Abstract
The influence of hypertonic agents on 64 isolated hypoxic cat papillary muscles was examined under isometric conditions in Krebs-Ringer bicarbonate solution with 18 mM glucose at 29°C. Nine papillary muscles pretreated before hypoxia and eight muscles exposed to hypertonic mannitol 6 min following hypoxia demonstrated a significantly reduced decline from prehypoxia control values for developed tension and its first derivative compared to the same muscles in the control solution. There was no significant change in resting tension. This improvement in muscle performance during hypoxia was present at osmolalities of 60 mOsm above control values. The performance of papillary muscles during hypoxia was similar for hypertonic mannitol, sucrose, and urea when the muscles were exposed to the agents for 30 min before hypoxia. However, longer periods (2 hours) of exposure to hypertonic mannitol or urea before hypoxia resulted in a reduced decline in developed tension and its first derivative during hypoxia only in the case of mannitol. These studies suggest that the beneficial effect of hyperosmolar agents on muscle performance during hypoxia may not be totally dependent on blood flow changes and may be associated with changes in cell size.
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