The extensive utilisation of in vitro tests of platelet aggregation presumes that
corresponding effects occur in vivo. Platelet aggregometry in vitro and in vivo have
been compared using a range of agonists in order to test this assumption.
PRP from citrated peripheral blood of man, rat and guinea-pig was exposed to ADP,
adrenaline, serotonin, collagen, thrombin and PAF in a Born aggregometer to define
the time course and amplitude of these responses. In rat and guinea-pig, these aggregatory
stimuli have also been used to define the time course and amplitude of intrathoracic
accumulation of 111 -Indium labelled platelets, using an automated monitoring system
(AIMS 8000).
Concordance between these tests was evident for ADP, collagen, thrombin and PAF in
both species; but, substantial discrepancy was observed between in vitro and in vivo
responses to serotonin and adrenaline, since sustained aggregation followed injection
of these agonists in the rat.
For these platelet stimuli, in vivo aggregometry in rat and guinea-pig may more faithfully
reflect the behaviour of human platelets than in vitro studies.
