Cytoplasmic fractions of rat myometrium. 2. Localization of some cellular constituents in the pregnant and ovariectomized states

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Abstract
Cytoplasmic fractions obtained by differential centrifuging were studied in the rat myometrium, both at the end of pregnancy and 3 weeks after ovariectomy. The general pattern of total nitrogen distribution was similar in the 2 states; the main changes were that after ovariectomy a smaller percentage of the total nitrogen occurred in the final supernatant and a higher percentage in the particle fractions. In the uterus at term succinic dehydrogenase was mainly found in the mitochondrial fraction (M). After ovariectomy the specific activity in M had fallen markedly whereas the specific activity in the microsomal fraction (P) was unchanged. The specific activity in the particles M and P taken together was lower than in pregnancy. The specific activity of Mg-adenosine triphosphatase (ATPase) was much higher after ovariectomy in fraction P. Both in pregnancy and after ovariectomy over half of the total ribonucleic acid (RNA) is centrifuged down with fraction N, the next richest fraction being P. It is probable that the high RNA content of fraction N is not due solely to incomplete cell breakage, but that some of it at least is intimately associated with a cell component sediment-able at low speed. After ovariectomy M and P both have lower RNA- P/N and lipid-P/N ratios than those found at the end of pregnancy. When compared on a cellular basis, RNA phospholipids, succinic de-hydrogenase, total nitrogen and Mg-ATPase all suffer a decrease after ovariectomy, the magnitude of this fall decreasing in the order given.