High Dose Of Isoproterenol Research Articles

PHARMACOLOGICAL ACTIVITY OF ULVA LACTUCA POLYPHENOLS FRACTION: CARDIOPROTECTIVE AND ANTIOXIDANT ACTIVITIES AGAINST ISOPROTERENOL-INDUCED MYOCARDIAL INFARCTION IN RATS

Objective: The objective of this study is to assess the activity of Ulva lactuca polyphenols fraction in protecting the myocardial infarction induced by a high dose of isoproterenol.
 Methods: This study was carried out using Wistar albino rats divided into six groups. Group 1 was the normal group. Groups 2, 3, 4, 5, and 6 received isoproterenol (85 mg/kg) i.p. twice at an interval of 24 h on the 14th and 15th day. In addition to isoproterenol, Group 3 received verapamil (5 μmol/kg) as a single dose intravenously on the 14th day 10 min before isoproterenol and Groups 4, 5, and 6 received U. lactuca polyphenols fraction at the doses of 50, 100, and 200 mg/kg, respectively, for 14 days. On the 16th day, serum and heart samples were harvested from the animals and the cardioprotective and antioxidant activities were assessed by studying the levels of cardiac functional heart marker enzymes, lipid profile, reduced glutathione, and antioxidant enzymes.
 Results: U. lactuca polyphenols fraction, at the tested doses, restored the levels of all serum markers and enzymes (aspartate aminotransferase, alanine aminotransferase, creatine phosphokinase, lactate dehydrogenase, cholesterol, triglycerides, and reduced glutathione) and heart homogenate antioxidant markers (reduced glutathione, superoxide dismutase, catalase, and glutathione peroxidase) significantly, in dose-dependent manner.
 Conclusion: This study suggests that U. lactuca polyphenols fraction has a cardioprotective effect against isoproterenol-induced myocardial infarction and possess antioxidant activities.

A11010 Changes of extracellular matrix metalloproteinase-2 of isoproterenol injured normotensive and hypertensive rats are hampered by treatment with omega-3 fatty acids and melatonin

Objectives: Experimental and clinical studies suggest that melatonin and omega-3 fatty acids (PUFA) are cardioprotective, but underlying molecular mechanisms are still not fully explored. We hypothesize that both compounds may affect extracellular matrix remodeling by modulation of extracellular matrix metalloproteinases (MMP) activity. We aimed to explore MMP-2 activity in plasma, aorta and heart in normotensive and hypertensive rats after infarct-like cardiac injury induced by high dose of isoproterenol (ISO) as well as the effects of treatments with PUFA and melatonin. Methods: We used in our experiment Wistar (W) and spontaneously hypertensive rats (SHR) which were divided into four groups. 1)Controls without treatment; 2)Iso-injured rats (118 mg/kg totally, s.c./7days); 3)Iso-injured rats treated with melatonin (10 mg/kg, p.o., 2-mo); 4)Iso-injured rats treated with PUFA (Omacor, 1.68 g/kg, p.o.,2-mo). Samples from plasma, left and right ventricles and aorta were used to determine activity of MMP-2 by using gelatin zymography. Results: There was higher plasma but lower heart tissue-related MMP-2 activity in non-treated SHR vs W rats and no difference in aorta. ISO caused an increase of MMP-2 activity in plasma as well as in atria and decrease in left and right ventricles of W rats. In contrast, ISO decreased MMP-2 activity in plasma, aorta and increased in left and right ventricles of SHR. Melatonin and Omacor suppressed plasma MMP-2 activity in Iso-treated W but not in Iso-SHR. Both compounds lowered MMP-2 activity in atria of Iso-W rats but elevated in iso-SHR as well as decreased MMP-2 activity in ventricles of Iso-treated SHR only. Conclusion: Data indicates that both melatonin and Omacor modulate circulating and cardiovascular tissue-related MMP-2 activity. Supported:VEGA 2/0167/15, 2/0076/12; APVV-15-0119

Nitric oxide synthase and cyclooxygenase modulate β-adrenergic cutaneous vasodilatation and sweating in young men.

