Angiogenesis in the heart and skeletal muscle

Capillary growth was induced in rabbits's hearts by long-term transvenous bradycardial pacing for 24h/day without any hypertrophy. Capillary density was up to 70% higher than in hearts of comparable size from control rabbits when pacing was applied for at least 14 days. When applied for a month to hearts made hypertrophic by aortic valve lesion, capillary density was higher by 62 +/- 17% than in hearts of control animals of similar body weight. Capillary growth was also induced in skeletal muscles by long-term electrical stimulation (8h/d) at 10 Hz after only 4 days, and after 7 days by stimulation with intermittent tetanic contractions. As the former type increased blood flow more than the latter we tried to find out whether mechanical factors connected with increased flow can stimulate capillary growth. Long-term administration of adenosine and xanthine derivative (HWA 285, Hoechst, Werk Albert, Wiesbaden) increased blood flow in the heart and skeletal muscles and induced capillary growth in both. Prazosin increased flow in muscles but not in the heart and induced capillary growth in muscles only. Limitation of flow to contracting muscles prevented growth of capillaries. Extracts of stimulated muscles had no angiogenic factor while extracts of paced hearts did. Thus capillary growth in skeletal muscle may be due to mechanical factors connected with increased blood flow while the presence of AF may be more important in the heart.