Conscious Rabbits Research Articles

599-P: Magnetic Field vs. Calcium Channel Blockade Effect on Microcirculation: Potential Implementation in Diabetic Foot Microvascular Dysfunction

The goal was to compare static magnetic field (SMF) vasodilator capacity with verapamil (VER) a potent Ca2+ channel blocking agent infusion, aimed to asses SMF potential implementation in conditions with vascular ischemia. Mean femoral artery blood pressure, heart rate and ear lobe skin microcirculatory blood flow measured by microphotoelectric plethysmogram (MPPG) were simultaneously recorded in conscious rabbits after 40-min carotid baroreceptor exposure to 0.35 T SMF (SMF-Car, n = 14) or 0.25 T SMF, generated by Nd-Fe-B magnets, exposed directly to ear microvascular net (SMF-Ves, n = 20), Fig. 1a, and compared with that after 30 min VER i.v. infusion (20 mg kg-1 min-1, n = 20), Fig. 1b. The principal finding is that SMF-Car, SMF-Ves and VER significantly increased microcirculation by: 22.6 ± 11.11%, 17.9 ± 9.58% and 30.5 ± 14.06% (mean ± SEM) resp. and that was no significant difference between all of three treatments (p = 0.986). Microvascular dilation was accompanied by significant decrease of baroreflex sensitivity in VER and its increase in SMF-Car coupled with enhanced vessel sensitivity to nitric oxide dilatory effect. This suggests SMF strong, comparable with VER vasodilator property tailored to address neural and myogenic component of microvascular dysfunction in diabetic foot and nephropathy especially employing both SMFs vasodilation synergy. Disclosure J. Gmitrov: None.

Empagliflozin modulates renal sympathetic and heart rate baroreflexes in a rabbit model of diabetes.

We determined whether empagliflozin altered renal sympathetic nerve activity (RSNA) and baroreflexes in a diabetes model in conscious rabbits. Diabetes was induced by alloxan, and RSNA, mean arterial pressure (MAP) and heart rate were measured before and after 1week of treatment with empagliflozin, insulin, the diuretic acetazolamide or the ACE inhibitor perindopril, or no treatment, in conscious rabbits. Four weeks after alloxan administration, blood glucose was threefold and MAP 9% higher than non-diabetic controls (p < 0.05). One week of treatment with empagliflozin produced a stable fall in blood glucose (-43%) and increased water intake (+49%) but did not change RSNA, MAP or heart rate compared with untreated diabetic rabbits. The maximum RSNA to hypotension was augmented by 75% (p < 0.01) in diabetic rabbits but the heart rate baroreflex was unaltered. Empagliflozin and acetazolamide reduced the augmentation of the RSNA baroreflex (p < 0.05) to be similar to the non-diabetic group. Noradrenaline (norepinephrine) spillover was similar in untreated diabetic and non-diabetic rabbits but twofold greater in empagliflozin- and acetazolamide-treated rabbits (p < 0.05). As empagliflozin can restore diabetes-induced augmented sympathetic reflexes, this may be beneficial in diabetic patients. A similar action of the diuretic acetazolamide suggests that the mechanism may involve increased sodium and water excretion. Graphical abstract.

Differential sympathetic response to lesion-induced chronic kidney disease in rabbits

Chronic kidney disease (CKD) is associated with greater sympathetic nerve activity but it is unclear if this is a kidney-specific response or due to generalized stimulation of sympathetic nervous system activity. To determine this, we used a rabbit model of CKD in which quantitative comparisons with control rabbits could be made of kidney sympathetic nerve activity and whole-body norepinephrine spillover. Rabbits either had surgery to lesion 5/6th of the cortex of one kidney by electro-lesioning and two weeks later removal of the contralateral kidney, or sham lesioning and sham nephrectomy. After three weeks, the blood pressure was statistically significantly 20% higher in conscious rabbits with CKD compared to rabbits with a sham operation, but their heart rate was similar. Strikingly, kidney nerve activity was 37% greater than in controls, with greater burst height and frequency. Total norepinephrine spillover was statistically significantly lower by 34%, and kidney baroreflex curves were shifted to the right in rabbits with CKD. Plasma creatinine and urine output were elevated by 38% and 131%, respectively, and the glomerular filtration rate was 37% lower than in sham-operated animals (all statistically significant). Kidney gene expression of fibronectin, transforming growth factor-β, monocyte chemotactic protein1, Nox4 and Nox5 was two- to eight-fold greater in rabbits with CKD than in control rabbits. Overall, the glomerular layer lesioning model in conscious rabbits produced a moderate, stable degree of CKD characterized by elevated blood pressure and increased kidney sympathetic nerve activity. Thus, our findings, together with that of a reduction in total norepinephrine spillover, suggest that kidney denervation, rather than generalized sympatholytic treatments, may represent a preferable management for CKD associated hypertension.