β-Adrenergic receptor agonists such as isoproterenol induce cutaneous vasodilatation and sweating in humans, but the mechanisms underpinning this response remain unresolved. Using intradermal microdialysis, we evaluated the roles of nitric oxide synthase (NOS) and cyclooxygenase (COX) in β-adrenergic cutaneous vasodilatation and sweating elicited by administration of isoproterenol. We show that while NOS contributes to β-adrenergic cutaneous vasodilatation, COX restricts cutaneous vasodilatation. We also show that combined inhibition of NOS and COX augments β-adrenergic sweating These new findings advance our basic knowledge regarding the physiological control of cutaneous blood flow and sweating, and provide important and new information to better understand the physiological significance of β-adrenergic receptors in the skin. β-Adrenergic receptor agonists such as isoproterenol can induce cutaneous vasodilatation and sweating in humans, but the mechanisms underpinning this response remain unresolved. We evaluated the hypotheses that (1) nitric oxide synthase (NOS) contributes to β-adrenergic cutaneous vasodilatation, whereas cyclooxygenase (COX) limits the vasodilatation, and (2) COX contributes to β-adrenergic sweating. In 10 young males (25±5years), cutaneous vascular conductance (CVC) and sweat rate were evaluated at four intradermal forearm skin sites infused with (1) lactated Ringer solution (control), (2) 10mm Nω -nitro-l-arginine (l-NNA), a non-specific NOS inhibitor, (3) 10mm ketorolac, a non-specific COX inhibitor, or (4) a combination of l-NNA and ketorolac. All sites were co-administered with a high dose of isoproterenol (100μm) for 3min to maximally induce β-adrenergic sweating (β-adrenergic sweating is significantly blunted by subsequent activations). Approximately 60min after the washout period, three incremental doses of isoproterenol were co-administered (1, 10 and 100μm each for 25min). Increases in CVC induced by the first and second 100μm isoproterenol were attenuated by l-NNA alone, and those in response to all doses of isoproterenol were reduced by l-NNA with co-infusion of ketorolac (all P≤0.05). Ketorolac alone augmented increases in CVC induced by 10μm and by the second 100μm isoproterenol (both P≤0.05). While isoproterenol-induced sweating was not affected by the separate administration of l-NNA or ketorolac (all P>0.05), their combined administration augmented sweating elicited by the first 3min of 100μm isoproterenol (P=0.05). We show that while NOS contributes to β-adrenergic cutaneous vasodilatation, COX restrains the vasodilatation. Finally, combined inhibition of NOS and COX augments β-adrenergic sweating.

Comparison of the specificity of cardiac troponin I and creatine kinase MB in isoproterenol-induced cardiotoxicity model in rats

The aim of this study was to implement the determination of cardiac markers in preclinical research at our department. For this purpose, the pathophysiological model of acute cardiotoxicity induced by high doses of isoproterenol was used. Isoproterenol hydrochloride was intraperitoneally administrated to 42 Wistar male rats at a dose of 50 mg/kg body weight. Cardiac injury was determined by assessing the concentrations of the cardiac markers (cTnI - cardiospecific troponin I and CKMB - cardiac isoenzyme creatine kinase) in the blood at predetermined time-intervals (2, 4, 6, 12, 24 and 36 h), and confirmed by ECG. Isoproterenol hydrochloride caused an elevation in the plasma concentrations of both markers. The results showed a significant difference (P< 0.01) in the concentrations of cTnI between the experimental and control groups at 2, 4, 6 and 24 h with a maximum peak between the fourth and sixth hour. However, the difference in the concentrations of CKMB between the experimental and control groups was non-significant. This experiment confirmed that cTnI is more cardiospecific than CKMB. It also revealed the possibility to use this marker in preclinical testing.

Forearm vasodilator responses to a β-adrenergic receptor agonist in premenopausal and postmenopausal women.

Beta‐adrenergic vasodilator responses may be blunted in humans who are at an increased risk for hypertension. Because menopause is associated with an increase in blood pressure, we tested the hypothesis that forearm blood flow responses to the β‐adrenergic receptor agonist isoproterenol are blunted in older, postmenopausal women compared to young, premenopausal women. We used venous occlusion plethysmography to measure forearm blood flow in young premenopausal (26 ± 1 years; n = 13) and postmenopausal (61 ± 2 years; n = 12) women. Forearm blood flow and mean arterial pressure were measured at baseline and during isoproterenol infusion at 1.0, 3.0, 6.0, and 12.0 ng/100 mL tissue/min. The two groups did not differ in body mass index or mean arterial pressure. Baseline forearm blood flow was similar between young and postmenopausal women (3.7 ± 0.5 vs. 2.9 ± 0.4 mL/100 mL tissue/min, respectively; P > 0.05). At the lowest dose of isoproterenol, forearm blood flow vasodilator responses were lower in postmenopausal women compared with young women (5.8 ± 0.4 vs. 7.4 ± 0.3 mL/100 mL tissue/min, respectively; P < 0.05). Thereafter, forearm blood flow remained similar between the groups for the remaining isoproterenol doses. In conclusion, β‐adrenergic receptor‐mediated forearm vasodilator responses are blunted in healthy, older postmenopausal women at lower but not higher doses of isoproterenol. This suggests that in aging women, β‐adrenergic receptor‐mediated vasodilator responses may be blunted at a moderate level of stimulation while maximum receptor responses are preserved.

