Effect of Hydralazine on Serial Measurements of Exchangeable Sodium and Blood Pressure in Spontaneously Hypertensive Rats

Hydralazine was dissolved in 0.5% drinking saline (40 mg/1000 ml) labelled with isotope 22Na and given to spontaneously hypertensive rats for four weeks. Another group of rats were given isotope labelled saline only and served as control. Measurements of total exchangeable sodium, blood pressure, pulse rate and weight were performed before and repeatedly during treatment. Before treatment exchangeable sodium, blood pressure, pulse rate, and weight were no different between the groups. The antihypertensive effect of hydralazine was marked and maintained throughout the experiment. No significant changes were found in pulse rate. Both groups gained weight similarly. Exchangeable sodium increased at the same rate in both groups along with the weight increase. Thus, chronic hydralazine treatment effectively reduces blood pressure in spontaneously hypertensive rats without causing measurable sodium or fluid retention.