RESUMO
Ischemic contracture of the left ventricle ("stone heart") was studied utilizing a previously described stone heart model. Our studies suggest that beta-adrenergic blockade is not quantitatively as important as hypothermia in protecting ischemic myocardium. On the basis of reduced fibrillatory activity and a slight protective effect shown by electron microscopy, it would appear that combining propranolol with hypothermia may be superior to either used singly.
Assuntos
Doença das Coronárias/complicações , Parada Cardíaca/prevenção & controle , Hipotermia Induzida , Contração Miocárdica , Propranolol/uso terapêutico , Animais , Cardiomegalia/complicações , Doença das Coronárias/tratamento farmacológico , Modelos Animais de Doenças , Cães , Parada Cardíaca/tratamento farmacológico , Parada Cardíaca/etiologia , Contração Miocárdica/efeitos dos fármacos , Miocárdio/ultraestrutura , Propranolol/farmacologia , Fibrilação Ventricular/complicações , Fibrilação Ventricular/tratamento farmacológicoRESUMO
Previous investigations into the mechanisms that control RNA Polymerase (Pol) I transcription have primarily focused on the process of transcription initiation, thus little is known regarding postinitiation steps in the transcription cycle. Spt4p and Spt5p are conserved throughout eukaryotes, and they affect elongation by Pol II. We have found that these two proteins copurify with Pol I and associate with the rDNA in vivo. Disruption of the gene for Spt4p resulted in a modest decrease in growth and rRNA synthesis rates at the permissive temperature, 30 degrees C. Furthermore, biochemical and EM analyses showed clear defects in rRNA processing. These data suggest that Spt4p, Spt5p, and, potentially, other regulators of Pol I transcription elongation play important roles in coupling rRNA transcription to its processing and ribosome assembly.