A comprehensive investigation of the interactions of human serum albumin with polymeric and hybrid nanoparticles

Nanoparticles (NPs) engineered as drug delivery systems continue to make breakthroughs as they offer numerous advantages over free therapeutics. However, the poor understanding of the interplay between the NPs and biomolecules, especially blood proteins, obstructs NP translation to clinics. Nano-bio interactions determine the NPs' in vivo fate, efficacy and immunotoxicity, potentially altering protein function. To fulfill the growing need to investigate nano-bio interactions, this study provides a systematic understanding of two key aspects: (i) protein corona (PC) formation and (ii) NP-induced modifications on protein's structure and stability. A methodology was developed by combining orthogonal techniques to analyze both quantitative and qualitative aspects of nano-bio interactions, using human serum albumin (HSA) as a model protein. Protein quantification via liquid chromatography-mass spectrometry, and capillary zone electrophoresis (CZE) clarified adsorbed protein quantity and stability. CZE further unveiled qualitative insights into HSA forms (native, glycated HSA and cysteinylated), while synchrotron radiation circular dichroism enabled analyzing HSA's secondary structure and thermal stability. Comparative investigations of NP cores (organic vs. hybrid), and shells (with or without polyethylene glycol (PEG)) revealed pivotal factors influencing nano-bio interactions. Polymeric NPs based on poly(lactic-co-glycolic acid) (PLGA) and hybrid NPs based on metal-organic frameworks (nanoMOFs) presented distinct HSA adsorption profiles. PLGA NPs had protein-repelling properties while inducing structural modifications on HSA. In contrast, HSA exhibited a high affinity for nanoMOFs forming a PC altering thereby the protein structure. A shielding effect was gained through PEGylation for both types of NPs, avoiding the PC formation as well as the alteration of unbound HSA structure.

Congenital tremor and myopathy secondary to novel MYBPC1 variant

Congenital myopathy with tremor (MYOTREM) is a recently described disorder characterized by mild myopathy and a postural and intention tremor present since early infancy. MYOTREM is associated with pathogenic variants in MYBPC1 which encodes slow myosin-binding protein C, a sarcomere protein with regulatory and structural roles. Here, we describe a family with three generations of variably affected members exhibiting a novel variant in MYBPC1 (c.656 T > C, p.Leu219Pro). Among the unique features of affected family members is the persistence of tremor in sleep. We also present the first muscle magnetic resonance images for this disorder, and report muscle atrophy and fatty infiltration.

Tone management: An environmental scan of current management practices across Canada

BACKGROUND

Currently, there are no standardized approaches to care or evaluation for tone dysfunction in Canada. The study authors hypothesize that there is significant practice variation across the country. This environmental scan is aimed to describe the current practice for management of paediatric patients with hypertonia across Canada.

METHODS

A web-based survey was developed by the authors with a multi-disciplinary approach and sent to representative paediatric rehabilitation sites in each province in Canada. Disciplines at the rehabilitation sites surveyed included all or some of the following disciplines: physiatry, neurology, neurosurgery, plastic surgery, orthopaedic surgery, physiotherapy and occupational therapy. All statistical analyses were performed using the R statistical software version 4.0. Fifteen rehabilitation sites were contacted, and 12 sites were used for the final analysis.

RESULTS

Cerebral palsy was found to be the most common diagnosis for tone dysfunction, with 58% of sites diagnosing greater than 20 new patients per year. In 67% of sites, patients were seen within a formal multidisciplinary clinic to manage hypertonia. All 12 sites utilized oral baclofen and gabapentin, and 92% of sites utilized trihexyphenidyl. Botulinum toxin injections were offered at 50% of sites. Upper and lower extremity surgical procedures were offered in 83% of the sites.

CONCLUSION

The information gained from this study provides some insight into the current practice across Canada for children with hypertonia. This study may assist in the development of a national, standardized strategy to tone management, potentially facilitating more equitable access to care for patients.

Seizure Burden and Neurologic Outcomes After Neonatal Encephalopathy

BACKGROUND AND OBJECTIVES

Seizures are common during neonatal encephalopathy (NE), but the contribution of seizure burden (SB) to outcomes remains controversial. This study aims to examine the relationship between electrographic SB and neurologic outcomes after NE.

