Impaired Endothelium-Dependent Relaxation by Alternating Protein Kinase C and Na+-K+ ATPase in Isolated Rabbit Corpus Cavernosum Exposed to Elevated Glucose

Jung, Suk Young; Hwang, Tae Kon; Yoon, Jai Young

Abstract

Impaired endothelium dependent relaxation occurs in diabetic rabbit corpus cavernosum and normal corpus cavernosum exposed to elevated glucose. Elevation of glucose can change the activities of two key enzymes, protein kinase C (PKC) and Na+-K+ ATPase. This study addresses the question of whether impaired endothelium dependent relaxation in isolated corpus cavernosum from normal rabbit exposed to elevated glucose is related to PKC and Na+-K+ ATPase activities and, if so, whether it is associated with altered ouabain sensitive 86-Rb uptake, an index of Na+-K+ ATPase activity, and contractile response of corpus cavernosum tissue to ouabain. Corpus cavernosal tissue suspended for measurement of isometric tension were incubated for 6 hours in control (5.5mM) or elevated glucose (44mM) to mimic euglycemic and hyperglycemic conditions. Relaxations of corpus cavernosum tissue in response to the endothelium-dependent vasodilator acetylcholine (ACh)were unaffected in control groups while significantly inhibited in the elevated glucose group. Relaxations of corporeal tissue to endothelium-independent vasodilators, sodium nitroprusside (SNP) were similar in the control and elevated glucose groups. Corporeal tissue treated with 4-phorbol 12-myristate 13-acetate (PMA), a PKC activator, showed decreased relaxations to ACh, similar to normal corporeal tissue exposed to elevated glucose. Relaxations in response to SNP were unaffected by treatment with PMA or exposure to elevated glucose. 1(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), PKC inhibitor, restored the abnormal Ach-induced relaxation in corporeal tissue exposed to elevated glucose. The contractions caused by ouabain, Na+-K+ ATPase inhibitor, were smaller in elevated glucose groups than control and elevated glucose groups treated with H-7. Ouabain sensitive 86-Rb uptake of elevated glucose groups was significantly less than that of control groups but ouabain sensitive 86-Rb uptake of elevated glucose groups treated with H-7 was similar to those of control groups. These results suggest that activation in PKC activity and inhibition in Na+-K+ ATPase activity caused by elevated glucose contribute to impaired endothelium dependent relaxation in corpus cavernosum smooth muscle.