Plasma renin activity, angiotensin II, and aldosterone after mental arithmetic.

Plasma renin activity (PRA) and the concentration of plasma angiotensin II and aldosterone, blood pressure, heart rate, serum electrolytes and some haematological parameters were measured in six male subjects who carried out exercises in mental arithmetic for a period of 20 min. After this mental exercise the PRA and angiotensin II values increased significantly, but plasma aldosterone showed a tendency to decrease. The highest mean increases in PRA (56.0%, P less than 0.02) and in angiotensin II (66.0%, P less than 0.001) were found 15 min after the challenge. Immediately after the mental activity systolic blood pressure was increased by 10.3% (P less than 0.005), diastolic blood pressure by 10.3% (P less than 0.02) and heart rate by 19.7% (P less than 0.001) over the pre-test values. There were no significant changes in serum electrolyte levels until 1 and 2 h after the exercises, at which time the serum potassium values were slightly, but significantly (P less than 0.005) decreased. There were no significant changes in the haematological parameters studied (blood erythrocytes, leucocytes, haemoglobin, haematocrit, and the volume, amount of haemoglobin, and haemoglobin concentration of the red cells). A positive correlation (r = 0.9389, P less than 0.01) was found between the increases observed in the PRA and in heart rate. The changes found in PRA and in the concentration of plasma angiotensin II after these exercises in mental arithmetic resemble those found previously, after physical and heat stress.