While much is known about the beneficial effects of myocardial stress adaptation, relatively less information is available about the adaptive mechanisms. To explore the signaling pathways of stress adaptation, isolated working rat hearts were divided into three groups. Group I was adapted to stress by conventional technique of repeated
ischemia and reperfusion consisting of 5 min of
ischemia followed by 10 min of reperfusion, repeated four times. Group II was treated with 100 microM of
genistein, a
tyrosine kinase inhibitor, followed by preconditioning as described for group I. The third group, perfused with
buffer only for 60 min, served as control. All hearts were subjected to 30 min of
ischemia followed by 30 min of reperfusion. The results of our study demonstrated better postischemic myocardial functions in the preconditioned hearts as evidenced by increased aortic flow, coronary flow, developed pressure and lesser amount of tissue injury as evidenced by the decreased
creatine kinase release. The preconditioning effects were associated with enhancement of
phospholipase D activity in the heart. The preconditioning effect was almost abolished by the
genistein treatment which also prevented the enhancement of
phospholipase D activities. Additionally, preconditioning of the rat hearts stimulated
protein kinase C, MAP
kinase, and
MAPKAP kinase 2 activities which were inhibited by
genistein. The results identifies for the first time
tyrosine kinase-
phospholipase D as potential signaling pathway for ischemic preconditioning, and implicates the involvement of multiple
protein kinases in myocardial adaptation to
ischemia.