Heart and lung hypertrophy, changes in blood volume, hematocrit and plasma renin activity in rats chronically exposed to increasing carbon monoxide concentrations

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Abstract
Changes in blood volume, heart and lung mass and composition and plasma renin activity were examined in two strains of male albino rats inhaling incrementally-increasing concentrations of CO: 250 ppm for 17 days, 500 ppm for 13–14 days, 750 ppm for 10 days, and 1300 ppm for 10 days. Blood volume increased 86% and erythrocyte mass increased 212% at 1300 ppm, while plasma volume was unchanged or decreased slightly. “Real” hematocrit (hematocrit corrected for plasma trapping) increased from 50% in controls to a peak of 75% at 1300 ppm CO. Wet weight of right ventricle (RV) and combined right and left atria (2A) increased linearly with CO concentration, paralleling changes in blood volume; while real hematocrit increased nonlinearly. Left ventricle + interventricular septum (LV+S) wet weight increased less than RV, but more in Sprague-Dawley than in Wistar rats. Plots of RV, LV+S and 2A weight vs real hematocrit showed sharp upward inflections at real hematocrit 65%, suggesting a possible role of increased viscosity in CO cardiomegaly at the higher hematocrit. Assymetric septal hypertrophy was not present. Lung weight increased with CO concentration, but was not due to increased lung blood volume or edema. Hydroxyproline measurements on heart and lung failed to show increased collagen content. Plasma renin activity measured by radioimmunoassay was depressed at 500 ppm, but was normal at 750 and 1300 ppm CO. Neither heart, lung,liver nor plasma renin measurements suggest congestive heart failure, supporting previous studies in the rat with chronic carboxyhemoglobinemia, in spite of enormously increased blood volume, hematocrit and heart weight.