1. Effects of treatment with
piretanide (10 and 30 mg/kg per day p.o.) for 9 weeks on blood pressure, urinary excretion of
electrolytes, and vascular reactivities to pressor substances were investigated in 10-week-old spontaneously hypertensive (SHR) rats. 2.
Piretanide (30 mg/kg) prevented development of
hypertension and produced a significant reduction in blood pressure from the 2nd week of the treatment. A slight decrease in blood pressure was observed in rats treated with the lower dose of
piretanide. 3.
Piretanide produced significant and dose-dependent diuresis throughout the experiment. Although significant natriuresis was observed in the 1st and 4th week of the treatment, natriuresis disappeared in the 8th week. Urinary excretion of
potassium was decreased significantly by
piretanide throughout the experiment. 4. Attenuation of pressor responses to
phenylephrine and
angiotensin II was observed after chronic administration of
piretanide (30 mg/kg). 5. These data demonstrate the contribution of attenuated vascular reactivities to pressor substances as well as a
diuretic action to the
antihypertensive effect of
piretanide during its long-term administration in SHR rats.