Inhibition by lidoflazine of the contractile response of the rat isolated colon to angiotensin

1. In the rat isolated ascending colon, lidoflazine in a concentration of 5 x 10(-7)M slightly enhanced the response to angiotensin, but in a concentration of 10(-6)M it was a strong and unsurmountable antagonist.2. Exposure to lidoflazine (10(-6)M) also inhibited the contractile responses to acetylcholine, 5-hydroxytryptamine and barium ions. The antagonism of acetylcholine and 5-hydroxytryptamine was unsurmountable and quantitatively similar to that of angiotensin. The antagonism of barium ions was much weaker and probably competitive.3. The inhibitory effect of papaverine (10(-5)M) showed a pattern similar to that found for lidoflazine.4. It is concluded that the antagonism of angiotensin by lidoflazine in the rat colon is non-specific.

The effect of drugs on the constriction of isolated depolarized blood vessels in response to calcium or barium

1. The rat isolated anterior mesenteric artery was perfused at a constant rate with a calcium-free depolarizing solution. Injection close to the cannula of 0.05-0.1 ml. of solutions of CaCl(2) (117 mM) or BaCl(2) (100 mM) caused a rise in perfusion pressure.2. The responses to injected CaCl(2) solution could be obtained repeatedly but those to successive injections of BaCl(2) solution slowly declined. When the responsiveness to barium had almost disappeared, it could be restored by the addition to the perfusing fluid of a small amount of calcium (0.05 mM).3. The contractile effects of calcium or barium were antagonized by the addition to the perfusing fluid of several anti-inflammatory substances, certain local anaesthetics and certain spasmolytic drugs.4. Perfusion of the mesenteric artery with a depolarizing solution containing 0.2 mM-CaCl(2) caused a persistent rise of the perfusion pressure. This was rapidly and completely reversed by the addition of indomethacin (4 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) to the perfusing fluid.5. The uptake of (45)Ca by rat aorta depleted of calcium was reduced by amethocaine hydrochloride (10 mg/100 ml.) or cinchocaine hydrochloride (2 mg/100 ml.) but not by indomethacin (10 mg/100 ml.) or desipramine hydrochloride (1 mg/100 ml.).