and renal vascular resistance (RVR) under control conditions and in two experimental periods after the i.v. Mg sulfate load. Mg sulfate administration in a dose 100 mg/kg followed by 50 mg/kg/h caused a significant fall (p < 0.001) in MAP, GFR and RPF, whereas the RVR increased (p < 0.01). FF did not change significantly (p: NS/0.05) and V remained constant. These results show that the acute i.v. administration of Mg sulfate to newborn rabbits causes systemic vasodilatation with a fall in MAP. The increase in RVR, without consistent change in FF, suggests that the renal vasculature of the 'immature' neonatal rabbit reacts to these changes by preferential afferent arteriolar vasoconstriction.