METHODS

This prospective cohort study recruited newborns ≥36 weeks postmenstrual age around 6 hours of life between August 2014 and November 2019 from a neonatal intensive care unit (NICU). Participants underwent continuous electroencephalography for at least 48 hours, brain MRI within 3-5 days of life, and structured follow-up at 18 months. Electrographic seizures were identified by board-certified neurophysiologists and quantified as total SB and maximum hourly SB. A medication exposure score was calculated based on all antiseizure medications given during NICU admission. Brain MRI injury severity was classified based on basal ganglia and watershed scores. Developmental outcomes were measured using the Bayley Scales of Infant Development, Third Edition. Multivariable regression analyses were performed, adjusting for significant potential confounders.

RESULTS

Of 108 enrolled infants, 98 had continuous EEG (cEEG) and MRI data collected, of which 5 were lost to follow-up, and 6 died before age 18 months. All infants with moderate-severe encephalopathy completed therapeutic hypothermia. cEEG-confirmed neonatal seizures occurred in 21 (24%) newborns, with a total SB mean of 12.5 ± 36.4 minutes and a maximum hourly SB mean of 4 ± 10 min/h. After adjusting for MRI brain injury severity and medication exposure, total SB was significantly associated with lower cognitive (-0.21, 95% CI -0.33 to -0.08, p = 0.002) and language (-0.25, 95% CI -0.39 to -0.11, p = 0.001) scores at 18 months. Total SB of 60 minutes was associated with 15-point decline in language scores and 70 minutes for cognitive scores. However, SB was not significantly associated with epilepsy, neuromotor score, or cerebral palsy (p > 0.1).

DISCUSSION

Higher SB during NE was independently associated with worse cognitive and language scores at 18 months, even after adjusting for exposure to antiseizure medications and severity of brain injury. These observations support the hypothesis that neonatal seizures occurring during NE independently contribute to long-term outcomes.

K+ channel mechanisms underlying cholinergic cutaneous vasodilation and sweating in young humans: roles of KCa, KATP, and KV channels?

Acetylcholine released from cholinergic nerves is involved in heat loss responses of cutaneous vasodilation and sweating. K(+) channels are thought to play a role in regulating cholinergic cutaneous vasodilation and sweating, though which K(+) channels are involved in their regulation remains unclear. We evaluated the hypotheses that 1) Ca(2+)-activated K(+) (KCa), ATP-sensitive K(+) (KATP), and voltage-gated K(+) (KV) channels all contribute to cholinergic cutaneous vasodilation; and 2) KV channels, but not KCa and KATP channels, contribute to cholinergic sweating. In 13 young adults (24 ± 5 years), cutaneous vascular conductance (CVC) and sweat rate were evaluated at intradermal microdialysis sites that were continuously perfused with: 1) lactated Ringer (Control), 2) 50 mM tetraethylammonium (KCa channel blocker), 3) 5 mM glybenclamide (KATP channel blocker), and 4) 10 mM 4-aminopyridine (KV channel blocker). At all sites, cholinergic cutaneous vasodilation and sweating were induced by coadministration of methacholine (0.0125, 0.25, 5, 100, and 2,000 mM, each for 25 min). The methacholine-induced increase in CVC was lower with the KCa channel blocker relative to Control at 0.0125 (1 ± 1 vs. 9 ± 6%max) and 5 (2 ± 5 vs. 17 ± 14%max) mM methacholine, whereas it was lower in the presence of KATP (69 ± 7%max) and KV (57 ± 14%max) channel blocker compared with Control (79 ± 6%max) at 100 mM methacholine. Furthermore, methacholine-induced sweating was lower at the KV channel blocker site (0.42 ± 0.17 mg·min(-1)·cm(-2)) compared with Control (0.58 ± 0.15 mg·min(-1)·cm(-2)) at 2,000 mM methacholine. In conclusion, we show that KCa, KATP, and KV channels play a role in cholinergic cutaneous vasodilation, whereas only KV channels contribute to cholinergic sweating in normothermic resting humans.

