A kallidin-like peptide is a protective cardiac kinin, released by ischaemic preconditioning of rat heart

Abstract

Bradykinin is thought to play a major role among the endogenous cardioprotective candidates of ischaemic preconditioning (IPC). Little attention has been paid to the fact that in the tissue kallidin (KAL), rather than bradykinin might be the physiological mediator of the kallikrein-kinin system. In order to evaluate the importance of one or the other peptide the release and effect of both kinins has been investigated in isolated rat hearts following IPC. Bradykinin- and a KAL-like peptide were measured in the effluent of the rat isolated Langendorff heart with two different specific radioimmunoassays. The creatine kinase activity in the effluent was judged as degree of cardiac injury caused by ischaemia. During IPC, which consists of three 5 min no-flow and 5 min reperfusion cycles prior to the 30 min ischaemia, the bradykinin level in the effluent did not change significantly (15.4-19.4 pg ml(-1)). In the control group the bradykinin levels were 15.9-16.6 pg ml(-1). During IPC KAL-like peptide (Arg(1)-, instead of Lys(1)-KAL), which has recently been verified by mass spectrometry, displays 5.8-fold higher levels in the effluent and significantly increases in the same time interval from 90.4 to 189 pg ml(-1). After 30 min ischaemia the bradykinin levels in the IPC group were not significantly different to those of the control group (18.7 vs 14.4 pg ml(-1)). The KAL-like peptide levels in the IPC group vs the control group were 105 vs 86.1 pg ml(-1). By the 30 min ischaemia the creatine kinase activity in the IPC group increased from 0.367 to 8.93 U l(-1) (before and 10-30 min after ischaemia). In the control group during the same time period the creatine kinase levels increased from 0.277 to 34.9 U l(-1). The low increase in creatine kinase activity following IPC was taken as equivalent of the cardioprotective action. A KAL antibody or HOE140 (kinin B(2)-receptor antagonist) completely abolished this beneficial effect of IPC (36.6 and 53.0 U l(-1)) when added to the perfusion medium during the reperfusion cycles of IPC prior to the 30 min ischaemia. Our data suggest that in rat hearts KAL-like peptide rather than bradykinin is the physiological compound activated by IPC and acting via the cardiac kinin B(2)-receptor. Thus, endogenously generated KAL-like peptide seems to play a major role in the cardioprotection of IPC.

Figure 1

Schematic of the four different protocols: (1) control group; (2) IPC group; (3) IPC+KALab group; and (4): IPC+HOE group.

Figure 2

Binding characteristic of a KAL antiserum at a dilution of 1 : 50000. ¹²⁵I-Tyr⁹-KAL was used as tracer molecule (5000 counts min⁻¹). The binding of bradykinin (BK: open circles; kallidin (KAL: white squares) and kallidin-like peptide (KLP: grey rhombus) is shown. B/B₀ (%): bound tracer in the presence and absence of cold antigen, respectively.

Figure 3

Release of (a) BK and (b) KLP from isolated rat heart of control group (open symbols) and of IPC group (closed symbols) before (0–30 min) and after (60–90 min) 30 min ischaemia. The dotted line represents the 30 min ischaemia period. N=10, mean values with s.e.m. ^*P<0.05, IPC vs control group.

Figure 4

CK activity (U l⁻¹) in coronary effluent before and after 30 min ischaemia of control group (white columns), of IPC group (light grey columns), of the IPC+KALab group (dark grey columns), and of the IPC+HOE group (black columns) before and 10, 20, and 30 min after 30 min ischaemia. N=10, mean values with s.e.m., ^**P<0.01, IPC vs control.

Figure 5

Change in LVP (mmHg) before and after 30 min ischaemia. Control group: open circles; IPC: grey squares; IPC+KALab: grey triangles; IPC+HOE: grey circles. N=10, mean values with s.e.m., n=10; ^***P<0.0001. Asterisk show statistical significance of IPC group vs control group. Not shown: ^**P<0.005: IPC+KALab group vs control group (time 10–30 and 70–90 min), ^**P<0.005: IPC+HOE group vs control group (time 10–30 min) and ^*P<0.05: IPC+HOE group vs control group (time 70–90 min).