Different tolerance to hypothermia and rewarming of isolated rat and guinea pig hearts

We examined the effect of hypothermia and rewarming on myocardial function and calcium control in Langendorff-perfused hearts from rat and guinea pig. Both rat and guinea pig hearts demonstrated a rise in myocardial calcium ( [Ca](total)) in response to hypothermic perfusion (40 min, 10 degrees C), w hich was accompanied by an increase in left ventricular end diastolic press ure (LVEDP). The elevation in [Ca](total) was severalfold higher in guinea pig than in rat hearts, reaching 12.9 +/- 0.8 and 3.1 +/- 0.6 mu mol.g dry wt(-1), respectively. The rise in LVEDP, however, was comparable in the two species: 62.5 +/- 2.5 (guinea pig) and 52.5 +/- 5.1 mm Hg (rat). Following rewarming, [Ca](total) remained elevated in guinea pig, whereas a moderate decline in [Ca](total) was observed in the rat (13.6 +/- 1.9 and 2.2 +/- 0 .3 mu mol.g dry wt(-1), respectively). Posthypothermic values of LVEDP were also significantly higher in guinea pig compared to rat hearts (42.5 +/- 6 .8 vs 20.5 +/- 5.1 mm Hg, P < 0.027). Furthermore, whereas rat hearts demon strated a 78 +/- 7% recovery of left ventricular developed pressure, there was only a 15 +/- 7% recovery in guinea pig hearts. Measurements of tissue levels of high energy phosphates and glycogen utilization indicated a highe r metabolic requirement in guinea pig than in rat hearts in order to oppose the hypothermia-induced calcium load. Thus, we conclude that isolated guin ea pig hearts are more sensitive to a hypothermic insult than rat hearts. ( C) 1999 Academic Press.