PREGNANCY-INDUCED CHANGES IN RABBIT MEDIAL COLLATERAL LIGAMENT VASOREGULATION

The ligaments of weight-bearing Joints are known to become mechanicall y inferior during pregnancy, and it has been postulated that this may be due to changes in tissue perfusion. Calcitonin gene-related peptide (CGRP) and epinephrine exert a tonic influence on the vasculature of the medial collateral ligament (MCL), and the present study examined w hether these vasoactive influences were altered by pregnancy. Ligament perfusion experiments were performed on primigravid New Zealand White rabbits with the use of laser Doppler perfusion imaging. In pregnant animals (day 29), MCL basal perfusion fell significantly compared with control; however, values returned to normal 5 days postpartum. In nor mal joints, topical application of CGRP resulted in a dose-dependent i ncrease in MCL perfusion, whereas epinephrine administration caused a dose-dependent fall in blood flow During pregnancy, the vasodilator ef fect of CGRP was completely abolished, whereas adrenergic vasoconstric tion was greater than normal. Both responses returned postpartum. Preg nancy in the rabbit produces hypoemia in the MCL, and this phenomenon may be effected by a tempering of CGRP dilator responses and an augmen tation of a-adrenoceptor-mediated vasoconstriction.