Changes in vascular alpha 1- and alpha 2-adrenoceptor responsiveness by selegiline treatment

Pharmacoepidemiological studies have reported an excess of mortality with selegiline, a MAO B inhibitor used in the treatment of Parkinson's disease. The mechanism of this putative adverse effect remains unknown but an interaction with the sympathetic nervous system was suggested. The aim of the present study was to investigate the influence of selegiline (10 mg/daily, orally during one week) on vascular alpha1- and alpha2-adrenoceptor responsiveness in conscious unrestrained dogs. Selegiline significantly increased resting values of both systolic and diastolic blood pressures and noradrenaline plasma levels (HPLC) without changing heart rate. Moreover, spectral analysis of systolic blood pressure (Fast Fourier Transformation) showed that selegiline increased the relative energy of a low frequency band without modifying the total spectrum. ED 50 calculated from dose-pressor response curves with phenylephrine (after beta-blockade by propranolol), an index of alpha1-adrenoceptor response or with noradrenaline (after alpha1- and beta blockade by prazosin plus propranolol), an index of alpha2-adrenoceptor response, were significantly higher after selegiline. Selegiline failed to modify the number of platelet alpha2-adrenoceptors measured by [(3)H] RX 821002 binding. Yohimbine-induced increase in noradrenaline release was significantly more marked after selegiline. These results support the evidence that selegiline induces a vascular alpha1- and alpha2-adrenoceptor-hyposensitivity that can be explained by the increase in noradrenaline release elicited by the drug.

Role of simian virus 40 Vp1 cysteines in virion infectivity

We have developed a new nonoverlapping infectious viral genome (NO-SV40) in order to facilitate structure-based analysis of the simian virus 40 (SV40) life cycle. We first tested the role of cysteine residues in the formation of infectious virions by individually mutating the seven cysteines in the major capsid protein, Vp1. All seven cysteine mutants-C9A, C49A, C87A, C104A, C207S, C254A, and C267L-retained viability. In the crystal structure of SV40, disulfide bridges are formed between certain Cys104 residues on neighboring pentamers. However, our results show that none of these disulfide bonds are required for virion infectivity in culture. We also introduced five different mutations into Cys254, the most strictly conserved cysteine across the polyomavirus family. We found that C254L, C254S, C254G, C254Q, and C254R mutants all showed greatly reduced (around 100,000-fold) plaque-forming ability. These mutants had no apparent defect in viral DNA replication. Mutant Vp1's, as well as wild-type Vp2/3, were mostly localized in the nucleus. Further analysis of the C254L mutant revealed that the mutant Vp1 was able to form pentamers in vitro. DNase I-resistant virion-like particles were present in NO-SV40-C254L-transfected cell lysate, but at about 1/18 the amount in wild-type-transfected lysate. An examination of the three-dimensional structure reveals that Cys254 is buried near the surface of Vp1, so that it cannot form disulfide bonds, and is not involved in intrapentamer interactions, consistent with the normal pentamer formation by the C254L mutant. It is, however, located at a critical junction between three pentamers, on a conserved loop (G2H) that packs against the dual interpentamer Ca(2+)-binding sites and the invading C-terminal helix of an adjacent pentamer. The substitution by the larger side chains is predicted to cause a localized shift in the G2H loop, which may disrupt Ca(2+) ion coordination and the packing of the invading helix, consistent with the defect in virion assembly. Our experimental system thus allows dissection of structure-function relationships during the distinct steps of the SV40 life cycle.

Fluoxetine-induced pressor response in freely moving rats: a role for vasopressin and sympathetic tone

