Oxytocin-specific RNA, oxytocin and progesterone concentrations in corpora lutea of heifers treated with oxytocin.

Sixteen virgin Holstein heifers were used to study the role of oxytocin in luteal function. Oxytocin (100 i.u.) was administered on Days 2-5 (Exp. 1) or Days 2-6 (Exp. 2), and the corpora lutea were collected and weighed on Day 6 or Day 8, respectively. Plasma progesterone values and tissue concentrations of progesterone and oxytocin were determined by radioimmunoassay. In addition, the tissue level of the oxytocin-specific transcript was measured by dot-blot hybridization. Expression of the oxytocin-specific transcript was not affected by oxytocin treatment in either experiment. In contrast, plasma progesterone values and tissue progesterone and oxytocin concentrations were all decreased after 5 days of oxytocin treatment (Exp. 2), but not after 4 days (Exp. 1). Since oxytocin concentrations were reduced while the level of its transcript remained unaffected, oxytocin injections might be influencing either peptide processing or release.