Cats with the Chediak-Higashi (CH) syndrome have abnormal hemostasis with prolonged bleeding times and normal coagulation times. Platelet aggregation induced by
serotonin,
ADP, and
collagen was impaired. Platelets from normal and CH cats were incubated with 14C-adenine and then gel-filtered. Gel-filtered platelets (GFP) from CH cats contained 63% of the
ATP, 38% of the
ADP, 100% of the Ca2+, and 75% of the Mg25 of normal platelets.
Serotonin could not be detected in CH platelets.
Acid hydrolase and total platelet
protein of CH platelets was similar to normal platelets. Gel-filtered platelets were treated with
thrombin to induce maximal secretion. Secretion of
ATP, Ca2+, and Mg2+ was 1.9%, 12.4%, and 16% respectively of normal platelets.
ADP secretion by CH platelets was not detectable. The
ATP/
ADP ratio in the 14C-labeled metabolic pool of normal platelets was similar to that of total measured
nucleotide pool of CH platelets. These findings suggest that in feline CH platelets, as in platelets from CH mink and cattle, there is
storage pool deficiency that is virtually complete, and the virtual absence of
ADP and 5HT may in part account for the abnormal hemostasis. Aggregation of platelets from CH cats was impaired, but these platelets did aggregate to arachidonate,
serotonin-induced biphasic aggregation, and the aggregation response to
ADP and
collagen varied according to the amount of
serotonin-induced TxB2 formed. These findings support a major role for arachidonate in platelet activation.