A study of catecholamine concentrations in selected renal segments of cats of different ages

Renal concentrations of the catecholamine neurotransmitters norepinephrine (NE) and dopamine (DA) in 19 cats were measured by reverse-phase high pressure liquid chromatography (HPLC) with electrochemical detection. Animals of five different age groups (2-4, 6-8, 10-12 and 16-20 weeks and adult animals one year and older) were anesthetized and the kidneys were excised, sectioned into cortical, outer medullary and inner medullary segments, and processed for HPLC. There were no statistical differences in cortical NE concentrations between the 2-4 week and adult age groups, suggesting that peak noradrenergic nerve terminal density in the cortex is achieved at or before 2-4 weeks of age. NE concentration in the outer medulla and DA concentration in the cortex and outer medulla increased from the 2-4 to the 10-12 week age group but did not change significantly in the older animals. There were significant decreases in inner medullary NE and DA concentrations from the 10-12-week to the 16-20 week age group. The decrease in concentration of inner medullary catecholamines in the early postnatal period is consistent with the reported total loss of tyrosine hydroxylase- and dopamine beta hydroxylase-immunoreactive inner medullary nerve terminals at approximately 12 weeks of age.