Gender differences in the effect of age on electrical field stimulation (EFS)-induced adrenergic vasoconstriction in rat mesenteric resistance arteries

The objective of this study was to examine the effects of gender and age on electrical field stimulation (EFS)-induced vasoconstriction. Fisher 344 rats were studied: young females (YF, n = 38), young males (YM, n = 29), old females (OF, n = 33), and old males (OM, n = 30). Isolated mesenteric resistance arteries (endothelium-intact or denuded) were pressurized, and outer diameter was monitored. Dose-response curves were performed to KCl and phenylephrine (PE). EFS (0.1-16 Hz) responses were expressed as percentage of constriction from baseline. Area under the curve (AUC) was calculated and comparisons were made using analysis of variance and t tests. Females became less responsive to EFS-induced constriction with age, whereas constrictor responses among males were unaffected (AUC: YF = 454 ± 15, OF = 284 ± 22, p < 0.001; YM = 391 ± 35, OM = 357 ± 31, p = 0.22). Endothelial denudation produced a significant increase in EFS-induced constriction in OF and OM. Endothelium removal in OF increased the EFS constrictor response to the level seen in arteries from YF. BQ 123 (ET_A receptor antagonist) significantly decreased EFS-induced constriction in YM and OM. In YM, SQ 29,548 [thromboxane A₂ (TXA₂)/PGH₂ receptor antagonist] and indomethacin depressed constrictor responses. There were no differences among groups in the sensitivity to KCl, but YF were the most sensitive to PE. In conclusion, EFS-induced vasoconstriction declined with age among females but not males. The decrease in EFS constrictor responses in OF may be due to a selective decrease in vascular smooth muscle sensitivity to adrenergic agonists and an increase in the production of an endothelium-derived vasodilator. Among males there is also an endothelin-1 and TXA₂/PGH₂ component to EFS-induced constriction that is absent among females.