Soluble oestrogen and progesterone receptors in the endometrium of the mare

Receptors for progesterone and oestrogen were measured in cytosol extracted from the endometrium of mares. Samples of endometrium were obtained from mares during the oestrous cycle and during other physiological and pathological states, and from mares with persistent endometritis. The concentration of binding sites was high around oestrus and early in dioestrus and was low by mid- to late dioestrus. Numbers of receptors were low in mares sampled on Day 15 of pregnancy and in mares in prolonged dioestrus, whereas receptor concentrations in ovariectomized mares were high. In 2 mares with endometritis, receptor concentrations were low in early dioestrus, which was markedly different from mares with a normal reproductive tract. The results of this study indicate that ovarian steroids may play a role in regulating concentrations of soluble endometrial receptors in the mare.