Modulation of vascular contractile responses to α1-and α2-adrenergic and neuropeptide Y receptor stimulation in rats with ischaemic heart failure

In order to evaluate adaptational changes in vascular function in congestive heart failure (CHF), we studied the contractile responses of isolated arterial and venous blood vessels from rats suffering from CHF induced by coronary artery ligature, resulting in a myocardial infarction. The contractile responses of the basilar, femoral and renal arteries and of the iliac vein were examined in relation to adrenergic and neuropeptide Y (NPY) receptor function by the action of the α₁ agonist phenylephrine, the α₂ agonist clonidine and NPY. The contractile force was measured (in mN) and in% of K⁺-induced contraction as well as pD₂ to each agonist. When stimulated by a 60 mM K⁺-buffer solution, the femoral and renal arteries from CHF rats responded with a stronger contraction (E_max; 9.4 ± 0.6 and 9.8 ± 0.6mN) than the corresponding Sham vessels (E_max; 6.2 ± 0.7 and 5.6 ± 0.4 mN respectively, P < 0.001). On the contrary, the iliac vein of CHF responded less to K⁺ than the Sham iliac vein (E_mas 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 (pD₂ 5.6 ± 0.1) than the corresponding sham vessel (E_max 5.7 ± 2.3mN and pD₂ 6.3 ± 0.5, P < 0.05). The CHF renal artery was less sensitive to clonidine (pD₂ 6.4 ± 0.6) than the Sham renal artery (pD₂ 7.2 ± 0.1, P < 0.05). The results indicate differences between CHF and Sham vessel segments according to both contractile capacity induced by K⁺-depolarization and to agonist induced contractile capacity and sensitivity. The differences are not of general nature but vary according to the vascular bed examined.