Sorbera L A, Callard I P
Department of Biology, Boston University, Massachusetts 02215, USA.
Am J Physiol. 1995 Aug;269(2 Pt 2):R389-97. doi: 10.1152/ajpregu.1995.269.2.R389.
The phylogenetic age of endocrine control of viviparous reproduction in vertebrates may be estimated by examination of elasmobranch models. We have shown in pregnant Squalus acanthias that Squalus relaxin (sRLX) significantly decreased the frequency of myometrial contractions in a dose-dependent reversible manner in vitro and in vivo, without altering the intensity or duration of contractions. In contrast, neurointermediate lobe extract provoked a marked and reversible enhancement of the duration and intensity of contractions but was ineffective in altering the frequency of contractions. In steroid-primed animals, untreated and estradiol-17 beta (E2)-treated animals exhibited a decrease in the frequency of activity after injection of sRLX in vivo while pretreatment with progesterone (P4) alone or in combination with E2 fully suppressed the effects of sRLX. These results suggest that homologous sRLX slows the frequency of spontaneous uterine contractions in third-trimester sharks (stage C) in which endogenous P4 is reduced and E2 levels are rising. These data demonstrate the physiological importance of these hormones and the antiquity of reproductive tract control mechanisms.
通过对板鳃亚纲动物模型的研究，可以估计脊椎动物中内分泌对胎生繁殖控制的系统发育年龄。我们在怀孕的棘鲨中发现，棘鲨松弛素（sRLX）在体外和体内均以剂量依赖性可逆方式显著降低子宫肌层收缩频率，且不改变收缩强度或持续时间。相比之下，神经中间叶提取物可引起收缩持续时间和强度的显著且可逆增强，但对改变收缩频率无效。在经类固醇预处理的动物中，未处理动物和经17β-雌二醇（E2）处理的动物在体内注射sRLX后活动频率降低，而单独使用孕酮（P4）或与E2联合预处理可完全抑制sRLX的作用。这些结果表明，同源的sRLX可降低妊娠晚期鲨鱼（C期）自发性子宫收缩的频率，此时内源性P4减少而E2水平升高。这些数据证明了这些激素的生理重要性以及生殖道控制机制的古老性。
