Age-dependent changes in prevalence, size and proliferation of arterial lesions in cockerels. I. Spontaneous lesions.

Age-dependent changes were determined in the prevalence, size and proliferation of early spontaneous aortic lesions in white leghorn cockerels. Groups of 6 animals received weekly intramuscular injections of dimethyl sulfoxide (DMSO) or remained uninjected. They were sacrificed at 6, 8, 12, 16, 20 and 38 weeks of age. Lesions were observed microscopically in all animals 8 weeks of age and older. They appeared in 20-30% of the aortic segments until 16 weeks of age and in 60% of the segments thereafter. The presence of a long single lesion along the aortic segments until 16 weeks of age and in 60% of the segments thereafter. The presence of a long single lesion along the aortic length was revealed by sectioning serially, at 50 micrometers intervals, 10-20 mm lengths of lesion-containing aorta. Between 8 and 20 weeks of age, lesion cross-sectional area increased by a factor of 2.4 while lesion volume index increased by a factor of 6. Similar patterns of proliferation were observed at each time point between lesion cells and those in the underlying media. Labeling indices of media and lesion cells were highest when the animals were growing rapidly and lowest when the animals reached full size. The results indicate that in the cockerel: (1) spontaneous lesions increase in depth and extend radially at a low constant level between 8 and 20 weeks of age and increase markedly in length between 16 and 20 weeks, (2) lesion cell proliferation is sufficient to account for the observed increase in lesion size, and (3) proliferation of lesion cells and medial cells may be governed by the same control mechanism(s).