Block of some non‐adrenergic inhibitory responses of smooth muscle by a substance from haemolysed erythrocytes

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Abstract
A preparation of hemolyzed rat erythrocytes (the hemolysate) blocked the relaxations of both the bovine retractor penis and the rat anococcygeus muscles in response to field stimulation of their nonadrenergic inhibitory nerves. The effective concentration range was 5-20 .mu.l/ml of hemolysate, equivalent to 0.25-1.0 .mu.l/ml of blood. The active principle in the hemolysate was a nondialyzable, heat-labile material of MW between 50,000 and 100,000 daltons. If the active component of the hemolysate was HbO2; its effective blocking concentration was 0.5-2 .mu.M. Hemolysate (5-20 .mu.l/ml) also blocked the relaxation of both the bovine retractor penis and the rat anococcygeus to the inhibitory factor extracted from the bovine retractor penis, an observation supporting the possibility that this inhibitory factor may be the transmitter released by the inhibitory nerves in these tissues. In the bovine retractor penis, hemolysate was also effective in blocking relaxations in response to sodium nitroprusside, but relaxations produced by prostaglandin E1 or isobutylmethylxanthine were unchanged or only slightly reduced. In contrast, in the tenia of the guinea pig cecum, hemolysate did not block the nonadrenergic inhibitory response to field stimulation or the relaxation produced by ATP, although it did block the relaxation produced by the inhibitory factor. In spiral strips of isolated rabbit aorta, hemolysate (10 .mu.l/ml) increased the contraction produced by noradrenaline [norepinephrine] and blocked the relaxation produced by the inhibitory factor. These were independent effects. Apamin, which blocked the relaxation of the tenia of the guinea pig cecum elicited by either ATP or field stimulation of its nonadrenergic nerves, was without effect on relaxations of the bovine retractor penis or rat anococcygeus muscles in effect on relaxations of the bovine retractor penis or rat anococcygeus muscles in response to field stimulation of inhibitory nerves or to inhibitory factor. These diffferences in the blocking effects of apamin and hemolysate suggest either that the transmitter in the bovine retractor penis and rat anococcygeus differs from that in the guinea pig tenia or, if the transmitter is the same, then its mechanism of action differs.