The Effects of Estrogen and Progesterone on Relaxation Rates in Rat Caudal Artery

Studies show that menopausal women are more at risk for heart problems, possibly due to diminishing production of reproductive hormones.  Heart problems arise from alteration in cardiovascular muscle functions. If these hormones upkeep cardiovascular health by altering protein functions that regulate smooth muscle and artery relaxation then we should note a difference in muscle output when hormone amounts differ. This project studies the effect of varying levels of naturally produced reproductive hormones on relaxation rates in rat caudal arteries. Retired breeding rats are used as models because of available literature and they are known to experience a peak and decline in natural progesterone and estrogen levels every four days.  Experiments were performed on tissue collected from rats during various phases of the cycle.  Changes in cell structure visualized on PAP smears were used to indicate hormone levels. Rat caudal artery, isometrically held, was electrically stimulated in muscle bath kept at physiological conditions. Arterial contraction and relaxation rates were recorded using data acquisition software. Relaxation curves matched a double exponential decay curve, and were analyzed by fitting results to an equation using JSIM modeling software. Comparing the faster relaxation rate constants, preliminary results show that from rats during the high progesterone days of the reproductive cycle, arteries consistently relaxed faster than those isolated from animals during the high estrogen cycle. These results have implications on the use of natural hormone replacement therapy as a preventative measure for a healthy heart. Experiments are being repeated for bigger sample size and statistical significance.