The response of the right ventricle to experimentally induced pulmonary artery obstruction.

Banding of the main pulmonary artery was undertaken in 11 litter-mate puppies and 8 young adult beagle dogs to study the response of the right ventricle to pressure loading. Five puppies and 3 young adult dogs acted as controls, undergoing sham surgical procedures without pulmonary artery banding. In one banded puppy and one banded young adult dog, adequate banding was not achieved and each was subsequently considered with its respective control group. A trans-band gradient of 15 mm Hg or greater was deemed a successful banding procedure. Banded puppies showed an increase in the trans-band pressure gradient in the year following surgery whereas young adult dogs showed a fall in the gradient, despite satisfactory banding as shown by cardiac catheterization 14 days after surgery. Cardiac muscle analyses indicated that the right ventricle of puppies responded to pulmonary banding by an increase in total organ weight, total tissue protein, DNA and RNA without altering the protein/DNA and RNA/DNA ratios. By contrast, young adult dogs showed only slight and insignificant increases in the protein/DNA and RNA/DNA ratios. Thus the response of the right ventricle to pulmonary artery banding in puppies is hyperplastic in nature, while in young adult animals the response to a similar stress load is with mild muscular hypertrophy and dilatation. This differential cellular response to the same stimulus based on the age of the organism is another demonstration of the principle that growth responses in the young involve cellular proliferation while those in the adult consist primarily of cell enlargement. It is, therefore, perhaps erroneous to refer to cardiac enlargement in newborns and infants as cardiac hypertrophy.