Plasma catecholamines in salt-sensitive hypertensive (Dahl) rats

Abstract

We examined the effects of low (0.4%) and high (8.0%) salt diets on basal and stress-induced increments in plasma levels of norepinephrine (NE) and epinephrine (EPI) in the Dahl lines of salt-sensitive (DS) and salt-resistant (DR) rats. DS rats develop sustained increases in blood pressure when maintained on a high salt diet while DR rats remain normotensive. For this study, blood samples were obtained via a chronic tail artery catheter from DS and DR rats under resting conditions or following exposure to stress. Plasma samples were later assayed for content of NE and EPI by a radioenzymatic assay. Basal plasma levels of both catecholamines were similar in DS and DR rats, irrespective of dietary salt content and mean arterial blood pressure. The mild stress of handling and transfer of rats to a different cage resulted in greater increments in plasma NE but not EPI in DS rats fed a high salt diet compared to DS rats fed a low salt diet. There was a significant effect of line and an interaction of line and diet with respect to the effects of immobilization stress on plasma catecholamines. DS rats had greater immobilization-induced increments in plasma NE and EPI compared to DR rats when both lines were fed a low salt diet. Maintenance on a diet high in salt resulted in lesser immobilization-induced increments in plasma catecholamines for DS rats and greater immobilization-induced increments in plasma catecholamines for DR rats when compared to their respective controls on a low salt diet. There was a significant effect of diet on plasma levels of both catecholamines when blood samples were obtained by decapitation. DS and DR rats that were fed a high salt diet had lower plasma levels of NE and EPI following decapitation compared to rats of the two lines that were fed a low salt diet. These findings demonstrate that dietary salt and genetic factors are important in regulating the activity and responsiveness of the sympathetic-adrenal medullary system to a variety of stressors. Our findings do not provide evidence for a critical role of the sympathetic nervous system in maintaining the diet-induced increase in the arterial blood pressure of DS rats.