Electron microscopy of the adrenal medulla of the newborn dog under hypothermia and asphyxia.

The left adrenal medullas of 20 (5 litters of 4) day-old dogs were studied with the electron microscope. The right adrenal medullas of the same animals had been examined by fluorescence microscopy and the results reported previously. In each litter one animal served as a coenothermic (37 degrees C) and one a hypothermic control (15 degrees C). The third animal (at 37 degrees C) was asphyxiated until twice its time of last gasp (about 32 min) and the fourth was cooled to 15 degrees C and asphyxiated for the same length of time as the third animal. The induction of hypothermia (to 15 degrees C) in unanesthetized puppies results in a decrease (32%) in dense-cored granules, an enlargement of mitochondria, and slight dilation of the endoplasmic reticulum. In coenothermic puppies asphyxiation to twice the time of last gasp is accompanied by the following changes: loss of dense-cored granules (52%); swelling of nuclei; clumping and marginal aggregation of nuclear chromatin material; dilation of the endoplasmic reticulum; swelling, loss of cristae and rarefaction of the matrices of mitochondria. The changes in some cells were greater than others. Many of these changes are considered to demonstrate anoxic damage. Under the conditions of the present experiments, hypothermia protected most of the adrenal medullary cells from anoxic damage.