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Samples of rat blood infected with Plasmodium yoelii (3% parasitized erythrocytes), Trypanosoma gambiense, or Trypanosoma equiperdum (greater than 50 trypanosomes per microscope field at 400 X) were fixed with 0.5% glutaraldehyde in phosphate buffered saline, then stained with acridine orange (AO) at 10(-4), 10(-5), or 10(-6) M for 0 to 15 min at 5 C or 25 C and/or ethidium bromide (EB) at 0.05 mg/ml for 20 min at 25 C. Stained cells were analyzed with a laser Cytofluorograf (Bio/Physics Systems, Inc.) to determine if parasites could be detected and differentiated from blood cells by their fluorescent characteristics. Samples of uninfected rat blood with and without leukocytes and P. yoelii-infected blood without leukocytes were treated similarly. In addition, suspensions of T. gambiense and T. equiperdum without all blood cells were stained with AO or EB and analyzed with the Cytofluorograf, as were mixed suspensions of both trypanosome species. EB- but not AO-stained P. yoelii-infected erythrocytes had fluorescent characteristics different from most blood cells. Neither AO- nor EB-stained T. gambiense or T. equiperdum could be differentiated from host blood cells or from each other. The results are discussed with respect to the use of laser flow systems in the detection and analysis of bloodstream dwelling protozoan parasites.

Unidirectional active and passive fluxes of 42K and 24Na were measured in red blood cells of ground squirrels (hibernators) and guinea pigs (nonhibernators). As temperature is lowered, "active" (ouabain-sensitive) K influx and Na efflux were more greatly diminished in guinea pig cells than in those of ground squirrels. The fraction of total K influx which is ouabain sensitive in red blood cells of ground squirrels was virtually constant at all temperatures, whereas it decreased abruptly in guinea pig cells as temperature was lowered. All the passive fluxes (i.e., Na influx, K efflux, and ouabain-insensitive K influx and Na efflux) decreased logarithmically with decrease in temperature in both species, but in ground squirrels the temperature dependence (Q10 2.5–3.0) was greater than in guinea pig (Q10 1.6–1.9). Thus, red blood cells of ground squirrel are able to resist loss of K and gain of Na at low temperature both because of relatively greater Na-K transport (than in cells of nonhibernators) and because of reduced passive leakage of ions.

The overall objective of these studies was to test the hypothesis that the suppression of erythropoiesis, which occurs during both spaceflight and bedrest, was mediated by reduction in circulating levels of erythropoietin. In each of two 7-day studies, groups of subjects were exposed to either horizontal or 6 degrees head-down tilt bedrest and no evidence was obtained to suggest that the erythropoietic effects were dependent on the angle of recumbency. An additional study involved six men who were exposed to horizontal bedrest for 28 days. Serum erythropoietin titers were not significantly depressed in any of the subjects but total red cell volume was decreased. Absolute increases in red cell numbers and reductions in plasma volume both elevate the haematocrit, but our data suggest that the mechanism of erythrosuppression in these two instances may be different.