Effect of environmental pollutants on oxytocin synthesis and secretion from corpus luteum and on contractions of uterus from pregnant cows

Jul 17, 2010Toxicology and applied pharmacology

Environmental pollutants may affect oxytocin production in the pregnancy hormone gland and uterine contractions in pregnant cows

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Abstract

Xenobiotics increased oxytocin secretion and decreased the progesterone to oxytocin ratio during early pregnancy.

Chloro-organic compounds are associated with changes in reproductive processes in cows.
All xenobiotics except hexachlorocyclohexane increased the expression of oxytocin synthesis-related genes during pregnancy.
DDE specifically stimulated progesterone secretion, while others primarily affected oxytocin levels.
The ratio of progesterone to oxytocin in the culture medium decreased due to all tested xenobiotics.
Myometrial contractions were enhanced when exposed to xenobiotics in combination with progesterone.

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Chloro-organic compounds are persistent environmental pollutants and affect many reproductive processes. Oxytocin (OT) synthesized in luteal cells is a local regulator of ovarian activity and uterine contractions. Therefore the effect of xenobiotics on the OT prohormone synthesis, secretion of OT and progesterone (P4) from luteal cells and on myometrial contractions during early pregnancy in cows was investigated. Luteal cells and myometrial strips from a cow at early pregnancy were treated with polychlorinated biphenyl 77 (PCB 77), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE) and hexachlorocyclohexane (HCH) (1 or 10 ng/ml). The mRNA expression of neurophysin-I/oxytocin (NP-I/OT) and peptidyl-glycine-alpha-amidating mono-oxygenase (PGA) and concentration of OT and P4 were determined by RT-PCR and EIA, respectively. Moreover, the effect of xenobiotics given with P4 (12 ng/ml) on the basal and OT (10(-7)M) stimulated contractions of myometrial strips was studied. Xenobiotics increased (P<0.05) OT secretion but DDE only stimulated P4 secretion. The ratio of P4 to OT in culture medium was decreased by all xenobiotics during 9-12 weeks of pregnancy. All xenobiotics, except HCH, increased (P<0.05) mRNA expression of NP-I/OT during all stages of pregnancy and all treatments decreased (P<0.05) expression of mRNA for PGA during 9-12 weeks of pregnancy. Myometrial strips were relaxed (P<0.01) after pre-incubation with P4, while each of the xenobiotics jointly with P4 increased (P<0.01) myometrial contractions. In conclusion, the xenobiotics used increased both expression of mRNA for genes involved in OT synthesis and secretion of OT from luteal cells. This decreases the ratio of P4 to OT and presumably, in this manner, the chloro-organic compounds can influence uterine contractions and enhance risk of abortions in pregnant females.

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Effect of environmental pollutants on oxytocin synthesis and secretion from corpus luteum and on contractions of uterus from pregnant cows

Abstract

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