Estimation of the vascular resistance amplifier in the renal vascular bed in conscious hypertensive rabbits: comparison with the total peripheral vasculature

ObjectivesThe vascular amplifier in hypertension is a result of structural changes in resistance arteries. We estimated the vascular amplifier hypertensive:normotensive (H:N) ratio in the renal bed compared with the total peripheral bed in conscious rabbits during infusion of vasoconstrictor and vasodilator stimuli. MethodsRabbits were subjected to bilateral renal cellophane wrap or sham operation. A perivascular ultrasonic flow probe was implanted on the left renal artery to measure renal blood flow. A catheter was inserted into the thoracic aorta for agonist administration. Blood pressure, heart rate and renal blood flow were measured on three separate days in conscious rabbits with intact effectors, ganglionic block or neurohumoral block. Dose-response curves were constructed to intra-arterial infusion of noradrenaline, angiotensin II, adenosine and acetylcholine. ResultsResting renal vascular resistance in hypertensive rabbits was markedly decreased by ganglionic block and further by neurohumoral block. With effectors intact, ganglionic block or neurohumoral block, the H:N ratio for renal vascular resistance was 2.32, 1.72 or 1.72, respectively. The ratio was generally maintained during the infusion of constrictor and dilator drugs although distortions occurred at higher concentrations of constrictor or dilator drugs. ConclusionsEstimation of the renal resistance amplifier in renal wrap hypertension with neurohumoral block accords with our earlier estimates of the total peripheral resistance amplifier (1.79). This vascular resistance amplifier is consistent with a decrease in internal radius through structural remodelling in the renal vascular bed as is reflected in the total arterial circulation in hypertension.

Treatment with SGLT2 Inhibitor Empagliflozin Modulates Renal Sympathetic Nerve Activity in Diabetic Rabbits

In patients with type 2 diabetes, antihyperglycemic treatment with the sodium‐glucose cotransporter 2 (SGLT2) inhibitor empagliflozin is associated with a reduction in cardiovascular mortality of 38% (EMPA‐REG OUTCOME trial). In individuals with poorly controlled type 2 diabetes, sympathetic nervous system (SNS) activation is associated with poor cardiovascular outcomes. We explored the notion that the mechanisms underlying the cardiovascular benefits of empagliflozin treatment may involve an action on the SNS.Diabetes was induced by a single dose of alloxan in New Zealand White rabbits. We determined the changes in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) as well as baroreflex responses to changes in BP and norepinephrine spillover in conscious rabbits. The effects of one‐week treatment with empagliflozin were compared to those of another blood glucose‐lowering treatment insulin, the proximally‐acting natriuretic acetazolamide, the ACE inhibitor perindopril, vehicle treatment and to an untreated diabetic group.Diabetic rabbits (n=39) were treated with daily insulin to maintain a stable elevation in blood glucose (20.5±0.4mM vs 6.5±0.4mM in controls) over 4 weeks. Diabetes was associated with 9% greater BP than in non‐diabetic rabbits (P=0.02) but no difference in RSNA or HR. One‐week treatment with empagliflozin lowered blood glucose by 43% (without insulin), and there was a 49% increase in water intake. There was no difference in BP, HR or RSNA between empagliflozin‐treated and untreated diabetic rabbits or those treated with acetazolamide. However, insulin lowered blood glucose similarly to empagliflozin (32%) and increased HR (+10%) while perindopril lowered BP (−9%). There was marked augmentation (+69%) of the maximum RSNA response to baroreceptor unloading in diabetic rabbits compared to non‐diabetic (P&lt;0.01). Empagliflozin attenuated the baroreflex by 34% and acetazolamide had a similar blunting effect (−29%, both P&lt;0.05). Empagliflozin also attenuated the HR baroreflex (−8%) but insulin and perindopril had no effect on either baroreflex. Diabetes did not alter BP or HR variability but empagliflozin and acetazolamide treatment increased mid frequency HR power. Norepinephrine spillover to plasma was similar in diabetic and non‐diabetic rabbits but was elevated after both empagliflozin (+147%) and acetazolamide (+134%, P&lt;0.05).In conclusion, empagliflozin effectively normalized the maximal RSNA response to acute BP lowering without altering resting hemodynamic or sympathetic activity in conscious diabetic rabbits. The similarity of these effects with those of acetazolamide suggests that the mechanism underlying the cardiovascular benefits of empagliflozin is linked to its natriuretic action.Support or Funding InformationThis work was supported by Boehringer Ingelheim.

