Effects of Nitroglycerin and Nitroprusside on Cerebral Veins

Abstract

Cerebral haemodynamic effects of intravenous nitroglycerin (NTG) and nitroprusside (NPR) were compared in ten anaesthetized, paralyzed, ventilated dogs, at normal cerebrospinal fluid pressure (Pcsf). NTG (5, 25, 50 μg/kg) increased Pcsf to 181, 250, and 273% of its control value and decreased arterial blood pressure to 89, 80, and 78% of the control level, respectively. NPR (5, 25, 50 μg/kg) increased Pcsf to 142, 169, and 177% of the control value and decreased arterial blood pressure to 88, 72, and 69% of the control level. Haemorrhagic hypotension to arterial blood pressure levels (54% of control) lower than those produced with either NTG or NPR did not alter Pcsf in five dogs. Cerebral blood flow was unchanged with NTG, NPR, or haemorrhagic hypotension. For any given decrease in arterial blood pressure, NTG produced a greater increase in Pcsf than NPR, or haemorrhagic hypotension. We conclude that NTG has a greater effect on cerebral veins than NPR. The increase in cerebral volume responsible for the increased Pcsf with these agents occurs as a consequence of an increase in the cerebral venous volume.