Lack of edema in toad lungs after pulmonary hypertension

Abstract

Pulmonary hypertension and hyperperfusion were experimentally induced in conscious toads (Bufo marinus) to test whether excessive transcapillary filtration might result in pulmonary edema. Elimination of pulmocutaneous baroreceptor afferent input by bilateral sectioning of recurrent laryngeal nerves caused mean pulmonary arterial pressure to increase by nearly 25 mmHg and pulmonary blood flow to increase fourfold. Left lungs of control (normotensive) and hypertensive toads were isolated by snares at the hilus and excised for compartmental lung fluid analysis. Total lung water was significantly elevated in hypertensive toads (8.44 +/- 0.30 ml/g dry mass) compared with control animals (7.15 +/- 0.22 ml/g dry mass), but this increase was apparently not due to an accumulation of transcapillary filtrate (extravascular fluid volumes = 4.57 +/- 0.21 and 4.35 +/- 0.17 ml/g dry mass, respectively). Instead, significant increases in pulmonary intravascular fluid volume accounted for 83% of the increase in total lung water. Such absence of pulmonary edema under these extreme cardiovascular states suggests that mobilization of pulmonary lymph is unusually effective in these animals.