Regional Variation of Postjunctional α- Adrenoceptor Responses in the Developing Renal Vascular Bed of Sheep

ABSTRACT: Postjunctional α1- and α2-adrenoceptor vasoconstrictor responses were evaluated in isolated segments of main renal artery, segmental renal artery, and renal vein from fetal

(130-138 d of gestation; term 145 d), newborn (3-5 d age), and nonpregnant adult sheep. Vascular rings were mounted at their optimal resting tension and responses to phenylephrine

(α1-adrenoceptor agonist) and guanabenz and UK 14304 (both α2-adrenoceptor agonists) were determined. Optimal resting tension increases with development in the main renal artery, segmental

renal artery, and renal vein of sheep. Arterial vessels develop more isometric tension to α1 -adrenoceptor stimulation than to < α2-adrenoceptor stimulation, whereas venous segments develop

similar isometric tension to α1 - and α2-adrenoceptor stimulation. The segmental renal artery develops more isometric tension to α 2-adrenoceptor stimulation than the main renal artery. No

large developmental differences exist among vessels in the sensitivity (concentration required for half maximal response, ED50) to α-adrenoceptor stimulation except for the renal vein with α

2-adrenoceptor stimulation. Maximum isometric tension corrected for vessel cross-sectional area decreases with age for all vessels with both α1- and α2-adrenoceptor stimulation. These

findings may reflect developmental differences in receptor number and affinity or differences in vascular smooth muscle function. In addition, these data suggest that whereas both atand

α2-adrenoceptors mediate vasoconstriction in the renal circulation, they may do so at different sites.

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