The ultrastructure of the parathyroid glands (PIG) of magnesium (Mg)-treated golden hamsters exposed to centrifugation at 1.2 G for 7 days was compared to that of the control, Mg-treated or centrifuged groups. In the PTG of the Mg-treated group exposed to centrifugation, the Golgi apparatus increased compared with that of the Mg-treated group, but was similar to that of the control and centrifuged groups. The cisternae of the rough endoplasmic reticulum (rER) increased compared with that of the

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... Mg-treated group and decreased compared with that of the centrifuged group, but was the same as that of the control group. There were no significant differences among the 4 groups with regard to lysosomes, large vacuolar bodies, lipid droplets and secretory granules. These observations suggest that the rER is sensitive to centrifugation compared with the Golgi apparatus and more importantly the inhibitive effect of Mg on the synthesis of the hamster parathyroid hormone is enfeebled by centrifugation at 1.2 G.