Design, synthesis and biological evaluation of pyrazolopyrimidinone based potent and selective PDE5 inhibitors for treatment of erectile dysfunction

Our previous discovery of series of pyrazolopyrimidinone based PDE5 inhibitors led to find potent leads but with low aqueous solubility and poor bioavailability, and low selectivity. Now, a new series of same pyrazolopyrimidinone scaffold is designed, synthesized and evaluated for its PDE5 inhibitory potential. In this study, some of the molecules are found more potent and selective PDE5 inhibitors in vitro than sildenafil. The studies revealed that compound 5 is 20 fold selective to PDE5 against PDE6. As PDE6 enzyme is involved in the phototransduction pathway in the retina and creates distortion problem, the selectivity for PDE5 specifically against PDE6 enzyme is preferred for any development candidate and in present study, compound 5 has been found to be devoid of this liability of selectivity issue. Moreover, compound 5 has shown excellent in vivo efficacy in conscious rabbit model, it's almost comparable to sildenafil. The preclinical pharmacology including pharmacokinetic and physicochemical parameter studies were also performed for compound 5, it was found to have good PK properties and other physicochemical parameters. The development of these selective PDE5 inhibitors can further lead to draw strategies for the novel preclinical and/or clinical candidates based on pyrazolopyrimidinone scaffold.

Melt-Cast Films Significantly Enhance Triamcinolone Acetonide Delivery to the Deeper Ocular Tissues.

Delivering an effective drug load to the posterior section of the ocular tissues, while using a non-invasive technique, has always been a challenge. In this regard, the goal of the present study was to develop sustained release triamcinolone acetonide (TA) loaded polymeric matrix films for ocular delivery. The TA-films were prepared in two different polymer matrices, with drug loadings of 10% and 20% w/w, and they were evaluated for ocular distribution in vivo in a conscious rabbit model. A 4% w/v TA suspension (TA-C) was used as a control for in vitro and in vivo studies. The TA-films, prepared with melt-cast technology, used polyethylene oxide (PEO) and Soluplus® as the polymer matrix. The films were evaluated with respect to assay, content uniformity, excipient interaction, and permeability across isolated rabbit sclera. The distribution of TA in the ocular tissues, post topical administration, was determined in New Zealand male albino rabbits as a function of dose, and was compared against TA-C. The assay of the 10% and 20% w/w film was in the range from 70–79% and 92–94% for the Soluplus® and PEO films, respectively, and content uniformity was in the range of 95–103% for both the films. The assay of the TA from Soluplus® films was less compared with the PEO films and showed an interaction with TA, as revealed by Differential Scanning Calorimetry (DSC). Hence, Soluplus® films were not selected for further studies. No interaction was observed between the drug and PEO polymer matrix. The enhancement of trans-scleral flux and permeability of TA was about 1.16 and 1.33-folds, respectively, from the 10% w/w PEO and 3.5 and 2.12-folds, respectively, from the 20% w/w PEO films, as compared with TA-C formulations. The in vivo studies demonstrate that significantly higher TA levels were observed in the anterior and posterior segments of the eye at the end of 6h with the PEO films. Therefore, the PEO based polymeric films were able to deliver TA into the back of the eye efficiently and for prolonged periods.

