FLOW DECREASES MYOGENIC REACTIVITY OF MESENTERIC-ARTERIES FROM PREGNANT RATS

OBJECTIVE: To determine whether pregnancy alters the response of small mesenteric arteries to increased pressure (myogenic reactivity) and f low. METHODS: Mesenteric arteries (300 mu m) from cycling nonpregnant (NP, n = 6) and late pregnant (20 days, LP, n = 6) Sprague-Dawley rats were dissected and mounted on an arteriograph system designed for the precise measurement of pressure and flow. Myogenic reactivity was mea sured as the percentage constriction after a pressure increase to 75 m mHg in the absence and presence of flow (60 mu L/minute). RESULTS: In the absence of flow, there was no difference in myogenic reactivity in arteries from NP versus LP animals (NP, 8.4 +/- 1.4%; LP, 11.0 +/- 1. 6%; not significant). In the presence of flow, myogenic reactivity was decreased in arteries from LP rats, but was unchanged in arteries fro m NP rats (NP, 13.2 +/- 1.1%; LP, 2.5 +/- 2.9%; P < .05). The differen tial group effect appeared to result not from differences in arterial response to changes in pressure or flow alone, but rather from the int eraction between pressure and flow. CONCLUSION: These results suggest that pregnancy alters the interaction of the physical forces of pressu re and flow on the arterial wall in a manner consistent with decreased vascular resistance. Copyright (C) 1997 by the Society for Gynecologi c Investigation.