Timing of parturition in two species of viviparous lizard: influences of b-adrenergic stimulation and temperature upon uterine responses to arginine vasotocin (AVT)

The southern snow skink Niveoscincus microlepidotus is a viviparous alpine lizard with biennial reproduction, in which embryos are fully developed before winter but parturition is delayed until spring. We aimed to determine whether, in this species, in vitro uterine preparations are responsive to arginine vasotocin (AVT) and prostaglandin (PGF 2α) in autumn and spring, and whether pre-treatment with the β-adrenergic agonist isoproterenol decreases the effectiveness of AVT in stimulating uterine contractions. Using the spotted snow skink (Niveoscincus ocellatus), an annually breeding species, we aimed to determine influences of temperature and the β-adrenergic system upon the response to AVT in vivo. In both N. microlepidotus and N. ocellatus females are more responsive to AVT than to PGF 2α, and that the response to AVT is decreased, but not prevented, by β-adrenergic stimulation. In N. microlepidotus, uteri are equally responsive in both seasons to the hormones administered. In N. ocellatus environmental conditions, specifically, temperature, modulate the response to AVT in vivo with the time to parturition increasing as temperature decreases. We conclude that in these viviparous squamates the endocrine cascade leading to parturition is modulated by the β-adrenergic system, and that this may reflect the mechanism by which the timing of parturition is tied to suitable environmental conditions. © 2006 Springer-Verlag.