Postjunctional alpha(2)-adrenoceptors in the rat tail artery: effect of sex and castration

To investigate sex-related differences in vasoconstrictor responses to post junctional alpha(2)-adrenoceptor activation, isolated ring segments of tail arteries from Fischer-344 rats were studied. Addition of the alpha(2)-adre noceptor agonist, UK-14304 [5-bromo-6-(2-imidazoline-2yl)-aminol-quinoxalin e], enhanced vasoconstriction to the selective alpha(1)-adrenoceptor agonis t, methoxamine, in arteries from both males and females. The response to UK -14304 was significantly greater in arteries from males as compared to fema le arteries. Addition of alpha(2)-adrenoceptor antagonist, idazoxan or rauw olscine, shifted norepinephrine concentration response curves to the right. Antagonist effects also tended to be greater in arteries from males as com pared to females. After gonadectomy, male-female differences persisted; thu s, removal of sex hormones in either males or females did not alter respons es to either agonists or antagonists of alpha(2)-adrenoceptors. These findi ngs suggest that sex differences in alpha(2)-adrenoceptor function are not maintained by either male or female gonadal steroid hormones but may be dev elopmentally regulated. (C) 1999 Elsevier Science B.V. All rights reserved.