Comparison of the post-mortem interval on the effect of vascular responses to the activation of ionotropic and metabotropic receptors.

The contractibility of blood vessels depends on their normal structure and the availability of calcium ions; it changes under the influence of numerous contracting and relaxing factors, which control the activities of various pathways of intracellular and intercellular signaling. The main aim of the study was to investigate, by means of perfusion pressure in rat tail arteries, the role of Ca2+ in vascular response to α-1 adrenoceptor activation by phenylephrine (PHE) and Bay K8644 agonist of the L-type calcium channel and caffeine before and after a post-mortem interval (PMI) of 2, 4, 6 and 8 h. A phasic increase of perfusion pressure in rat tail arteries, as induced by PHE or caffeine, in Ca2+-free solutions was used as an indicator of intracellular Ca2+ release through the inositol 1,4,5-triphosphate and ryanodine receptor pathways, respectively. In Ca2+-free-ethylene glycol tetraacetic acid (EGTA)-poly(sodium styrenesulfonate) (PSS) and in Ca2+-EGTA-PSS, the PHE induced elevation of perfusion pressure significantly decreased. Vascular responses to caffeine (20 mmol/1) in Ca2+-free-EGTA-PSS, with an increase of PMI from 2-8 h, did not change significantly. A similar effect was observed with vascular responses to KCl 40 mmol/1 in Ca2+-EGTA-PSS. To confirm whether the inhibitory effect of 2, 4, 6 and 8 h PMI was mediated through the formation of NO, nitro-L-arginine (L-NNA), a potent NO synthase inhibitor, was used. Exposure to L-NNA (10-5 M) blocked the inhibition induced by an increase of PMI. The blocked effects of L-NNA were reversed by L-arginine (10-4 M). In conclusion, these patterns of change in artery responses provide insight into the post-mortem change in the receptor-mediated signaling components in epithelial and smooth muscle cells, and support the further study of post-mortem vascular responses triggered by G protein-coupled receptors (metabotropic) and channel-linked receptors (ionotropic) as potential markers for estimating short and long-term PMIs, respectively.