Blood pressure and sympathetic activity in spontaneously hypertensive rats during food restriction

Young (7 weeks) spontaneously hypertensive rats (SHR) were kept on food-restriction (33%) during 4 weeks with (0.3% saline as drinking water) or without sodium supplementation. Body weight and indirect systolic blood pressure (tail plethysmography) were followed each weak. During the last week of the intervention period 24 hour excretions of sodium, dopamine and noradrenaline were measured. Vascular pressor responses to noradrenaline were evaluated in pithed rats and the sympathetic nerve activity was assessed from the disappearance of endogenous noradrenaline in the heart after synthesis inhibition. Despite a clear retardation of the growth rate in food-restricted rats the development of hypertension was not influenced. Food-restriction was associated with a moderate suppression of sympathetic activity. Furthermore, the vascular pressor responses to noradrenaline were decreased but this was reversed following sodium supplementation. It is concluded that despite evidence of sympathetic suppression weight reduction does not reduce the blood pressure in SHR once the blood pressure has started to rise.