| Abstrakt: |
Inhibitory factor (IF), an extract of the bovine retractor penis muscle, when treated with acid, becomes a vasodilator with properties similar to endothelium-derived relaxing factor (EDRF). EDRF has been proposed to be nitric oxide (NO), long known to be a potent vasodilator. Recently, biologically active IF was proposed to be NO, as well, generated by acid activation of inorganic nitrite. We compared acid-activated IF with acid-activated nitrite and found that NO formation was not sufficient to explain the properties of acid-activated IF. Endothelium-denuded rings of rabbit aorta were used to test the smooth muscle-relaxing properties of IF and nitrite. Although both IF (0.5 ml) and nitrite (1 microM) relaxed phenylephrine-contracted rabbit aorta to a similar extent after acid activation (approximately 30%), several significant differences were observed. IF was most active when acid activated by a 5-min, pH 2 step followed by neutralization; nitrite was relatively inactive when acid activated in this manner, and was most active when assayed immediately after acidification to pH 2. Purging with argon for 5 min reduced the smooth muscle-relaxing activity of 1.0 microM nitrite from 27 +/- 2 to 10 +/- 2% relaxation, whereas the activity of IF was not changed by argon purging (control, 31 +/- 2% relaxation; argon purged, 34 +/- 2% relaxation). When IF samples were assayed for nitrite content, the amount of nitrite found (0.5-5 nmol/0.5 ml sample) was not sufficient to explained the observed smooth muscle relaxing activity. Furthermore, acid-activated IF significantly stimulated cyclic GMP production by platelet-soluble guanylate cyclase from 3.2 +/- 0.2 to 12.4 +/- 0.4 pmol/min/mg protein.(ABSTRACT TRUNCATED AT 250 WORDS) |