Clinically-relevant consecutive treatment with isoproterenol and adenosine protects the failing heart against ischaemia and reperfusion.

BackgroundConsecutive treatment of normal heart with a high dose of isoproterenol and adenosine (Iso/Ade treatment), confers strong protection against ischaemia/reperfusion injury. In preparation for translation of this cardioprotective strategy into clinical practice during heart surgery, we further optimised conditions for this intervention using a clinically-relevant dose of Iso and determined its cardioprotective efficacy in hearts isolated from a model of surgically-induced heart failure.MethodsIsolated Langendorff-perfused rat hearts were treated sequentially with 5 nM Iso and 30 μM Ade followed by different durations of washout prior to 30 min global ischaemia and 2 hrs reperfusion. Reperfusion injury was assessed by measuring haemodynamic function, lactate dehydrogenase (LDH) release and infarct size. Protein kinase C (PKC) activity and glycogen content were measured in hearts after the treatment. In a separate group of hearts, Cyclosporine A (CsA), a mitochondria permeability transition pore (MPTP) inhibitor, was added with Iso/Ade. Failing hearts extracted after 16 weeks of ligation of left coronary artery in 2 months old rats were also subjected to Iso/Ade treatment followed by ischaemia/reperfusion.ResultsRecovery of the rate pressure product (RPP) in Iso/Ade-treated hearts was significantly higher than in controls. Thus in Iso/Ade treated hearts with 5 nM Iso and no washout period, RPP recovery was 76.3 ± 6.9% of initial value vs. 28.5 ± 5.2% in controls. This was associated with a 3 fold reduction in LDH release irrespective to the duration of the washout period. Hearts with no washout of the drugs (Ade) had least infarct size, highest PKC activity and also showed reduced glycogen content. Cardioprotection with CsA was not additive to the effect of Iso/Ade treatment. Iso/Ade treatment conferred significant protection to failing hearts. Thus, RPP recovery in failing hearts subjected to the treatment was 69.0 ± 16.3% while in Control hearts 19.7 ± 4.0%. LDH release in these hearts was also 3 fold lower compared to Control.ConclusionsConsecutive Iso/Ade treatment of normal heart can be effective at clinically-relevant doses and this effect appears to be mediated by glycogen depletion and inhibition of MPTP. This intervention protects clinically relevant failing heart model making it a promising candidate for clinical use.

The autoimmune nature of post-infarct myocardial healing: oral tolerance to cardiac antigens as a novel strategy to improve cardiac healing

Following a myocardial infarction, lymphocytes have been suggested to react with the damaged heart tissue, which can impair proper tissue healing. In the present work, we investigate whether ingestion of a myocardial homogenate and the consequent development of immunological tolerance can modify the course of post-infarction myocardial repair. Infarction-like myocardial lesions were induced in Wistar rats by injecting high doses of isoproterenol. The healing process was evaluated morphologically and functionally for 60 days. Cardiac function was evaluated using isolated and perfused heart (Langendorff) preparations. At day 14 after isoproterenol treatment, lymphocytes from the mediastinal lymph nodes proliferated when exposed in vitro to myocardial homogenate. Moreover, TNF-α, IFN-γ and CCL-5, but not FOXP3+ expression, was increased in draining lymph nodes in isoproterenol-injured animals, indicating that the observed lymphocyte population that proliferated in response to cardiac components presented a pro-inflammatory and pro-fibrotic profile. In contrast, lymphocytes from draining lymph nodes of rats given a heart homogenate by gavage 7 days before isoproterenol did not proliferate. Furthermore, the group rendered tolerant expressed cardiac FOXP3+ earlier than did the control group, and showed a milder inflammatory infiltrate, lower MMP-9 expression, less collagen deposition, and improved cardiac performance when compared to animals that received only isoproterenol administration. The present findings suggest that the establishment of oral tolerance to heart components prior to myocardial infarction may drive the cardiac healing process to proceed with less inflammation and fibrosis, thus preserving contractile organ function.

