MODULATION OF VASCULAR CONTRACTILE RESPONSES TO ALPHA(1)-ADRENERGIC AND ALPHA(2)-ADRENERGIC AND NEUROPEPTIDE-Y RECEPTOR STIMULATION IN RATSWITH ISCHEMIC HEART-FAILURE

In order to evaluate adaptational changes in vascular function in cong estive heart failure (CHF), we studied the contractile responses of is olated arterial and venous blood vessels from rats suffering from CHF induced by coronary artery ligature, resulting in a myocardial infarct ion. The contractile responses of the basilar, femoral and renal arter ies and of the iliac vein were examined in relation to adrenergic and neuropeptide Y (NPY) receptor function by the action of the alpha(1), agonist phenylephrine, the alpha(2), agonist clonidine and NPY. The co ntractile force was measured (in mN) and in % of K+-induced contractio n as well as pD(2) to each agonist. When stimulated by a 60 mM K+-buff er solution, the femoral and renal arteries from CHF rats responded wi th a stronger contraction (E(max); 9.4 +/- 0.6 and 9.8 +/- 0.6 mN) tha n the corresponding Sham vessels 6.2 +/- 0.7 and 5.6 +/- 0.4 mN respec tively, P < 0.001). On the contrary, the iliac vein of CHF responded l ess to K+ than the Sham iliac vein (E(max) 2.5 +/- 0.2 and 3.7 +/- 0.5 mN, P < 0.01). The CHF iliac vein responded with a weaker contraction when stimulated with phenylephrine (E(max) 1.9 +/- 0.4 mN) and showed a lower sensitivity (pD(2) 5.6 +/- 0.1) than the corresponding sham v essel (E(max) 5.7 +/- 2.3 mN and pD(2) 6.3 +/- 0.5, P < 0.05). The CHF renal artery was less sensitive to clonidine (pD(2) 6.4 +/- 0.6) than the Sham renal artery (pD(2) 7.2 +/- 0.1, P < 0.05). The results indi cate differences between CHF and Sham vessel segments according to bot h contractile capacity induced by K+-depolarization and to agonist ind uced contractile capacity and sensitivity. The differences are not of general nature but vary according to the vascular bed examined.