Control of the mare's oestrous cycle by prostaglandins.

Several authors have recently demonstrated the luteolytic action of exogenous prostaglandin F2\g=a\(PGF2\g=a\)in various laboratory and domestic animals and there is now ample evidence that PGF2\g=a\is the uterine luteolytic hormone which terminates the life of the CL in many species (McCracken, 1972; McCracken, Carlson, Glew, Goding, Baird, Gr\l=e'\en & Samuelsson, 1972). In cattle, Rowson, Tervit & Brand (1972) showed that an intrauterine (i/u) infusion of PGF2\g=a\on 2 successive days at any time between the 5th and 16th day of the cycle, induces oestrus 3 days later; they found that for 0\m=.\5mg PGF2\g=a\to be strongly luteolytic in the cow, the substance must be placed in the uterine horn which is ipsilateral to the ovary containing the active CL. This observation is in accordance with the experiments of Moor & Rowson (1966), Harrison, Heap & Linzell (1968) and others, which have indicated that in the sheep, cow and pig, uterine luteolysin passes directly from the uterine horn to the adjacent ovary by way of a local pathway. In the mare, however, unilateral hysterectomy prolongs the life-span of the CL in some animals but not in others, and the proportion in which luteal maintenance