INVESTIGATIONS INTO MECHANISM OF BLOOD PRESSURE RESPONSE TO ANAPHYLATOXIN IN CATS AND GUINEA PIGS

1. Guinea pigs respond to anaphylatoxin (AT) with an initial hypotension followed by a hypertensive phase. 2. The hypotensive effect occurs independently of respiratory effects of AT, and is not mediated by histamine, serotonin, acetylcholine or catecholamines. Presumably it is due to a direct action of AT on pulmonary vessels. 3. The hypertensive effect is also independent of respiratory changes. It is probably not caused by a release of adrenaline from the adrenals but rather by stimulation of peripheral adrenergic nerve endings. 4. The responses of cats to AT are similar to those seen in guinea pigs. The effects are, however, less constant and never lethal. In the systemic circulation a fall of blood pressure is predominant. Less often, a rise or biphasic response is seen. In the pulmonary artery the pressure rises consistently by 30 to 40 mm Hg, whereas in the pulmonary veins it remains unaltered or slightly decreases. 5. All blood pressure responses of cats are subject to tachyphylaxis. Neither antihistaminics nor atropine, methysergide, acetylsalicylic acid or α- and β-receptor blocking agents are effective antagonists. Thus the circulatory effects of AT in cats seem to be direct actions. The respiratory effects (tachypnoea, bronchospasm) can be blocked by antihistaminics. © 1969 Springer-Verlag.