Abstract

We examined the direct effects of toxaphene and endrin, chlorinated insecticides that are widespread in the environment, on myometrial contractions and on the secretion of hormones involved in regulating these contractions. Granulosa, luteal, endometrial and myometrial cells, and myometrial strips from non-pregnant cows were incubated with both insecticides at environmentally relevant doses.

Toxaphene inhibited and endrin stimulated the secretion of testosterone and oestradiol from granulosa cells. Toxaphene also inhibited and endrin stimulated the expression of the mRNA encoding the precursor of oxytocin (OT), as well OT secretion in luteal cell cultures. Moreover, endrin increased OT secretion from granulosa cells. Neither insecticide exerted an effect on progesterone secretion from luteal cells. Only toxaphene decreased the secretion of prostaglandins (PGF2 and PGE2) from endometrial cells. Meanwhile, only endrin decreased basal myometrial contractions, which was accompanied by inhibition of PGF2 secretion from the myometrium. Both endrin and toxaphene also decreased the force of the OT-stimulated myometrial contractions, whereas only toxaphene inhibited the stimulatory effect of OT on the force of myometrial contractions.

In contrast to endrin, toxaphene decreased synthesis and secretion of one of the primary stimulators of myometrial contractions (OT) and indirectly inhibited OT signal reception in the myometrium by reducing E2 secretion. Both insecticides decreased OT-stimulated myometrial contractions; therefore, they may inhibit further transmission of the OT signal. Moreover, endrin inhibited basal myometrial contractions, potentially resulting from reduced PGF2 secretion from the myometrium. Our data indicate the potential of these insecticides to disturb the course of the oestrous cycle or fertilisation.