Nitric oxide production and plasma cyclic guanosine monophosphate in premature infants with respiratory distress syndrome.

A low blood pressure is common in preterm infants with respiratory distress syndrome (RDS). A diminished vascular resistance appears to be an important cause. The endogenous production of nitric oxide (NO), a mediator of vascular smooth muscle relaxation, has been shown to be higher in infants with RDS than in those without. Infants with persistent pulmonary hypertension showed decreased endogenous NO levels as compared with controls. Severe RDS in preterm infants may be accompanied by persistent pulmonary hypertension. To elucidate the role of NO in RDS and low blood pressure, we determined the endogenous NO production in infants with and without RDS by measuring urinary nitrite and nitrate excretions and plasma cGMP levels. In consecutively admitted preterm infants (gestational age <32 weeks), urine samples for measurement of NO(2) and NO(3) and plasma samples for the determination of the cGMP concentrations were serially collected during the 1st week of life. Arterial blood pressure, therapy to support blood pressure, and additional relevant clinical data were registered simultaneously. 27 infants with and 39 without RDS were included. The urinary NO(x) levels increased in all patients and were not different between both groups. The plasma cGMP concentrations were higher in the RDS group on days 2, 3, 4, and 7 (p < 0.05). The severity of RDS was positively correlated with plasma cGMP (r = 0.50, p = 0.0001). Although the arterial blood pressure did not differ between the groups, more blood pressure support was needed in the RDS infants during the first 4 days (p < 0.05). A positive correlation was found between blood pressure support and plasma cGMP (r = 0.34, p < 0.0001). The endogenous NO production was not different in infants with and without RDS. Increased plasma cGMP levels in the RDS infants were associated with the severity of RDS and the intensity of antihypotensive treatment. The origin of cGMP in infants with RDS requires further research.