Effects of estrous synchronization on response to nitric oxide donors, nitric oxide synthase inhibitors, and endothelin-1 in vitro

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Two experiments were conducted to determine the effects of nitric oxide (NO) donors, endothelin-1 (ET-1), and NO synthase (NOS) inhibitors on bovine luteal function in vitro. In experiment 1, estrus in Brahman cows was synchronized with Synchro-Mate-B (SMB) and day-13–14 corpora luteal slices were weighed, diced and incubated in vitro. Treatments (100 ng/ml) were: vehicle, N ϖ-nitro- l-arginine- l-methyl ester ( l-NAME), N G -monomethyl- l-arginine acetate ( l-NMMA), diethylenetriamine (DETA), DETA-NONOate, sodium nitroprusside (SNP), or ET-1. In experiment 2, estrus was synchronized with Lutalyse, a Controlled Intravaginal Progesterone Releasing Device (CIDR), or cows were not synchronized. Corpora lutea were collected, weighed, and luteal slices were weighed, diced and incubated in vitro with treatments. Treatments (100 ng/ml) were: vehicle, l- NAME, l-NMMA, DETA, DETA-NONOate, sodium nitroprusside, S-nitroso- N-acetylpenicillamine (SNAP) or endothelin-1. Tissues were incubated in M-199 for 1 h without treatments and for 4 and 8 h in both experiments with treatments in both experiments. Media were analyzed for progesterone, prostaglandins E 2 and F 2α (PGE 2, PGF 2α) by radioimmunoassay (RIA). Hormone data in experiments 1 and 2 were analyzed by 2 × 7 and 3 × 2 × 8 factorial design for analysis of variance (ANOVA), respectively. Luteal weights in experiment 2 were analyzed by a one-way ANOVA. Concentrations of progesterone in media were similar ( P ≥ 0.05) among treatments within experiments. Concentrations of PGE 2 in media in experiment 1 were undetectable in 90 and 57% of the samples at 4 and 8 h, respectively. PGF 2α increased ( P ≤ 0.05) with time, but did not differ ( P ≥ 0.05) among treatments. Secretion of PGF 2α was not affected by treatments ( P ≥ 0.05). In experiment 2, luteal weights of the induced estrous cycle were decreased ( P ≤ 0.05) by Lutalyse. Concentrations of PGE 2 and PGF 2α increased ( P ≤ 0.05) with time in control of all three synchronization regimens. DETA-NONOate, SNAP, sodium nitroprusside (NO donors) and ET-1 increased ( P ≤ 0.05) PGE 2 except in the CIDR synchronized group ( P ≥ 0.05). No treatment increased ( P ≥ 0.05) PGF 2α in any synchronization regimen. It is concluded that either SMB containing norgestomet or a CIDR containing progesterone alters luteal secretion of PGE 2, Lutalyse lowers luteal weights in the induced estrous cycle, and NO or ET-1 given alone are not luteolytic agents. It is suggested that NO and ET-1 could have indirect antiluteolytic/luteotropic effects via increasing PGE 2 secretion by luteal tissue rather than being luteolytic.