RELEASE OF PROSTAGLANDIN F-2\g=a\DURING FOALING IN MARES

Summary. The concentrations of PGF-2\g=a\in the peripheral blood of five foaling mares were measured by radioimmunoassay. Low levels of PGF-2\g=a\were detected as early as 1 week before foaling in two of the mares. These levels increased steadily, reaching a peak (1\m=.\74\m=+-\0\m=.\44 ng/ml) during fetal expulsion. A relatively high PGF-2\g=a\level was found in samples collected 60 min after foaling. Prostaglandins have only recently been implicated in the process of parturition. Increased concentrations of prostaglandin F-2a before and during parturition in women (Karim, 1968; Guttierrez-Cernosek et al, 1972), and sheep (Liggins & Grieves, 1971; Thorburn et al, 1972) have been reported. This paper de¬ scribes the circulating levels of PGF-2a in the peripheral blood of mares at the time of foaling. Five healthy light-grade mares, weighing approximately 450 kg and insemi¬ nated by two normal fertile stallions, were used. All mares were palpated rec-tally for the presence of a conceptus 45 days after mating. The expected foalin