Electrolytes and Biochemical Changes in Cerebrospinal Fluid in Drowning: Experimental Rabbit Model.

The diagnosis of drowning is still a difficult task in forensic science. Biochemical changes in different body fluids have been examined for the identification of drowning. However, none of them alone gives accurate results in the diagnosis of drowning and differentiation of saltwater and freshwater drowning. This study aimed to examine cerebrospinal fluid changes in drowned rabbits. Six groups of rabbits were used including immersed dead rabbits in freshwater or saltwater (as control groups), alive fully conscious rabbits drowned in freshwater and saltwater, and anesthetized rabbits drowned in freshwater and saltwater. Cerebrospinal fluid electrolytes except for potassium levels were significantly higher in rabbits drowned consciously in saltwater than their level in the control group. In rabbit drowned in freshwater, the examined electrolytes decreased significantly. In addition, urea, creatinine, uric acid, glucose, and tumor necrosis factor were different in cases of freshwater and saltwater drowning from those of control rabbits. Electrolytes and biochemical changes of unconscious rabbits drowned in water showed no significant difference from those of control rabbits. Cerebrospinal fluid examination in drowning gives promising results in the diagnosis of drowning. In addition, the differentiation between freshwater and saltwater drowning was possible.

Sublingual spray drug delivery of ketorolac-loaded chitosan nanoparticles

Introduction: The aim of this study was to investigate ketorolac (KT) systemic absolute bioavailability after sublingual (SL) administration in vivo to conscious rabbits. Furthermore, the study investigated the potential use of chitosan nanoparticles as a delivery system to enhance the systemic bioavailability of KT following SL administration.Methods: Ketorolac-loaded chitosan nanoparticles were prepared through ionotropic gelation of chitosan with tripolyphosphate anions. The KT-nanoparticles were administered SL as a spray to rabbits and KT plasma concentration at predetermined time points was compared to SL spray administration of KT in solution. The concentrations of KT in plasma were analyzed by ultra-performance liquid chromatography mass spectroscopy (UPLC/MS).Results: KT-loaded chitosan nanoparticles significantly (p < .05) enhanced systemic absorption with 97% absolute bioavailability as compared to 70% after SL administration of KT solution.Conclusions: The results of the present study suggest that SL absorption of KT illustrated flip-flop kinetics with prolonged persistence in the body compared to intravenous administration. Formulation of KT as chitosan nanoparticles has increased its systemic bioavailability after SL spray administration. The new delivery system could be an attractive approach for the delivery of KT.

Rapamycin Alters MicroRNA Signature Profile in Diabetic Rabbit following Myocardial Ischemia Reperfusion Injury: A Preclinical Approach for Cardioprotection.

