ABSTRACT
El reflejo barorreceptor es poco conocido por la mayoría de los médicos a pesar de que es fundamental en la estabilización de la presión arterial latido a latido y es crucial para la supervivencia. Su fascinante historia es brevemente revisada en este artículo. En 1852 Claude Bernard descubrió que los nervios simpáticos del cuello inervan los vasos sanguíneos de la piel. En 1932 Edgar Douglas Adrian demostró que los nervios simpáticos que inervan los vasos sanguíneos de la piel descargan en forma espontánea a una frecuencia de cuatro a seis por segundo y de esta forma encontró las bases fisiológicas del tono vasomotor. En el siglo XIX Ludwig Traube y Karl Constantine Ewald Hering descubrieron que la presión arterial fluctúa sincrónicamente con la respiración y Sigmund Mayer observó que también existían oscilaciones más lentas no relacionadas con la respiración. En 1921 Heinrich Ewald Hering mostró la existencia de barorreceptores de alta presión en los senos carotideos y probó que la estimulación de los nervios aferentes que inervan estos receptores induce bradicardia e hipotensión. Estos estudios fueron más tarde avanzados por Corneille Heymans quien ganó el premio Nobel por estos estudios en 1938. En la época de los setentas Cowley y Guyton produjeron denervación sino-aórtica en los perros y de esta manera demostraron la importancia fundamental del reflejo barorreceptor en la estabilización de la presión arterial.
The baroreceptor reflex is poorly known by most physicians even though is fundamental in stabilizing the blood pressure on a beat to beat basis and is crucial for survival. Its fascinating history is briefy reviewed in this article. In 1852 Claude Bernard discovered that the sympathetic nerves of the neck innervate the blood vessels of the skin of the rabbit. Edgar Douglas Adrian in 1932 demonstrated that the sympathetic nerves that innervate the blood vessels discharge spontaneously at a rate of 4-6 per second and thus discovered the physiological basis of the vasomotor tone. In the XIX century Ludwig Traube and Karl Constantine Ewald Hering discovered that blood pressure fluctuates synchronously with respiratory movements and Sigmund Mayer observed that there are also slow non respiratory fluctuations of blood pressure. In 1921 Heinrich Ewald Hering found that high pressure baroreceptors are located in the carotid sinuses and demonstrated that the stimulation of the afferent nerve that innervates it induces bradycardia and hypotension. These studies were further advanced by Corneille Heymans who won the Nobel Prize for these studies in 1938. Later Cowley and Guyton produced sino-aortic denervation in dogs and thereby could demonstrate the fundamental importance of the baroreceptor reflex in the stabilization of blood pressure.
Subject(s)
History, 19th Century , History, 20th Century , History, 21st Century , Humans , Baroreflex , Cardiology/history , Neurology/history , Physiology/history , France , United StatesABSTRACT
BACKGROUND: The nucleus tractus solitarius (NTS), the region of the brain stem in which primary baroreceptor afferents teminate, is critically important in the normal regulation of arterial pressure (AP). In the NTS, excitatory amino acids such as L-glutamate serve as the main neurotransmitter in the regulation of AP. However, the function of GABA in the NTS has not been established. To test the function of GABA, we applied GABAergic agents to the NTS. METHODS: The experiments were conducted on adult male Sprague-Dawley rats weighing 300-500g. A cannula (PE-50 tubing filled with heparinized saline) was inserted into the femoral artery for recording of AP and heart rate(HR). Another cannula was inserted into the femoral vein for administration of nitroprusside or phenylephrine. After rats were placed on a sterotaxic instrument, the dorsal surface of the medulla was exposed, and with the aid of a surgical microscope, the NTS was visualized. Drug injections were made into the NTS using single- or three-barreled grass micropipettes pulled to an outer diameter of 80-100(micro)m and connected to a 1(micro)l Hamilton syringe. RESULTS: The follwing results were obtained in this experiment. Injection into the NTS of 10 or 20 nmol nipecitic acid, a selective inhibitor of GABA untake, produced an increase in AP. The pressor responses evoked by two doses of nipecotic acid were not significantly different. Injection of GABA(A) agonist, musciml(5 pmol in 80 nl artificial CSF) and GABA(B) agonist, baclofen (20 pmol in 80 nl) into the NTS of urethane-anesthetized rats prodused an increase in AP of 16.6+/-1.3 and 27.6+/-1.5 mmHg, respectively. Thus the pressor response to GABA(B) agonist was greater than to GABA(A) agonist. On the other hand, microinjection of GABA(A) antagonist, bicuculline and GABA(B) antagonist, phaclofen into the NTS decreased AP by approximately 13.4+/-1.0 and 20.9+/- mmHg, respectively. Thus injection of nipecotic acid into the NTS was greater in control group compared with the muscimiol or baclofen groups. The AP changes caused by i.v. injection of nitroprusside or phenylephrine were smallest in control group and greatest in the baclofen group. When calculated as baroreflex sensitivity, the change was greatest in control group and smallest in the baclofen group. CONCLUSION: From these results it was concluded that GABA in the NTS plays an important role in the regulation of AP, especially through GABA(B) receptors, and have an inhibitory effect on baroreceptor reflex.
