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.