Objectives: To evaluate the course of nitrite and nitrate blood concentrations in lambs as indicator for endogenous nitric oxide (NO) production in relation to age and to the presence of a large left to right shunt through a patent ductus arteriosus which was maintained by repeated angioplasty.

Methods: In 12 lambs, nitrite and nitrate serum concentrations were determined on day 1, during the third week as well as after 2 to 5 months of life. Blood samples were taken during heart catheterisation from the right ventricle and from the descending aorta. In 6 lambs there was a significant left to right shunt (Qp/Qs>2.5) at the time of the third intervention.

Results: On the first day of life, arterial plasma concentrations of nitrite and nitrate were significantly different from venous concentrations(p<0,05). Plasma concentrations of nitrite and nitrate decreased significantly in all lambs from the first day of life on up to the third week(p<0,005) and further up to the age of 2 to 5 months (p<0,05). There was no significant difference in nitrite and nitrate concentrations between lambs with and without PDA in nitrite and nitrate concentrations.

Conclusion: Our results imply a decline of endogenous NO production in lambs during the first months of life. The transpulmonary gradient on the first day of life suggests that the lung as a significant source of endogenous NO at this time. A PDA does not seem to be an no additional stimulus for endogenous NO-production in lambs.