Norepinephrine sensitivity of mesenteric veins in pregnant rats

Abstract

This study was designed to test the hypothesis that during the course of pregnancy there is a decrease in the venous response to adrenergic stimulation that is characterized by a decrease in venoconstriction to both exogenous norepinephrine (NE) and to transmural electric stimulation of endogenous sympathetic nerves. Capacitance-size mesenteric veins were removed from nonpregnant and early- (7/8 day) and late-pregnant (18/19 and 20/21 day) Sprague-Dawley rats and studied in vitro under pressurized conditions. Lumen diameter was measured continuously by a video-electronic method. There was a marked increase in the sensitivity of the veins to exogenous NE stimulation at the end of pregnancy, which was most dramatic at a transmural pressure of 6 compared with 2 mmHg. The increase in exogenous NE sensitivity was associated with a progressive decline in the response to transmural nerve stimulation during pregnancy. Cocaine, an inhibitor of neuronal uptake, resulted in a greater potentiation of the response to transmural nerve stimulation in the pregnant rats compared to controls, suggesting an increased reuptake mechanism during pregnancy. Additional studies in the pseudopregnant, lactating, and nonlactating rat suggested that the conceptus was necessary for the alterations in neural response but not for the increase in exogenous NE sensitivity. In conclusion there is a dramatic change in venous function during pregnancy in the rat that is characterized by a difference between endogenous and exogenous NE sensitivity. The fact that transmural pressure can profoundly affect exogenous NE sensitivity suggests that pregnancy-induced changes in venous volume could contribute to changes in venous reactivity.

Mesenteric arterial function in the rat in pregnancy: role of sympathetic and sensory‐motor perivascular nerves, endothelium, smooth muscle, nitric oxide and prostaglandins

“…Supersensitivity to NA as a consequence of reduced sym--8 7 pathetic innervation could explain the relative lack of blunting of responses to exogenous NA in pregnancy, in contrast to the substantially reduced responses observed to other similarly efficacious vasoconstrictors (vasopressin and endothelin). Concurrent supersensitivity to exogenous NA and depression of contractile responses mediated by electrical stimulation of sympathetic nerves has previously been reported in isolated capacitance-size rat mesenteric veins in pregnancy (Hohmann et al, 1990). …”

Repeated pregnancies (multiparity) increases venous tone and reduces compliance

“…Focusing as we did on the splanchnic circulation, we found mesenteric venous reactivity to be higher and compliance lower in parous than in virgin rats. This suggests that, even long after pregnancy, the splanchnic venous circulation retains many of the characteristics acquired during pregnancy (18,20,21).…”

“…Part of the difficulty in evaluating these results arises from the fact that both the splanchnic and peripheral vascular beds contribute to whole body compliance and that the degree to which each contributes probably varies according to the experimental conditions (anesthesia, species). Whereas compliance of the limb veins increases during pregnancy (42), mesenteric venous reactivity increases and compliance decreases (18,20,21). This reflects the very different functional roles of these vascular beds, the splanchnic circulation being important not only in delivering blood to the tissues, but also in controlling blood distribution and cardiac preload (13,15,32).…”

Topical vasoconstrictor use for nasal intubation during pregnancy complicated by cardiomyopathy and preeclampsia

“…12 The venous sinuses of the nose are capable of significant engorgement during pregnancy. Agents used clinically for nasal vasoconstriction act on the arterial blood supply and venous plexuses, 13 and their predominant effect appears to be venoconstriction. The role of arterial versus venous vasoconstriction in epistaxis is unclear and the prevalence of epistaxis following topical vasoconstrictor use and nasal instrumentation during pregnancy is not known.…”