Mapping, expression and regulation of the TRα gene in porcine adipose tissue

Thyroid hormone receptors (TR) are members of the nuclear receptor superfamily. There are at least two TR isoforms, TRα and TRβ. The TRα isoform plays a critical role in mediating the action of thyroid hormone in adipose tissue. We mapped the porcine TRα gene to chromosome 12 p11-p13, by using the ImpRH panel. We examined tissue-localization of TRα and determined expression patterns of TRα in porcine adipose tissue with quantitative real-time PCR. TRα was expressed in all tissues, including heart, liver, spleen, stomach, pancreas, brain, small intestine, skeletal muscle, and subcutaneous adipose tissue. In the adipose tissue, the expression of TRα decreased postnatally. Compared to Yorkshire pigs, Jinhua pigs had significantly lower expression levels of TRα gene in the subcutaneous fat tissue. The expression levels of β2-AR, HSL and ATGL were also significantly lower in Jinhua pigs than in Yorkshire pigs. However, no significant differences in PPARγ and SREBP-1C expression levels were found between Jinhua and Yorkshire pigs. Incubation of porcine adipose tissue explants with high doses of isoproterenol (100 and 1000 nM) significantly increased the expression levels of TRα. We conclude that there is considerable evidence that TRα plays an important role in fat deposition in porcine adipose tissue.

Disruption of Protein Kinase A Interaction with A-kinase-anchoring Proteins in the Heart in Vivo: EFFECTS ON CARDIAC CONTRACTILITY, PROTEIN KINASE A PHOSPHORYLATION, AND TROPONIN I PROTEOLYSIS

Protein kinase A (PKA)-dependent phosphorylation is regulated by targeting of PKA to its substrate as a result of binding of regulatory subunit, R, to A-kinase-anchoring proteins (AKAPs). We investigated the effects of disrupting PKA targeting to AKAPs in the heart by expressing the 24-amino acid regulatory subunit RII-binding peptide, Ht31, its inactive analog, Ht31P, or enhanced green fluorescent protein by adenoviral gene transfer into rat hearts in vivo. Ht31 expression resulted in loss of the striated staining pattern of type II PKA (RII), indicating loss of PKA from binding sites on endogenous AKAPs. In the absence of isoproterenol stimulation, Ht31-expressing hearts had decreased +dP/dtmax and -dP/dtmin but no change in left ventricular ejection fraction or stroke volume and decreased end diastolic pressure versus controls. This suggests that cardiac output is unchanged despite decreased +dP/dt and -dP/dt. There was also no difference in PKA phosphorylation of cardiac troponin I (cTnI), phospholamban, or ryanodine receptor (RyR2). Upon isoproterenol infusion, +dP/dtmax and -dP/dtmin did not differ between Ht31 hearts and controls. At higher doses of isoproterenol, left ventricular ejection fraction and stroke volume increased versus isoproterenol-stimulated controls. This occurred in the context of decreased PKA phosphorylation of cTnI, RyR2, and phospholamban versus controls. We previously showed that expression of N-terminal-cleaved cTnI (cTnI-ND) in transgenic mice improves cardiac function. Increased cTnI N-terminal truncation was also observed in Ht31-expressing hearts versus controls. Increased cTnI-ND may help compensate for reduced PKA phosphorylation as occurs in heart failure.

Regulation of cAMP Responses by the G12/13 Pathway Converges on Adenylyl Cyclase VII

Regulation of intracellular cAMP by multiple pathways enables differential function of this ubiquitous second messenger in a context-dependent manner. Modulation of G(s)-stimulated intracellular cAMP has long been known to be modulated by the G(i) and G(q)/Ca(2+) pathways. Recently, the G(13) pathway was also shown to facilitate cAMP responses in murine macrophage cells. We report here that this synergistic regulation of cAMP synthesis by the G(s) and G(13) pathways is mediated by a specific isoform of adenylyl cyclase, AC7. Furthermore, this signaling paradigm exists in several hematopoietic lineages and can be recapitulated by exogenous expression of AC7 in HEK 293 cells. Mechanistic characterization of this synergistic interaction indicates that it occurs downstream of receptor activation and it can be mediated by the alpha subunit of either G(12) or G(13). Our results demonstrate that AC7 is a specific downstream effector of the G(12/13) pathway.

Troponin T and histological characteristics of rat myocardial infarction induced by isoproterenol.

