Effects of aqueous hop (Humulus Lupulus L.) extract on vascular reactivity in rats: Mechanisms and influence of gender and hormonal status

Abstract

Phytoestrogens, naturally occurring plant compounds having oestrogenic and/or anti-oestrogenic activity, are present in many human foodstuffs including hop. Moderate intakes of isoflavonoid phytoestrogens have been associated with a reduction in cardiovascular diseases incidence. So, it is possible that hop (Humulus Lupulus L.) might similarly contribute to the reported health-beneficial effects of moderate beer consumption. Thus, the purpose of this study was to investigate in vitro effects of aqueous hop extract on thoracic vascular reactivity in Sprague Dawley male and female rats. Endothelium-intact thoracic arterial rings from male rats (MALE, n=8), sham-ovariectomized (Sham OVX) female (n=8) and ovariectomized (OVX) female rats (n=8) were used. We assessed the relaxation induced by aqueous hop extract (10(-9), 10(-2)g/l) in aortic rings precontracted with norepinephrine (10(-7)M), in the absence or in the presence of l-NAME (10(-4)M), indomethacin (10(-5)M), thapsigargin (10(-4)M), iberiotoxin (3.10(-8)M), apamin (3.10(-8)M) and TEA (3.10(-4)M). Aqueous hop extract induced relaxation of endothelium-intact thoracic arterial rings in MALE and Sham OVX rats, whereas a weak effect was observed in OVX rats. This vasorelaxation was strongly inhibited in presence of l-NAME, indomethacin and thapsigargin. These data indicated that aqueous hop extract-induced vasodilation, in male and intact female rats, is mediated by NOS activation, cyclooxygenase products and Ca(2+) pathways. Moreover, our results suggested that effect of hop in enhancing vascular reactivity was independent of gender but strongly related to hormonal status.