Myogenic responses of isolated adipose tissue arterioles

Previous in vivo studies indicate that vascular autoregulation does take place in adipose tissue. We tested the hypothesis that adipose tissue arterioles can develop a myogenic response to increases in transmural pressure. Arterioles, isolated from the inguinal fat pad of male Wistar rats, were placed in a microvessel chamber containing a Kreb's bicarbonate-buffered solution (pH 7.4) gassed with 10% O2 (5% CO2; 85% N2). Vessels were cannulated and pressurized to 100 mm Hg and studied under no-flow conditions. Control diameters were obtained at 100 mm Hg. Changes in arteriolar diameter were observed and measured by television microscopy and video caliper. Diameters, in response to 20 mm Hg step increases in transmural pressure, were measured before and after removal either of extracellular calcium or of the endothelium, and administration of indomethacin (10(-5) M) or L-NAME (3 x 10(-4) M). Removal of calcium resulted in an increase in control diameter of 81% and completely eliminated the myogenic response. In contrast, administration of indomethacin increased control diameter by 13%. L-NAME significantly enhanced the myogenic response; however, neither endothelium removal nor indomethacin had any significant effect. These results indicate that adipose tissue arterioles are capable of eliciting a myogenic response that could contribute to the regulation of blood flow in vivo. Furthermore, it appears that calcium is essential for the myogenic response and that nitric oxide significantly contributes to the modulation of baseline myogenic tone, as well as the myogenic response.