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

Abstract

ABSTRACT. Postjunctional a]-and a2-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 (3-15 d age), and nonpregnant adult sheep. Vascular rings were mounted a t their optimal resting tension and responses to phenylephrine (aI-adrenoceptor agonist) and guanabenz and UK14304 (both az-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 al-adrenoceptor stimulation than to a2-adrenoceptor stimulation, whereas venous segments develop similar isometric tension to al-and az-adrenoceptor stimulation. The segmental renal artery develops more isometric tension to a2-adrenoceptor stimulation than the main renal artery. No large developmental differences exist among vessels in the sensitivity (concentration required for half maximal response, EDs0) to a-adrenoceptor stimulation except for the renal vein with a2-adrenoceptor stimulation. Maximum isometric tension corrected for vessel cross-sectional area decreases with age for all vessels with both a,-and a2-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 aland a2-adrenoceptors mediate vasoconstriction in the renal circulation, they may do so at different sites. (Pediatr Res 25:461-465, 1989 46Recent studies in this laboratory have demonstrated that renal vascular a l -and az-adrenoceptors are functional and can produce renal vasoconstriction in fetal sheep and newborn lambs (I). Moreover, the renal hemodynamic response to a l -and a2-adrenoceptor stimulation changes during maturation with fetal and newborn a?-adrenoceptor responses less than those observed in adult sheep, whereas the 0,-adrenoceptor responses were similar (1).Contrary to our results (I), recent studies by Tayo et ul. (2) using isolated vascular rings demonstrated that the a2-adrenoceptor-mediated contractile response is greater in 4-to 8-wk-old rabbits than in adult animals, suggesting that there may be a loss of a2-adrenoceptor-mediated contraction with maturation. Differences between the study by Tayo et a/. (2) and our previous results (1) are difficult to explain. However, some of the differences between the two studies may be due to comparing in vivo experiments, where the overall hemodynamic response is studied. with in vitro experiments, where specific vascular segments arc studied.Therefore, the present study was designed to examine possible regional developmental differences in a , -and a?-adrenoceptor-, mediated vasoconstrictor responses in the developing renal vas-. cular bed. Isolated segments of MRA, SRA, and RV from fetal. newborn, and nonpregnant adult sheep were studied. MATERIALS A N D METHODSAnirnu1.r. Vessels from seven fetal...

Development of fetal vascular responses to endothelin-1 and acetylcholine in the sheep

“…Several studies have demonstrated that vascular reactivity varies dramatically with postnatal developmental age. This observation holds for a variety of vascular beds, including cerebral (19,40,41), renal (18,28), femoral (36), and pulmonary (14,15,42) circulations. These data have been obtained in various species such as sheep (1,41), rat (12), pig (36,42), dog (37), rabbit (14,18), baboon (19,20), and human (5).…”

Endothelin-1-induced activation of rat renal pelvic contractions depends on cyclooxygenase-1 and Rho kinase

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