The effect of potassium loading on sodium status and pressor responsiveness in the sheep.

The effect of increased potassium (K) intake (800 mmol/day) was investigated in conscious sheep to elucidate the mechanism of the anti-hypertensive effect of K loading. Mean arterial pressure rose (4mm Hg, n = 13, p less than 0.001). Cardiac output (n = 5) increased from 4.4 +/- 0.1 to 6.1 +/- 0.2 1/min (p less than 0.001). Calculated total peripheral resistance fell from 17 +/- 1 to 12 +/- 1 mmHg.min/1 (p less than 0.001). There was no change in plasma volume (n = 5), but extracellular fluid volume (n = 5) increased from 221 +/- 26 to 271 +/- 27 ml/kg (p less than 0.05). Glomerular filtration rate and effective renal plasma flow (n = 5) were unchanged. Plasma K concentration, fluid intake and urine volume increased. Urinary Na excretion increased from 106 +/- 11 to a maximum of 217 +/- 28 mmol/day on day 2 (p less than 0.001), and was decreased on day 7, 44 +/- 13 mmol/day (p less than 0.05). Calculated Na deficit was -268 mmol by day 10, but there was no change in responsiveness to infused angiotensin II, noradrenaline, vasopressin or tyramine. These changes differ from those seen with Na depletion alone in sheep, and are not compatible with the hypothesis that K loading exerts its effects solely by increasing Na excretion.