Immunohistochemical Localization of Prolactin Receptors Within the Equine Ovary

Prolactin receptors (PRLr) were detected in anestrous (n=3), winter cycling (n=2), follicular (n=3) and luteal phase (n=3) equine ovaries by IHC. Follicle stages evaluated were primordial, preantral and antral. Receptors were detected in all follicle stages and in CL. PRLr staining was not different (P \u3e 0.05) between primordial and preantral, but was greater (P \u3c 0.001) in antral follicles. Primordial follicles stained weakest in anestrous and follicular phase ovaries, followed by luteal phase ovaries and was most intense in winter cycling. Staining in preantral follicles was weakest in anestrus, followed by follicular phase and highest in winter cycling and luteal phase. Staining was most intense in antral follicles with no difference (P \u3e 0.05) between any of the reproductive states. Oocytes and ovulation fossa also possessed PRLr. In conclusion, concentrations of PRLr are highest in large, antral follicles suggesting a mechanistic role for PRL around the time of ovulation