In our investigation,we used short-time model of myocardial infarction of rats induced by high dose of isoproterenol (ISP). We investigated cardiac troponin T blood level (cTnT) and histological characteristics of rat myocardium. ISP, single, intraperitoneal dose 250 mg/kg was given to male, adult, Wistar rats (n=12). Rats were distributed depending on their body weight in subgroups: ISP I (BW 260-280g) and ISP II (BW 250-400g).Control group (n=9) was treated with intraperitoneal dose of 0,95% NaCl. Cardiac TnT was measured by electrochemiluminiscence (ECLA) sandwich immunoassay in rat serum 4 hours after ISP application. Rats' hearts were dissected and examined by qualitative histological method (HE). Statistical significance was set at 0,05. There was significant difference in cTnT of ISP II (p=0,0001) vs. control and ISP I (p<0,05) vs. control. Significant difference was between ISP I and ISP II subgroups (p<0.001). The accent of histological changes of myocardium was on nuclei of cell. Cells showed acidophilic changes and nuclei disappearance as signs of coagulative necrosis development. Extensivity of histological changes were different between ISP I and ISP II subgroup. Used dose of ISP induced development of myocardial necrosis in rats. Subendocardial portion of myocardium was more vulnerability than subepicardial portion. Rats of ISP II had more extensive histological changes than these in ISP I. Administered doses of ISP enabled cTnT utilization as a marker of myocardial necrosis.

Overexpressed cardiac Gsα in rabbits

We overexpressed cardiac Gsα in rabbits using the β-myosin heavy chain promoter. Gsα protein levels in the heart were increased 3-fold by Western blotting in both juvenile (3–4 months), adult (8–10 months), and older (11–16 months) rabbits, compared with wild type (WT) littermates. In transgenic (TG) rabbits, baseline levels of heart rate were elevated, P < 0.05 (268 ± 17 vs. 209 ± 15 beats/min), as well as left ventricular (LV) contractility (LV dP/dt 5475 ± 482 vs. 3740 ± 246 mm Hg/s). These values and LV ejection fraction remained significantly elevated in older TG rabbits (11–16 months). However, maximal levels of LV dP/dt and heart rate with a high dose of isoproterenol (0.4 μg/kg/min) were similar in adult TG and WT rabbits. In isolated myocytes from the LV of adult rabbits, baseline percent contraction was increased, P < 0.05, in TG (11.2 ± 0.5%) compared to WT (9.3 ± 0.5%), while maximal responses to isoproterenol (100 nM) were similar in adult TG (16.2 ± 0.5%) and WT myocytes (15.6 ± 0.4%). Although TG mice with overexpressed cardiac Gsα develop cardiomyopathy at 8–12 months of age, even at 16 months of age, there was no evidence of cardiomyopathy either in terms of LV function or histology in TG rabbits. In addition, Giα was elevated in the LV of adult (8–10 months old) TG rabbits compared to WT, but not in juvenile (3–5 months old) TG rabbits. Although both TG mice and rabbits with overexpressed cardiac Gsα exhibited enhanced heart rate and contractility, the TG rabbit does not develop cardiomyopathy, potentially due to a compensatory increase in Giα.

Serum Cardiac Troponin T as a Biomarker for Acute Myocardial Injury Induced by Low Doses of Isoproterenol in Rats

In rats, high doses of isoproterenol (Iso) have caused acute myocardial lesions and increased serum levels of cardiac troponin T (cTnT). We determined whether low doses of Iso also cause cardiac alterations and whether monitoring cTnT levels could detect this injury. Rats received 8 to 500 microg/kg Iso and were followed for 3 to 48 h. Lesion severity was scored from 0 to 5. Within 3 h, mean cTnT was elevated in all 29 rats receiving 8, 16, 32, or 64 microg/kg Iso (0.20 to 0.28 ng/mL ), but minimal lesions occurred in only two animals. However, by 6 h, cardiac lesions and increases in serum cTnT (mean = 0.21 to 0.23 ng/mL) were observed in all 14 rats receiving 32 or 64 microg/kg Iso. Doses of 125, 250, or 500 microg/kg Iso caused more significant increases in cTnT levels and marked myocardial lesions that reached a peak 3 to 6 h after dosing. The magnitude of the lesions and cTnT levels declined between 12 and 48 h post treatment. Thus, a range of low Iso doses can cause myocardial lesions, and serum cTnT levels can be monitored to detect the onset and progression of this type of acute cardiac injury in rats; however, careful attention to dosing and sampling times is critical to interpretation.

Mitral cell beta1 and 5-HT2A receptor colocalization and cAMP coregulation: a new model of norepinephrine-induced learning in the olfactory bulb.

