A comparison of haemoglobin and erythrocytes as inhibitors of smooth muscle relaxation by the NANC transmitter in the BRP and rat anococcygeus and by EDRF in the rabbit aortic strip

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Abstract
The inhibitory effect of erythrocyte suspensions and haemoglobin solutions on the response of the bovine retractor penis muscle (BRP) and the rat anococcygeus to field stimulation of their non-adrenergic non-cholinergic (NANC) nerves has been compared. Haemoglobin 3 .mu.M greatly reduced the relaxant response in both tissues whereas a haemoglobin-equivalent suspension of erythrocytes was without effect. A similar comparison of erythrocytes and haemoglobin on the response of the rabbit aortic strip to EDRF liberated by acetylcholine (ACh) showed that both reduced EDRF-mediated relaxation, though haemoglobin was significantly more effective. These results suggest that the NANC transmitter may not be as freely diffusible through the erythrocyte membrane as EDRF and may therefore not be nitric oxide.