DECREASED ACCUMULATION OF BETA(1)-ADRENERGIC RECEPTOR, G-ALPHA-S AND TOTAL MYOSIN HEAVY-CHAIN MESSENGER-RNAS IN THE LEFT-VENTRICLE OF SENESCENT RAT-HEART

The expression of genes coding for the beta(1)-adrenergic receptor (be ta(1)-AR), the alpha subunit of Gs and total myosin heavy chain (MHC) was compared between left ventricles (LV's) from young (6-7 weeks old) and old (22 months old) rats. The mRNA levels were quantitated by Nor thern or Slot blots analyses using specific DNA probes. Ageing was fou nd to be associated with a reduction in beta 1-AR (77%), G alpha s (33 %) and total MHC (51%) mRNA levels with no concomitant change in 18S R NA and poly(A(+)) mRNA levels. These results indicate that transcripti onal and/or post-transcriptional mechanisms participate in the control of beta-adrenergic receptor density during ageing. As in the senescen t LV, beta(1)-AR mRNA level is reduced in the hypertrophied LV, wherea s the level of G alpha s mRNA is reduced in the senescent but not in t he hypertrophied LV. From our data we conclude (1) that a dual mechani sm may operate during ageing, mechanical factors indirectly regulating beta(1)-AR mRNA level, while changes in G alpha s mRNA level do not d epend on hemodynamic load and (2) that the re-expression of beta-MHC m RNA does not compensate for the decreased accumulation of alpha-MHC mR NA which results in a large decrease in the level of total MHC mRNA in the senescent LV.