Studies comparing relative organ weight (per gram of body weight) in spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar-Kyoto rats (WKY), have shown that the heart and kidney of SHR are enlarged at birth. In addition, higher DNA concentrations in these organs provide evidence of cardiac and renal cellular hyperplasia in newborn SHR. The rate of DNA synthesis was estimated with [methyl-3H]thymidine labeling in vivo for heart, kidney, liver, adrenals, and aorta of newborn WKY and SHR, and significantly higher relative organ weights, protein levels, and DNA contents were observed only for heart and kidney from SHR. In contrast, relative weight was significantly lower for liver from SHR and the same for adrenals from WKY and SHR despite lower adrenal protein and DNA contents for SHR. Relative weight and protein content of aorta were higher in SHR, possibly indicating hypertrophy of this organ. Several differences in [methyl-3H]thymidine labeling were observed in organs from SHR. Significantly higher organ accumulation (cpm/mg organ weight) was observed for heart from SHR (p less than 0.01), and higher incorporation into DNA (cpm/cpm) was observed for kidney and liver from SHR (p less than 0.001). Most significant was the finding of higher DNA specific activity for heart (+33%; p less than 0.05) and kidney (+39%; p less than 0.001) from SHR. These data provide evidence of enhanced DNA synthesis in the heart and kidney of newborn SHR.
