In order to assess the effect of opioid receptor antagonists, naloxone and noradrenaline, on renal cortical microcirculation, India ink infusion was made through the renal artery, one hour after treatment with each drug, in dogs subjected to haemorrhagic shock. Naloxone (1 mg/kg) treatment showed a dual beneficial effect of significant improvement (P<0.001) in the mean arterial pressure without increasing the renal resistance as indicated by the presence of ink particles in about 75 of the cortical glomeruli. However, in the case of noradrenaline (2 Μ/kg/min)-treated animals, although mean arterial pressure increased significantly (P<0.001) only very few glomeruli (25) in the cortical region showed ink particles, demonstrating severe vasoconstriction. In the control group infused only with saline, although most of the glomeruli (92) were filled with ink particles, there was a significant decline in the mean arterial pressure (P<0.001)
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