EFFECTS OF ANGIOTENSIN, BRADYKININ AND OXYTOCIN ON ELECTRICAL AND MECHANICAL ACTIVITIES IN THE TAENIA COLI OF THE GUINEA PIG

Abstract

The electrical and mechanical responses of the taenia coli of the guinea pig to angiotensin, bradykinin and oxytocin were studied by the sucrose-gap method. Angiotensin increased the membrane activity of the smooth muscle, namely depolarization and increase in spike frequency, which was accompanied by a rise in tension. Bradykinin had a diphasic action, causing an initial hyper-polarization and loss of spike activity, followed by the depolarization and increase in spike frequency. These were associated with an initial fall and then an increase in tension. Oxytocin decreased the excitability of the muscle, abolished spike activity and raised the membrane potential, inducing a resultant fall in tension. The effects of angiotensin, bradykinin and oxytocin were unchanged in the presence of hexamethonium. The excitatory effects of angiotensin and bradykinin were neither inhibited by atropine, nor potentiated by neostigmine and the inhibitory effects of bradykinin and oxytocin were unaffected by adrenergic blocking agents. All polypeptides retained their contractile or relaxing effects on the muscle completely depolarized by K ions. These effects were dependent on the Ca concentration of the solution. The polypeptides act directly, without the intervention of nervous elements, on the smooth muscle, producing their excitatory or inhibitory effects. The possibility that the direct actions of drugs are mediated through 2 ways was discussed.