Role of LH and prostaglandin F2alpha on the development and regression of corpus luteum in mithun (Bos frontalis) estrous cycle.

The present investigation was designed to study the role of LH and prostaglandin F2alpha (PGF2alpha) on the development and regression of corpus luteum (CL) in the mithun estrous cycle. Blood samples were collected from jugular vein and PGF2alpha secretion was evaluated on the basis of peripheral 15-keto-13,14-dihydro-PGF2alpha (PGFM) concentration. The daily variations in plasma LH, PGFM, and progesterone (P4) concentrations throughout the estrous cycle were monitored in morning and evening blood samples. The variations in plasma LH, PGFM, and P4 concentrations during the early luteal phase were monitored in blood samples that were collected every 2 h until 120 h following the onset of estrus (Day 0). The pulsatile secretion patterns of plasma LH, PGFM and P4 during estrus (Day 1), mid-diestrus (Day 10), and luteolysis (Day 14) were assessed in blood samples that were collected every 15 min for 6h. In the estrous cycle, P4 concentration increased above basal level on day 6-7, peaked on day 10-12 and declined thereafter. Following estrus, a significant (P<0.01) gradual increase in P4 concentration was observed. LH concentration was found to be significantly (P<0.01) greater around estrus and it declined gradually (P<0.01) following estrus. In the estrous cycle, PGFM concentration increased above basal level on day 9-11, peaked on day 16-17, and declined thereafter. The frequency of LH pulses and basal LH concentration were found to be significantly (P<0.01) greater on day 1, but significantly (P<0.01) greater amplitude of LH pulses was found on day 10 and 14. The frequency of P4 and PGFM pulses was found to be significantly (P<0.01) greater on day 1. In contrast, the amplitude of P4 and PGFM pulses and basal P4 and PGFM concentrations were found to be significantly (P<0.01) greater on day 10 and 14. The results indicate that probably the early stages of CL development continued until day 5-6 of the estrous cycle and a fully functional CL existed approximately at the mid estrous cycle. Luteolysis probably started since day 11-13 of the cycle and completed before the onset of the next estrus. The elevated basal LH concentration along with frequent low amplitude LH pulses were probably required for the early stages of CL development. In contrast, the high amplitude LH pulses of lower frequency during the mid estrous cycle were either sufficient or not required for maintaining the luteal function. Whereas, PGF2alpha pulses of greater amplitude and elevated basal PGF2alpha concentration during the mid and late estrous cycle were probably responsible for luteolysis.