In vitro comparison of myometrial contractility induced by aglepristone-oxytocin and aglepristone-PGF2alpha combinations at different stages of the estrus cycle in the bitch

Aug 17, 2010Theriogenology

Laboratory study of uterus muscle contractions caused by aglepristone combined with oxytocin or PGF2alpha at different stages of the dog’s heat cycle

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Abstract

Oxytocin and PGF2α induced concentration-dependent contractions in myometrial fibers from 33 bitches.

Both oxytocin and PGF2α activated myometrial contractions in longitudinal and circular fibers, indicating functional receptors for these hormones.
The contractile response to oxytocin was consistently greater in longitudinal fibers compared to circular fibers across all groups.
In anestrus non-treated bitches and metestrus treated bitches, PGF2α also elicited a stronger contraction in longitudinal fibers than circular fibers.
Agilepristone treatment significantly enhanced the contractile response to oxytocin and PGF2α in longitudinal fibers during metestrus.
Differences in receptor sensitivity or distribution may exist in the myometrial layers, independent of hormonal status.

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The aim of this in vitro study was to compare the uterokinetic activity of oxytocin and dinoprost, the natural PGF2α, with or without aglepristone, in canine myometrial fibers. Thirty-three bitches were allocated into one of four groups, depending on their estrous stage and whether or not they had received a treatment with aglepristone (metestrus aglepristone, n = 5; metestrus without treatment, n = 9; anestrus aglepristone, n = 9; anestrus without treatment, n = 10). After hysterectomy, longitudinal and circular uterine strips were mounted in organ baths. Oxytocin or PGF2α (10 nmol/l to 10 micromol/l) were applied non-cumulatively. A linear mixed effects models theory was used to compare the fiber effect, the aglepristone effect, and the treatment effect, from the area under the curves calculated from the contractile effect/concentration curves for each drug. Oxytocin and PGF2α induced concentration-dependent myometrial contractions in longitudinal (LF) and circular myometrial fibers (CF), indicating the presence of functional contractile oxytocin- and PGF2α-receptors in metestrus and anestrus. The contractile response to oxytocin was greater in LF than in CF in all of the groups; the response to PGF2α was greater in LF than in CF in non-treated bitches in anestrus and in treated bitches in metestrus. These results suggest that there is a difference in sensitivity or a heterogeneous distribution of oxytocin and PGF2α-receptors in the myometrial layers, which is independent of hormonal impregnation. The contractile response to oxytocin and PGF2α was significantly increased after aglepristone treatment in LF during metestrus, suggesting that the progesterone withdrawal induced by aglepristone has a role to play. The longitudinal myometrial layer also appeared to be the target for the two drugs at this stage. This study provides new information about canine uterine contractile activity, notably the differing behavior of myometrial CF and LF; in vivo studies are required to test the use of a combination of aglepristone and oxytocin in the treatment of canine pyometra.

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In vitro comparison of myometrial contractility induced by aglepristone-oxytocin and aglepristone-PGF2alpha combinations at different stages of the estrus cycle in the bitch

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