Variations in the mechanical behavior of the rabbit cervix with endocrine state and anatomic site.

The mechanical test of stress-strain and stress-relaxation were done on excised cervical strips from New Zealand rabbits in estrus, less than 10 hours after luteinizing hormone (LH), 10 to 18 hours after LH, 18 to 50 hours after LH, 30 days pregnant, and castrate. The stretch moduli obtained from these tests indicated that a significant softening of the cervix occurred at 10 to 18 hours after LH and during pregnancy. Normally, the internal os is stiffer than the external os, but this difference disappears at 30 days of pregnancy, and both values are lower and identical. The changes in the stretch modulus are not thought to be due to smooth muscle, particularly in the external os, because of the low contractility of this tissue. The conclusion reached is that the rabbit cervix is a good model to use in the investigation of the mechanical behavior of the cervix and may be comparable to the human cervix in physiologic responses.