Loss of adenosine A2B receptor mediated relaxant responses in the aged female rat bladder; effects of dietary phytoestrogens

Abstract

This study examined the effect of age, ovariectomy and dietary phytoestrogen ingestion on adenosine A(2B) receptor mediated relaxant responses and mRNA expression of adenosine receptor subtypes in the rat isolated bladder. Female Wistar rats (8weeks) were anaesthetised and the ovaries were removed (ovx) or left intact (sham). Rats were fed either normal rat chow (soy, phytoestrogens) or a non-soy (phytoestrogen free) diet. Isolated bladder from rats aged 12, 24 or 52weeks were pre-contracted with 3μM carbachol prior to a concentration response curve to 5'-(N-ethylcarboxamido) adenosine (NECA) being obtained. In 12-week-old rats, the bladder exhibited enhanced relaxant responses to NECA in soy-fed rats (P < 0.05), whilst at 24weeks of age, the relaxant responses to NECA were attenuated in all the groups studied except soy-treated sham rat bladders in which the relaxant responses were enhanced. At 52weeks of age, no relaxant effects were observed in any of the treatment groups and NECA-induced contractile responses occurred. In all bladders, the adenosine A(2B) receptor was the most abundantly expressed. In bladders from young and mature female rats, the mRNA expression of adenosine receptors (A(1), A(2A) and A(2B)) was lowest in the bladder from non-soy-fed ovariectomised animals and the use of phytoestrogens in the diet increased the mRNA expression of these receptors (P < 0.05). While a soy diet improves the relaxant effects to the adenosine analogue via adenosine A(2B) receptors in bladders from younger rats, the benefits are lost with advancing age.