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Hypothermia (HYP) induces tachycardia, not bradycardia in free‐ranging (FR) rats
Author(s) -
DuBose D. A.,
Morehouse D. H.,
Rufolo D. M.,
Leon L. R.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1450-c
Subject(s) - bradycardia , hypothermia , tachycardia , heart rate , chemistry , zoology , sinus bradycardia , ventricular tachycardia , medicine , anesthesia , endocrinology , biology , blood pressure
Animal models of HYP employing anesthesia are characterized by bradycardia. This is in contrast to HYP in conscious humans in which tachycardia in conjunction with increased metabolism helps defend core temperature (T c ). This study determined if rats in the FR state reflected similar HYP‐related heart rate (HR) responses as noted in conscious humans. Two weeks post surgical implantation of radiotelemetry devices (Data Sciences; St. Paul MN) for T c and HR measurements, FR, male, Sprague‐Dawley rats (N=12; 249.4±5.7g) were exposed to cool/wet (CW; 5 cm, 10°C water; N=4), warm/wet (WW; 5 cm, 35°C water; N=4) or temperate/dry (TD; no water; 25°C air; N=4) conditions for 4h (values are means ± S.E.; analyzed by ANOVA with significance at p<0.05). Pre‐exposure 1h T c (37.4±0.01°C) and HR (336±1 bpm) were similar among conditions. The 4h exposure T c and HR for CW (33.4±1.4°C and 514±12 bpm) were significantly reduced or elevated, respectively compared to WW (37.7±1.1°C and 387±12 bpm) or TD (37.8±1.1°C and 381±12 bpm). WW and TD responses were similar. Comparison of early (0.5 to 1h) to late (3.5 to 4h) exposure time segments revealed a similar degree (%) in tachycardia abatement (CW=7.2±0.2%; WW=5.8±0.8%; TD=9.6±0.8%). Similar abatement relative to controls (WW and TD) suggested habituation to the novel exposure environment contributed to CW HR decreases. Thus unlike anesthetized animals, but similar to conscious humans, HYP in FR rats was associated with significant tachycardia that was generally sustained throughout the cold exposure. This demonstrated enhanced relevance to the human condition of the FR state in animal modeling of HYP. Research support MRMC