Effect of β-adrenergic stimulation on uterine contraction in response to arginine vasotocin and prostaglandin F(2α) in the gecko Hoplodactylus maculatus

Abstract

The effects of β-adrenergic stimulation on uterine contractions occurring in response to arginine vasotocin (AVT) and prostaglandin F(2α) (PGF(2α)) were compared during late pregnancy in the s gecko Hoplodactylus maculatus. High doses of AVT (150 or 1500 ng/g body weight) induced birth in vivo, but PGF(2α) at doses of up to 2000 ng/g did not induce birth. The effect of AVT (150 ng/g) on birth rate in vivo was not enhanced by pretreatment 20 min before hand with the β-adrenoreceptor antagoinst dichloroisoproterenol (2 μg/g), whereas the effect of PGF(2α) (200 ng/g) was markedly enhanced: geckos treated with dichloroisoproterenol and then with PGF(2α) showed rapid birth-related behavior and gave birth. Isolated uteri showed a tonic contraction in response to AVT (100 ng/ml) and to PGF(2α) (1000 ng/ml). Pre-exposure of isolated uteri to the β-adrenoreceptor agonist isoproterenol (1 μg/ml) caused relaxation; this pre-exposure did not block the tonic contraction occurring in response to AVT, whereas it completely blocked the tonic contraction induced by PGF(2α). We conclude that in H. maculatus, β-adrenergic stimulation inhibits uterine contractions induced by PGF(2α) but not those induced by AVT. These data are the first to show that β-adrenergic stimulation inhibits uterotonic responses to PGF(2α) in a reptile, and they suggest that the cellular mechanisms by which AVT and PGF(2α) induce contraction may differ in this species. They also provide further evidence for similarities between mammals and reptiles in the effects of β-adrenergic stimulation on uterine relaxation.