Drug-protein binding and blood-brain barrier permeability.
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The permeability surface area (PS) product, an index of permeability of the blood-brain barrier (BBB), was measured by using the in situ perfusion method. In the cerebral circulation, the fraction of drug that permeates into the brain through the BBB is not only the unbound fraction but also the fraction dissociated from the protein in the perfusate. The sum of these two fractions, the apparent exchangeable fraction, was estimated by fitting the parameters of the BBB permeability under the condition of varying BSA concentrations in the perfusate. The unbound fraction of drugs in a buffer containing 0.5 mM BSA was measured by using the ultrafiltration method in vitro, and the apparent exchangeable fraction was measured in vivo by using the intracarotid artery injection method. The apparent exchange fraction was 100% for S-8510, 96.5% for diazepam, 90.9% for caffeine, 38.3% for S-312-d, 33.1% for propranolol, and 6.68% for (+)-S-145 Na, and each of these was higher than the corresponding unbound fraction in vitro in all drugs. The apparent exchangeable fractions, for example, were 8 times higher for diazepam and 38 times for S-312-d than the unbound fractions in vitro. The apparent exchangeable fraction of drugs was also estimated from the parameters obtained with the perfusion method. Because drugs can be infused for an arbitrary length of time in the perfusion method, substances with low permeability can be measured. The apparent exchangeable fractions obtained with this method were almost the same as those obtained with the intracarotid artery injection method. (+info)
The role of the sympathetic nervous system in the regulation of leptin synthesis in C57BL/6 mice.
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The objectives of this study were to determine whether leptin synthesis is regulated by the sympathetic nervous system and if so whether beta-adrenergic receptors mediate this effect. We show that sympathetic blockade by reserpine increases leptin mRNA levels in brown but not white adipose tissue, while acute cold-exposure decreases leptin expression 10-fold in brown adipose tissue and 2-fold in white adipose tissue. The cold-induced reduction in leptin mRNA can be prevented by a combination of propranolol and SR 59230A but not by either antagonist alone, indicating that beta3-adrenergic receptors and classical beta1/beta2-adrenergic receptors both mediate responses to sympathetic stimulation. Circulating leptin levels reflect synthesis in white adipose tissue but not in brown adipose tissue. (+info)
Neuroregulation by vasoactive intestinal peptide (VIP) of mucus secretion in ferret trachea: activation of BK(Ca) channels and inhibition of neurotransmitter release.
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1. The aims of this study were to determine: (1) whether vasoactive intestinal peptide (VIP) regulates cholinergic and 'sensory-efferent' (tachykininergic) 35SO4 labelled mucus output in ferret trachea in vitro, using a VIP antibody, (2) the class of potassium (K+) channel involved in VIP-regulation of cholinergic neural secretion using glibenclamide (an ATP-sensitive K+ (K(ATP)) channel inhibitor), iberiotoxin (a large conductance calcium activated K+ (BK(ca)) channel blocker), and apamin (a small conductance K(ca) (SK(ca)) channel blocker), and (3) the effect of VIP on cholinergic neurotransmission using [3H]-choline overflow as a marker for acetylcholine (ACh) release. 2. Exogenous VIP (1 and 10 microM) alone increased 35SO4 output by up to 53% above baseline, but suppressed (by up to 80% at 1 microM) cholinergic and tachykininergic neural secretion without altering secretion induced by ACh or substance P (1 microM each). Endogenous VIP accounted for the minor increase in non-adrenergic, non-cholinergic (NANC), non-tachykininergic neural secretion, which was compatible with the secretory response of exogenous VIP. 3. Iberiotoxin (3 microM), but not apamin (1 microM) or glibenclamide (0.1 microM), reversed the inhibition by VIP (10 nM) of cholinergic neural secretion. 4. Both endogenous VIP (by use of the VIP antibody; 1:500 dilution) and exogenous VIP (0.1 microM), the latter by 34%, inhibited ACh release from cholinergic nerve terminals and this suppression was completely reversed by iberiotoxin (0.1 microM). 5. We conclude that, in ferret trachea in vitro, endogenous VIP has dual activity whereby its small direct stimulatory action on mucus secretion is secondary to its marked regulation of cholinergic and tachykininergic neurogenic mucus secretion. Regulation is via inhibition of neurotransmitter release, consequent upon opening of BK(Ca) channels. In the context of neurogenic mucus secretion, we propose that VIP joins NO as a neurotransmitter of i-NANC nerves in ferret trachea. (+info)
Wavelet transform to quantify heart rate variability and to assess its instantaneous changes.
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Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information. (+info)
Assessment of cardiac sympathetic regulation by respiratory-related arterial pressure variability in the rat.
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1. Mechanical ventilation evokes a corresponding arterial pressure variability (APV) which is decreased by beta-adrenoceptor antagonism. Therefore, in this study we set out to determine whether the respiratory-related APV can be used to assess cardiac sympathetic tone. 2. Computer-generated broad-band mechanical ventilation (0-3 Hz) was applied to Sprague-Dawley rats that had been anaesthetized with ketamine and paralysed with pancuronium. APV and its relationship to lung volume variability (LVV-APV) was systematically quantified with auto- or cross-spectral frequency domain analysis. 3. APV and LVV-APV transfer magnitudes between 0.5 and 1.5 Hz showed dose-dependent suppression by propranolol from 0.01 to 1 mg kg-1, while the static value of arterial pressure remained unchanged. Stroke volume variability, assessed by the use of a pulse contour method, exhibited a similar pattern of suppression by propranolol. In contrast, heart rate variability was not lowered with propranolol. 4. The effect of propranolol on respiratory-related APV persisted even in the presence of combined alpha-adrenoceptor and muscarinic receptor blockade by phentolamine and atropine. 5. The frequency range of 0.5-1.0 Hz was optimal for LVV-APV transfer magnitude to correlate with cardiac sympathetic tone. 6. We conclude that respiratory-related APV may provide a valid assessment of cardiac sympathetic regulation which is independent of parasympathetic and vascular sympathetic influences in ketamine-anaesthetized and positive pressure-ventilated rats. (+info)
beta2-adrenergic receptor-selective agonist clenbuterol prevents Fas-induced liver apoptosis and death in mice.
