EVIDENCE FOR AN AGE-DEPENDENT FUNCTIONAL EXPRESSION OF ALPHA(1D)-ADRENOCEPTORS IN THE RAT VASCULATURE

The role of the alpha(1)-adrenoceptor subtypes, and their possible cha nge with maturation, in alpha(1)-adrenoceptor-induced presser response s in the rat has not been established. Thus, the effects of the alpha( 1D)-, alpha(1A/1D)- and alpha(1B/1D)-adrenoceptor antagonists, BMY 737 8 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl) 8-azaspiro (4.5) dec ane-7,9-dione 2HCl), 5-methyl-urapidil and chloroethylclonidine, respe ctively, on the presser responses induced by phenylephrine in 1- and 5 -month-old pithed rats were investigated. The presser responses induce d by phenylephrine were competitively antagonized by both BMY 7378 and chloroethylclonidine in 5-month-old, but not in young immature animal s; in marked contrast, 5-methylurapidil antagonized with similar poten cy the phenylephrine-induced presser responses in animals of both ages . The present pharmacological data suggest that functional expression of alpha(1D)-adrenoceptors in the rat resistance vessels increases wit h age; alpha(1A)-, but not alpha(1B) or alpha(1D)-adrenoceptors, seem to predominate in immature animals. These findings represent the first evidence that age-related changes in functional alpha(1)-adrenoceptor subtypes occur in the systemic vasculature in vivo. (C) 1997 Elsevier Science B.V.