Vitamin D insufficiency is associated with impaired vascular endothelial and smooth muscle function and hypertension in young rats

Abstract

Increasing evidence links vitamin D deficiency and cardiovascular dysfunction in human adults. There is a worldwide increase in the prevalence of vitamin D deficiency in women of reproductive age, particularly dark-skinned and/or veiled women and their infants. We used a rat model to determine the functional impact of vitamin D deficiency during intra uterine and early life on resistance artery reactivity and blood pressure in the offspring as young adults. Rat dams were maintained on vitamin D deficient or replete chow before and during pregnancy and lactation. The offspring were maintained on the same chow until studied at 7-8 weeks of age. Conscious blood pressure was measured. Endothelial and smooth muscle function were tested in mesenteric arteries on a pressure myograph. Vitamin D deficient male and female offspring had a 10-fold lower serum 25-hydroxyvitamin D (P < 0.0001) and markedly elevated blood pressures (11-20 mmHg, P < 0.001) and heart rates (21-40 beats min(-1), P < 0.02) than control fed offspring. Serum calcium was unchanged. Mesenteric artery myogenic tone was doubled in vitamin D deficiency. Endothelium-derived nitric oxide-evoked dilation was halved in arteries from vitamin D deficient males and dioestrous females. Dilation attributed to endothelium-derived hyperpolarizing factor was all but abolished in vitamin D deficient oestrous females. Nitroprusside-evoked dilation was unaltered in arteries from males, but was markedly reduced in vessels of vitamin D deplete females. In conclusion, early life vitamin D deficiency is associated with endothelial vasodilator dysfunction, and this is likely to contribute to the accompanying elevation in blood pressure and an increased cardiovascular disease risk.

Figure 6. Influence of VitD deficiency on endothelium-independent vasodilation and vasoconstriction in mesenteric arteries

A, dilation evoked by sodium nitroprusside (SNP 10⁻⁵m) in PSS containing l-NAME plus indomethacin (males, n = 10; dioestrous females, n = 6; oestrous females n = 8). *Difference from control fed; †difference between females and males. B, diameter changes evoked by 100 mm K⁺ (HiK); and by 10 μm phenylephrine (PE). n = 5 in each group. Level of preconstriction in the presence of arginine vasopressin (AVP) (n = 4–6 per group).

Figure 1. Growth of male and female offspring

Growth of Control and VitD deplete male (n = 14/group) and female (n = 14/group) offspring. *Difference from control fed.

Figure 2. VitD insufficiency on myogenic tone

Effects of VitD and sex on basal tone development in isolated small mesenteric arteries of males (n = 7–12) and of females in dioestrus (n = 7) and in oestrus (n = 6). *Difference from control fed; †difference from dioestrous females and males.

Figure 3. Influence of VitD insufficiency on vasodilation

Examples of raw traces showing vasodilation evoked by endothelial stimulation with ACh 10 μm in mesenteric arteries from Control (upper trace) and VitD deplete (lower trace) rats.

Figure 4. Effect of VitD deficiency on endothelium-dependent vasodilation

Integrated endothelium-dependent vasodilation in arteries from control fed (left panels) and VitD deplete rats (right panels), in control solution and in the presence of NO synthase blockade (l-NAME), and additional block of prostanoid synthesis (l-NAME + indomethacin, Indo). Number of animals: n = 6–7 for each group of control fed and n = 8–11 for VitD deplete rats. †Significant difference between VitD replete and VitD deplete in control PSS (ANOVA). *Individual point differences in control PSS versus in l-NAME.

Figure 5. Contribution of NO, EDHF and prostanoids to endothelium-dependent vasodilation

Responses in individual tissues were subtracted to reveal the absolute contribution of NO, EDHF and prostanoids to endothelium-dependent responses. Dilation, positive values; constriction, negative values. †Significance difference between VitD replete and VitD deplete (ANOVA; *individual point differences, same n as for Fig. 4).