DIFFERENT EFFECTS ON RAT ARTERIAL-PRESSURE AND HEART-RATE WHEN LOSARTAN IS INJECTED INTO THE 3RD-VENTRICLE OR 4TH-VENTRICLE

Cardiovascular responses to central losartan (LOS), a non-peptide angi otensin II (ANG II) receptor antagonist, were investigated by comparin g the effects of LOS injection into the 3rd and 4th cerebral ventricle s (3rdV, 4thV) on mean arterial pressure (MAP) and heart rate (HR). Ad ult male Holtzman rats were used (N = 6 animals per group). Average ba sal MAP and HR were 114 +/- 3 mmHg and 343 +/- 9 bpm (N = 23), respect ively. LOS (50, 100 or 200 nmol/2 mu l) injected into the 3rdV induced presser (peak of 25 +/- 3 mmHg) and tachycardic (peak of 60 +/- 25 bp m) responses. LOS injected into the 4thV had no effect on MAP, but it induced bradycardia (peak of -35 +/- 15 bpm). KCl (200 nmol/2 mu l) in jected into the 3rdV or into the 4thV had no effect on either MAP or H R compared to 0.9% saline injection. The results indicate that LOS inj ected into the third ventricle acts on forebrain structures to induce its presser and tachycardic effects and that bradycardia, likely depen dent on hindbrain structures, is obtained when LOS is injected into th e fourth ventricle.