The concentration of prostaglandin F (PGF) has been measured in the peripheral plasma of normal rhesus monkeys (Macaca mulatta) during the final third of gestation, and in monkeys treated with dexamethasone or PGF2α after day 145 of pregnancy. Daily administration of PGF2α (10-15 mg/day im) reliably induced abortion within 3-6 days. However, dexamethasone (8 mg/day im from day 145) had no effect on the length of gestation. The concentration of PGF in the femoral venous plasma of untreated or dexamethasone-treated monkeys was highly variable, both in serial samples taken from the same animal and in samples taken from different animals at the same time of gestation. There was no indication of an effect of dexamethasone treatment on the plasma PGF levels, nor did the concentration of PGF increase during late pregnancy before spontaneous parturition. These results show that the myometrium of the pregnant rhesus monkey is highly sensitive to exogenous PGF2α during late gestation. However, a significant increase in the peripheral plasma concentration of PGF prior to the onset of labor was not observed.
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