Continuous measurement of vascular responses in consecutive sections of cat skeletal muscle vasculature including changes in permeability to albumin: Effects of histamine-like agonists

Quantitative analysis of peptide levels and neurogenic extravasation following regeneration of afferents to appropriate and inappropriate targets

We have studied quantitatively the levels of substance P and calcitonin gene-related peptide in nerves innervating skin and muscle of rats, and examined the effects of cross-anastomosing these nerves so that they regenerate to an inappropriate target. We have also compared the ability of nerves to induce neurogenic extravasation with their peptide content. Peptide was measured by radioimmunoassay in the proximal section of ligated peripheral nerves, and neurogenic oedema was measured by determination of Evans Blue extravasation induced by either systemic capsaicin treatment or topical mustard oil application. The levels of these peptides are higher in cutaneous nerves than muscle nerves. This cannot be explained by differences in the number of fibres in the nerves studied. The levels of peptides fall when cutaneous afferents reinnervate muscle, and rise when muscle afferents reinnervate skin. We suggest that these changes occur because of some tissue-specific trophic influence arising from the tissue innervated. The ability to produce extravasation in skin is highly correlated with the substance P and calcitonin gene-related peptide levels of its innervation, even when this occurs in inappropriate nerves which do not normally produce extravasation.

Neurogenic extravasation and substance P levels are low in muscle as compared to skin the rat hindlimb

Activation of cutaneous chemosensitive afferents results in the release of substances which increase the permeability of the microcirculation, producing inflammation. That this inflammation is neurogenic is readily demonstrated by antidromic electrical stimulation of afferent fibres. In the present study we have used the technique of dye extravasation to compare both qualitatively and quantitatively neurogenic extravasation skin and skeletal muscle. Plasma extravasation has been found to occur in skeletal muscle after stimulation but only at less than 10% of the levels seen in skin. We have also found that the levels of the C-fibre markers substance P and fluoride-resistant acid phosphatase are greatly reduced in muscle compared with skin nerves. These results show that there are substantial differences in the population of C-fibres supplying muscle compared with those supplying skin.

Histamine H1- and H2- receptor antagonists reduce histamine-induced increases in vascular permeability and oedema formation in cat skeletal muscle

Intra-arterial fusions of histamine cause vasodilation of resistance vessels, extravasation of albumin and oedema in cat skeletal muscle. Treatment with either mepyramine or metiamide significantly reduced the extravasation of albumin and rate of oedema formation. The doses of mepyramine and metiamide used did not modify the vascular responses to bradykinin.