Physiology, Endocrinology, and Reproduction

Broilers (B, 19 d old; 507 ± 40 g BW) and Leghorns (L, 63 d old, 861 ± 87 g BW) had surgical pulmonary artery occlusion (B–PAO and L–PAO; n = 12 each) or were sham–operated (B–SHAM and L–SHAM; n = 12 each). Birds had free access to a commercial broiler feed (NRC, 1994). Medial thickness (%, Thick) was determined in 2 sizes of resistance pulmonary arteries (RPA): ≤ 100 μm (small diameter, SD) and 101–200 μm (medium diameter, MD). %Thick (average medial thickness/average diameter*100) was determined in RPA from 6 histological sections from the paleopulmo, one section per chicken, at one d presurgery, and at 7 and 14 d postsurgery. Data was analyzed using One-Way ANOVA. At presurgery, %Thick of SD RPA was similar in L-chickens and in B-chickens (17.5 ± 1.1% vs 15.8 ± 1.4%). Seven d postsurgery, B-PAO SD RPA (21.1 ± 1%) were thicker than the B-SHAM (18.8 ± 0.9%), L-PAO (16.6 ± 1.0%) and L-SHAM (17.2 ± 0.9%); with no differences among the last 3 groups. Fourteen d post-surgery, B-PAO SD RPAs (21.6 ± 0.7%) were thicker than the B-SHAM (20.1 ± 0.07%). In tun, the B-SHAM SD RPAs were thicker than both, the L-SHAM (17.4 ± 0.8%) and the L-PAO (17.6 ± 0.8%), with no differences between the 2 Leghorn groups. %Thick of MD RPA was larger in B–chickens than in L–chickens (16.5 ± 0.7% vs 14.0 ± 0.7%) at presurgery. Seven d postsurgery, the B-SHAM MD RPA (17.1 ± 0.9%) were the thickest, but with no differences among the remaining 3 groups (14.3 ± 1.3%, 13.9 ± 0.9%, 14.4 ± 1.1% for the B-PAO, L-PAO and L-SHAM, respectively). At d 14 postsurgery, the B-PAO MD PRA (18.0 ± 0.7%) were thicker than the L-PAO (14.8 ± 1.0%); but not different than those of the B-SHAM (16.7 ± 0.7%) or L-SHAM birds (15.9 ± 0.8%). Results show that doubling the cardiac output through one lung in Leghorns does not cause RPA remodeling. In broilers %Thick increased with PAO and age. Presumably, Leghorn chickens avoided high pulmonary artery resistance to blood flow by increased vasodilation.