Dynorphin administered to newborn rats modulates morphogenesis of the heart

Proliferation, activity of the nucleolar organizer region, and protein content in cardiomyocytes were studied in 21-day-old rats intraperitoneally treated with kappa-opioid receptor agonist dynorphin A(1-13) in a dose of 100 microg/kg on postnatal days 2-6. The content of catecholamines in the heart and proliferative activity of cardiomyocytes remained unaffected, but the number of nucleoli in cardiomyocyte nuclei and the integral optical density of cardiomyocytes stained with amido black B (protein content) increased. The data suggest that administration of dynorphin to newborn rats considerably modulates morphogenesis of the heart at later terms.