Plasma atriopeptin during exercise in dogs under beta-blockade.

The purpose of this study was to describe plasma atriopeptin concentrations at rest and in response to moderate treadmill exercise (10 min, 4 km/h, 26% slope) performed with or without nonspecific beta-adrenergic blockade (1 mg/kg iv propranolol) in 10 mongrel dogs [19 +/- 2 (SE) kg]. A small (20%) but significant (P less than 0.05) increase in plasma atriopeptin concentration was observed from rest (43 +/- 5 pg/ml) to exercise (52 +/- 6 pg/ml) without beta-blockade. Propranolol significantly reduced heart rate at rest (89 +/- 7 vs. 104 +/- 7 beats/min) and during exercise (96 +/- 10 vs. 176 +/- 11 beats/min), and this was associated with a larger increase in plasma atriopeptin concentration during exercise (rest 46 +/- 6 pg/ml; exercise 171 +/- 22 pg/ml). Exercise under beta-blockade is associated with an increased preload of the heart. These results further support the hypothesis that atriopeptin release during exercise is under the control of atrial stretch. The higher plasma atriopeptin concentration observed during exercise under beta-blockade may contribute to the reduction of the response of plasma renin activity (1.0 +/- 0.1 vs. 3.0 +/- 0.6 ng.ml-1.h-1) and aldosterone concentration (87 +/- 36 vs. 138 +/- 25 pg/ml). Vasopressin concentration was lower at rest and during exercise under propranolol (3.5 +/- 1.3 vs. 4.9 +/- 0.9 and 6.1 +/- 2.2 vs. 9.9 +/- 1.5 pg/ml, respectively), which might reflect a dissociation between activity of the renin-angiotensin system and vasopressin release.