RESUMEN
Dogs were allocated into three different groups of equal size. Group I was injected with atrial extract, group II was injected with phenylephrine [alpha 1 agonist] followed by atrial extract, while group III was injected with prazosin [alpha 1 antagonist] followed by atrial extract. The intravenous injection of atrial extract was coupled by a significant reduction in portal venous pressure in dogs whose portal venous pressure has not been altered as well as those which have been subjected to a pressure increase by the intravenous injection of phenylephrine or a decrease by the intravenous injection of prazocin. Moreover, atrial extract injection reduced significantly the serum sodium level in all groups without any effects on serum potassium level. It was concluded that, atrial extract has a hypotensive effect on portal venous pressure raising the possibility of using ANF as a new natural agent to reduce portal hypertension