Influence of prostaglandins and nitric oxide on pulmonary vascular resistance during hypothermia in the isolated dog lung

We examined whether nitric oxide (NO) or prostaglandins modulate the effects of hypothermia on vascular resistance in the isolated dog lung. Right lower lung lobes were removed, ventilated and perfused with autologous blood at a constant flow (8.32±0.03 ml/min/g lobe weight) and a venous pressure of 4 cmH₂O After stabilization at 37°C, hypothermia was induced by cooling the blood perfusing the lobe to 23, 19, and 13°C At each temperature, lobar vascular resistance was partitioned into vascular segments using arterial, venous, and double occlusion techniques. Lobes were studied under control conditions (n=5), after inhibition of NO synthesis with 2 mM N^G-nitro-L-arginine methyl ester (L-NAME) (n=5), and after cyclooxygenase inhibition (COI) with 45 μM meclofenamate (n=4). Hypothermia increased total resistance as well as resistance in all segments (P<0 05). L-NAME did not alter any responses from control levels, while COI increased total resistance as well as resistance in large arteries and large veins when compared to control values (P<0.05) Our results suggest that vasodilator prostaglandins are more important than NO in modulating the increase in vascular resistance to hypothermia in the dog lung.