Seasonal changes in hematological and respiratory properties of muskrat (Ondatra zibethicus) blood

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Abstract
Hematological and respiratory properties of muskrat blood were measured in summer and in late winter. Field-acclimatized muskrats captured in Aug. and Feb. were compared with muskrats acclimated for 30-60 days in the laboratory during summer and also with Sprague-Dawley rats. Hematocrit, Hb, erythrocyte count and mean corpuscular Hb concentration were highest in winter-trapped animals. Estimated O2 capacity of muskrat blood increased from 17.2 vol.% in August, to 23.6 vol.% in February. Mean P50 [O2 tension of 50% saturating Hb] of whole blood at 37.degree. C and pH 7.4 was reduced from 29.0 mmHg in summer, to 23.3 mmHg in winter (1 mmHg = 133.322 Pa [pascal]). The P50 of acclimated muskrats (29.1 mmHg) averaged 23% below that of the laboratory rat (35.7 mmHg). Enhanced O2 affinity of muskrat blood in winter correlated with a reduction in mean 2,3-diphosphoglycerate concentration from 5.56 .mu.M/ml packed red cells (16.27 .mu.M/g Hb) in August, to 3.04 .mu.M/ml packed red cells (7.94 .mu.M/g Hb) in February. Hill plots for muskrat blood were highly linear over a saturation range of 10-90%, with n coefficients varying from 2.62-2.93. The Bohr effect (.DELTA.log P50/.DELTA.pH) increased slightly from -0.536 in acclimated and -0.573 in acclimatized muskrats in summer, to -0.626 in winter-acclimatized animals. Buffering capacity was evaluated by titrating whole blood with CO2 and regressing log PCO2 [CO2 tension] on blood pH. The buffer slope obtained for muskrat blood in February (-1.453) was marginally elevated compared with that in August (-1.328), and indistinguishable from that recorded in the laboratory rat (-1.449).