The present study was performed in order to assess, in freely moving rats, the cardiovascular effects of central administration of fluoxetine, a serotonin reuptake inhibitor. Two kinds of experiments were performed: 1) acute central administration of fluoxetine. and 2) chronic intraperitoneal administration of fluoxetine plus selegiline, a monoamine oxidase B inhibitor. Intracerebroventricular (i.c.v.) administration of fluoxetine (5-50 microg) induced an increase in blood pressure. This fluoxetine-induced pressor response reached its maximal 1 hour after injection without any significant change in heart rate. At the dose of 10 microg i.c.v., fluoxetine significantly increased mean blood pressure by 16 +/- 4 mmHg. This pressor response was reduced by an intravenous (i.v.) pretreatment with the alpha1-adrenoceptor antagonist, prazosin (500 microg kg(-1)) (+ 7 +/- 4 mmHg, P <0.05) or with the V1A-vasopressin receptor antagonist (20 microg kg(-1)) (+5 +/- 3 mmHg, P < 0.05). The pressor response was completely abolished by a concomitant pretreatment with prazosin plus the V1A-vasopressin receptor antagonist. Pretreatment with the beta-adrenoceptor antagonist, propranolol (1 mg kg(-1) i.v.), or the 5-HT2 receptor antagonist, ketanserine (5 mg kg(-1) i.v.), did not modify the fluoxetine-induced pressor response. In freely moving rats receiving fluoxetine (10 microg i.c.v.), vasopressin plasma levels were significantly higher (39 +/- 5 pg mL(-1) than in rats receiving 10 microL i.c.v. saline (14 +/- 4 pg mL(-1)). A 30 day intraperitoneal (i.p.) administration of fluoxetine in association with selegiline induced an increase in noradrenaline plasma levels and locomotor activity without any significant change in blood pressure and heart rate. These data suggest that, the pressor response elicited by central acute administration of fluoxetine is mediated by both an increase in sympathetic tone and vasopressin release. This observation could suggest the putative interest of alpha1-adrenoceptor and or V1A-vasopressin receptor antagonists in the treatment of "Serotonin Syndrome".

Characterization of the central muscarinic cholinoceptors involved in the cholinergic pressor response in anesthetized dogs

Previous reports have shown that an intracisternal (i.c.) injection of acetylcholine in the dog increases both arterial blood pressure and plasma levels of noradrenaline and vasopressin via central muscarinic receptors. The aim of the present study was to characterize the central muscarinic cholinoceptor subtypes involved in such central cholinergic responses in anesthetized male Beagle-Harrier dogs (n = 12). For this purpose, we studied the relative potency of various muscarinic receptor antagonists to block the acetylcholine-induced pressor responses (30 microg kg(-1) i.c.). The acetylcholine-induced pressor response was inhibited in a dose-dependent manner by the i.c. administration of the non-selective muscarinic receptor antagonist atropine (ID50 = 0.5 microg kg(-1)), the muscarinic M receptor antagonist pirenzepine (ID50 = 0.45 microg kg(-1)), the muscarinic M2 receptor antagonist methoctramine (ID50 = 8.5 microg kg(-1)) and the muscarinic M3 receptor antagonist para-fluoro-hexahydro-sila-difenidol (ID50) = 43.7 microg kg(-1)). The order of potency of these four muscarinic receptor antagonists was: atropine = pirenzepine > methoctramine >> para-fluoro-hexahydro-sila-difenidol. In order to confirm the selectivity for muscarinic M1 receptors of this dose of pirenzepine, we checked that 40- to 50-fold higher concentrations were necessary to block a typical muscarinic M2 receptor response (bradycardia) and a typical muscarinic M3 receptor response (endothelial vasodilation) compared with methoctramine and para-fluoro-hexahydro-sila-difenidol, respectively. These results suggest that the pressor response elicited by intracisternal injection of acetylcholine in anesthetized Beagle-Harrier dogs is mediated through the activation of the muscarinic M1 cholinoceptor subtype.

Spontaneously hypertensive rats cholinergic hyper-responsiveness: central and peripheral pharmacological mechanisms

