The effects of prolonged exposure to cold on hypoxic pulmonary hypertension in rats

Pulmonary artery hypertension is a common occurrence in mammals exposed to high altitude, yet little is known about the response of cold-acclimated animals. To study this problem pulmonary arterial pressure (Ppa), systemic blood pressure (Psa) and the ratio of Ppa/Psa in cold-acclimated rats (CA, 8 weeks, 6 °C, n = 11) during exposure to low oxygen (10% O₂) were measured by direct catheter methods and compared with those of controls raised at 22 °C (C, n = 10). There was no difference between CA and C in values of Ppa at a normal oxygen level (20.9% O₂). When rats were exposed to 10% O₂ Ppa increased significantly in C, while the increase in CA was not significant. The weights of the total ventricle (TV), right ventricle (RV) and left ventricle (LV) in the CA animals were increased significantly above the C values. The ratio of RV weight (RVW) to LV weight (LVW), however, was higher in C than in CA. During exposure to low oxygen, Psa did not change between the two groups. The ratio of Ppa/Psa was increased significantly in both groups when exposed to hypoxia. There were no significant differences in hematological measurements, including hematocrit (Ht), blood viscosity (CP) and red blood cells (RBC) between the CA and the C. It was concluded that the animals exposed to cold over a long period had no right ventricular hypertrophy (RVH) and the response to hypoxia in Ppa was lower in CA than that in C. The depression in hypoxic pulmonary vasoconstriction in CA may be caused by the decrease of RVW/LVW.