RESTRAINING EFFECTS OF CAPTOPRIL ON SYMPATHETIC EXCITATORY RESPONSES IN DOGS - A SPECTRAL-ANALYSIS APPROACH

This study was planned to clarify the effects of captopril administrat ion on the autonomic control of the circulation in conscious dogs and in dynamic conditions using spectral analysis of R-R interval and syst olic arterial pressure (SAP) variabilities. Changes in sym pathovagal balance modulating the sinoatrial (SA) node were inferred, respectivel y, from the low (LF(R-R))- and high-frequency (HFR-R) components of R- R variability; LF(SAP) furnished a marker of sympathetic vasomotor con trol. Increases in sympathetic activity were induced by three differen t experimental maneuvers [bilateral carotid occlusion (BCO), coronary artery occlusion (CAO), and dynamic exercise] capable of increasing sy mpathetic outflow to the SA node and to the vessels. Studies were perf ormed both before and after intravenous captopril administration. Duri ng BCO, only LF(SAP) increased from 4.3 +/- 1.5 to 19.7 +/- 4.1 mmHg(2 ); during CAO, both LF(R-R) and LF(SAP) increased, respectively, from 3 +/- 1 to 21 +/- 2 normalized units (nu) and from 4.1 +/- 1.3 to 7.2 +/- 1.5 mmHg(2). Dynamic exercise at 2 and 4 km/h progressively raised LF(R-R) from 8 +/- 2 to 58 +/- 7 and 75 +/- 5 nu, respectively; LF(SA P) showed a parallel trend increasing from 2.5 +/- 0.7 to 8.04 +/- 1.9 and 12.7 +/- 2.2 mmHg(2). In all experimental conditions, captopril s ignificantly (P < 0.05) blunted the increase of LF(SAP) A restraining effect on LF(R-R) was apparent only with CAO. Spectral analysis of car diovascular variabilities indicates that, in the conscious dog, acute captopril administration has an important inhibitory effect on cardiac sympathetic excitatory mechanisms as well as on sympathetic vasomotor control.