1. The mechanisms and the subtypes of muscarinic receptors implicated in the cardiovascular effects of physostigmine were investigated in conscious normotensive and spontaneously hypertensive rats. 2. Intravenous (i.v.) physostigmine (50 microg kg-1) induced in both strains a long pressor response, accompanied by a bradycardia. This pressor response was larger in spontaneously hypertensive (+41+/-6 mmHg) than in Wistar-Kyoto (+25+/-2 mmHg) rats (P<0.05). 3. Pretreatment with atropine sulphate (0.4 mg kg-1 i.v.), completely abolished the physostigmine-induced pressor response in both normotensive and hypertensive rats. In both strains, the physostigmine pressor response was significantly reduced by the systemic administration of either an alpha1-adrenoceptor antagonist (prazosin, 1 mg kg-1) or a V1A-vasopressin receptor antagonist (AVPX, 20 microg kg-1). This physostigmine pressor effect was completely abolished in both strains when both antagonists were administered concomitantly. 4. In WKY rats, the pressor response to physostigmine (50 microg kg-1 i.v.) was inhibited in a dose-dependent manner by i. c.v. administration of atropine (ID50=3.70 nmoles), the M1 receptor antagonist pirenzepine (ID50=10.71 nmoles), the M2 receptor antagonist methoctramine (ID50=4.31 nmoles), the M3 receptor antagonist p-F-HHSiD (ID50=60.52 nmoles) and the M4 receptor antagonist tropicamide (ID50=214.20 nmoles). In the hypertensive strain, the ID50 were found to be significantly higher for atropine (7.34 nmoles), pirenzepine (21.60 nmoles) and p-F-HHSiD (139.50 nmoles) (P<0.05). 5. The present results indicate that physostigmine acts in normotensive and spontaneously hypertensive rats, through stimulation of both central M2 and M1 cholinoceptors to induce a rise in blood pressure mediated by an increase in plasma vasopressin and sympathetic outflow. Moreover, our results suggest that some modifications of the M1 receptor subtypes in terms of expression or affinity could be responsible for the hyper-responsiveness of the hypertensive strain to cholinomimetic agents.

[Reduction of the pressor effect of fluoxetine after V1A-vasopressin receptor blockade in the conscious rats]

Pharmacovigilance data have reported some cases of arterial hypertension in patients treated with serotonin reuptake inhibitors. This side effect is now called serotonin syndrome. Moreover, some authors have shown that these drugs could reduce, at least in part, the fall in blood pressure (BP) observed in experimental models or in human forms of orthostatic hypotension, suggesting a modulation of the autonomic nervous system by these drugs. These data led us to study in freely moving Wistar rats the mechanisms involved and the putative involvement of autonomic nervous system. Intracerebroventricular (i.c.v.) administration of fluoxetine (5-50 micrograms) induced an increase in BP similar to which was obtained following central administration of serotonin (5-HT) (0.5-5 micrograms). After 5-HT, the pressor effect was immediate (1 min following injection) and involved the baroreflex pathway (bradycardia). The fluoxetine-induced pressor response reached its maximal 1 hour after injection without any significant change in heart rate (HR). At the dose of 10 micrograms i.c.v., fluoxetine significantly increased mean BP by 16 +/- 4 mmHg. This pressor response was partially but significantly reduced by a pretreatment by the alpha 1-adrenoreceptor antagonist, prazosin (500 micrograms.kg-1 i.v.) (+7 +/- 4 mmHg, p < 0.05) or by a V1A-vasopressin receptor antagonist (20 micrograms.kg-1 i.v.) (+5 +/- 3 mmHg, p < 0.05). However, pretreatment by the beta-adrenoreceptor antagonist, propranolol (1 mg.kg-1 i.v.) and the antagonist 5-HT2, ketanserine (5 mg.kg-1 i.v.) did not modify the fluoxetine-induced pressor response. In freely moving rats receiving fluoxetine (10 micrograms i.c.v.), vasopressin plasma levels were significantly higher (+39 +/- 5 pg.mL-1) than in rats receiving saline (100 microL i.c.v.) (+14 +/- 4 pg.mL-1), thus confirming the involvement of vasopressinergic mechanisms in the fluoxetine-induced pressor response. These data suggest that in freely moving Wistar rats, central acute administration of fluoxetine induces a pressor response mediated by both an increase in sympathetic tone and a vasopressin release. This observation could suggest the putative use of alpha 1-adrenoreceptors antagonists and/or V1A-vasopressin receptor antagonists in the treatment of the serotonin syndrome.

