Effect of vasoactive agents on chronic saline loaded anaesthetised rats

Male albino rats were chronically loaded with sodium by giving 1% NaCl solution as the sole source of drinking water. Daily fluid intake, daily urinary output and daily Na+ and K+ excretion rates were compared with control rats receiving tap water for six weeks. At the end ofsix weeks, sodium loaded animals were found to have raised plasma Na+ concentration, lowered plasma K+ concentration and lowered haematocrit value. Sodium loaded rats were also significantly more responsive to the pressor effect of submaximal doses of adrenaline, noradrenaline and angiotensin II given intravenously. It is concluded that the increase in sensitivity to adrenaline and noradrenaline may be due to changes in EGF and alterations of plasma electrolytes concentration. For angiotensin II, additionally, it may be due to low circulating endogenous angiotensin II, consequent of reduction in renin release attributed to chronic sodium loading.