LACK OF EDEMA IN TOAD LUNGS AFTER PULMONARY-HYPERTENSION

Pulmonary hypertension and hyperperfusion were experimentally induced in conscious toads (Bufo marinus) to test whether excessive transcapil lary filtration might result in pulmonary edema. Elimination of pulmoc utaneous baroreceptor afferent input by bilateral sectioning of recurr ent laryngeal nerves caused mean pulmonary arterial pressure to increa se by nearly 25 mmHg and pulmonary blood flow to increase fourfold. Le ft lungs of control (normotensive) and hypertensive toads were isolate d by snares at the hilus and excised for compartmental lung fluid anal ysis. Total lung water was significantly elevated in hypertensive toad s (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 accoun ted for 83% of the increase in total lung water. Such absence of pulmo nary edema under these extreme cardiovascular states suggests that mob ilization of pulmonary lymph is unusually effective in these animals.