Endogenous central cholinergic systems and baroreflex modulation in the conscious dog

Intracisternal atropine and mecamylamine failed to modify baroreflex sensitivity in dogs, suggesting a lack of cholinergic neurons integrated in baroreflex pathways. Conversely, neostigmine lowered baroreflex sensitivity suggesting a putative cholinergic modulation.

Pressor and bradycardic effects of tacrine and other acetylcholinesterase inhibitors in the rat

The cardiovascular effects of three different acetylcholinesterase inhibitors: physostigmine, tacrine and rivastigmine injected by intravenous (i.v.) route were compared in freely moving Wistar rats. The three drugs significantly increased both systolic and diastolic blood pressure and decreased heart rate. Compared to physostigmine, a 20-fold higher dose of tacrine and a 40-fold higher dose of rivastigmine was necessary to induce a comparable pressor effect. Tacrine was chosen as a model to study the mechanisms underlying the cardiovascular effects of i.v. cholinesterase inhibitors. Atropine totally abolished while methylatropine did not affect tacrine pressor effects. Conversely, both drugs abolished tacrine-induced bradycardia. The alpha1-adrenoceptor antagonist prazosin or the vasopressin V1 receptor antagonist, [beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2, Arg8] vasopressin partially but significantly reduced tacrine pressor effect and mostly abolished it when administered concomitantly. The tacrine pressor response was inhibited in a dose-dependent manner by the i.c.v. administration of the non-selective muscarinic receptor antagonist atropine (ID50 = 1.45 microg), the muscarinic M1 receptor antagonist pirenzepine (ID50 = 4.33 microg), the muscarinic M2 receptor antagonist methoctramine (ID50 = 1.39 microg) and the muscarinic M3 receptor antagonist para-fluoro-hexahydro-sila-difenidol (ID50 = 31.19 microg). Central injection of such muscarinic receptor antagonists did not affect tacrine-induced bradycardia. Our results show that acetylcholinesterase inhibitors induce significant cardiovascular effects with a pressor response mediated mainly by the stimulation of central muscarinic M2 receptors inducing a secondary increase in sympathetic outflow and vasopressin release. Conversely, acetylcholinesterase inhibitor-induced bradycardia appears to be mediated by peripheral muscarinic mechanisms.

Fluoxetine in orthostatic hypotension of Parkinson's disease: a clinical and experimental pilot study

Recent clinical studies have reported a beneficial effect of fluoxetine, a serotonin reuptake inhibitor, in patients with severe refractory orthostatic hypotension. The present study was undertaken to investigate the effect of fluoxetine in orthostatic hypotension occurring during Parkinson's disease on both blood pressure values and number of clinical symptoms during orthostatic procedure evaluated using a validated clinical rating scale. In a pilot study performed in fourteen patients with idiopathic Parkinson's disease plus orthostatic hypotension, fluoxetine hydrochloride (20 mg orally daily during one month) significantly reduced the fall in systolic blood pressure [-33 +/- 21 (SD) mmHg before fluoxetine vs -22 +/- 19 mmHg after fluoxetine, P = 0.03] elicited by standing without modifying heart rate. The drug also significantly reduced the number of postural symptoms occurring during the orthostatic procedure [2.9 +/- 1.5 (SD) before fluoxetine vs 1.2 +/- 1.3 after fluoxetine, P = 0.006]. A similar pattern of response was obtained in an experimental model of neurogenic orthostatic hypotension obtained in chronically sino-aortic denervated dogs submitted to an 80 degrees head-up tilt test procedure under chloralose anaesthesia. Fluoxetine did not change plasma noradrenaline levels. This pilot study suggests a slight but clinically significant effect of fluoxetine on both hemodynamic parameters and clinical symptoms in parkinsonian patients suffering from orthostatic hypotension.

