Intraluteal administration of a nitric oxide synthase blocker stimulates progesterone and oxytocin secretion and prolongs the life span of the bovinecorpus luteum

To test the role of nitric oxide (NO) in secretory functions of bovine corp ora lutea (CL), two groups of four Holstein heifers each were treated as fo llows: Group 1, N omega-Nitro-L-Arginine Methyl Ester (L-NAME), an inhibito r of nitric oxide synthase (NOS), on Day 11 or 12 of the cycle and Group 2, L-NAME on Days 17 and 18 of the cycle. All treatments were administered by an intraluteal microdialysis system (MDS), Drugs were infused for 4-hr per iods on the designated days, and the treatment periods were preceded and fo llowed by 4-hr control periods. Perfusate and jugular blood samples were co llected at half-hour intervals. Perfusate samples were analyzed for progest erone (P4), oxytocin (OT), prostaglandin F-2 alpha (PGF(2 alpha)), and leuk otriene C-4 (LTC4); jugular plasma samples were analyzed for P-4, OT, and L H. Perfusion of L-NAME on Day 11 or 12 consistently increased P-4 concentra tion in the perfusate, but had no effect on the life span of the CL. Perfus ion of L-NAME on Days 17-18 also elevated P-4 levels in the perfusate, and in addition, maintained P-4 levels in the plasma of three of the four treat ed animals through Day 25 of the cycle. L-NAME perfusion also increased OT release concomitant with P-4 into the perfusate at both the mid- and late-l uteal phase treatments. For the most part, concentrations of LH, OT, and P- 4 in the jugular plasma samples collected during the perfusions were unaffe cted by treatments. L-NAME perfusion caused small, but significant (P < 0.0 5) increases in perfusate PGF(2 alpha) and LTC4 at Days 17 and 18 and in LT C4 on Day 11 or 12. These data indicate that NO plays a direct luteolytic r ole in regression of the bovine CL.