Effect of diet-induced obesity on endothelium-dependent relaxation in rat saphenous artery

Preet Chadha, Rebecca Haddock, Lauren Howitt, T. Hilton Grayson, Margaret Morris, Timothy Murphy, Shaun Sandow

1Department of Pharmacology, University of New South Wales, Sydney, Australia,
2Department of Physiology, University of New South Wales, Sydney, Australia

Endothelium-dependent relaxation (EDR) is critical for control of vascular tone and is mediated by nitric oxide (NO), prostaglandin (PGI2) and non-NO/PGI2 endothelium-derived hyperpolarization (EDH); the latter characterized by small and intermediate conductance calcium-activated potassium channel (S/IKCa) and myoendothelial gap junction (MEGJ) activity. The present study determines the characteristics of endothelium-dependent relaxation in adult rat saphenous artery (SA), where EDR has been shown to be entirely NO dependent. The hypothesis examined is that the EDR mechanism is altered in a rat model of diet-induced obesity.

Adult male SD rats were fed chow (control) or high fat (obese) diet for 20wks. Control (536 ± 38g) or diet-induced obese (772 ± 79g; P<0.05) SA were isolated and cannulated in a pressure myograph (80 mmHg basal pressure). Vessels were pre-constricted with phenylephrine (PE; 1 μM) and subsequent responses to ACh (0.001-10 μM) assessed endothelium-dependent relaxation. Vessel diameter changes were monitored using computer tracking (Diamtrak). L-NAME and ODQ blocked NOS/sGC activity. EDH-type responses were characterized by inhibiting S/IKCa using apamin (Apa) and TRAM-34, respectively, or through MEGJ block using connexin (Cx)-mimetic peptides. Confocal immunohistochemistry, electron microscopy and Western blotting examined S/IKCa and MEGJ distribution and expression.

P<0.05: #compared to vehicle treated vessels in control group, *compared to vehicle treated vessels in obese group

In control, apamin and TRAM-34 had no effect on ACh-induced relaxation; with EDR being primarily mediated by NO; L-NAME and ODQ abolishing the response (Table). However, in obese animals, ACh-induced an EDH-type response sensitive to apamin and TRAM-34, compared to vehicle (Table). In addition, gap junction block with Cx-mimetic peptides attenuated ACh-induced relaxation. Moreover, IKCa and MEGJ expression increased in obese compared to control SA.

The present data suggest that in rat SA, endothelium-dependent vasodilation switches from an entirely NO-mediated event in normal conditions to a significant EDH contribution under condition of vascular stress, such as that associated with obesity. The manipulation of this compensatory mechanism may provide selective therapeutic targets against obesity-related vascular disease.