In vivo quantification of ageing changes in the rat liver from early juvenile to senescent life

Using high resolution multifluorescence in vivo microscopy, the present study was undertaken to determine the changes in rat hepatic tissue architecture and microvasculature during the growth associated with juvenile maturation and adult senescence, i.e. the age of 1, 3, 12 and 24 months.

By 1 month of age the liver attained its full size and functional capacity, as assessed by relative organ weight and hepatic bile flow. Survey of liver architecture revealed a progressive growth of lobular area with postsinusoidal venules exhibiting a proportional increase in length, diameter and inter-vascular distance up to the age of 12-24 months. In regard to the 3.5-4-fold average increase of lobular units, a minor reduction of sinusoidal density to 87% over life strongly implies the recruitment or formation of new sinusoidal microvessels as contributing mechanism to meet oxygen demand due to overall tissue enlargement. The sinusoidal perfusion rate remained above 98% over the whole lifespan. Leukocytic interaction with the hepatic microvascular endothelium was found within the physiological range in all age groups. Moreover, kinetics of clearance of latex beads as well as lobular distribution of Kupffer cells did not differ between animals of different age. Hepatic stellate cell-associated area of ultraviolet vitamin A-autofluorescence increased with age and significantly correlated with increasing tissue concentrations of vitamin A metabolites. Biochemical parameters serving as measures of tissue integrity did not indicate age-associated tissue alterations.

These age-associated physiological changes should be carefully taken into account as a relevant variable in experimental research.