Adrenoceptor control of lung fluid and protein exchange.

We studied the effects of alpha- and beta-adrenergic antagonists on lung fluid and protein exchange in anesthetized sheep. alpha-Adrenergic blockade with 2 mg/kg phentolamine caused a transient and small decrease in lung lymph flow (Qlym), which was associated with a decrease in mean pulmonary arterial pressure (Ppa); but the steady-state Qlym and mean left atrial pressure were not different from base-line values. In contrast, beta-adrenergic blockade with propranolol (2 mg/kg) caused an increase in Qlym from a base-line value of 7.7 +/- 2.2 ml/h to a steady-state value of 10.6 +/-2.3 ml/h within 2 h (P less than 0.05), which was not associated with a change in Ppa. The increase in Qlym persisted for the 4-h duration of the study. The 39% increase in Qlym after propranolol was associated with a 50% increase in transvascular protein clearance (CL), whereas in control animals the 100% increase in Qlym after left atrial hypertension was associated with only a 36% increase in CL, indicating increased transvascular transport of proteins after propranolol. The transient decrease in Qlym after phentolamine may be due to the short-lasting decreased in pulmonary microvascular pressure and vascular surface area. However, the long-lasting increases in Qlym and CL after propranolol may be due to an increase in vascular surface area and to an increase in endothelial permeability of proteins. The results suggests that beta-adrenergic receptors regulate the transendothelial transport of fluid and proteins.