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Stimulation of the cAMP-signaling pathway modulates apoptosis in several cell types and inhibits Jo2-mediated apoptosis in cultured rat hepatocytes. No information is yet available as to whether the hepatic beta2-adrenergic receptor (AR) expression level, including beta2-AR-dependent adenylyl cyclase activation, modulates hepatocyte sensitivity to apoptosis in vivo or whether this sensitivity can be modified by beta2-AR ligands. We have examined this using C57BL/6 mice, in which hepatic beta2-AR densities are low, and transgenic F28 mice, which overexpress beta2-ARs and have elevated basal liver adenylyl cyclase activity. The F28 mice were resistant to Jo2-induced liver apoptosis and death. The beta-AR antagonist propranolol sensitized the F28 livers to Jo2. In normal mice clenbuterol, a beta2-AR-specific agonist, considerably reduced Jo2-induced liver apoptosis and death; salbutamol, another beta2-AR-selective agonist, also reduced Jo2-induced apoptosis and retarded death but with less efficacy than clenbuterol; and propranolol blocked the protective effect of clenbuterol. This indicates that the expression level of functional beta2-ARs modulates Fas-regulated liver apoptosis and that this apoptosis can be inhibited in vivo by giving beta2-AR agonists. This may well form the basis for a new therapeutic approach to diseases involving abnormal apoptosis. (+info)
Endothelin antagonists block alpha1-adrenergic constriction of coronary arterioles.
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We have previously observed that intracoronary administration of the alpha1-adrenergic agonist phenylephrine (PE) over a period of minutes induced both an immediate and long-lasting (2 h) vasoconstriction of epicardial coronary arterioles. Because it is unlikely that alpha1-adrenergic constriction would persist for hours after removal of the agonist, this observation supports the view that another constrictor(s) is released during alpha1-adrenergic activation and induces the prolonged vasoconstriction. Therefore, we hypothesized that the prolonged microvascular constriction after PE is due to the production of endothelin (ET). We focused on ET not only because this peptide produces potent vasoconstriction but also because its vasoconstrictor action is characterized by a long duration. To test this hypothesis, the diameters of coronary arterioles (<222 micrometers) in the beating heart of pentobarbital-anesthetized dogs with stroboscopic intravital microscopy were measured during a 15-min intracoronary infusion of PE (1 microgram. kg-1 . min-1) and at 15-min intervals for a total of 120 min. All experiments were performed in the presence of beta-adrenergic blockade with propranolol. At 120 min, arterioles in the PE group were constricted (-23 +/- 9% change in diameter vs. baseline). Pretreatment with the ET-converting enzyme inhibitor phosphoramidon or the ETA-receptor antagonist FR-139317 prevented the PE-induced constriction at 120 min (-1 +/- 3 and -6 +/- 3%, respectively, P < 0.01 vs. PE). Pretreatment with the selective alpha1-adrenergic antagonist prazosin (Prz) also prevented the sustained constriction (0 +/- 2%, P < 0.01 vs. PE) but Prz given 60 min after PE infusion did not (-13 +/- 3%). In the aggregate, these results show that vasoconstriction of epicardial coronary arterioles via alpha1-adrenergic activation is blocked by an ET antagonist and an inhibitor of its production. From these data, we conclude that alpha1-adrenergic activation promotes the production and/or release of ET, which produces or facilitates microvascular constriction of epicardial canine coronary arterioles. (+info)
beta2-adrenoceptor agonists reduce the decline of rat diaphragm twitch force during severe hypoxia.
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The aim of the present study was to investigate the in vitro effects of the short-acting beta2-adrenoceptor agonist salbutamol and the long-acting beta2-adrenoceptor agonist salmeterol on hypoxia-induced rat diaphragm force reduction. In vitro diaphragm twitch force (Pt) and maximal tetanic force (Po) of isolated diaphragm muscle strips were measured for 90 min during hyperoxia (tissue bath PO2 83.8 +/- 0.9 kPa and PCO2 3.9 +/- 0.1 kPa) or severe hypoxia (PO2 7.1 +/- 0.3 kPa and PCO2 3.9 +/- 0.1 kPa) in the presence and absence of 1 microM salbutamol or 1 microM salmeterol. During hyperoxia, salbutamol and salmeterol did not significantly alter the time-related decreases in Pt and Po (to approximately 50% of initial values). Salbutamol had no effects on Po or the Pt-to-Po ratio. Salmeterol treatment significantly reduced Po and increased the Pt-to-Po ratio during hyperoxia (P < 0.05 compared with control value). Hypoxia resulted in a severe decrease in Pt (to approximately 30% of initial value) and Po after 90 min. Both salbutamol and salmeterol significantly reduced the decline in Pt during hypoxia (P < 0.05). The reduction in Po was not prevented. Salbutamol increased Pt rapidly but transiently. Salmeterol had a delayed onset of effect and a longer duration of action. Addition of 1 microM propranolol (a nonselective beta-adrenoceptor antagonist) did not alter Pt, Po, or the Pt-to-Po ratio during hypoxia but completely blocked the inotropic effects of salbutamol and salmeterol, indicating that these effects are dependent on beta2-adrenoceptor agonist-related processes. (+info)