Subject(s)
Adult , Animals , Humans , Male , Rats , Arterial Pressure , Baclofen , Baroreflex , Bicuculline , Blood Pressure , Brain Stem , Catheters , Excitatory Amino Acids , Femoral Artery , Femoral Vein , GABA Agents , gamma-Aminobutyric Acid , Glutamic Acid , Hand , Heart , Heparin , Microinjections , Neurotransmitter Agents , Nitroprusside , Phenylephrine , Poaceae , Pressoreceptors , Rats, Sprague-Dawley , Solitary Nucleus , SyringesABSTRACT
Aim To determine the roles of peripheral ? 1 and ? 2 -adrenoceptors (? 1-AR,? 2-AR) in inhibition of carotid sinus barore ceptor reflex(CSR) induced by intracerebroventricular injection (icv) of histami ne (HA).Methods The left and right carotid sinus regions were i solated from the systemic circulation in 22 male Sprague-Dawley rats anesthetiz ed with pentobarbital sodium.The intracarotid sinus pressure (ISP) was altered in a stepwise ma nner in vivo.ISP-mean arterial pressure (MAP) relationship curve and its ch aracteristic parameters were constructed by fitting to the logistic function wit h five parameters.The changes in CSR performance induced by icv HA and the effec ts of pretreatment with ? 1-AR or ? 2-AR selective antagonist into the per ipheral vein on the responses of CSR to HA were examined.Results icv microinjection of HA (60 ?mol?L -1 in 5 ?l) significantly shifted the ISP-MAP relationship curve upwards (P0.05).Conclusion The intracerebroventricular administration of HA results in a rapid resetting of CSR and a decrease in reflex sensitivity, and the functions of both the peripheral ? 1-AR and ? 2-AR may attenuate CSR resetting induced by icv microinjection of HA. Furthermore,the peripheral ? 1-AR might play an important role in mediating the responses of CSR to central HA.
ABSTRACT
In order to characterize the neural control of the circulation in an organism undergoing a rapid somatic growth, we compared the arterial baroreceptor reflex in two groups of male Wistar rats anesthetized with urethane. The first group consisted of 36 rats of 6-7 weeks old, known to exhibit the greatest rate of increase of the body weight during the life span, whereas the second group consisted of 30 full-grown rats of 20-22 weeks old. When arterial pressure was controlled by phenylephrine or nitroglycerin, the reflex change in renal nerve activity was elicited over the arterial pressure range 15-30 mmHg lower than that of full-grown rats. The difference was attributable partly, but not exclusively, to the lower operating range of arterial baroreceptors in the former groups. Although no difference was observed between the two groups with respect to the reflex fall in arterial pressure in response to graded electrical stimulation of the aortic nerve, the accompanying bradycardia was significantly smaller in 6-7 weeks old rats primarily due to the difference in the vagally mediated component of the reflex response. In conclusion, the arterial baroreceptor reflex of growing rats, as compared to full-grown counterparts, is characterized by deviation of the operating range of arterial baroreceptors as well as the arterial baroreceptor reflex itself to lower arterial pressure range and poor development of the vagally mediated reflex bradycardia.
ABSTRACT
Objective:To investigate the correlation between arterial baroreceptor reflex (ABR) function and target organ dam age (TOD) in spontaneously hypertensive rats (SHR) .Methods:Twenty- four- hour blood pressure (SBP and DBP ) ,blood pressure variability (BPV ) ,heart rate (HR ) and HR variability (HRV ) were m easured in conscious, unrestrained SHR and Wistar- Kyoto (WKY ) rats.ABR function control of heart period (ABR- HP) and blood pressure (ABR- BP) were determined respectively.Hypertensive TOD was evaluated according to the scoring system.Results:SBP, DBP and their BPV were significantly increased in SHR compared with those of WKY rats.No difference of HR was found between the 2 strains,but HRV was significantly decreased in SHR when com pared with WKY rats.ABR- HP and ABR- BP of SHR were significantly decreased compared with those of WKY rats (P