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Specific adrenomedullin receptors mediate vasodilation in the rat systemic vascular bed
205 SECRETONEURIN IMMUNOREACTIVITY IN THE INNERVATION OF RAT GASTROINTESTINAL TRACT: INTRINSIC AND EXTRINSIC SOURCES B Tarakqi & C VaiUant, Veterinary Preclinical Sciences, University of Liverpool, UK.
Secretoneurin is a novel neuropeptide produced in the central nervous system by cleavage of secretogranin II (Kirchmair et al., 1993, Neuroscience 53: 359). In the present study, we examine if secretoneurin is present in the peripheral nervous system. Tissue samples were taken from rats either treated neonatally with capsaicin, or seven days after injection of retrograde tracer, True Blue (TB), into the wall of the stomach, proximal or distal colon, and processed for staining with antiserum raised against rat secretoneurin, kindly donated by Prof. Hans Winkler, Innsbruck. Secretoneurin immunoreactivity was detected in myenteric and submucosal neurons and in fibres in all layers of the gut wall. Numbers of labeUed fibres were reduced in capsaicin-treated rats. Immunoreactivity was found in subsets of TB-labelled spinal afferents projecting to stomach, proximal colon or distal colon and TB-labelled vagal afferents projecting to stomach or proximal colon. Coeliac and inferior mesenteric ganglia contained no immunoreactive cells but numerous labelled fibres which were not significantly depleted in capsaicin-treated animals. Conclusions: In the periphery, secretoneurin is produced by subsets of enteric neurons and spinal and vagal afferents projecting to the gut. Prevertebral neurons appear not to produce secretoneurin, but to be innervated by immunoreactive preganglionic fibres.
Specific adrenomedullin receptors mediate vasodilation in the rat systemic vascular bed. G.M. Taylor, K.A. Nandha, D.M. Smith, A.A Owji, M.A Ghatei and S.R Bloom. Department of Medicine~ Royal Postgraduate Medical School, Hammersmith Hospital, Du Cane Road, London, W12 ONN. The potent hypotensive peptide, adrenomedullin, has been shown to be present in plasma suggesting a physiological role in cardiovascular control. Here we investigated the mechanism of action of adrenomedullin in vivo, using the anaesthetised rat as the bioassay model, and ligand binding assays on rat blood vessel membranes. Rat aCGRP and both human and rat adrenomeduUins induced dose-dependent, potent and long-lasting hypotensive effects. Rat aCGRP was found to be 10 times more potent than human or rat. The CGRP 1 receptor antagonist, human CGRP(8-37) (200 nmol/kg) was able to almost completely inhibit the hypotensive effect of rat aCGRP (0.2 nmol/kg) but not that of rat adrenomedullin (2 nmol/kg), implying that the adrenomedullin action is independent of CGRP t receptors. Ligand binding assays confirmed the presence of both CGRP and adrenomedullin binding sites in rat blood vessels. The t2sI- rat adrenomedullin binding site has a KD = 0.32 q- 0.12 nM (n=4) for rat adrenomeduUin but has a lg > 10"6M for rat aCGRP. Chemical cross-linking and SDS-PAGE analysis revealed the adrenomedullin binding protein to have a M~ of 83,000. The results suggests that the hypotensive effect of adrenomedullin may be mediated in vivo via specific adrenomedullin binding sites.
Secretoneurin is a novel neuropeptide produced in the central nervous system by cleavage of secretogranin II (Kirchmair et al., 1993, Neuroscience 53: 359). In the present study, we examine if secretoneurin is present in the peripheral nervous system. Tissue samples were taken from rats either treated neonatally with capsaicin, or seven days after injection of retrograde tracer, True Blue (TB), into the wall of the stomach, proximal or distal colon, and processed for staining with antiserum raised against rat secretoneurin, kindly donated by Prof. Hans Winkler, Innsbruck. Secretoneurin immunoreactivity was detected in myenteric and submucosal neurons and in fibres in all layers of the gut wall. Numbers of labeUed fibres were reduced in capsaicin-treated rats. Immunoreactivity was found in subsets of TB-labelled spinal afferents projecting to stomach, proximal colon or distal colon and TB-labelled vagal afferents projecting to stomach or proximal colon. Coeliac and inferior mesenteric ganglia contained no immunoreactive cells but numerous labelled fibres which were not significantly depleted in capsaicin-treated animals. Conclusions: In the periphery, secretoneurin is produced by subsets of enteric neurons and spinal and vagal afferents projecting to the gut. Prevertebral neurons appear not to produce secretoneurin, but to be innervated by immunoreactive preganglionic fibres.
Specific adrenomedullin receptors mediate vasodilation in the rat systemic vascular bed. G.M. Taylor, K.A. Nandha, D.M. Smith, A.A Owji, M.A Ghatei and S.R Bloom. Department of Medicine~ Royal Postgraduate Medical School, Hammersmith Hospital, Du Cane Road, London, W12 ONN. The potent hypotensive peptide, adrenomedullin, has been shown to be present in plasma suggesting a physiological role in cardiovascular control. Here we investigated the mechanism of action of adrenomedullin in vivo, using the anaesthetised rat as the bioassay model, and ligand binding assays on rat blood vessel membranes. Rat aCGRP and both human and rat adrenomeduUins induced dose-dependent, potent and long-lasting hypotensive effects. Rat aCGRP was found to be 10 times more potent than human or rat. The CGRP 1 receptor antagonist, human CGRP(8-37) (200 nmol/kg) was able to almost completely inhibit the hypotensive effect of rat aCGRP (0.2 nmol/kg) but not that of rat adrenomedullin (2 nmol/kg), implying that the adrenomedullin action is independent of CGRP t receptors. Ligand binding assays confirmed the presence of both CGRP and adrenomedullin binding sites in rat blood vessels. The t2sI- rat adrenomedullin binding site has a KD = 0.32 q- 0.12 nM (n=4) for rat adrenomeduUin but has a lg > 10"6M for rat aCGRP. Chemical cross-linking and SDS-PAGE analysis revealed the adrenomedullin binding protein to have a M~ of 83,000. The results suggests that the hypotensive effect of adrenomedullin may be mediated in vivo via specific adrenomedullin binding sites.