Excitatory effects of adrenaline upon isolated preparations of human colon.

The effect of beta-adrenergic blockade with oxprenolol upon adrenaline-induced relaxation of strips of human sigmoid colon was investigated. Following blockade of beta-adrenoceptors with oxprenolol, adrenaline evoked dose-dependent contractions of both longitudinal and circular muscle strips. Storage of the tissues for periods up to 24 hours at 4 degrees C did not modify the responses to adrenaline. Furthermore, the contractions induced by adrenaline following oxprenolol were significantly diminished by the addition of phentolamine, an alpha-adrenoceptor blocking agent. Our results would suggest that oxprenolol has the property of unmasking or revealing alpha receptors responsible for the excitatory effects of adrenaline upon isolated strips of human colon.