A hypoxic episode during cardiogenesis downregulates the adenosinergic system and alters the myocardial anoxic tolerance

Diabetes Affects the A1 Adenosine Receptor-Dependent Action of Diadenosine Tetraphosphate (Ap4A) on Cortical and Medullary Renal Blood Flow

Diabetes through adenosine A1 receptor (A1R) and P2 receptors (P2Rs) may lead to disturbances in renal microvasculature. We investigated the renal microvascular response to Ap4A, an agonist of P2Rs, in streptozotocin-induced diabetic rats. Using laser Doppler flowmetry, renal blood perfusion (RBP) was measured during infusion of Ap4A alone or in the presence of A1R antagonist, either DPCPX (8-cyclopentyl-1,3-dipropylxanthine) or 8-cyclopentyltheophylline (CPT). Ap4A induced a biphasic response in RBP: a phase of rapid decrease was followed by a rapid increase, which was transient in diabetic rats but extended for 30 min in nondiabetic rats. Phase of decreased RBP was not affected by DPCPX or CPT in either group. Early and extended increases in RBP were prevented by DPCPX and CPT in nondiabetic rats, while in diabetic rats, the early increase in RBP was not affected by these antagonists. A1R mRNA and protein levels were increased in isolated glomeruli of diabetic rats, but no changes were detected in P2Y1R and P2Y2R mRNA. Presence of unblocked A1R is a prerequisite for the P2R-mediated relaxing effect of Ap4A in nondiabetic conditions, but influence of A1R on P2R-mediated renal vasorelaxation is abolished under diabetic conditions.

Role of adenosine signaling in coordinating cardiomyocyte function and coronary vascular growth in chronic fetal anemia

Fetal anemia causes rapid and profound changes in cardiac structure and function, stimulating proliferation of the cardiac myocytes, expansion of the coronary vascular tree, and impairing early contraction and relaxation. Although hypoxia-inducible factor-1α is sure to play a role, adenosine, a metabolic byproduct that increases coronary flow and growth, is implicated as a major stimulus for these adaptations. We hypothesized that genes involved in myocardial adenosine signaling would be upregulated in chronically anemic fetuses and that calcium-handling genes would be downregulated. After sterile surgical instrumentation under anesthesia, gestationally timed fetal sheep were made anemic by isovolumetric hemorrhage for 1 wk (16% vs. 35% hematocrit). At 87% of gestation, necropsy was performed to collect heart tissue for PCR and immunohistochemical analysis. Anemia increased mRNA expression levels of adenosine receptors ADORA 1, ADORA2A, and ADORA2B in the left and right ventricles (adenosine receptor ADORA3 was unchanged). In both ventricles, anemia also increased expression of ectonucleoside triphosphate diphosphohydrolase 1 and ecto-5'-nucleotidase. The genes for both equilibrative nucleoside transporters 1 and 2 were expressed more abundantly in the anemic right ventricle but were not different in the left ventricle. Neither adenosine deaminase nor adenosine kinase cardiac levels were significantly changed by chronic fetal anemia. Chronic fetal anemia did not significantly change cardiac mRNA expression levels of the voltage-dependent L-type calcium channel, ryanodine receptor 1, sodium-calcium exchanger, sarcoplasmic/endoplasmic reticulum calcium transporting ATPase 2, phospholamban, or cardiac calsequestrin. These data support local metabolic integration of vascular and myocyte function through adenosine signaling in the anemic fetal heart.