LUTEINIZING-HORMONE HAS A ROLE IN DEVELOPMENT OF FULLY FUNCTIONAL CORPORA-LUTEA (CL) BUT IS NOT REQUIRED TO MAINTAIN CL FUNCTION IN HEIFERS

We tested the hypothesis that endogenous pulses of LH have a role in d evelopment and maintenance of CL during the estrous cycle of the bovin e female. Twenty heifers were synchronized to estrus by treating two t imes with prostaglandin F-2 alpha 11 days apart (Day 0 = behavioral es trus). Heifers were then randomly assigned to one of four treatments ( n = 5/group). Heifers were treated with an antagonist to LHRH (LHRH-An t; ,4Cl-D-Phe(2),D-Pal[3](3),D-Cit(6),D-Ala(10)-LHRH; 10 mu g/kg body weight) or vehicle (5% mannitol) once every 24 h: 1)LHRH-Ant Days 2-7, 2) LHRH-Ant Days 7-12, 3) LHRH-Ant Days 12-17, 4) no LHRH-Ant (contro l). Blood samples were collected from the jugular vein twice daily on Days 0-24, and area under the profile of progesterone in circulation d uring the luteal phase of the estrous cycle was characterized from the start of each treatment period until the demise of CL or Day 24, whic hever came first. Luteolysis was considered to have occurred when thre e consecutive samples contained less than 1 ng progesterone/ml plasma. Areas under the profile of progesterone in circulation during the lut eal phase of the estrous cycle were compared to those of heifers from the control group for the same period. LHRH-Ant treatment diminished L H pulses in all treatment groups compared to control (p < 0.05). Treat ment with LHRH-Ant on Days 2-7 diminished function of CL (3.72 +/- 0.9 3 vs. 7.36 +/- 1.02 units, respectively; p < 0.05). Heifers treated wi th LHRH-Ant on Days 7-12 also had reduced function of CL (3.02 +/- 0.3 3 vs. 6.75 +/- 0.99 units, respectively; p < 0.01). However, treatment with LHRH-Ant on Days 12-17 did not influence function of CL (3.97 +/ - 1.02 vs. 4.27 +/- 0.80 units, respectively; p > 0.10). The data supp ort our hypothesis that endogenous pulses of LH have a role in develop ment and maintenance of CL during the estrous cycle of bovine females.