MECHANISMS INVOLVED IN THE CONTRACTILE RESPONSES OF KININS IN RAT PORTAL-VEIN RINGS - MEDIATION BY B-1 AND B-2 RECEPTORS

This study investigates the mechanisms involved in kinin-induced contr actions in rings of rat portal vein (RPV). Bradykinin (BK), Lys-BK, Me t-Lys-BK,Tyr-BK (TBK) and des-Arg(9)-BK (DABK) all caused graded contr actions in RPV, with the following order of potency (EC(50), nanomolar ): Met-Lys-BK (0.3)>Lys-BK (0.5)> BK (0.9)>TBK (2.3)much greater than DABK (46.0). The potency of DABK and maximal contractions for DABK and BK, but not for TBK or NE, increased as a function of in vitro incuba tion period, reaching the maximum at 4.5 hr. Cycloheximide (a protein synthesis inhibitor, 70 mu M), incubated for 4.5 hr, inhibited almost completely the CRCs for DABK and blocked the latter phase of CRCs for BK, not altering contractions induced by U46619 {9,11-dideoxy-9 alpha, 11 alpha -methano-epoxy prostaglandin F-2 alpha} (a thromboxane A(2)/ prostaglandin H-2-mimetic). Incubation of RPV with D-Arg-[Hyp(3),Thi(5 ),D-Tic(7),Oic(8)]-BK (HOE 140, a selective B-2 receptor antagonist, 0 .01-100 nM), caused a parallel rightward displacement of the BK and TB K concentration-response curves (CRCs). Schild plots were linear, yiel ding pA(2) values of 11.4 and 9.3, respectively. The slope for HOE 140 against TBK-induced contractions did not differ from unity (1.23 +/- 0.21), whereas against BK was significantly lesser than unity (0.72 +/ - 0.20). The CRCs induced by DABK were not affected by HOE 140 (100 nM ). In addition, the CRCs for DABK at 4.5 hr were shifted to the right in a parallel form in the presence of des-Arg(9)-[Leu(8)]-BK (a select ive B-1-receptor antagonist, 1 mu M), yielding a pA(2) value of 6.7. T he CRCs for BK were not affected by des-Arg(9)-[Leu(8)]-BK (1 mu M). R esponses of RPV for BK were unaffected by atropine (0.1 mu M), pyrilam ine (1 mu M), yohimbine (0.1 mu M), prazosin (0.1 mu M), apamin (0.1 m u M), glibenclamide (3 mu M) or tetrodotoxin (0.1 mu M). Either the re moval of Ca++ from the bath or addition of staurosporine (a protein ki nase C inhibitor, 10 nM) inhibited BK-mediated contractions. The contr actions caused by BK(1 nM), DARK (100 nM) and TBK (3 nM), but not by U 46619 (3 nM) and NE (1 uM), were blocked by indomethacin (3 mu M), BK- induced contractions were also attenuated by dazoxiben [a thromboxane (TX)A(2)-synthase inhibitor, 30 nM]. Similarly, L-655,240 )-5-fluoro-3 -methylindol-2y1]2,2-dimethylpropanoic acid} (a selective TXA(2)-recep tor antagonist, 3 nM), caused a shift to the right (132-fold) of BK CR Cs, without interfering with NE responses. We conclude that: 1) kinins cause potent contractions in RPV through activation of both B-1 and B p receptor subtypes, this effect being mediated indirectly by TXA(2) g eneration; 2) the increase of responsiveness to DABK and, to a lesser extent, to BK, as a function of time and the inhibition of this phenom enum by cycloheximide strongly suggest de novo formation of B-1 recept or via protein synthesis; and 3) BK-induced contractions appear to rel y largely on extracellular Ca++ influx and activation of protein kinas e C-dependent mechanisms.