Hematology in developing guinea pigs—II chronic exposure to 5°C

Abstract

1. 1. Weanling male guinea pigs were exposed for up to 18 weeks in environmental chambers to 5°C and an ambient P o 2 of 133 torr before sacrifice (range of BW at 5° C = 239−1,074 g). Growth rates of animals raised at 5°C were not significantly different from animals maintained at 22°C. Hematological measurements were made on each animal, including hematocrit, [Hb], RBC indices, WBC differentials, and the molar ratio of 2,3-diphosphoglycerate (2,3-DPG) to Hb. 2. 2. Cold exposure results in significant ( P < 0.001) increases of 6–12% in Hct and [Hb], due to greater No. RBC's, compared to controls of similar BW. Within 2 weeks of exposure to 5°C, the 2,3-DPG/Hb ratio rose transiently to 1.84 M/M, and then was constant at about 1.40 M/M in animals exposed to 5°C for longer times. When compared to values for adult controls of 0.92 M/M, such an increase in the 2,3-DPG/Hb ratio would increase the P 50 of blood from cold acclimated guinea pigs by 5–6 torr. 3. 3. The significant increases over control values in circulating [Hb] and in 2,3-DPG would substantially improve tissue O 2 delivery in cold acclimated guinea pigs, by facilitating the transport and unloading of O 2.