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This Article Full Text Full Text (PDF) All Versions of this Article: 287/1/R174    most recent 00710.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Ninomiya-Alarcón, J. G. Articles by Guevara-Guzmán, R. Search for Related Content PubMed PubMed Citation Articles by Ninomiya-Alarcón, J. G. Articles by Guevara-Guzmán, R.

DEVELOPMENT AND TISSUE PLASTICITY

Effect of photoperiod on the mechanical response of the pregnant rabbit uterus to oxytocin

¹Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, 04510; ²Departamento de Fisiología, Escuela de Medicina, Universidad Quetzalcóatl, Irapuato, Guanajuato, 36615; ³Departamento de Biología Celular y Fisiología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, 04510; and ⁴Departamento de Biología de la Reproducción, Universidad Autónoma Metropolitana-Iztapalapa, México 09340

Submitted 12 December 2003 ; accepted in final form 16 March 2004

We present findings suggesting that photoperiod is important in determining the sensitivity of the late-pregnant rabbit uterus to oxytocin (OT). Longitudinal myometrial strips were taken from term-pregnant and estrous rabbits and mounted in an organ bath for isometric myographic recording at different times during a 16:8-h light-dark cycle (lights on 0600–2200; n = 5/group), and the strength of contractions was registered in response to the application of OT or KCl. Strength of contractions was dose dependent and was up to 200 times greater at doses three to four orders of magnitude lower in tissue taken from pregnant animals during the light phase (0700 and 1300) than during the dark phase (2400 and 0400). Strips from nonpregnant estrous females also showed greater sensitivity and contractile force when taken in the light (0700) than in the dark (0400), although the differences were not significant. Consistent with the influence of photoperiod on uterine sensitivity to OT, strips taken from two groups of pregnant females (n = 5/group) maintained on a light-dark cycle advanced 12 h showed significantly greater sensitivity and force in response to OT during the new subjective light than during the new subjective dark phase. The photoperiod-dependent contractile response to OT was specific and not simply the result of a change in general mechanical properties of the muscle, because administration of KCl resulted in dose-dependent contractions of similar magnitude in both the light and dark phase. These results are consistent with the fact that rabbits, like other nocturnal mammals, typically give birth during the day.

parturition; electromyographic uterine recording; circadian rhythmicity