Age and reproductive status affect basal venous tone in the rat.

Objective: Changes in venous tone alter vessel diameter and capacitance of veins. These alterations may be induced by the steroid hormonal milieu. Therefore, our question was whether venous tone differs between estrous cycle, pregnancy and old rats.

Study Design: Mesenteric veins from young, pregnant and old Sprague-Dawley rats were dissected and cannulated in a venograph system with a continous readout of pressure-dependent lumen diameter.

Results: During estrous cycle venous tone was increased in metestrous (P < 0.05), whereas it was decreased in all old rats (P < 0.05). There was higher venous tone in pregnant animals compared to controls (P < 0.05).

Conclusions: Venous tone exhibits marked differences during rat estrous cycle. It is increased during pregnancy and decreased in old rats.