Gelsleichter James, Steinetz Bernard G, Manire Charles A, Ange Cristal
Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA.
Gen Comp Endocrinol. 2003 Jun 1;132(1):27-34. doi: 10.1016/s0016-6480(03)00030-3.
Relaxin is a 6-kd polypeptide hormone that is responsible for regulating several reproductive processes in female vertebrates, but its role in male reproduction remains unclear. To aid in clarifying this role, the objective of the present study was to investigate changes in endogenous relaxin levels associated with reproductive events in male elasmobranchs, which represent one of only three vertebrate groups known to possess this hormone. Serum relaxin concentrations were measured in 27 immature and 66 mature male bonnethead sharks (Sphyrna tiburo), a species with a well-characterized, seasonal reproductive cycle. Temporal changes in serum relaxin concentrations of immature male S. tiburo were not observed. In contrast, a temporal cycle in serum relaxin concentrations of mature male S. tiburo was observed in individuals from two sampling locations. Significant increases (P<0.05) in serum relaxin concentrations of mature male S. tiburo from both collection sites occurred during late spermatogenesis and the mating period, two critical stages of the reproductive cycle. The results from this study suggest that relaxin may play an important role in regulating semen quality, or other aspects of reproduction in male sharks. This is the first study to demonstrate a temporal pattern in endogenous serum Rlx concentrations associated with reproductive events in feral vertebrates. As such, it strengthens earlier hypotheses that suggested a role for this hormone in regulating male vertebrate fertility and copulatory success.
松弛素是一种6千道尔顿的多肽激素，负责调节雌性脊椎动物的多种生殖过程，但其在雄性生殖中的作用仍不清楚。为了有助于阐明这一作用，本研究的目的是调查与雄性板鳃亚类动物生殖事件相关的内源性松弛素水平变化，板鳃亚类动物是已知仅有的三个拥有这种激素的脊椎动物群体之一。对27条未成熟和66条成熟的窄头双髻鲨（Sphyrna tiburo）进行了血清松弛素浓度测量，该物种具有特征明确的季节性生殖周期。未观察到未成熟雄性窄头双髻鲨血清松弛素浓度的时间变化。相比之下，在两个采样地点的个体中观察到了成熟雄性窄头双髻鲨血清松弛素浓度的时间周期。来自两个采集地点的成熟雄性窄头双髻鲨在精子发生后期和交配期（生殖周期的两个关键阶段）血清松弛素浓度显著增加（P<0.05）。本研究结果表明，松弛素可能在调节雄性鲨鱼的精液质量或生殖的其他方面发挥重要作用。这是第一项证明与野生脊椎动物生殖事件相关的内源性血清松弛素浓度存在时间模式的研究。因此，它强化了早期的假设，即该激素在调节雄性脊椎动物的生育能力和交配成功率方面发挥作用。