In the present study we assess a new model for classical conditioning of odor preference learning in rat pups. In preference learning beta(1)-adrenoceptors activated by the locus coeruleus mediate the unconditioned stimulus, whereas olfactory nerve input mediates the conditioned stimulus, odor. Serotonin (5-HT) depletion prevents odor learning, with 5-HT(2A/2C) agonists correcting the deficit. Our new model proposes that the interaction of noradrenergic and serotonergic input with odor occurs in the mitral cells of the olfactory bulb through activation of cyclic adenosine monophosphate (cAMP). Here, using selective antibodies and immunofluorescence examined with confocal microscopy, we demonstrate that beta(1)-adrenoceptors and 5-HT(2A) receptors colocalize primarily on mitral cells. Using a cAMP assay and cAMP immunocytochemistry, we find that beta-adrenoceptor activation by isoproterenol, at learning-effective and higher doses, significantly increases bulbar cAMP, as does stroking. As predicted by our model, the cAMP increases are localized to mitral cells. 5-HT depletion of the olfactory bulb does not affect basal levels of cAMP but prevents isoproterenol-induced cAMP elevation. These results support the model. We suggest the mitral-cell cAMP cascade converges with a Ca(2+) pathway activated by odor to recruit CREB phosphorylation and memory-associated changes in the olfactory bulb. The dose-related increase in cAMP with isoproterenol implies a critical cAMP window because the highest dose of isoproterenol does not produce learning.

High isoproterenol doses are required to activate beta3-adrenoceptor-mediated functions in dogs.

The "in vivo" conditions for beta3-adrenoceptors (beta-AR) activation by isoproterenol were investigated in dog. Experiments were carried out in anesthetized dogs using isoproterenol as a nonselective beta-AR agonist. Intravenous infusion of isoproterenol (0.4 nmol/kg/min) induced arterial hypotension and tachycardia with a slight decrease in cutaneous blood flow. At this dose, isoproterenol increased glucose, glycerol, and nonesterified fatty acid plasma levels. The changes in cardiovascular and endocrine-metabolic parameters, induced by the low dose of isoproterenol, were suppressed by pretreatment with nadolol (1 mg/kg, i.v.). After nadolol administration, however, a 10-fold higher dose (4 nmol/kg/min) of isoproterenol was able to induce a decrease in arterial blood pressure with a slight tachycardia and an increase in cutaneous blood flow. This high dose of isoproterenol increased nonesterified fatty acid and glycerol plasma levels but failed to change glucose plasma levels. All these effects were abolished by a pretreatment with nadolol (1 mg/kg, i.v.) plus SR59230A [a selective beta3-adrenoceptor antagonist; (3-(2-ethylphenoxy)-1(1S)-1,2,3,4-tetrahydronaphth-1-ylaminol-(2S)2-propanol oxalate); 1 mg/kg, i.v.]. Moreover, as observed with the high dose of isoproterenol under nadolol pretreatment, an infusion of SR58611A [a selective beta3-adrenoceptor agonist; ((N2S)-7-carbethoxymethoxy-1,2,3,4-tetrahydronaphth-2-yl-(2R)-2-hydroxy-2-chlorophenyl) ethanamine hydrochloride] induces a decrease in mean arterial blood pressure associated with an increase in heart rate, cutaneous blood flow, and nonesterified fatty acid and glycerol plasma levels. These results demonstrate that the in vivo activation of beta3-adrenoceptors requires higher doses of catecholamine than those necessary for beta1- and/or beta2-adrenoceptor stimulation. These results also argue for the lack of a beta3-AR involvement in the control of heart rate and glycogenolysis in dogs.

Eta-Adrenergic inhibition of leptin production is attenuated in obese individuals

