Effect of L-arginine methyl ester (L-NAME) on hormonal profile and estrous cycle length in buffaloes (Bubalus bubalis).

The present study was undertaken to evaluate the effect of L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor on serum nitric oxide, progesterone, estradiol profiles and estrous cycle length in buffaloes. Murrah buffaloes (n = 16) exhibiting regular estrous cycles were randomly allocated to two groups of eight animals. In the treatment group, buffaloes were administered 400 mg/h L-NAME over 2 h (total dose = 800 mg) via the coccygeal artery and the aorta abdominalis on day 15 of the estrous cycle. In the control group, normal saline was infused on the same day of the cycle by the same route. Blood samples were collected every 4 h on days 15 and 16, and once daily from days 17 to 21 of the estrous cycle for the assay of progesterone, estradiol and nitric oxide. L-NAME treatment significantly (p < 0.05) reduced serum nitric oxide concentration from 4 h of day 15 until day 20 of the cycle. Serum progesterone concentration increased significantly (p < 0.05) between 0 and 20 h post treatment on day 15. The estrous cycle length was 19.8 ± 0.36 and 23.6 ± 0.17 days for control and treated group buffalo (p < 0.05), respectively. It was concluded that treatment of buffalo with L-NAME in the late luteal phase of the estrous cycle inhibited serum nitric oxide concentration resulting in increased progesterone production and extension of the effective life of the corpus luteum, thus prolonging the estrous cycle length.