Effect of Endothelin-1 and Atrial Natriuretic Peptide-II on Heart Morphogenesis in Albino Rats

Computer morphometry and histochemical analysis were used to study the delayed effects induced by endothelin-1 and atrial natriuretic peptide-II (single doses 50 and 100 mug/kg, respectively) in neonatal albino rats subjected to 5 repeated intraperitoneal injections of the drugs during postpartum days 2-6. Injections of endothelin-1 to 21-day-old neonatal rats promoted activation of the nucleolus organizer regions by increasing the number and area of nucleoli and the number of DOT (optically dense regions corresponding to the number of silver grains determined visually). The area and protein content in cardiomyocytes also increased. Protein content in cardiomyocytes remained high in 45-day-old rats. Repeated injections of atrial natriuretic peptide-II to neonatal rats decreased the area of nucleoli in 21-day-old rats, but produced no significant changes in morphometric parameters of nucleoli and cardiomyocytes in 45-day-old rats. The number of nuclei expressing proliferating cell nuclear antigen (PCNA) did not change significantly after administration of endothelin-1 and atrial natriuretic peptide-II in both age groups. These data suggest on delayed opposite effects of the examined neuropeptides on heart morphogenesis.