Search

Rat tail tendon collagen-initiated platelet aggregation exhibits a collagen age-dependent lag time. This lag time is an inverse function of the previously determined rate of fibril formation of collagen, and corresponds to the elapsed time necessary to form a collagen fibril of requisite size under the platelet aggregation conditions chosen. Such fibers exhibit native spacing and appear to be 45 to 90 A in diameter. Fibers preformed to that size (less than 2 min for 21- to 1,100-day-old collagen), no matter what the age of the collagen, give rise to identical platelet aggregations. Fibers formed after more prolonged incubation, greater than or equal to 20 min, have impaired platelet aggregating ability.

The rates of collagen fibril formation are, under otherwise identical conditions, a function of the age of the acid-soluble rat tail tendon collagen utilized. The rate is most rapid with young adult (165 day) collagen, which exhibits no induction period before collagen multimerization begins. In contrast, 21-day collagen exhibits both a 30% slower rate and an induction period. Collagens from older animals also have age-dependent fibril formation rates going from a maximum at 165 days to 80% of that for 1,100-day-old material. These age-related differences in collagen fibril formation kinetics appear to be related to the degree of cross-linking of the collagen involved.

Noncovalently bound fluorescent probes have been used to study changes in the platelet which may occur during platelet aggregation. Platelets were exposed to either N-phenyl-naphthylamine (NPN) or 8-anilino-1-naphthalene-sulfonic acid (ANS). Both dyes were bound by the platelet, and platelet aggregation by collagen or thrombin was unaffected by the presence of the label. No change in fluorescence intensity or wavelength of maximum intensity was observed during platelet aggregation.