BackgroundMyocardial ischemia reperfusion (I/R) injury associated with cardiovascular risk factors and comorbidities, including Diabetes (DM), is a major complication for development of heart failure. Mammalian target of Rapamycin (mTOR) is robustly active in DM and further exacerbated during I/R. mTOR inhibition with rapamycin at reperfusion preserves cardiac function with reduction of myocardial infarction in diabetic mice. Recent advances in non‐coding RNA analysis demonstrates microRNA (miR) plays an important role in cardiovascular diseases. We examined the effect of rapamycin treatment at the onset of reperfusion in a conscious diabetic rabbit model of I/R and identified differentially regulated miRs.Methods and ResultsTo induce diabetes, alloxan monohydrate (125 mg/kg, i.v.) was administered in New Zealand male rabbits (n=26; average 3 kg, 4 month old). Blood glucose levels increased to 345±66 mg/dL (n=10) following 2 weeks of alloxan administration. The animals were categorized to three groups: Diabetes (DM), Diabetes subjected to I/R (DM+I/R) and Diabetes underwent I/R and treated with Rapamycin (DM+I/R+Rapa). Post 7 days of implantation of balloon occluders on the top of the coronary artery, the conscious rabbits were subjected to 45‐min ischemia and 3 days of reperfusion by inflating/deflating the balloon. Rapamycin (0.25 mg/kg, i.v.) or DMSO (vehicle) was infused 5 min before reperfusion. Plasma was collected at baseline, 1, 2, 4 and 24 hours during the reperfusion and cardiac Troponin I (cTnI) release was measured by ELISA. The results show that rapamycin significantly reduced myocardial infarction in DM rabbits following I/R (Figure A) as assessed by triphenyltetrazolium chloride staining. Rapamycin also reduced cTnI at 1 hr and 2 hr of reperfusion as compared to vehicle alone (Figure B). RNA isolated from risk area of left ventricle heart tissue from different groups (n=3) was subjected to miRNA‐Array analysis using μParaflo® Microfluidic Biochip Technology (Figure C). The results show 34 out of 761 miRs were differentially regulated with Rapamycin treatment (p&lt;0.01) (Figure D). Enrichment Analysis and Annotation of selected miRs were performed using miEAA and DAVID tools to identify potential targets and its interaction with mTOR signaling pathway.ConclusionThis Preclinical translational study demonstrates that rapamycin could be a promising drug in attenuation of reperfusion injury in diabetic patients following acute MI by altering novel miRs.Support or Funding InformationNIH RO1HL134366 (AD &amp; RCK) &amp; CCTR Endowment Fund UL1RR031990 (AD)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Postconditioning Effect of PDE5 inhibitor, Sildenafil in Normal and Diabetic Rabbits following Myocardial Ischemia/Reperfusion injury.

BackgroundSeveral studies have demonstrated cardioprotective effects of the phosphodiesterase 5 inhibitor, sildenafil (SILD), in the setting of myocardial ischemia and reperfusion (MI/R) in mice and rabbits. However, it is unclear whether sildenafil exerts postconditioning effect in normal and diabetic rabbits.Methods and ResultsTo induce diabetes, alloxan monohydrate (125 mg/kg, i.v.) was administered in New Zealand white male rabbits (n=10; ~3 kg, 4 months old). Blood glucose level increased to 342±21 mg/dL following 2 weeks of alloxan administration. Balloon occluders were implanted on the top of the coronary artery and 7 days later, conscious rabbits were subjected to 45‐min ischemia (I) and 3 days of reperfusion (R) by inflating/deflating the balloon. Saline (as control) or Sildenafil (0.71 or 1.4 mg/kg; i.v.) was infused for 60 min starting 5 min before reperfusion. Myocardial infarct size was determined by triphenyltetrazolium chloride staining and troponin I (cTnI) was measured using ELISA method in the plasma. The result showed that sildenafil (both concentrations) significantly reduced myocardial infarct size (Figure A) and peak plasma levels of cardiac troponin I. Similarly, sildenafil reduced infarct size in diabetic rabbits (DM) following MI/R (Figure C). There were no differences in hemodynamics during MI/R or myocardial area‐at‐risk (AAR) (Figure B and D).ConclusionSildenafil exerts significant postconditioning effect in normal and diabetic rabbits of conscious I/R model that is potentially is free of confounding factors associated with open‐chest preparations.Support or Funding InformationNIHRO1HL134366 (AD &amp; RCK), RO1HL118808 (RCK), RO1HL133167 (RCK)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cardiovascular Monitoring in the Conscious Young Rabbit Using Telemetry

Cardiovascular Monitoring in the Conscious Young Rabbit Using Telemetry

Measurements of Arterial Blood Pressure and ECG Parameters in Conscious Non-telemetered Rabbits: A Suitable Approach for the Integration of Safety Pharmacology End-points in Toxicology Studies

Measurements of Arterial Blood Pressure and ECG Parameters in Conscious Non-telemetered Rabbits: A Suitable Approach for the Integration of Safety Pharmacology End-points in Toxicology Studies

Electrical Stimulation of the Vagus Nerve Modulates the Development of Oxygen Epilepsy in Rabbits

