Effects of human anaphylatoxins on guinea pig atria

Purified human C3a and C5a produce positive inotropic effects on spontaneously contracting atria isolated from guinea pigs. The increased amplitude of contraction induced by C5a has a threshold at 1 X 10(-9)M. This effect is concentration dependent, increasing by 180% at 1.7 X 10(-7)M C5a. The threshold concentration for a C3a-induced effect is four times greater than that for C5a. The C3a-induced effect is also concentration dependent, maximizing at 1 X 10(-7)M. Above that concentration, the increased response to C3a reaches a plateau value at approximately a 70% greater amplitude than that of untreated tissue. Unlike effects induced by anaphylatoxins in other tissues, these positive inotropic responses are not tachyphylactic. The same atrium will respond repeatedly to either C3a or C5a for a period of up to 4 h. Studies with histamine, leukotriene and prostaglandin inhibitors revealed that the anaphylatoxin-induced responses are not solely histamine mediated. Cimetidine partially inhibited the response of isolated guinea pig atria to C5a (e.g. 25%) and failed to affect the response of this tissue preparation induced by C3a. FPL 55712 inhibited the response to both anaphylatoxins by approximately 40%. The atrial response to C3a was inhibited by more than 70% by indomethacin, whereas the response to C5a was unaffected. This is the first report characterizing the specific action of purified C3a and C5a on isolated cardiac tissue. It was concluded that C3a acts primarily via prostaglandins and leukotrienes while C5a affects contractile intensity via vasoamines and leukotrienes.