Transient pleural effusion in norepinephrine-stimulated rats

Transient pleural effusions occurred in rats receiving continuous intraveno us infusion of norepinephrine (NE, 0.1 mg/kg/h). We hypothesized that these pleural effusions result from a NE-induced increase in right ventricular s ystolic pressure (RVSP) and total peripheral resistance (TPR). NE was admin istered over time intervals between 20 min and 72 h. It induced an immediat e doubling in RVSP whereas LVSP remained at the control level. TPR increase d with a delay of 6 h. At this time, pleural effusions occurred in NE-treat ed animals, reached their maximum after 8h and disappeared after 24 h of NE stimulation. Combining NE with the alpha -blocker prazosin normalized TPR and prevented pleural effusions. Therefore, we interpret the pleural effusi on as a consequence of pulmonary venous congestion, mainly caused by an inc reased TPR. LV hypertrophy which developed after 24 h of NE stimulation is considered to compensate for the hemodynamic disturbance due to the NE-indu ced elevation in TPR. This is reflected in the disappearance of pleural eff usion.