We report here our studies of the effects of electrical stimulation of the vagus nerve on the development of oxygen convulsions and cardiovascular reactions in hyperbaric oxygen (HBO2). The motor signs of the neurotoxic action of HBO2 were identified in conscious rabbits exposed to O2 at 5 atm, along with EEG, ECG, external respiration, and brain blood filling in conditions of stimulation of the cervical component of the vagus nerve. Oxygen convulsions were found to be preceded by increased sympathetic tone, with a specific EEG pattern (synchronization of slow waves), changes in the ECG (tachycardia) and respiration (hyperventilation). Vagal stimulation enhanced the parasympathetic component of the autonomic system and significantly delayed the prodromal signs of oxygen toxicity and the onset of convulsions. Afferent spike activity from the visceral organs is regarded as a new target for countering the neurotoxic effects of hyperbaric oxygen.

Acute Effect of Central Administration of Urotensin II on Baroreflex and Blood Pressure in Conscious Normotensive Rabbits.

In the present study, we examined the effects of central administration of Urotensin II on blood pressure, heart rate, and baroreceptor heart rate reflexes in conscious normotensive rabbits. Preliminary operations were undertaken to implant a balloon cuff on the inferior vena cava for baroreflex assessments and to implant cannula into the lateral and fourth ventricle. After 2 weeks of recovery cumulative dose response curves to Urotensin II (10, 100 ng, 1, 10, and 100 μg) given into the ventricles, or Ringer's solution as a vehicle were performed on separate days. Injections were given each hour and baroreflex assessments were made 30 min after each administration. Analysis of the dose response curves to Urotensin II compared to vehicle administered into the lateral or fourth ventricle, indicated little change to blood pressure or heart rate. Analysis of the time course to the highest dose over a 30 min period revealed a small (−5 mmHg) depressor response maximal at 10 min when injected into the fourth ventricle but no effect when injected into the lateral ventricle. Baroreflex assessments made at each dose showed that there was no change in baroreflex sensitivity but that an increase in the upper plateau was observed when Urotensin was injected into the lateral ventricle and a tendency for a reduced lower heart rate plateau was observed after fourth ventricle administration. Clonidine administration in the fourth ventricle decreased blood pressure and heart rate, thus confirming catheter patency. In conclusion, our findings suggest that Urotensin II in the forebrain and brainstem may play a role in modulating cardiac sympathetic and vagal baroreflexes but only during large acute changes in blood pressure.

Diclofenac sodium ion exchange resin complex loaded melt cast films for sustained release ocular delivery

Purpose: The goal of the present study is to develop polymeric matrix films loaded with a combination of free diclofenac sodium (DFSfree) and DFS:Ion exchange resin complexes (DFS:IR) for immediate and sustained release profiles, respectively.Methods: Effect of ratio of DFS and IR on the DFS:IR complexation efficiency was studied using batch processing. DFS:IR complex, DFSfree, or a combination of DFSfree + DFS:IR loaded matrix films were prepared by melt-cast technology. DFS content was 20% w/w in these matrix films. In vitro transcorneal permeability from the film formulations were compared against DFS solution, using a side-by-side diffusion apparatus, over a 6 h period. Ocular disposition of DFS from the solution, films and corresponding suspensions were evaluated in conscious New Zealand albino rabbits, 4 h and 8 h post-topical administration. All in vivo studies were carried out as per the University of Mississippi IACUC approved protocol.Results: Complexation efficiency of DFS:IR was found to be 99% with a 1:1 ratio of DFS:IR. DFS release from DFS:IR suspension and the film were best-fit to a Higuchi model. In vitro transcorneal flux with the DFSfree + DFS:IR(1:1)(1 + 1) was twice that of only DFS:IR(1:1) film. In vivo, DFS solution and DFS:IR(1:1) suspension formulations were not able to maintain therapeutic DFS levels in the aqueous humor (AH). Both DFSfree and DFSfree + DFS:IR(1:1)(3 + 1) loaded matrix films were able to achieve and maintain high DFS concentrations in the AH, but elimination of DFS from the ocular tissues was much faster with the DFSfree formulation.Conclusion: DFSfree + DFS:IR combination loaded matrix films were able to deliver and maintain therapeutic DFS concentrations in the anterior ocular chamber for up to 8 h. Thus, free drug/IR complex loaded matrix films could be a potential topical ocular delivery platform for achieving immediate and sustained release characteristics.

