Cardiovascular and endocrine effects of potassium in spontaneously hypertensive rats

Although potassium is known to lower blood pressure in a number of forms of experimental and human hypertension, the mechanism for this effect remains unclear. We studied several possible mechanisms for this effect in the spontaneously hypertensive rat (SHR). Fourteen-week-old SHR were given 0.5% KCl in the drinking water. This potassium supplement resulted in a 16-mmHg fall in mean arterial pressure and a 22% decrease in peripheral vascular resistance. Plasma potassium increased 0.4 meq/l, while muscle potassium was unchanged. Potassium supplementation resulted in no change in plasma renin activity, plasma aldosterone, or plasma norepinephrine. Urinary excretion of prostaglandin (PG) E₂ and 6-keto-PGF(1α) was also not altered by potassium supplementation. Potassium-supplemented SHR were found to have no difference in sodium excretion compared with control SHR, and plasma volume was similar in both groups. The pressor response to angiotensin II and norepinephrine was not substantially affected by potassium supplementation. Furthermore, baroreflex control of heart rate was not altered by potassium supplementation. Finally, potassium supplementation resulted in no change in mesenteric artery angiotensin II receptor number or receptor affinity. Therefore, although potassium lowers blood pressure in the SHR by decreasing peripheral vascular resistance, the mechanism of this effect on vascular resistance remains unknown.