Salt moderation is often recommended to prevent excessive increases in blood pressure during pregnancy, particularly in women who are prone to pregnancy-induced hypertension; however, the vascular effects of low dietary salt intake during pregnancy are unclear. We investigated whether a low-salt diet during pregnancy alters the mechanisms of vascular smooth muscle contraction. Active stress and ⁴⁵ Ca ²⁺ influx were measured in endothelium-denuded aortic strips of virgin and normal pregnant Sprague-Dawley rats and a hypertensive pregnant rat model produced by reduction in uterine perfusion pressure (RUPP), fed either a normal-sodium (NS, 1% NaCl) or low-sodium diet (LS, 0.2% NaCl) for 7 days. The mean arterial pressure was as follows: virgin/NS 108±8, virgin/LS 117±7, pregnant/NS 102±3, pregnant/LS 117±4, RUPP/NS 119±3, and RUPP/LS 133±6 mm Hg. Phenylephrine (Phe) caused concentration-dependent increases in active stress and ⁴⁵ Ca ²⁺ influx that were greater in RUPP rats than in normal pregnant or virgin rats and were enhanced in pregnant/LS and RUPP/LS compared with pregnant/NS and RUPP/NS, respectively. High KCl (16 to 96 mmol/L), which stimulates Ca ²⁺ entry from the extracellular space, also caused increases in active stress that were greater in RUPP than in normal pregnant, in pregnant/LS than in pregnant/NS, and in RUPP/LS than in RUPP/NS rats. The Phe-induced ⁴⁵ Ca ²⁺ influx–active stress relation was greater in RUPP/NS than in pregnant/NS and was enhanced in pregnant/LS and RUPP/LS compared with pregnant/NS and RUPP/NS, respectively. In Ca ²⁺ -free (2 mmol/L ethylene glycol bis(β-aminoethylether)-N,N,N′,N′-tetra-acetic acid) Krebs, stimulation of intracellular Ca ²⁺ release by Phe (10 ⁻⁵ mol/L) or caffeine (25 mmol/L) caused a transient contraction that was not significantly different in all groups of rats. Thus, a low-salt diet in pregnant and RUPP rats is associated with increases in vascular reactivity that involves Ca ²⁺ entry from the extracellular space but not Ca ²⁺ release from the intracellular stores. The enhancement of the Phe-induced Ca ²⁺ influx–active stress relation in pregnant and RUPP rats on a low-salt diet suggests activation of other vascular contraction mechanisms in addition to Ca ²⁺ entry. Although it is difficult to extrapolate the experimental data in rats to clinical data in women, the increased vascular reactivity and Ca ²⁺ entry and the possible enhancement of additional vascular contraction mechanisms with a low-salt diet suggest that reduction of dietary salt intake should be carefully monitored during pregnancy and pregnancy-induced hypertension.