The cultured fetal mouse heart as a model for studying myocardial ischemic necrosis

A flow-independent model of anoxic injury employing the whole fetal mouse heart in organ culture was used to define the extent of ultrastructural damage and eventual necrosis resulting from hypoxia alone or hypoxia plus substrate depletion. In order to assess early ultrastructural damage fetal mouse hearts either received 1, 3 or 5 hr of hypoxia with or without substrate, following which the hearts were processed for electron microscopy. In order to assess extent of necrosis another group of hearts received 1, 3 or 5 hr of hypoxia with or without substrate followed by a recovery phase which consisted of 24 hr of reoxygenation with substrate. The percent of the fetal hearts which showed histologic necrosis was determined from 1 μm thick toluidine blue stained sections. Several ultrastructural changes were seen during the early phases of anoxic injury including nuclear chromatin clumping and margination, loss of glycogen, intracellular swelling and vacuolization which became progressively worse as the duration of hypoxia increased from 1 to 5 hr. In hearts submitted to substrate deprivation as well as hypoxia intracellular swelling was more severe with 3 to 5 hr of injury. In hearts which received 1 to 5 hr of hypoxia plus 24 hr of recovery well delineated areas of necrosis could be visualized. In hearts with 1 hr of hypoxia plus recovery 4 ± 2% of the myocardium was necrotic; with 3 hr of hypoxia plus recovery 15 ± 3% was necrotic, and with 5 hr of hypoxia plus recovery 52 ± 3% of the myocardium was necrotic. With the addition of substrate depletion hearts developed more necrosis at 3 hr (29±4%) and 5 hr (64 ± 4%) compared to exposure to hypoxia alone (P < 0.05).In conclusion, the fetal mouse heart is a flow-independent model which can be used to test the effects of hypoxia and substrate deprivation on the extent of myocardial damage; the duration of hypoxia is the major determinant of the extent of necrosis in this model while substrate depletion also increases damage.