BOTH T-KININOGEN AND K-KININOGEN INCREASE IN THE SERUM OF OLD RATS BUT BY DIFFERENT MECHANISMS

In the rat, kininogens are produced from two distinctly regulated gene families, T- and K-kininogens. We have previously established that T- kininogen (T-KG, thiostatin) gene expression is increased in the liver of old rats, as compared to their younger counterparts. In this repor t, we have used Northern blot analysis to show that the steady state m RNA levels for either the LMW (Low Molecular Weight) or HMW (High Mole cular Weight) forms of K-KG do not change significantly between 15 and 25 months of age. On the other hand, probing of Western blots contain ing total serum proteins showed that, as for T-KG, old animals have co nsistently elevated levels of HMW-KG. These results indicate that old rats contain elevated serum levels of both T- and K-KG. Nuclear run on experiments have shown that the increase in T-KG gene expression is c ontrolled primarily at the transcriptional level. Our present results with K-KG, on the other hand, indicate that its expression is controll ed post-transcriptionally.