Hormonal responses following treatment with different prostaglandin analogues for estrous cycle regulation in cattle

The effect of four different prostaglandin F(2)alpha analogues on secretion of the pituitary hormones prolactin, LH, FSH and oxytocin was evaluated in heifers. In addition, the luteolytic activity was measured by means of progesterone concentrations. For the sake of comparison, the corpus luteum of two heifers was enucleated and the effect on the above hormones determined. There seemed to be no differences among the various analogues concerning their luteolytic action on the corpus luteum. No effect on FSH secretion was observed. Basal concentrations of LH increased about 4 - 5 h after injection of the analogues, concurrently with the decrease of progesterone. Enucleation of the corpus luteum was followed by a similar pattern of hormone secretion. Therefore, the increase in LH concentrations did not appear to be a specific effect of the analogues, but was probably a result of the decrease in progesterone concentration. Within twenty minutes after administration of the analogues a clear increase in plasma prolactin (2-4 h) and oxytocin concentrations (1-2 h) could be demonstrated.