The influence of gender on parasympathetic vasodilatation in the submandibular gland of the rat

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Experimental Physiology









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Parasympathetic vasodilatation in the rat submandibular gland is mediated by nitric oxide-dependent and -independent mechanisms (prostacyclin and endothelium-derived hyperpolarizing factor (EDHF)). The purpose of this study was to determine the influence of gender on the relative contributions of each pathway to nerve-stimulated vasodilatation. Absolute increases in perfusion (laser Doppler flowmetry) were similar in male and female rats (in arbitrary perfusion units: 6159 ± 4530 and 5601 ± 3877 at 2 Hz; 15645 ± 6830 and 14848 ± 6118 at 5 Hz; and 22418 ± 7660 and 18878 ± 5864 at 10 Hz). However, expressed as a percentage increase above resting values, stimulated perfusion was higher in males than in females (P < 0.05). In males both N -nitro-l-arginine methyl ester (l-NAME) and indomethacin partly blocked parasympathetic vasodilatation at all frequencies tested (P < 0.05). In female rats significant reductions in nerve-stimulated perfusion were observed only at 2 and 5 Hz, but the effects of l-NAME were greater than in males (-64 compared with -45% at 2 Hz and -45 compared with -33% at 5 Hz, P < 0.05). Indomethacin by itself had no apparent effect in females. The combined effects of l-NAME and indomethacin were dependent on the order of administration and on gender. Following l-NAME, indomethacin had no further effect in males or females. l-NAME reduced indomethacin-resistant vasodilatation in males and females, but the added effect of indomethacin was more pronounced in males. Finally, atropine-resistant vasodilatation was partly blocked by l-NAME, and the remaining vasodilatation was abolished by spantide I (substance P receptor antagonist). We conclude that NO, products of cyclo-oxygenase activity and EDHF all play a role in parasympathetic vasodilatation, but that NO and EDHF are the major endothelium-derived vasodilators in the rat submandibular gland. In addition, when other pathways are blocked EDHF makes a greater contribution in females. Lastly, both vasoactive intestinal peptide and substance P contribute to the atropine-resistant vasodilatation. © 2006 The Authors. ω