Effects of adrenoceptor antagonists on the cutaneous blood flow increase response to sympathetic nerve stimulation in rats with persistent inflammation

Preemptive Analgesic and Antioxidative Effect of Curcumin for Experimental Migraine

OBJECTIVE

Our study aimed to investigate the analgesic and antioxidative stress effects of Curcumin (CC) in experimental migraine induced by Nitroglycerin (NTG) on rats, compared with Indomethacin (ID) and Propranolol (PP) treatments.

MATERIAL AND METHODS

Five groups of 10 rats treated i.p. were investigated: control group (healthy rats) injected with saline solution (0.9%), NTG-control group injected with NTG (1 mg/100 gbw, bw = body weight), and three groups with pretreatment applied 30 min previous to the formalin test (NTG + CC group: Curcumin (10 mg/100 gbw), NTG + PP group: Propranolol (100 μg/100 gbw), and NTG + ID group: Indomethacin (0.5 mg/100 gbw)). Formalin test was performed and number of flinches and shakes were counted. Several oxidative stress parameters were also assessed.

RESULTS

The smallest values of malondialdehyde (MDA), nitric oxide (NOx), and total oxidative status (TOS) were observed on NTG + CC with significant differences as compared with the control group (p < 0.0001). The group pretreated with Curcumin proved significantly smaller number of flinches and shakes compared with both NTG + PP and NTG + ID.

CONCLUSION

Our study demonstrates a superior activity of Curcumin not only versus control, but also versus Propranolol and Indomethacin.

Substance P is involved in the cutaneous blood flow increase response to sympathetic nerve stimulation in persistently inflamed rats

Changed vascular functions have been reported in several pathological conditions, such as chronic regional pain syndrome, obstructive vascular disease, and inflammation. Our previous experiments also showed that electrical stimulation of the lumbar sympathetic trunk (sympathetic stimulation: SS), which normally induces a decrease in blood flow (BF), caused a BF increase in about half of the measured sites in rats persistently inflamed with complete Freund's Adjuvant (AI rats). We also showed that the BF-increase response was only partially suppressed by the alpha1 antagonist at a higher dosage, suggesting the involvement of nonadrenergic mechanisms. We hypothesize that nonadrenergic mechanisms mediating vasodilatation might involve a vasodilating neuropeptide such as substance P (SP) that is released from sympathetic nerve terminals. In this experiment, we conducted an examination using an NK-1 receptor antagonist to determine whether SP plays any role in changed response to SS in AI rats, and also an immunohistochemical examination of whether SP is expressed in the lumbar sympathetic nerve ganglia (SG) of AI rats. The administration of an NK-1 receptor antagonist, CP-96,345, significantly reduced the BF-increase response to SS in AI rats, but its inactive enantiomer, CP-96,344, had no effect. Immunohistochemistry for SP revealed that SP-ir positive SG neurons (mean 13 neurons/rat) were found in 5 of 8 AI rats, whereas only one neuron was stained in 8 control rats. These results suggest that NK-1 receptor activation is involved in the BF-increase response to SS, and that this activation is in part mediated by SP from lumbar SG that was synthesized de novo in inflamed animals.

Regulation of postburn ischemia by α- and β-adrenoceptor subtypes

Deep skin burns are characterised by progressive ischemia secondary to vasoconstriction and thrombosis formation. Burn trauma elicits increased sympathetic activity and elevation of circulating catecholamines acting on adrenoceptors in vascular tissue playing an important role in the regulation of organ blood flow. The present study in rats investigated the role of alpha- and beta-adrenoceptors in the circulatory changes taking place in normal skin and in partial- and full-thickness skin burns using laser Doppler flowmetry. Evaluation was based on intravenous administration of the following adrenergic agonists and antagonists: l-phenylephrine (alpha(1)-agonist), prazosin (alpha(1)-antagonist), clonidine (alpha(2)-agonist), yohimbine (alpha(2)-antagonist), prenalterol (beta(1)-agonist), terbutaline (beta(2)-agonist), and propranolol (beta(1)- and beta(2)-antagonist). Blood flow in normal skin was reduced by phenylephrine (p<0.001), clonidine (p<0.001) and propranolol (p<0.01), and increased by prazosin (p<0.05), yohimbine (p<0.05), prenalterol (p<0.05) and terbutaline (p<0.01). In partial-thickness burns, blood flow was reduced by phenylephrine (p<0.01), clonidine (p<0.01) and propranolol (p<0.05). In full-thickness burns, only clonidine reduced perfusion (p<0.05). In conclusion, beta(1)- and beta(2)-adrenoceptors play important role in the physiological regulation of skin perfusion but are of lesser importance for postburn skin perfusion. Vasoconstrictive alpha(1)- and alpha(2)-adrenoceptors were shown to be tonically active in normal skin and in partial-thickness burns, exerting a negative effect on skin perfusion which was further potentiated by exogenous administration of alpha(1)- and alpha(2)-agonists and reversed by selective alpha-blockers. In full-thickness burns, activation of alpha(2)-receptors was shown to significantly impair skin circulation, raising a flag of warning for the use of clonidine to treat pain in burn patients.