MYOGENIC RESPONSE IN LARGE PULMONARY-ARTERIES AND ITS ONTOGENY

To evaluate the myogenic response and its ontogeny in large pulmonary arteries, we studied 45 newborn and 30 adult guinea pigs. Compared wit h the those of the adult, the newborn arterial vessels possessed a sig nificantly (p < 0.01) smaller diameter (1153 +/- 34 versus 1656 +/- 65 mu m), static compliance (2.2 +/- 0.3 versus 4.6 +/- 0.7 mu m/mN), an d active stress (3.4 +/- 0.4 versus 5.8 +/- 0.7 mN/mm(2)). Stretch-ind uced contraction was obtained by quick stretch of the vessel segments to 120, 140, 160, 180, or 200% of their optimal length, and the myogen ic response was measured as the change in force after muscle relaxatio n with papaverine. A myogenic response was observed in 94% of the newb orn and 93% of adult vessel segments, and significant age differences in the response were present. The magnitude of the active force genera ted for any stretch over 120% was significantly greater in the newborn (p < 0.01), and as a percentage of K+ (127 mM) stimulation, a 2-fold stretch of the vessels' optimal length resulted in a force of 1073 +/- 159% in the newborn compared with 51 +/- 16% in the adult (p < 0.01). The myogenic response in these large pulmonary vessels was completely suppressed by a calcium channel blocker (D-600) but unaltered by addi tion of a nitric oxide synthase inhibitor (N-G-methyl-L-arginine) or i ndomethacin. We conclude that the large pulmonary arterial vessels of the guinea pig exhibit a powerful stretch-induced myogenic response th at is greater in the newborn period. Changes in vessel wall stiffness brought about by the myogenic response of large pulmonary arteries may play a role in the control of lung vascular resistance.