Catecholamines in kidneys of normotensive and genetically hypertensive rats. Effects of salt load

The tissue content of norepinephrine, dopamine, and epinephrine was determined in different zones of the kidney in normotensive Sprague-Dawley and Otago Wistar rats and in genetically hypertensive Otago Wistar rats. One kidney in each animal was chronically denervated to allow estimation of the neuronal contribution to renal catecholamine content. In all strains, the renal cortex contained negligible amounts of nonneuronal norepinephrine and dopamine, while outer and inner medullary layers contained progressively larger amounts. Nonneuronal epinephrine was distributed fairly evenly through cortex and medulla. Neuronal norepinephrine content was similar in inner and outer cortex, substantially less in outer medulla, and not discernible in inner medulla. The amounts of neuronal dopamine were consistent with its localization predominantly in noradrenergic nerves. The renal cortices of normotensive Wistar rats contained more neuronal norepinephrine and less neuronal dopamine than those of Sprague-Dawley rats, and the cortices of hypertensive Wistar rats contained slightly more norepinephrine than those of normotensive Wistar rats. In both normotensive strains, long-term salt loading decreased selectively the neuronal norepinephrine in renal cortex. By contrast, in hypertensive animals, cortical norepinephrine was not reduced by salt loading. These results indicate that the genetically hypertensive rat may have an abnormal sympathetic reflex response to increased blood volume.