Maturation reveals a decrease in endothelium-dependent contraction inducedby depolarization in the aorta of spontaneously hypertensive rats

The influence of the endothelium on aortic contractility to KCI 100 mM was studied during maturation and aging in normotensive Wistar and spontaneousl y hypertensive rats (SHR). In Wistar rats, there was no significant differe nce in maximal responses in the course of aging whether the endothelium was present (E+) or not (E-). A similar result was obtained in SHR E- rings. H owever, contraction was significantly higher in E+ rings of young (9 weeks) compared to adult and old SHR (18, 25, 36 and 72 weeks) (in mN/mm(2) : 34. 8 +/- 3.1 versus 24.8 +/- 1.8, 16.0 +/- 2.5, 17.4 +/- 2.0 and 12.9 +/- 1.8, p<0.01). This increase remained significant in 18- compared to that of 25- , 36- and 72-week-old rats (p<0.01). No change appeared with age in noradre naline-induced contractions of E+ rings neither in Wistar nor in SHR. A dos e-dependent decrease in response to KCl was observed after an in vivo pretr eatment of the young SHR with acetylsalicylic acid. Finally, blocking the T XA(2)/PGH(2) receptor by addition of GR 32191B or ONO-3708 led to a decreas e in the response of young SHR aortic rings to KCl. This study points out a decrease in the response of SHR aortic rings to a depolarizing agent durin g maturation. The enhanced contraction observed in young SHR seems to be th e result of an increased participation of an endothelium-derived, cyclooxyg enase-dependent contracting factor(s), most likely either TXA(2) or PGH(2). This factor might play a key role in the onset of hypertension in the spon taneously hypertensive strain. (C) 2001 Elsevier Science Inc. All rights re served.