Total sleep deprivation alters endothelial function in rats: a nonsympathetic mechanism

Abstract

Study objectives: Sleep loss is suspected to induce endothelial dysfunction, a key factor in cardiovascular risk. We examined whether sympathetic activity is involved in the endothelial dysfunction caused by total sleep deprivation (TSD).

Design: TWO GROUPS: TSD (24-h wakefulness), using slowly rotating wheels, and wheel control (WC).

Participants: Seven-month-old male Wistar rats.

Interventions: Pharmacological sympathectomy (reserpine, 5 mg/kg, intraperitoneal), nitric oxide synthase (NOS) inhibition (N (G)-nitro-L-arginine, 20 mg/kg, intraperitoneally 30 min before experiment) and cyclooxygenase (COX) inhibition (indomethacin, 5 mg/kg, intraperitoneally 30 min before experiment).

Measurements and results: In protocol 1, changes in heart rate (HR) and blood pressure were continuously recorded in the sympathectomized and non-sympathectomized rats. Blood pressure and HR increased during TSD in non-sympathectomized rats. In protocol 2, changes in skin blood flow (vasodilation) were assessed in the sympathectomized and non-sympathectomized rats using laser-Doppler flowmetry coupled with iontophoretic delivery of acetylcholine (ACh), sodium nitroprusside (SNP), and anodal and cathodal currents. ACh- and cathodal current-induced vasodilations were significantly attenuated after TSD in non-sympathectomized and sympathectomized rats (51% and 60%, respectively). In protocol 3, ACh-induced vasodilation was attenuated after NOS and COX inhibition (66% and 49%, respectively). Cathodal current-induced vasodilation decreased by 40% after COX inhibition. In TSD compared to WC a decrease in ACh-induced vasodilation was still observed after COX inhibition. No changes in SNP- and anodal current-induced vasodilation were detected.

Conclusion: These results demonstrate that total sleep deprivation induces a reduction in endothelial-dependent vasodilation. This endothelial dysfunction is independent of blood pressure and sympathetic activity but associated with nitric oxide synthase and cyclooxygenase pathway alterations.

Keywords: Acetylcholine; arterial pressure; current-induced vasodilation; endothelial dysfunction; iontophoresis; skin blood flow; sodium nitroprusside; sympathectomy; vascular reactivity.

Figure 1

Mechanisms involved in iontophoretic-induced vasodilation. SNP, sodium nitroprusside; NO, nitric oxide; COX-1, cyclooxygenase-1; PGI₂, prostacyclin (prostaglandin I₂); Indo, indomethacin, an inhibitor of cyclooxygenases; L-NNA, N^G-Nitro-L-arginine, an inhibitor of nitric oxide synthase.

Figure 2

Examples of changes in skin blood flow (SkBf) after iontophoretic application (0.1 mA, 30 sec) of acetylcholine (ACh), anodal current (-), sodium nitroprusside (SNP) and cathodal current (+).

Figure 3

Effects of 24 h of wakefulness on the circadian rhythm of mean arterial pressure (MAP), heart rate (HR), and body temperature (Tco) in nonsympathectomized (A) and sympathectomized (B) rats. Groups are wheel control (WC) and total sleep deprivation (TSD). Values are mean ± standard error of the mean. n = 6. *Differences between TSD and WC (P < 0.05).

Figure 4

Maximal relative increases in skin blood flow in non-sympathectomized and sympathectomized rats (A) After acetylcholine (ACh) application. (B) After anodal current application. (C) After sodium nitroprusside (SNP) application. (D) After cathodal current application. Groups are wheel control (WC) and total sleep deprivation (TSD). n = 8. Values are mean ± standard error of the mean. *Difference versus WC (P < 0.05); ^†Difference versus nonsympathectomized rats (P < 0.05).

Figure 5

Maximal relative increases in skin blood flow in rats treated with saline solution (Control) or indomethacin [Cyclooxygenase (COX) inhibition] or L-NNA [Nitric oxide synthase (NOS) inhibition] or with a combination of indomethacin and L-NNA [COX + NOS inhibition]. (A) After acetylcholine (ACh) application. (B) After anodal current application. (C) After sodium nitroprusside (SNP) application. (D) After cathodal current application. Groups are wheel control (WC) and total sleep deprivation (TSD). n = 8. Values are mean ± standard error of the mean. *Difference versus WC (P < 0.05); ^†Difference versus control (i.e., rats treated with a saline solution) (P < 0.05).