Comparison in Conscious Rabbits of the Baroreceptor-Heart Rate Reflex Effects of Chronic Treatment with Rilmenidine, Moxonidine, and Clonidine.

We investigated the effects of chronic subcutaneous treatment with centrally-acting antihypertensive agents moxonidine, rilmenidine, and clonidine on the baroreflex control of heart rate (HR) in conscious normotensive rabbits over 3 weeks. Infusions of phenylephrine and nitroprusside were performed at week 0 and at weeks 1 and 3 of treatment to determine mean arterial pressure (MAP)-HR baroreflex relationships. A second curve was performed after intravenous methscopolamine to determine the sympathetic baroreflex relationship. The vagal component of the reflex was determined by subtracting the sympathetic curve from the intact curve. Clonidine and moxonidine (both 1 mg/kg/day), and rilmenidine (5 mg/kg/day), reduced MAP by 13 ± 3, 15 ± 2, and 13 ± 2 mmHg, respectively, but had no effect on HR over the 3-week treatment period. Whilst all three antihypertensive agents shifted baroreflex curves to the left, parallel to the degree of hypotension, moxonidine and rilmenidine decreased the vagal contribution to the baroreflex by decreasing the HR range of the reflex but moxonidine also increased sympathetic baroreflex range and sensitivity. By contrast clonidine had little chronic effect on the cardiac baroreflex. The present study shows that second generation agents moxonidine and rilmenidine but not first generation agent clonidine chronically shift the balance of baroreflex control of HR toward greater sympathetic and lesser vagal influences. These changes if translated to hypertensive subjects, may not be particularly helpful in view of the already reduced vagal contribution in hypertension.

How Sound Modulates Responses to Light with Different Time Intervals Between Stimuli of Different Modalities

Extracellular recording of 34 neurons in the primary visual cortex of three conscious rabbits was performed in chronic experimental studies addressing the effects of sound (2000 Hz, 70 dB, 40 msec) on the discrimination of weak light intensities (0.3–1 cd/m2). Sound was delivered with different time intervals before and after substitution of one light intensity by another (using a total of 15 intervals in the range –750 to +150 msec). Factor analysis of variance (ANOVA) showed that the time interval between the sound and the light had statistically significant influences on neuron responses. Sound itself provoked no response. Neuron reactions consisted of responses to increases (on responses) and decreases (off responses) in light intensity. The most marked effect of sound was seen in the initial phase of the response (40–100 msec from the moment at which intensities were substituted). For every interval, neurons demonstrated both increases and decreases in reactions to complexes as compared with their responses to light. Wilcoxon’s T test was used to assess differences in sets of responses to light and to complexes. For the on responses of the whole group of neurons, the absolute values of responses to sound + light complexes were significantly (p < 0.05) different from responses to light (increased reactions) at intervals of –150, –40, and 0 msec. Two groups of neurons were identified, for which the effects of sound on responses to light were markedly different. Neurons of group 1 (n = 16) showed significant positive influences of light on on responses over a wide range of intervals (–150, –40, –20, 0, +20, +100 msec), along with a larger increase in the number of spikes due to sound (by 18–28%) as compared with responses to light. Neurons of group 2 (n = 18) had no significant intervals, i.e., at which reactions to complexes were not significantly different from responses to light. None of the study groups of neurons showed intervals with significant decreases in responses to complexes, though there was a tendency for reactions to complexes to shift towards weakening of responses at intervals of –750 and –80 msec for group 1 (p < 0.07) and at intervals of –500 and +20 sec for group 2 (p < 0.1). On responses were found to be more strongly affected by sound than off responses. The effects of sound on the second phases of responses to light (120–160 msec and later, n = 23) were also studied. Sound had markedly weaker effects on the second phase than the first. For the whole group of neurons with late phases, sound had significant influences on on responses with an interval of 0 msec and on off responses with intervals of +100 and +150 msec. Our study demonstrated similarity in the time intervals for modulation of reactions to light by sound in experiments on animals and psychophysical studies in humans. These data provide for more detailed studies of the integration of light and sound when used simultaneously.

