Recent studies have suggested that the lung plays an important role in modifying concentrations of circulating vasoactive compounds. Isolated lungs of spontaneously hypertensive rats (SHR) were examined for their ability to modify concentrations of perfused norepinephrine, 5-hydroxytryptamine, or angiotensin I. Lungs from 4- or 14-wk-old SHR removed significantly more perfused 0.1 microM norepinephrine (NE) than lungs of normotensive controls (Wistar-Kyoto rats, WKY) of the same age. For example, lungs of 14-wk-old WKY removed 18.5 +/- 1.8% of perfused NE in a single pass through the pulmonary vasculature, whereas lungs from SHR removed 31.7 +/- 1.0%. Lungs of 14-wk-old SHR also produced more O-methylated NE metabolite than did lungs of WKY. Conversely, lungs of 14-wk-old SHR removed slightly less perfused 5-hydroxytryptamine and produced less 5-hydroxyindoleacetic acid metabolite than those of WKY. Monoamine oxidase activity, determined in 600 g supernatant fractions of lung homogenates, was the same in SHR and WKY. In addition, no difference in the ability of lungs of WKY and SHR to remove perfused angiotensin I was found either in animals 4 or 14 wk of age. These results suggest that lung may contribute to differences in concentrations of circulating biogenic amines observed in SHR and WKY.