Quantitative and comparative studies of the vocal fold extracellular matrix II: Collagen

Objectives: This study examines the collagen content and turnover in the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets. Methods: The LP collagen levels were assessed by quantifying tissue hydroxyproline. Quantitative histology allowed evaluation of the collagen content in specific LP regions. Several collagen types and two markers of collagen turnover were examined immunohistochemically. Results: Collagen made up 43.4% +/- 2.6% of human LP total protein (TP), with men having approximately 30% higher collagen content than women (p < .024). The collagen levels in pigs (52.6% +/- 1.9% of TP) and ferrets (29.8% +/- 3.7% of TP), but not that in dogs (45.3% +/- 1.2% of TP), varied significantly from that in humans (pigs, p < .016; ferrets, p < .011). Quantitative histology indicated marked interspecies differences in total collagen distribution. Collagen types I, III, and IV were detected in the LP, and spatially complex staining patterns were observed for the two markers of collagen turnover studied. Conclusions: The collagen content of the human LP is approximately 60% to 70% of that of human dermis. Although canine LP collagen levels are most similar to those of humans, quantitative histology indicates that the collagen distribution of the human LP is best matched by the porcine LP. Collagen types I and III seem to be the dominant LP collagens. Spatial variations in collagen turnover appear to exist that may contribute to normal LP physiology.