ALTERATIONS IN BLOOD-PLATELET MORPHOLOGY DURING AGGREGATE FORMATION IN THE ASIAN ELEPHANT (ELEPHAS-MAXIMUS)

The ultrastructure of Asian elephant (Elephas maximus) platelets befor e and after activation with the agonist platelet activating factor (PA F) was studied. The unactivated platelet has a distinct ultrastructura l appearance: the cytoplasm contains large randomly distributed granul es but lacks the internal cristae that typify the open canalicular sys tem in many types of mammalian platelets. Following PAF stimulation, l arge platelet aggregates form, but many platelets remain discrete, wit h Little evidence of pseudopod formation or fusion of membranes. Two t ypes of platelets are visible within the aggregates: those that are mo rphologically intact and those with gaplike features on the outer memb rane and that have become degranulated, appearing as empty swollen sac s. The lack of platelet membrane fusion within the aggregates may perm it the reversal of aggregation that is a characteristic response of el ephant platelets to PAF.