Study On Amino Acids In Striatum And Blood Pressure

INTRODUCTIONAs an important part of basal ganglia, striatum has many functions. More and more attention has been paid to the regulation of striatum on cardiavasvular system. Microinjection of glutamic acid (Glu) into striatum cause elevation of blood pressure (BP) in rats. Since there are lots of receptors of neurotransmitters in striatum, we speculated that altering the contents of other amino acids in striatum might also change BP of rats. In addition, contents of Glu andγ-aminobutyric acid (GABA) in nucleus of solitary tract (NTS) and medulla can be changed by alteration of BP through arterial baroreflex ( ABR). ABR may also affect the release of dopamine in striatum. How about the contents of amino acids in striatum when changing BP? Is ABR involved in it? Therefore, the present work was designed to determine the relationship between amino acids in striatum and blood pressure.Three parts of experiment were completed. In experiment 1, changes of systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured after microinjection of antagonists of N-methyl-D-aspartate (NMDA) and GABA receptors into striatum of Sprague-Dawley (SD) rats, to study the influence of amino acids in striatum on BP. In experiment 2, contents of amino acids in striatum of SD rats were measured and compared after alteration of BP separately through administration of different drugs, to study the influence of BP on amino acids in striatum. In experiment 3, contents of amino acids in striatum of SD rats were measured and compared after sinoaortic denervation (SAD) which completely destroys ABR responses and sham operation (Sham), to study the influence of ABR on amino acids in striatum. METHODSExperiment 1SBP and DBP of male SD rats were determined continuously after catheterization under anesthesia. Dizocilpine (MK801, 5mM, 0.5ul, n=7), bicuculline (10mM, 0.5ul, n=7) and solvent, artificial cerebrospinal fluid (aCSF, 0.5ul, n=7) were microinjected into striatum respectively (coordinates: A: +0.5mm from bregma, L: +3mm from midline and H: -5mm from dura). The Student paired t test was used to evaluate the differences in SBP and DBP between predrug and post-drug.Experiment 2SBP and DBP of male SD rats were determined continuously after catheterization under anesthesia. Phenylephrine (Phe, 0.2mg/ml, n=13), sodium nitroprusside (SNP, 0.2mg/ml, n=13) and solvent, normal saline (NS, n=13) was administered intravenously (50ul/min). After BP reached a stable state (about 10min later), the rats were killed by decapitation. The striatum was dissected out and homogenized immediately. The homogenate was centrifuged, and the contents of amino acids in supernatant were measured through high performance liquid chromatogram-electrochemical detection (HPLC-ECD). The Student unpaired t test was used to evaluate the differences in the contents of amino acids between Phe, SNP and NS groups.Detection of amino acidsMobile phase: 100mM di-sodium hydrogen phosphate; 22% methanol; 3.5% acetonitrile; PH 6.7 with perchloric acid.Parameters and conditions: flow rate, 0.6ml/min; injection volume, 20ul; sensitiveness, 200uA; E1 = +150mv; E2 = +550mv; EGC = +600mv; baseline frequence, 10HZ.Experiment 3Male SD rats were divided into two groups: group1 for SAD, group2 for Sham. Two weeks after SAD or Sham, the animals underwent catheterization under anesthesia. Two days later, haemodynamic parameters were determined in the conscious state. The completeness of SAD was assessed. The rats failed in SAD assessment were rejected. Then all the rats (SAD, n=12; Sham, n=12) were killed by decapitation. The striatum was dissected out and homogenized immediately. The homogenate was centrifuged, and the contents of amino acids in supernatant were measured through HPLC-ECD. The Student unpaired t test was used to evaluate the differences in the contents of amino acids between SAD and Sham rats. Detection of amino acids was similar to Experiment 2.RESULTSEffect of amino acids in striatum on blood pressureBlockage of NMDA receptors, may decrease blood pressure significantly (p<0.05); and blockage of GABA receptors, may increase blood pressure significantly (p<0.01). aCSF (control group) has no effect on blood pressure (p>0.05).Effect of blood pressure on amino acids in striatumElevation of blood pressure may increase the contents of amino acids in striatum significantly (p<0.05), especially for Glu (p<0.01); and reduction of blood pressure may decrease the contents of amino acids in striatum significantly (p<0.05).Effect of sinoaortic denervation on amino acids in striatumCompared with Sham, the contents of amino acids in striatum of SAD decreased significantly (p<0.01).CONCLUSIONAmino acids in striatum may affect blood pressure, and blood pressure may also affect the contents of amino acids in striatum conversely. Arterial baroreflex function is one of the important factors which affect the contents of amino acids in striatum.