During pregnancy, endothelium-derived vasodilatation is enhanced in the rat aorta (Bobadilla et al. 1997; Dantas et al. 1999). Impairment of endothelium-dependent relaxation in the vasculature may lead to increased vascular resistance and thus possible complications in pregnancy. Dietary protein restriction in pregnant rats attenuates endothelium-dependent relaxation in small mesenteric (Koumentaki et al. 2001) and uterine (Itoh et al. 2001) arteries. However, no studies have investigated vascular responses in thoracic aorta using this nutritional model. Therefore, the aim of this study was to assess the vasoreactivity of the isolated thoracic aorta from control and protein-restricted pregnant rats.

Experiments were carried out in accordance with UK legislation. Pregnant Wistar rats were fed either a control (18 % casein, C) or a low protein (9 % casein, PR) diet. They were humanely killed on day 18/19 by CO₂ inhalation and cervical dislocation. The thoracic aorta was removed and cut into ring segments which were suspended in 20 ml organ baths containing oxygenated physiological salt solution at 37 °C. After an equilibration period of 1 h, phenylephrine (PE, 1 nM-100 µM) and potassium chloride (KCl, 10.88-130.88 mM) cumulative concentration curves (CRCs) were constructed. Following preconstriction with PE (EC₈₀), cumulative concentration-response curves to the endothelium-dependent dilator acetylcholine (ACh, 1 nM-30 µM) were carried out. Data are expressed as means ± S.E.M. of 5-6 observations and differences between groups are determined by Student’s t test for unpaired data.

Both PE and KCl produced a concentration-dependent contraction of rat thoracic aortic rings. Dietary protein restriction failed to alter PE (% maximum constriction: C, 106 ± 1; PR, 105 ± 1, P > 0.05, n = 6) or KCl-induced constriction (% maximum constriction: C, 105 ± 1, n = 5; PR, 100 ± 1, n = 6, P > 0.05). ACh produced a concentration-dependent relaxation of phenylephrine preconstricted rat thoracic aortic rings which was similar in the C and PR groups (-log EC₅₀ values: C, 7.54 ± 0.03, n = 6; PR, 7.56 ± 0.04, n = 6, P > 0.05; % maximum relaxation: C, 85 ± 1; PR, 86 ± 1, P > 0.05, n = 5-6).

In conclusion, protein restriction does not affect the vascular reactivity of the thoracic aorta from pregnant rats. Nutritional restriction in pregnancy induces vascular abnormalities which vary between vessels.

This work is supported by the British Heart Foundation.