Effects of relaxin and insulin on reproductive tract size and early fetal loss in Squalus acanthias.

These experiments demonstrate that both porcine relaxin and bovine insulin can increase the cervical cross-sectional area in Squalus acanthias. When given after estradiol priming, the magnitude of this response is greater. This effect is limited to Stage C females in which pregnancy is over 75% complete. The overall result is premature loss of developing fetuses. The effect of relaxin or insulin on cervical cross-sectional area and fetal loss is unrelated to an effect on blood sugar. Cervical weights are affected little by hormone treatment. Relaxin and insulin do not increase the cross-sectional area of the anterior uterine constriction. These results suggest the involvement of a relaxin-like molecule during normal parturition in the spiny dogfish.