Role of Beta Blockers on Adrenaline Induced Leukocytosis in Rabbits

Background: Plasma Leukocytosis is known to occur in a variety of clinical conditions viz. infections, inflammations and collagen disorders. Apart from these many physiological factors like heat, solar radiation and high altitude also causes leukocytosis. It has been reported that even corticosteroids can cause leucocytosis which is usually polY morphonuclear leucocytosis. Adrenaline administered by various routes like I/M, I/V and S/C is also known to cause a rise in blood leukocytes. It has been reported that even corticosteroids can cause leukocytosis, which is usually polymorphonuclear leukocytosis. Since catecholamines have been implicated in the release of polymorphs from bone marrow into blood in the glucocorticoids induced leukocytosis, this could be a likely mechanism. If so then adrenergic receptors may be mediating this release. Attempt will be made to characterize these adrenergic receptors by studying the effect of some beta blockers on adrenaline induced Leukocytosis. Materials and Methods: The study was conducted in conscious albino rabbit. The rabbits were divided into 3 groups with 6 rabbits in each group beta blockers used in the study were propranolol (0.5mg/kg) and atenolol (0.5mg/kg). Cell counts before drug administration served as control values. Adrenaline was used in the dose of 200microgram/kg. Result: Group1- significant rise in total leukocytes count in the form of 2 peaks, first occurring at 1hr with 21.85% rise and 2nd at 4hr with 41.89 % rise, at 2hr rise was not significant. At 24hr the counts came back to normal values Group2- significant fall in TLC at 1hr +1.2% and at 4hr +5% while at 2hr +2.4%. The fall in TLC at 24hr was insignificant.Group3- significant fall in TLC at 1hr +1.5% and at 4hr +10.2% while at 2hr +7.94%. The fall in TLC at 24hr was insignificant. Conclusion: The beta-blockers Propranolol and Atenolol successfully blocked the rise in blood leukocyte counts induced by Adrenaline which shows that Adrenaline induced leukocytosis occurs through the activation of beta-adrenoreceptors.

Central Angiotensin-II Increases Blood Pressure and Sympathetic Outflow via Rho Kinase Activation in Conscious Rabbits.

Elevated sympathetic tone and activation of the renin-angiotensin system are pathophysiologic hallmarks of hypertension, and the interactions between these systems are particularly deleterious. The importance of Rho kinase as a mediator of the effects of angiotensin-II (AngII) in the periphery is clear, but the role of Rho kinase in sympathoexcitation caused by central AngII is not well established. We hypothesized that AngII mediates its effects in the brain by the activation of the RhoA/Rho kinase pathway. Chronically instrumented, conscious rabbits received the following intracerebroventricular infusion treatments for 2 weeks via osmotic minipump: AngII, Rho kinase inhibitor Fasudil, AngII plus Fasudil, or a vehicle control. AngII increased mean arterial pressure over the course of the infusion, and this effect was prevented by the coadministration of Fasudil. AngII increased cardiac and vascular sympathetic outflow as quantified by the heart rate response to metoprolol and the depressor effect of hexamethonium; coadministration of Fasudil abolished both of these effects. AngII increased baseline renal sympathetic nerve activity in conscious animals and impaired baroreflex control of sympathetic nerve activity; again Fasudil coinfusion prevented these effects. Each of these end points showed a statistically significant interaction between AngII and Fasudil. Quantitative immunofluorescence of brain slices confirmed that Rho kinase activity was increased by AngII and decreased by Fasudil. Taken together, these data indicate that hypertension, elevated sympathetic outflow, and baroreflex dysfunction caused by central AngII are mediated by Rho kinase activation and suggest that Rho kinase inhibition may be an important therapeutic target in sympathoexcitatory cardiovascular diseases.