Age related evolution of stable collagen reticulation in human skin

The relaxation time of hydrothermal isometric tensions (HIT) was measured in different tissues during collagen hydrolysis. This hydrolysis was shown to have the same activation energy in all skin samples studied, whatever the species and age. Therefore, variations in the HIT relaxation half-time at the boiling point, exclusively reflected variations in the reticulation degree of the stable infinite network of denatured collagen. Stable collagen reticulation was studied in human skin from birth to 70 yrs of age in 113 biopsies, by measuring the relaxation half-time of hydrothermal isometric tension (HIT) at boiling point. This time was observed to vary in three different ways as a function of age: 1) from birth to eight or 10 yrs and from 14-15 yrs until adulthood, it increased constantly, and at the same rate; 2) during early puberty, the striking observation was the dramatic decrease of relaxation time value which remained low for 4-5 yrs thereafter, and 3) from adulthood to 70 yrs of age, relaxation time values were scattered along several plateaux, apparently separated by similar incremental steps. A parallel study on rat and pig skin showed a similar age-related evolution for collagen stable reticulation i.e., a sudden drop of reticulation at puberty, and low values for several months thereafter, followed by a linear increase, at the same rate as that observed for human skin. The study of collagen reticulation in various pathological situations may help to clarify and increase our understanding of the different mechanisms involved in collagen modifications during in vivo growth and aging.