Background: Leptin regulates body weight and may affect cardiovascular function. Leptin expression from adipocytes is suppressed by beta-receptor stimulation. Obese subjects have high leptin levels and are at increased risk for cardiovascular disease, We tested the hypothesis that suppression of leptin production from adipocytes following betareceptor stimulation is attenuated in obese subjects. Methods: We studied 8 obese (age 35 ± 3 yrs, BMI 35 ± 2 kg/m2) and 8 age and gender matched lean controls (age 35 ± 3 yrs, BMI 24 ± 1 kg/m2). All subjects were norrnotensire, free of disease and were not taking any medications. In a randomized fashion, subjects received either a 4 hour infusion of normal saline or isoproterenol (to increase resting heart rate by 25%) on two separate days. Blood samples for plasma leptin were drawn at baseline and at 30 minute intervals during both infusions. Results: Leptin levels decreased by 7.8 ± 1.5% at the end of isoproterenol and increased by 3.1 ± 4,8% during normal saline in obese subjects (p < 0.05). in controls, leptin decreased by 16,8 ± 3.4% and 9.0 ± 4,8% with isoproterenol and normal saline, respectively (p < 0.05). During isoproterenol, the maximum percent decrease from baseline in leptin was 10.3 ± 3.3% in obese subjects and 19.2 ± 2.1% in lean controls (p < 0.02). The area under the curve (AUC) for percent change in leptin levels with isoproterenol was significantly less in obese subjects compared to lean controls (1799 ± 287 versus 2818 ± 203, p < 0.05), The infusion rate of isoproterenol in obese subjects was 0.47 ± 0,1 rncg/ rain and 0.36 ± 0.06 mcg/min in controls (p = 0.05). Conclusion: Isoproterenol significantly decreased plasma leptin levels in both obese and tean subjects compared to normal saline. Beta-adrenergic stimulation that induced comparable increases in heart rate in both Jean and obese subjects resulted in a lower level of leptin suppression in obese subjects. This blunted suppression of leptin production is even evident dudng higher doses of isoproterenol in obese subjects. Thus, there appears to be an attenuated beta-adrenergic suppression of leptin production in obese individuals.

Pyruvate Potentiatesβ-Adrenergic Inotropism of Stunned Guinea-Pig Myocardium

This study tested the hypotheses that the sensitivity of stunned myocardium toβ-adrenergic stimulation is diminished, and that metabolic intervention with pyruvate can restoreβ-adrenergic responsiveness to pre-ischemic levels. Isolated working guinea-pig hearts metabolizing 10 mMglucose were stunned by 45 min of low flow ischemia, and pyruvate and/or isoproterenol treatments were initiated 15 and 30 min after reperfusion, respectively. The dose:response for cardiac power from 0.1–100 nMisoproterenol was significantly shifted to the right in stunned hearts: EC50(nM) increased from 0.3±0.06 to 5.2±1.86. Pyruvate (5 mM) largely restored isoproterenol responsiveness of stunned myocardium, lowering EC50to 1.1±0.34 nM. Maximum power was similar in each group. Additional stunned hearts were treated with intermediate (2 nM) or high (30 nM) isoproterenol concentrations with or without pyruvate. Combining treatments produced a significant interaction at the low dose of isoproterenol, increasing cardiac power (mJ·min−1·g−1) to 149±20, twice the sum of the individual treatments (2 nMisoproterenol: 34±11; pyruvate: 33±8). Cyclic AMP content was unaltered by isoproterenol or pyruvate alone but was increased 41% by the combination. Power was maximized by 30 nMisoproterenol, which tripled cyclic AMP content; pyruvate did not augment these responses, but lessened the isoproterenol-induced decline in cytosolic phosphorylation potential.Conclusions: β-adrenergic inotropism is attenuated in stunned myocardium, although the maximal response is unchanged. Pyruvate potentiated the effects of sub-maximal doses of isoproterenol without depleting cellular energy reserves further, and attenuated energy depletion by high doses of isoproterenol. Pyruvate may allow restoration of contractile performance with lower, energetically less costly doses of β-adrenergic agents.

Effects of isoproterenol on blood-brain barrier permeability in rats

This study was performed to examine whether the direct topical application of isoproterenol to the cerebral cortex could modify the blood-brain barrier (BBB) permeability and whether this effect could be blocked by Timololl a β-adrenergic receptor antagonist without a membrane stabilizing effect. After a craniotomy in each animall a low-dose (10-4 M, n = 6) or a high-dose (10-3 M, n = 6) isoproterenol patch was placed on one cortex (Ipsilateral Cortex: IC) and a normal saline patch was placed on the other cortex (Control Cortex: CC). Another 6 animals were pretreated with Timolol 1.5 mg kg-1 i.v. before the placement of high dose isoproterenol patches. The BBB transfer coefficient (Ki) was determined using 14C-α-aminoisobutyric acid. Mean arterial blood pressure decreased after low- and high-dose isoproterenol patches. The low- and highdose of isoproterenol increased Ki by 58% (IC: 5.94 ± 2.021 CC: 3.77± 1.75 µlg min-1) and 66% (IC: 6.97± 3.661 CC: 4.19± 2.48 µlg min-1) respectively when compared to that of the corresponding CC. Pretreatment with Timolol Prevented the increase of the Ki by a high-dose of isoproterenol (IC: 5.33 ± 1.88, CC: 5.66 ± 1.72 µlg min-1). Our data demonstrate that a direct application of a β-adrenergic receptor agonist to the brain parenchyma increased the permeability of the BBBI and that this effect could be prevented with a β-adrenoceptor antagonist. [Neural Res 1998; 20: 259-264]

Forearm beta adrenergic receptor-mediated vasodilation is impaired, without alteration of forearm norepinephrine spillover, in borderline hypertension.

