Objective: To determine whether pregnancy alters the response of small mesenteric arteries to increased pressure (myogenic reactivity) and flow.
Methods: Mesenteric arteries (300 μm) 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 measured as the percentage constriction after a pressure increase to 75 mmHg in the absence and presence of flow (60 μL/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 from NP rats (NP, 13.2 ± 1.1%; LP, 2.5 ± 2.9%; P < .05). The differential group effect appeared to result not from differences in arterial response to changes in pressure or flow alone, but rather from the interaction between pressure and flow.
Conclusion: These results suggest that pregnancy alters the interaction of the physical forces of pressure and flow on the arterial wall in a manner consistent with decreased vascular resistance.
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