| Abstract: | Pregnant rabbits were treated with indomethacin (8-10 mg/kh/day) or dexamethasone (1-2-1-8 mg/kh/day) during late gestation. The effects of these treatments on the concentrations of progesterone and prostaglandin F (PGF) in the peripheral plasma, and the outcome of gestation was studied. Treatment with indomethacin significantly prolonged the length of gestation (P smaller than 0-01) compared iwth control, untreated animals. In these treated animals, the plasma progesterone levels declined at a similar time to that in control rabbits but the increase in systemic PGF normally seen during late pregnancy was reduced. Dexamethasone treatemnt reliably induced premature delivery within 3-6 days. The plasma progesterone concentration fell rapidly during the first 24 h of dexamethasone administration, but in no animal was this associated with a significant increase in the plasma levels of PGF. These results are consistent with the suggestion that prostaglandins are involved in the normal initiation of parturition in the rabbit. They do not support the hypothesis that the effect of dexamethasone on the length of gestation is mediated through an increase in the production of prostaglandin F. |
