Infusion Of Nitric Oxide Synthase Inhibitor Research Articles

Abstract 524: Renal Hemodynamic and Excretory Responses to Infusion of Tyrosine Kinase Inhibitor, Imatinib in Anesthetized Mice

Systemic administration of a tyrosine kinase inhibitor, imatinib has been shown to have potent vasodilator activity in pulmonary and systemic vascular beds in rats. Chronic treatment with imatinib was also shown to cause marked attenuation of the renal injury in AngII induced hypertensive rats. However, the involvement of tyrosine kinases in the regulation of renal hemodynamics and excretory function is not yet clearly defined. To examine the role of constitutively active tyrosine kinases in the kidney, we have examined the renal effects of intravenous infusion of imatinib mesylate (Novartis Pharma, AG, Basel, Switzerland) at incremental doses (0.02, 0.2 and 2 mg/min/kg bw) as well as its interaction with nitric oxide (NO) activity in anesthetized mice. Systemic blood pressure (SBP) was recorded from a cannula placed in the left carotid artery. Renal blood flow (RBF) and glomerular filtration rate (GFR) were measured by renal clearances of PAH and inulin respectively. From a control SBP value of 91 ± 3 mmHg in one group of mice (n=5), imatinib caused minimal changes in SBP at lower doses (87 ± 4 and 86 ± 5mmHg; n=5) but caused significant reduction (75 ± 4 mmHg; P<0.01) at the highest dose. During infusion of imatinib doses, there were no significant changes in RBF (from control value of 9.2 ± 0.9 to 9.2 ± 1.1, 9.9 ± 1.8 and 8.7 ± 2.2 mL/min/g kw respectively), but interestingly, there were dose-depended reductions in GFR (from a control value of 1.8 ± 0.2 to 1.7 ± 0.3, 1.5 ± 0.3, and 1.1 ± 0.3 mmHg). However, only at the highest dose, there were significant reductions in urine flow (from 6.5 ± 0.9 to 4.6 ± 0.5 μL/min/g) and sodium excretion (from 0.42 ± 0.09 to 0.17 ± 0.03 μmol/min/g) but not in fractional excretion of sodium (0.16 ± 0.04 to 0.13 ± 0.04 % ) indicating that the excretory changes were mostly dependent on hemodynamic changes. It is also observed that the usual responses (reductions in RBF, GFR etc) to the infusion of NO synthase inhibitor, nitro-L-arginine (L-NAME; 200mg/min/kg) remain intact in mice (separate group; n=5) pretreated with imatinib (0.2 mg/min/kg). These data suggest that a constitutively active tyrosine kinase pathway plays a regulatory role in maintaining glomerular filtration rate and excretory function in the kidney which seems independent of NO activity.

Haemoglobin and vascular function in the human retinal vascular bed

Haemoglobin is a potential nitric oxide (NO) scavenger. Haemoglobin is associated with blood viscosity and the red blood cell free layer width of microvessels that impact on shear stress in the microcirculation. We hypothesized that haemoglobin modulates retinal vascular function. In 139 nondiabetic male patients with haemoglobin levels within the normal range, the vasodilatatory response of retinal capillary blood flow (RCF) to flicker light exposure and the vasoconstrictor response of RCF to infusion of NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA) were assessed. The latter, because of the selective nature of L-NMMA, reflects a parameter of basal NO activity of retinal vasculature. Examinations of retinal parameters were performed noninvasively and in vivo using scanning laser Doppler flowmetry. Patients with haemoglobin greater or equal the median revealed reduced increase of RCF to flicker light exposure (2.83 ± 12 vs. 9.52 ± 14 (%), P adjusted = 0.002), and greater decrease of RCF to L-NMMA infusion (-7.35 ± 13 vs. -0.92 ± 14 (%), P adjusted = 0.008), compared with patients with haemoglobin below the median. Haemoglobin was negatively related to the percentage change of RCF to flicker light exposure (r = -0.249, P = 0.004) and to L-NMMA infusion (r = -0.201, P = 0.018). In multiple linear regression analysis haemoglobin was an independent determinant of the percentage change of RCF to flicker light exposure (model 1: ß = -0.278, P = 0.003 and model 2: ß = -0.283, P = 0.002) and to L-NMMA infusion (model 1: ß = -0.256, P = 0.005 and model 2: ß = -0.269, P = 0.004). Haemoglobin emerged as an independent determinant of vascular function in the human retinal vascular bed.

Changes of GABA A receptor binding and subunit mRNA level in rat brain by infusion of NOS inhibitor

In the present study, we have investigated the effects of prolonged inhibition of nitric oxide synthase (NOS) by infusion of NOS inhibitor, l-nitroarginine, to examine the pentobarbital-induced sleep, modulation of GABA A receptor binding, and GABA A receptor subunit mRNA level in rat brain. Pre-treatment with l-nitroarginine 30 min before pentobarbital treatment (60 mg/kg, i.p.) significantly increased the duration of sleep in rats. However, the duration of pentobarbital-induced sleep was shortened by the prolonged infusion of l-nitroarginine into ventricle. We have investigated the effect of NOS inhibitor on GABA A receptor binding characteristics in discrete areas of brain regions by using autoradiographic and in situ hybridization techniques. Rats were infused with l-nitroarginine (10, 100 pmol/10 μl/h, i.c.v.) for 7 days, through pre-implanted cannula by osmotic minipumps. The levels of [ 3H]muscimol and [ 3H]flunitrazepam binding were markedly elevated in almost all of brain regions including cortex, caudate putamen, thalamus, hippocampus, and cerebellum. However, there was no change in the level of [ 35S]TBPS binding. The levels of β2-subunit were elevated in the cortex, brainstem, and cerebellar granule layers. By contrast, the levels of β3-subunit were significantly decreased in the cortex, hippocampus, and cerebellar granule layers in l-nitroarginine-infused rats. Following l-nitroarginine treatment, the levels of α6- and δ-subunits which were strictly localized to the cerebellum, were not changed in the cerebellar granule layer. These results show that the prolonged inhibition of NOS by l-nitroarginine-infusion markedly elevates [ 3H]muscimol and [ 3H]flunitrazepam binding throughout the brain, and alters GABA A receptor subunit mRNA levels in different directions. Chronic inhibition of NO generation has differential effects on the various expressions of GABA A receptor subunits. These suggest the involvement of different regulatory mechanisms for the NO-induced expression of GABA A receptor.

Nitric oxide

Nitric oxide (NO) is a gas with diverse biological activities produced from arginine by NO synthases. It is capable of interacting with a number of molecules, most notably superoxide, forming peroxynitrite, which, in turn, can mediate bactericidal or cytotoxic reactions. Nitric oxide also mediates smooth muscle relaxation, neurotransmission, and modulation of inflammation in a number of organ systems and pathophysiologic conditions. Modulation of NO by administration of inhaled NO for respiratory distress syndromes and infusion of NO synthase inhibitors in bacterial sepsis are ongoing. Levels of exhaled NO are being evaluated for their utility in assessing inflammation in respiratory disorders such as asthma.