The ability of tannin to cross from the abluminal to the luminal surface of isolated rabbit pulmonary arteries was examined using modified Ussing chambers which permitted the measurement of isometric force generation. Tannin was purified from Acala-SJ5 cotton bracts. All tissues were precontracted with an EC(50) concentration of phenyephrine (PE). Addition of 25 ug/ml tannin to the luminal side elicited a diphasic response consisting of a transient relaxation (61±8% decrease in tone at approximately 2.5 minutes), followed by a prolonged contraction that reached 114±14% of the original PE mediated contraction in approximately 17 minutes. Only the contraction was evident upon repeat exposure of the luminal surface. In contrast, when tannin was added to the abluminal side of the tissue it caused no significant change in tone and had no effect on the diphasic response to a subsequent luminal exposure of tannin. The thromboxane A(2) antagorist SQ 29548 (3x10^-6M) abolished contractions caused by the addition of tannin, whereas removal of the endothelium abolished all response to tannin. Thus, tannin induces the release of both endothelium-dependent relaxing (EDRF) and contracting (TXA2) factors. Acetylcholine (10^-8-3x10^-7M) also caused endothelium-dependent relaxations when added to the luminal side of the tissue. Although the Ach-induced relaxations were reproducible, they could be abolished by previous exposure of the luminal surface to tannin. These observations indicate that tannin applied to the abluminal surface of pulmonary arteries appears not to gain access to the luminal surface where the greatest moderating effects of the agent on smooth muscle tone are observed. Moreover, tannin also appears to have a toxic effect on the release of an endothelium-dependent relaxing factor.