ABSTRACT
The interactions between neuronal, glial, and vascular cells play a key role in regulating blood flow in the retina. In the present study, we examined the role of the interactions between neuronal and glial cells in regulating the retinal vascular tone in rats upon stimulation of retinal neuronal cells by intravitreal injection of N-methyl-d-aspartic acid (NMDA). The retinal vascular response was assessed by measuring the diameter of the retinal arterioles in the in vivo fundus images. Intravitreal injection of NMDA produced retinal vasodilation that was significantly diminished following the pharmacological inhibition of nitric oxide (NO) synthase (nNOS), loss of inner retinal neurons, or intravitreal injection of glial toxins. Immunohistochemistry revealed the expression of nNOS in ganglion and calretinin-positive amacrine cells. Moreover, glial toxins significantly prevented the retinal vasodilator response induced by intravitreal injection of NOR3, an NO donor. Mechanistic analysis revealed that NO enhanced the production of vasodilatory prostanoids and epoxyeicosatrienoic acids in glial cells in a ryanodine receptor type 1-dependent manner, subsequently inducing the retinal vasodilator response. These results suggest that the NO released from stimulated neuronal cells acts as a key messenger in neuron-glia signaling, thereby causing neuronal activity-dependent and glial cell-mediated vasodilation in the retina.
Subject(s)
Neuroglia/metabolism , Neurons/metabolism , Retinal Vessels/metabolism , Signal Transduction , Animals , Gangliosides/metabolism , Hydroxylamines , Inositol 1,4,5-Trisphosphate Receptors/metabolism , Male , Models, Biological , N-Methylaspartate/metabolism , N-Methylaspartate/pharmacology , Neuroglia/drug effects , Neurons/drug effects , Nitric Oxide Synthase Type I/metabolism , Nitro Compounds , Prostaglandins/metabolism , Rats, Wistar , Retinal Vessels/pathology , Ryanodine Receptor Calcium Release Channel/metabolism , Signal Transduction/drug effects , Vasodilation/drug effectsABSTRACT
BACKGROUND: Although antihypertensive therapy reduces cardiovascular events, it is unclear whether there are differences in cardiac remodeling and function between treatments with nifedipine retard and angiotensin-converting enzyme inhibitors (ACE-Is). It is also not clear how antihypertensive therapy influences cardiac remodeling and function. METHODS: Hypertensive patients with coronary artery disease were randomly assigned to the nifedipine retard (n = 108) or ACE inhibitors groups (n = 102) and treated for 3 years. The primary endpoints were changes in end-diastolic volume index (EDVI) and end-systolic volume index (ESVI) as indices of cardiac remodeling, whereas the secondary endpoints were changes in ejection fraction (EF), stroke volume index (SVI), cardiac index (CI) and regional wall motion as indices of cardiac function. Left ventriculography was performed at baseline and after 3 years of treatment. Fifty-eight and 61 patients, respectively, were subjected to the final analysis. RESULTS: Comparable changes in remodeling and function were obtained in the nifedipine retard group and the ACE-Is group. Both groups showed a significant reduction of EDVI and ESVI, and a significant increase in EF, SVI, and CI, whereas the decreased regional wall motion significantly improved. In both groups, weak but significant correlations were noted between treatment-induced changes of systolic blood pressure and those of primary and secondary endpoints. CONCLUSION: The above findings show that treatments with nifedipine retard or ACE-Is cause a comparable change in remodeling and cardiac function. Lowering of the blood pressure by either drug leads to reverse remodeling or improvement of cardiac function. In addition to alleviation of coronary artery damage by reducing blood pressure, there is a favorable effect on the left ventricular structure and function. Reducing the blood pressure is critically important for hypertensive patients with coronary artery disease.
