Frequency-dependent contractile response of isolated cardiac trabeculae under hypo-, normo-, and hyperthermic conditions
| Autor: | Paul M.L. Janssen, Michelle M. Monasky, Nitisha Hiranandani, Kenneth D. Varian |
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| Rok vydání: | 2006 |
| Předmět: |
Male
Hyperthermia Agonist medicine.medical_specialty Fever Physiology medicine.drug_class Hypothermia β2 adrenergic receptor Adrenergic stimulation Physiology (medical) Internal medicine Isoprenaline medicine Animals Isoprenalina Chemistry Contractile response Isoproterenol Temperature Rats Inbred Strains Adrenergic beta-Agonists Thermoregulation medicine.disease Myocardial Contraction Rats Endocrinology Body Temperature Regulation medicine.drug |
| Zdroj: | Journal of Applied Physiology. 100:1727-1732 |
| ISSN: | 1522-1601 8750-7587 |
| Popis: | The body is from time to time exposed to nonnormothermic conditions; both hypo- and hyperthermia can occur as a result of external (environment) or internal (pathogens, allergens) stressors. To preserve life under hypo- and hyperthermic conditions, adequate perfusion of vital organs is mandated. Although cardiac output regulation under hyperthermic conditions has been studied, the mechanical response of basic contractile function of the myocardium itself is incompletely understood. Accordingly, we set out to test mechanical output of isolated myocardium under hyperthermic conditions and to compare the results with the hypo- and normothermic response in the same tissue. We observed that, in absence of a frequency change, developed force decreased markedly. At a physiological normal stimulation rate of 6 Hz, developed force decreases to 67.2 +/- 2.6% at 42 degrees C compared with 37 degrees C. In addition, twitch timing characteristics also accelerate, allowing for a faster relaxation; time from peak tension to 50% relaxation is approximately 23% faster (from 31.4 +/- 2.6 to 24.4 +/- 1.7 ms). Although this faster relaxation in turn prevents a steep increase in diastolic tension at high frequencies, the very fast calcium kinetics now prevent a more complete activation of the myofilaments, resulting in a lower twitch-force maximum at hyperthermic conditions. Even at maximal beta-adrenergic stimulation, developed force is well below levels reached at physiological temperature. |
| Databáze: | OpenAIRE |
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