Functional and morphological properties of human omental resistance vessels

We have examined the functional and morphological properties of arterial resistance vessels with lumen diameters about 200 micrometer from the human omentum. The vascular smooth muscle cells were circumferentially oriented and arranged in about 3 layers within the media. The cells, when held at a length where their contractile response was maximal, were 97 micrometer long and had a mean diameter of 3.9 micrometer. In response to maximum potassium stimulation the force developed per cell was 2.4 micro N. The maximum response to norepinephrine (NE) was about 90% of the response to potassium, while the sensitivity to NE (NE-ED 50 = 0.4 micro M) was about the same as the NE sensitivity reported for larger human vessels. The sensitivity to NE was unaffected by cocaine, while the response to potassium was unaffected by phentolamine. Fluorescence microscopy indicated that the vessels contained few adrenergic nerve terminals. These findings suggest that although the vessels are well supplied with alpha-receptor, the vessels are only of minor importance for sympathetic blood pressure control.