Figure 1.
Body temperature dependent platelet count of functional platelets during torpor and arousal in natural hibernating Syrian hamster at 5°C ambient temperature.
A) During spontaneous entrance into torpor body temperature gradually declines from 35°C to 8°C in a matter of hours. B) Increase in body temperature during a spontaneous arousal, demonstrating the rapid increase to euthermic level. Line represents one of thirty-one Syrian hamsters, measured with an intraperitoneal implanted Thermochron iButton. C) Normal platelet count in summer-euthermic Syrian hamster (n = 5, open dots; n = 7, black dots). D) Platelet count decreases with lower body temperature from euthermic stage to deep torpor in the Syrian hamster (n = 31), both during natural hibernation as well as during forced hypothermia (n = 8, multiple sampling). Curves from D) and E) are fitted to a polynomial quadratic curve with equation y = y0+ax+bx2 and constraints of y0>0 and y0≤ lowest platelet count for torpor. Black dots (•) are natural hibernating hamsters, open dots (°) are forced-cooled hamsters. E) Platelet number increases rapidly to a normal level during arousal (n = 42) or rewarming from forced hypothermia (n = 7, multiple sampling). F) P-selectin positive platelets are absent in torpid hamsters. G) The platelets are activatible following addition of ADP and the subsequent percentage of P-selectin positive platelets is similar to euthermic and aroused animals. H) The P-selectin expression level per platelet was significantly decreased in non-activated platelets from torpor compared to euthermia and arousal hamsters. I) Upon activation with ADP, P-selectin expression reaches similar levels in euthermia (eu), torpor (trp) and arousal (arsl). Please note that F-I are n = 2 per group. J) Circulating platelet count is reduced during daily torpor in the Djungarian hamster, and restored upon arousal. Bars represent mean ± SEM of 5 to 9 animals per group. *P<0.05, **P<0.01.
Figure 2.
Decreased platelet count with preserved function during forced hypothermia.
A) Rats forced to hypothermia of 15°C have a decreased amount of platelets, which partially restores during rewarming. B) No difference in amount of activatable platelets from anestethized euthermic, cooled or rewarmed rats. C) Unchanged P-selectin expression at all time points in both non-activated and activated whole blood samples. D) Unchanged aggregometry at all time points upon addition of ADP. E) Mathematical approach for velocity and max amplitude of platelet aggregation. ν, velocity of aggregation; Δ%, change in percentage light transmission; Δt, timespan over which velocity is determined; MA, maximum aggregation in % light transmission. F) Mice forced to hypothermia of 20°C have a decreased amount of platelets, which partially restores during rewarming. Panels G) and H) show unchanged platelet P-selectin expression between time points in non-activated and activated whole blood samples. Bars represent mean ± SEM of 7 to 27 rats per group and 3 to 9 mice per group. *P<0.05, **P<0.01.
Table 1.
Aggregation of platelets from forced-cooled rats.
Figure 3.
Pharmacologically induced torpor by 5′-AMP does not decrease platelet count despite decreased body temperature.
A) Pharmacologically induced torpor by 5′-AMP in mice does not decrease platelet count during torpor and shows an increase upon arousal. Body temperature drops during torpor and restores during arousal. B) Leukocyte level decreases with falling body temperature. C) The correlation of decreased body temperature and reduced platelet count is prominent in deep hibernating hamster (n = 31), daily hibernating hamster (n = 15), forced-cooled hamster (n = 8, multiple sampling), forced-cooled rat (n = 25), and forced-cooled mouse (n = 15), but absent in 5′-AMP induced torpor in mice (n = 10). Bars represent mean ± SEM of 5 to 6 animals per group. *P<0.05, **P<0.01.
Figure 4.
Restoration of circulating platelet numbers during arousal and rewarming does not originate from spleen or bone marrow.
A) Immature platelet fraction (IPF) is increased in torpor, but decreases in arousal toward normal euthermic percentage in Syrian hamster. B) In rat, IPF decreases during cooling and rewarming. C) In mice IPF only increases during arousal. D) Splenectomy prior to hibernation does not inhibit induction of thrombocytopenia in torpor. E) Splenectomy during torpor does not prevent restoration of platelet count during the subsequent arousal. Bars represent mean ± SEM of 4 to 12 animals per group. *P<0.05, **P<0.01.