Effect of losartan on afferent nerve stimulation

The present study was undertaken to investigate the effects of losartan, a non-peptide angiotensin II subtype 1 (AT1) receptor antagonist, on both the pressor responses elicited by stimulation of afferent vagal nociceptive fibres and the involvement of the sympathetic nervous system (evaluated by plasma levels of noradrenaline and its co-neurotransmitter neuropeptide Y) in dogs. Electrical stimulation of the afferent fibres of the vagus (1, 5, 10 and 20 Hz) elicited a frequency-dependent increase in blood pressure and heart rate. Plasma noradrenaline levels only increased after stimulation at frequencies of 10 and 20 Hz. Plasma neuropeptide Y levels did not change. Losartan (10 mg/kg i.v.) induced both a decrease in resting blood pressure and an increase in basal plasma levels of noradrenaline and neuropeptide Y. Losartan failed to modify the magnitude of the electrically-evoked pressor and positive chronotropic responses. The angiotensin AT1 receptor antagonist elicited a fall in plasma noradrenaline values after a 1 Hz stimulation and abolished the increase in plasma noradrenaline levels induced by the 10 (but not 20) Hz stimulation. The data suggest that angiotensin AT1 receptors are not directly involved in acute pressor responses induced by stimulation of afferent vagal fibres. Moreover, the results show that, besides its sympatho-inhibitory effect, losartan can exert a sympatho-excitatory action as shown by the increase in the plasma levels of both noradrenaline and its coneurotransmitter, neuropeptide Y.

[Functional decoupling of left ventricular beta-adrenoceptor in a canine model of obesity-hypertension]

OBJECTIVE

To assess cardiac beta-adrenoceptors (beta-AR) in an obesity-hypertension model.

METHODS

Six male beagle dogs (aged 35 +/- 5 months) receiving during 30 weeks a high-fat diet with 60% uncooked beef fat were compared to 6 normal beagle dogs. With right auricular and left ventricular samples we analysed cardiac beta-AR density through binding study using [125I]-cyanopindolol. beta 1 and beta 2 densities were obtained by competition with CGP 20712A. Affinity state of beta-AR was assessed by competition with isoproterenol. Noradrenaline plasma level was assayed by HPLC. Left ventricular mass (LV mass) was measured by echocardiography. Results are expressed as mean +/- SE. All comparisons were performed using a variance analysis (*: p < 0.05).

RESULTS

Systolic blood pressure was significantly higher in obesses (245 +/- 8 vs 197 +/- 10 mmHg in controls). Diastolic blood pressure did not differed between both groups (93 +/- 3 vs 84 +/- 3 mmHg in controls). Noradrenaline plasma levels were similar in both groups (276 +/- 30 vs 235 +/- 50 pg/mL in controls). Obesses were characterized by higher LV mass (80 +/- 24 vs 67 +/- 15 g in controls*). Right auricular and left ventricular beta-AR densities were not different in obesses (57 +/- 6 and 67 +/- 4 fmoles/mg protein) and in controls (68 +/- 7 and 63 +/- 9 fmoles/mg protein). The beta 1-AR proportion was the same in obesses and controls in right auricule (63 +/- 4 vs 64 +/- 3% in controls) and left ventricule (59 +/- 3 vs 60 +/- 4% in controls). The proportion of beta-AR receptors in a high affinity state was similar in right auricular samples (69 +/- 4 vs 67 +/- 3%) in controls) but was significantly different in left ventricule (28 +/- 6 vs 74 +/- 6%) in controls).

CONCLUSION

Left ventricular beta-adrenoceptors came under a specific desensibilisation independent of plasma noradrenaline levels. This functional decoupling of beta-adrenoceptors may account for the progressive systolic dysfunction of hypertensive cardiomyopathy.

Central cardiovascular effects of tacrine in the conscious dog: a role for catecholamines and vasopressin release

