Delayed luteolysis after intra-uterine infusions of nordihydroguaiaretic acid in the ewe.
Intrauterine administration of nordihydroguaiaretic acid (5 mg, bid. NDGA), an inhibitor of the enzyme 5-lipoxygenase, on days 10-14 of the oestrous cycle, maintained luteal function and delayed oestrus in the ewe. The duration (mean +/- SD) of the oestrous cycle in the treatment group (n = 4) was 24 +/- 1 days, which was significantly (P < 0.001) longer than that of 16 +/- 1 days in vehicle-treated controls (n = 4); plasma progesterone concentrations were also significantly (P < 0.01) higher in the treatment group. On days 13 and 14 of the cycle (oestrus = Day 0) in the control group large pulses of 13,14-dihydro-15-keto prostaglandin F2alpha (PGFM) were evident, with mean (+/- SD) maximum concentrations of 232.5 +/- 66 and 415 +/- 309 pg ml(-1), respectively. In the treatment group, however, concentrations of PGFM were below detection level (< 50 pg ml(-1)). Similarly, in the control group, oxytocin release was highly pulsatile, with mean (+/- SD) peak concentrations of 21.8 +/- 5 and 18.5 +/- 6 pg ml(-1) on days 13 and 14, respectively; these were significantly (P < 0.01) higher than values of 7.6 +/- 3 and 6.1 +/- 3 pg ml(-1) in NDGA-treated ewes, where pulses were of relatively low amplitude. These results suggest that 5-lipoxygenase products of arachidonic acid metabolism may be involved in the positive feedback mechanism between luteal oxytocin and uterine PGF2alpha during luteolysis in the ewe.
Department of Veterinary Preclinical Sciences, University of Liverpool, South Wirral, Cheshire, UK. cooker@liv.ac.uk
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RG
Cooke
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Ahmad
D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects* / Q000502:physiology*; D015237:Dinoprost / Q000031:analogs & derivatives / Q000378:metabolism; D004971:Estrus; D005260:Female; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology*; D009637:Masoprocol / Q000008:administration & dosage / Q000494:pharmacology*; D010121:Oxytocin / Q000378:metabolism; D010507:Periodicity; D011374:Progesterone / Q000097:blood; D012756:Sheep / Q000502:physiology*; D014599:Uterus / Q000187:drug effects*
D016859:Lipoxygenase Inhibitors; C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D011374:Progesterone; D010121:Oxytocin; D009637:Masoprocol; D015237:Dinoprost