Impaired beta adrenoceptor-mediated vasodilation associated with enhanced sympathetic activity has been reported in established hypertension. We examined whether altered beta adrenoceptor-mediated vasodilation occurs early in the disease process, when structural vascular changes are likely to be less marked, by measurement of forearm blood flow by strain gauge plethysmography after the intraarterial administration of increasing doses of a beta receptor agonist, isoproterenol, in eight subjects with borderline hypertension (BHT) and 13 normotensive (NT) controls. To determine the role of sympathetic activation in the regulation of responsiveness, we measured local sympathetic activity in the forearm by a radioisotope dilution technique. Vasodilation in response to isoproterenol, measured either as changes in forearm blood flow or forearm vascular resistance, was impaired in the BHT group so that flow at the highest dose of isoproterenol (400 ng/min) increased less (15.2 +/- 1.5 ml/100 ml per min) than in the NT group (24.4 +/- 2.4 ml/100 ml per minute) (P < 0.001). Although, systemic norepinephrine spillover was significantly greater in BHT, the difference in blood flow response to isoproterenol was not accounted for by increased local sympathetic activity since forearm norepinephrine spillover at baseline (BHT 1.0 +/- 0.4 ng/min vs. NT 0.64 +/- 0.13 ng/min) and after the administration of isoproterenol 60 ng/min (BHT 5.2 +/- 1.4 ng/min vs. NT 6.0 +/- 1.5 ng/min) and 400 ng/min (BHT 13.5 +/- 2.9 ng/min vs. NT 16.5 +/- 2.7 ng/min) did not differ between the two groups. We therefore conclude that vasodilation in response to isoproterenol is impaired in subjects with BHT and that this impairment is not explained by locally increased basal, or stimulated, sympathetic activity.

Characterization of junctional rhythm after atrioventricular node ablation.

Catheter ablation of the atrioventricular (AV) node with radiofrequency current (RFC) is associated with the short-term onset of a junctional escape rhythm (JER) in nearly all patients. However, the origin of the JER and short-term thermal effects of RFC on this junctional pacemaker activity are ill defined. Short-term and noninvasive long-term follow-up studies were performed to examine the electrophysiological characteristics of the underlying JER in 45 patients who had undergone AV nodal ablation with RFC. Baseline characteristics and responses to overdrive ventricular pacing and intravenous atropine followed by an incremental isoproterenol infusion were determined. Short- and long-term responses were compared. HV intervals before and after ablation were 49 +/- 9 and 48 +/- 9 milliseconds, respectively (P = NS). Follow-up was 11 +/- 8.3 months. JER cycle length was 1526 +/- 298 milliseconds in the short-term setting and was present in 44 patients (98%) in the long-term setting, measuring 1426 +/- 223 milliseconds (P < .005). Junctional recovery times increased exponentially as overdrive pacing rates increased-there was no difference between short-term and long-term responses. Drug responses within each study were all significant when compared with baseline. However, there was no significant difference between short- and long-term responses, except at the highest dose of isoproterenol. Intravenous atropine (1 mg) caused an 8.6 +/- 9.3% decrease in JER cycle length in the short-term setting compared with a 7.6 +/- 7.3% decrease in the long-term setting. The decreases in JER cycle length with isoproterenol infusion (short-term versus long-term) were 10.1 +/- 9.6% versus 9.6 +/- 7.4% with 1 microgram/min, 15.8 +/- 11.7% versus 17.4 +/- 8.5% with 2 micrograms/min, 17.9 +/- 11.2% versus 21.4 +/- 9.1% with 3 micrograms/min (all P = NS), and 20.6 +/- 12.1% versus 24.8 +/- 9.1% with 4 micrograms/min (P < .01). Radiofrequency ablation of the AV node is associated with development of a JER that is stable in the long-term setting. The lack of change in HV interval after ablation locates the junctional pacemaker proximal to the central fibrous body. The pattern of drug responses suggests an origin within the proximal His bundle at its junction with the AV node rather than the AV node itself. The overall similarity between short- and long-term characteristics of junctional pacemaker activity mitigates against any reversible thermal effects of RFC on this pacemaker focus.