The effect of sodium based hypo-osmolality on arterial smooth muscle reactivity in vitro

Abstract

The study tested the hypothesis that the reduced [Na+]e and hypo-osmolality of normal pregnancy are causally linked to the attenuation of vascular smooth muscle reactivity in vitro. Aortic rings from nonpregnant female rats were incubated in physiological medium containing 114 mM NaCl/l and the contractile responses to phenylephrine, KCl and CaCl2 as well as the relaxations to acetylcholine and KCl were compared with those of rings incubated in normal medium containing 119 mM NaCl/l. There was no solute substituted for the lowered [Na+]. Experiments with phenylephrine were repeated using de-endothelialized rings and intact rings pretreated with indomethacin. Contractile responses of intact rings (n = 11) in hypo-osmolar solution to phenylephrine were significantly (P < 0.001) lower than of those in normal medium (n = 11). Responses were partially restored by endothelial denudation but not in the presence of indomethacin. Relaxations to acetylcholine (n = 7 for hypo-osmolar; n = 6 for normal solution) and KCl (n = 7 for each of hypo- and normal osmolar) were significantly enhanced (P < 0.05) in rings incubated in hypo-osmolar solution. There was no significant difference between the responses of the rings to KCl, and CaCl2 in either solution. These effects are similar to some of those previously described for vascular smooth muscle in normal pregnancy suggesting that the reduced [Na+]e and hypo-osmolarity of normal pregnancy may be contributing to the diminished vascular reactivity.

Glucose dilates renal afferent arterioles via glucose transporter-1

“…Thus, in the present study, we determined the vasodilatory effect of increased glucose concentration in isolated and perfused mouse Af-Arts with preconstriction, and our results demonstrated that an increase in glucose level dilated Af-Art. Additionally, because the osmolality could affect vascular reactivity (20,65), L-glucose, the enantiomer of D-glucose, was used to balance the osmolality as control. Our results demonstrated that same concentration of L-glucose had no significant effect on the diameter of Af-Art, which indicates that the high glucoseinduced vasodilation of Af-Art was independent of the alteration in osmolality.…”

Hypotonic swelling stimulates L-type Ca2+ channel activity in vascular smooth muscle cells through PKC

“…Hypotonicity of the extracellular environment occurs in several situations including reduced extracellular Na ϩ concentration seen in normal pregnancy (11), overhydration following intense exercise (1,12), and treatment with citalopram (15). Other hyposmotic states are found in situations involving deficits in plasma proteins secondary to hepatic dysfunction and nutritional deficits.…”

The Hypo-Osmolality of Pregnancy Does Not Alter Baroreceptor Responses to Acute Changes in Osmolality

“…Similar to the in vitro findings reported by Thoren, we showed in vivo that baroreceptor discharge in anesthetized pregnant rats increased in the initial minute of a step pressure increase but appeared to adapt or decay more rapidly in pregnant compared with virgin rats during the 10-min exposure to a step pressure stimulus (Hines, 2000). Hyponatremia has also been shown to decrease vascular responsiveness to pressor agents in aortic rings from female rats, suggesting that hypoosmolality could decrease baroreceptor discharge through effects on vessel wall distension during increases in pressure as well as via direct effects on cell discharge (Ezimokhai & Osman, 1998).…”