Renal circulatory effects of adrenergic stimuli in anesthetized piglets and mature swine

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Abstract
The relative maturity of renal circulatory responses to efferent renal nerve stimulation and to exogenous norepinephrine and isoproterenol, was tested in 62 piglets (1-16 days old) under pentobarbital anesthesia (10-25 mg/kg). Aortic pressure, heart rate and renal and femoral arterial flows (measured by electromagnetic flow transducers) were recorded simultaneously. Renal vascular resistance was calculated as mean aortic pressure/mean flow. Transection of the renal nerve resulted in decreased renal resistance in all animals. Efferent renal nerve stimulation at increasing frequencies (2-12.5 Hz, at 1.2 ms pulse duration and 1.0 mA current) showed age-dependent differences in the threshold and also in the magnitude of increase in renal resistance. Norepinephrine (0.05-1.0 .mu.g/kg) caused age-dependent increases in renal resistance. Restoration of renal flow toward control level occurred during the peak pressor effect of norepinephrine only in older piglets. Isoproterenol (0.05-1.0 .mu.g/kg) did not alter renal resistance consistently in piglets younger than 1 week. Phentolamine (0.25 mg/kg) attenuated or blocked resistance increases to 0.5 .mu.g norepinephrine/kg or to renal nerve stimulation at 12.5 Hz in all animals. Propranolol (0.1 mg/kg) attenuated or blocked resistance decreases to 0.1 .mu.g isoproterenol/kg, which ocurred only in older piglets. An active .alpha.-adrenergic vasoconstrictor mechanism and absence of the .beta.-adrenergic vasodilator mechanism may exist in the renal circulation of swine at birth.