Glomerular hemodynamic alterations during renal nerve stimulation in rats on high- and low-salt diets

Renal adrenergic nerve activity exerts a major influence on glomerular hemodynamics and tubular fluid reabsorption. Modulation of the functional expression of adrenergic activity in the kidney can be mediated, in part, by the renin-angiotensin system and by prostanoid activity. Alterations in dietary salt intake have been previously shown to modify the activity of various vasoactive systems, including angiotensin and prostaglandin activity and thereby have a potential of modifying the glomerular hemodynamic response to a given renal adrenergic stimulus. Munich-Wistar rats were fed either a high-, low-, or normal salt diet for 2 wk before the day of the study. Measurements of glomerular hemodynamics were performed in both unstimulated with basal renal nerve traffic eliminated and during exogenous renal nerve stimulation (RNS) (3 Hz). RNS decreased glomerular capillary hydrostatic pressure and single-nephron plasma flow to a similar extent in all three dietary conditions via increases in afferent arteriolar resistance. The data demonstrated that dietary preconditioning does not alter the glomerular hemodynamic response to an exogenous, fixed RNS. Glomerular prostaglandin E2 production and plasma renin activity were significantly greater in rats fed a low-salt diet compared with either normal- or high-salt diet. The constancy of glomerular hemodynamic responses to RNS in spite of wide variations in dietary salt intake indicates that functional renal hemodynamic differences observed as a result of NaCl intake must be primarily the consequence of differences in renal nerve traffic and not hormonal alterations.