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Am J Physiol Regul Integr Comp Physiol (March 24, 2005). doi:10.1152/ajpregu.00034.2005
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Submitted on January 18, 2005
Accepted on March 1, 2005

Repeated pregnancies (multiparity) increases venous tone and reduces compliance

Vivek Dhawan1, Zoe L. S Brookes2, and Susan Kaufman1*

1 Physiology, University of Alberta, Edmonton, Alberta, Canada
2 Division of Clinical Sciences (South), Section of Surgical and Anaesthetic Sciences, University of Sheffield, Sheffield, United Kingdom

* To whom correspondence should be addressed. E-mail: susan.jacobs{at}ualberta.ca.

In humans, multiparity (repeated pregnancy) is associated with increased risk of cardiovascular disease. In rats, multiparity increases the pressor response to phenylephrine and to acute stress, due in part to changes in tone of the splanchnic arterial vasculature. Given that the venous system also changes during pregnancy, we studied the effects of multiparity on venous tone and compliance. Cardiovascular responses to volume loading (2mL/100g BWt), and mean circulatory filling pressure (MCFP, an index of venomotor tone) were measured in conscious, repeatedly bred (RB) and age-matched virgin rats. In addition, passive compliance and venous reactivity of isolated mesenteric veins were measured by pressure myography. There was a greater increase in mean arterial pressure after volume loading in RB rats (+7.2±2.5 mmHg, n=8) than virgins (-1.4±1.7 mmHg, n=7) (p<0.05). The increase in MCFP in response to noradrenaline (NA) was also greater in RB rats (ED50: 3.09±0.48 nmol/kg/min, n=6) than virgins (ED50: 12.6±2.66 nmol/kg/min, n=6) (p<0.05). Pressure-induced changes in passive diameter were lower in isolated mesenteric veins from RB rats (29.3±1.84 µm/mmHg, n=6) than from virgins (38.9±2.15 µm/mmHg, n=7) (p<0.05). Venous reactivity to NA in isolated veins was also greater in RB rats (EC50: 2.68 ±0.37x10-8 M, n=5) than virgins (EC50: 4.67±0.93x10-8 M, n=8). We conclude that repeated pregnancy induces a long-term reduction in splanchnic venous compliance, and augments splanchnic venous reactivity and sympathetic tonic control of total body venous tone. This compromises the ability of the capacitance (venous) system to accommodate volume overloads and to buffer changes in cardiac preload.




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[Abstract] [Full Text] [PDF]




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