Age-related changes in structure and relative collagen content of the human and feline sinoatrial node. A comparative study.

Age-related changes in the structure and size of the human and cat sinoatrial nodes were studied by light microscopy, with emphasis on changes in relative collagen volume. Sinoatrial nodes from 41 humans (aged 0-94 years) and 21 cats (aged 6 weeks-18 years) were used. It was found that there were no changes in the dimensions of the sinoatrial node during adult life in either species. In Sirius Red F3 Ba stained sections, the relative volume of collagen was measured using an interactive image analysis system. The relative volume of collagen in the human sinoatrial node increases from 38% during childhood to 70% during adulthood. Once adulthood is reached, there are no further changes in the relative volume of collagen. In the cat sinoatrial node the relative volume of collagen is only 27% and does not change with age. The organisation of collagen in the sinoatrial node, however, demonstrates an age-dependent change in both humans and cats. From coarse strands between clusters of nodal cells it gradually changes into a fine network of isolated collagen fibres which surround individual nodal cells. This process is more pronounced in humans. It is concluded that age-related changes in sinoatrial node function are not related to an increase in collagen content in the sinoatrial node.