ULTRASTRUCTURE OF MITOCHONDRIA IN ATRIAL MUSCLE ASSOCIATED WITH DEPRESSION AND SUPERSENSITIVITY PRODUCED BY RESERPINE

¹ Department of Zoology, University of Melbourne, Melbourne, Australia

Sections of right atrium were studied by electron microscopy after pretreatment of guinea pigs with various doses and schedules of reserpine. A large dose of reserpine. 5 mg/kg, produced marked alterations in the mitochondria, including the development of aberrant shapes, breakdown of cristae and the deposit of lipid-like material. Many mitochondria appeared to be in advanced stages of degeneration. The changes were minimal six hours after reserpine but were very marked at periods of 12, 18 and 24 hours after reserpine. This is a dose which has been shown previously to cause depression of the maximal rate which guinea-pig atria can attain. In contrast, neither one dose nor seven daily doses of reserpine, 0.1 mg/kg, produced any detectable differences in mitochondria as compared to controls. This dose has been shown previously to cause maximal depletion of myocardial norepinephrine and, in seven daily doses, to produce a nonspecific supersensitivity of the heart without depressing its maximal response. It thus appears that mitochondrial damage is associated with excessive amounts of reserpine. larger than those required to deplete catecholamine stores and to produce supersensitivity.