The Effect of Indomethacin on Ovarian Prostaglandin Release in Hens1

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Abstract
Indometbacin, an inhibitor of prostaglandin (PG) syntbetase, will block uterine muscle electromyographic activity (EMG activity) and oviposition at a midsequence oviposition and ovulation in domestic hens, but does not block the increase in EMG activity associated with the first ovulation of a sequence. To assess the potential relationship between prostaglandin release from the ovarian follicles and EMG activity in egg-laying hens, we determined the concentrations of PGF2α, 13,14-dibydro-15-keto-PGF2α (PGFM), and PGE2 in brachial, ovarian follicular and uterine venous plasma and tissues in relation to uterine muscle EMG activity at the first ovulation and at a midsequence oviposition. The concentrations were measured after an i.m. injection (25 mg/ben) of indometbacin. In control hens sampled hourly, beginning 4 h before the peak of EMG activity at the first ovulation of a sequence, there was a sharp increase (p2α and PGFM in brachial vein plasma coincident with the increase (p2α and PGFM levels (p2α in the venous effluent from the largest preovulatory follicle at the first ovulation (36.0 ± 9.9 ng/ml vs. 14.4 ± 1.8 ng/ml). At midsequence oviposition, indometbacin treatment decreased (p2α and PGFM and blocked the rise in venous plasma concentrations of PGF2α from the largest preovulatory follicle (9.5 ± 3.8 ng/ml in control hens to 0.4 ± 0.2 ng/ml in treated hens, p 2α concentration in the venous effluent from the largest preovulatory follicle before the first ovulation of the sequence compared to a midsequence oviposition and ovulation (14.4 ± 1.8 ng/ml vs. 0.4 ± 0.2 ng/ml, p<0.0001). It is concluded that indometbacin does not block uterine EMG activity at the first ovulation of a sequence because it does not completely block prostaglandin release from the largest ovarian follicle. These results may suggest that follicular prostaglandin production is related to follicular maturation in hens.