CIRCULATORY EFFECTS OF THE VENOM OF THE INDIAN COBRA (NAIA NAIA)

¹ Sao Paolo
² New York City

1. In cats and rabbits the intravenous injection of a small dose of cobra venom (6 to 9 µ grams per kilogram) causes a long lasting rise of arterial blood pressure, occasionally preceded by an evanescent depressor effect. When the blood pressure has returned to normal the injection of a second similar dose of venom is ineffective (tachyphylaxie).

2. Cobra venom causes vasoconstriction in the rabbit's ear perfused with physiological salt solution and there is no or only little diminution of the effect by repeated administration of the venom.

3. In the heart-lung preparation of the dog the injection of cobra venom (60 µ grams) produces long lasting dilatation of the coronary vessels which can readily be desensitized against the venom by a previous injection of a subthreshold dose.

4. The intravenous injection into cats of 9 µ grams of cobra venom per kilogram produces profound alterations in the electrocardiogram.

5. Cobra venom causes systolic standstill of the auricular strip (rabbit's and guinea-pig's heart) and of the fibre of Purkinje (dog's heart). No tachyphylaxie could be obtained in these preparations.

6. In the isolated frog's heart cobra venom causes irreversible systolic contracture. During the development of the contracture the electrocardiogram shows signs of impairment of conduction, shortening of the duration of the systole and changes in the QRS complex and T wave. The absence of calcium ions in the perfusion fluid alters the response. The muscle becomes less sensitive to the venom which produces stoppage of beat without signs of systolic contracture.