Association of circulating angiotensin converting enzyme activity with respiratory muscle function in infants

BACKGROUND: Angiotensin converting enzyme (ACE) gene contains a polymorphism, consisting of either the presence (I) or absence (D) of a 287 base pair fragment. Deletion (D) is associated with increased circulating ACE (cACE) activity. It has been suggested that the D-allele of ACE genotype is associated with power-oriented performance and that cACE activity is correlated with muscle strength. Respiratory muscle function may be similarly influenced. Respiratory muscle strength in infants can be assessed specifically by measurement of the maximum inspiratory pressure during crying (Pi(max)). Pressure-time index of the respiratory muscles (PTImus) is a non-invasive method, which assesses the load to capacity ratio of the respiratory muscles. The objective of this study was to determine whether increased cACE activity in infants could be related to greater respiratory muscle strength and to investigate the potential association of cACE with PTImus measurements as well as the association of ACE genotypes with cACE activity and respiratory muscle strength in this population. METHODS: Serum ACE activity was assayed by using a UV-kinetic method. ACE genotyping was performed by polymerase chain reaction amplification, using DNA from peripheral blood. PTImus was calculated as (Pi(mean)/Pi(max)) × (Ti/Ttot), where Pi(mean )was the mean inspiratory pressure estimated from airway pressure, generated 100 milliseconds after an occlusion (P(0.1)), Pi(max )was the maximum inspiratory pressure and Ti/Ttot was the ratio of the inspiratory time to the total respiratory cycle time. Pi(max )was the largest pressure generated during brief airway occlusions performed at the end of a spontaneous crying effort. RESULTS: A hundred and ten infants were studied. Infants with D/D genotype had significantly higher serum ACE activity than infants with I/I or I/D genotypes. cACE activity was significantly related to Pi(max )and inversely related to PTImus. No association between ACE genotypes and Pdi(max )measurements was found. CONCLUSIONS: These results suggest that a relation in cACE activity and respiratory muscle function may exist in infants. In addition, an association between ACE genotypes and cACE activity, but not respiratory muscle strength, was demonstrated.