Adrenergic mechanisms during hypertension induced by sucrose and/or salt in the spontaneously hypertensive rat.

Spontaneously hypertensive rats received tap water, 1% NaCl, 5% sucrose or NaCl and sucrose in combination for 4 weeks. The blood pressure (tail plethysmography) and renal excretions of sodium and catecholamines were followed. After 4 weeks the noradrenaline turnover (disappearance after alpha-methyltyrosine) was assessed in the heart and brain. In pithed rats the pressor responses to intravenous noradrenaline and to electrical stimulation of the spinal sympathetic nerves (SNS) were determined together with the rise in plasma noradrenaline concentrations during the SNS. Salt alone caused an increase in peripheral sympathetic activity, measured as turnover of noradrenaline in the heart and spillover of noradrenaline in the urine, a modest enhancement of vascular responsiveness to noradrenaline and a blood pressure elevation. Sucrose alone increased the peripheral sympathetic activity but influenced neither the vascular responsiveness to noradrenaline nor the basal blood pressure. The largest increase in sympathetic activity and in blood pressure was observed with sucrose and salt in combination. The release of noradrenaline from the sympathetic nerve endings was not significantly influenced by any diet regime. The changes in noradrenaline turnover in the heart was accompanied by reciprocal changes in brain stem noradrenaline turnover.