The hemodynamic effect and degree of damage in grafts of single lung transplants for pulmonary hypertension were studied in rats with monocrotaline-induced pulmonary hypertension. Inbred male Lewis rats (weight 200-230 g) were divided into two groups. Group 1 (control group, n = 16) underwent isogenic left lung transplantation, while group 2 (n = 15) received an intravenous administration of monocrotaline (80 mg/kg i.v.) and underwent isogenic left single lung transplantation 3 week later. Hemodynamic evaluations were performed prior to transplantation, at 1 h postoperatively, and on days 3 and 7 after transplantation. Mean pulmonary arterial pressure (mPAP) rapidly declined after transplantation in group 2, from 39.3 +/- 8.7 mmHg to 18.5 +/- 3.0 mmHg 1 h after transplantation, and remained stable on day 7 after transplantation. No significant difference in the mPAP between the two groups was observed after transplantation. The extravascular lung water volume (ELWV: dry/wet ratio) in the right lung of group 2 significantly increased on day 3 (0.86 +/- 0.02) (P < 0.01), and subsequently decreased to control levels on day 7 (0.83 +/- 0.02). There was no significant difference in the ELWV in the grafted lungs between the two groups (0.84 +/- 0.03 vs 0.86 +/- 0.04), but there was tendency toward an increase in ELWV in group 2 on days 3 and 7. These data thus demonstrated that a hemodynamic improvement was obtained by single lung transplantation; however the degree of graft damage was remarkable in the pulmonary hypertension group.