Changes in collagen content of the diaphragm in rats of different ages.

: Rat diaphragm showed a nine to ten-fold increase in the dry and wet weights and a four-fold increase in its surface area between 21 and 540 days of age. The increase was the most rapid between days 21 and 90, thereafter a non-significant trend of increase was maintained at least up to 360 days of age followed by a tendency to decrease. The total collagen content of the diaphragm paralleled the increase in surface area with progressing age. The collagen content significantly dropped when expressed relative to the dry weight of the diaphragm, between 21 and 90 days of age. This trend was maintained till 180 days of age but thereafter significantly rise was seen. These later changes may be due to elenated synthesis and/or reduced degradation of collagen, and may contribute to the decline in contractility of the diaphragm as age advances.