Effects of porcine calcitonin on human platelet fuction

The effects of different doses of porcine calcitonin (pCT) were tested in vitro and in vivo. In vitro, pCT at a concentration ranging from 0.1 to 5 M. R. C. Units/ml induced a dose-dependent inhibition of ADP (1.2 microM) and collagen- (2 micrograms/ml) induced platelet aggregation, showing a prevalent action on the second wave of ADP-induced aggregation and causing prolongation of the lag time and reduction of both maximum aggregation and slope in collagen-induced aggregation. 45Ca uptake by platelets in the presence of the ionophore A23187 and 14C-serotonin release were also inhibited in a dose-related fashion, using concentrations ranging from 1 to 10 M. R. C. Units of pCT. The in vivo tests, performed before and after a 7-day treatment with 2 different doses of pCT (1 and 160 M. R. C. Units/daily, i. m.) confirmed the inhibitory effect of pCT on ADP- and collagen-induced platelet aggregation. It should be stressed that the effect of 1 unit was stronger than that of 160 units. It is therefore postulated that in vitro and in vivo effects of pCT on platelet functions probably depend on different mechanisms of action.