Centrally acting cholinergic agents are currently reported to increase blood pressure in various species through the stimulation of muscarinic cholinoceptors. Moreover, several cardiovascular adverse effects have been reported from clinical studies. The aim of this study was to investigate the effects of tacrine, an acetylcholinesterase inhibitor which has been reported to have therapeutic potential in Alzheimer's disease, on blood pressure and two vasopressor systems (sympathetic and vasopressinergic) in Beagle dogs. Intravenous (i.v.) tacrine (2 mg kg(-1)) induced, in conscious and anesthetized dogs, an increase in systolic and diastolic blood pressure, accompanied by bradycardia. This increase was dose-dependent with a peak effect at 1.5 min following administration. Tacrine also induced an increase in noradrenaline, adrenaline and vasopressin plasma levels. Pretreatment with the muscarinic receptor antagonist, atropine (2 mg kg(-1), i.v.), abolished the pressor response to i.v. injection of tacrine while pretreatment with the peripheral muscarinic receptor antagonist, methylscopolamine (0.2 mg kg(-1), i.v.), did not alter the increase in blood pressure. Similarly, noradrenaline and adrenaline changes in plasma levels were not modified by methylscopolamine but were abolished by atropine pretreatment. A similar tendency although not significant was observed for vasopressin plasma levels. The present results demonstrate that in dogs, tacrine (2 mg kg(-1), i.v.) stimulates central muscarinic cholinoceptors to increase blood pressure through activation of the two components of the sympathetic nervous system (i.e., neuroneuronal noradrenergic and the neurohormonal adrenergic pathways) as well as through increasing noradrenaline, adrenaline and vasopressin plasma levels.

Effects of yohimbine, an alpha 2-adrenoceptor antagonist, on experimental neurogenic orthostatic hypotension

Yohimbine has been proposed for the treatment of neurogenic orthostatic hypotension; however, no controlled trial has been performed in experimental models of orthostatic hypotension or in patients with autonomic failure. The aim of the present study was to compare the effects of yohimbine (0.05 mg/kg, intravenously [i.v.]) and placebo (saline) in a new model of neurogenic orthostatic hypotension obtained by sinoaortic denervation (SAD) in chloralose-anaesthetized dogs. Blood pressure, heart rate, noradrenaline plasma levels and systolic blood pressure and heart rate short-term variabilities (calculated on low frequency [40-50 MHz] and high frequency [390-490 MHz] bands) were measured in supine position and after a 10 min 80 degrees head-up tilting. The drugs were administered in a double-blind cross-over randomized fashion. The head-up tilting performed in normal animals increased diastolic blood pressure (+12 +/- 4 mmHg), heart rate (+39 +/- 12 beats per minute [bpm]), the low frequency band of systolic blood pressure and noradrenaline plasma level, without changing systolic blood pressure or heart rate variability. In SAD dogs, a marked fall in systolic (-80 +/- 11 mmHg) and diastolic (-43 +/- 4 mmHg) blood pressures was observed within 1 min after placebo, without modification in heart rate, systolic blood pressure and heart rate short-term variabilities and noradrenaline plasma levels. In SAD dogs, yohimbine (0.05 mg/kg, i.v.) delayed the blood pressure fall elicited by head-up tilting, but failed to modify its magnitude. These results show that, in the model of orthostatic hypotension obtained by SAD, yohimbine, at an alpha 2-adrenoceptor selective dose (0.05 mg/kg), delays the fall in blood pressure elicited by head-up tilting. The effect of yohimbine can be explained by an increase in sympathetic tone.

[Autonomic nervous system abnormalities in the initial phase of insulin resistance syndrome. Value of the study of variability of cardiac rate and blood pressure on a model of nutritional obesity]

Changes in the activity of the sympathetic activity are often involved in the development of human insulin-resistance syndrome. However, the nature of changes in both the parasympathetic and orthosympathetic components are still controversial. We have recently developed an experimental model reproducing in dog this morbid triptyque (obesity, hypertension and hyperinsulinism), obtained by hypercaloric hyperlipidic diet. The aim of the present study was to characterize the changes in autonomic nervous system and spontaneous baroreflex in the initial period of obesity-hypertension syndrome. Ten male Beagle-Harrier dogs were used in this study. We investigated before and during 20 weeks after the beginning of the hypercaloric diet, plasma insulin, noradrenaline levels, spontaneous baroreflex efficiency (using the sequence method), arterial blood pressure, heart rate and their spectral analysis (fast Fourier Transformation) in both low (LF: 50-150 mHz, reflecting sympathetic activity) and high (HF: respiratory rate +/- 50 mHz, reflecting parasympathetic activity) frequency bands. Body weight (+20%), systolic (SBP: +23%) and diastolic (+16%) blood pressure and heart rate (+19%) increased during 6 weeks and then remained stable. Concomitantly, high frequency of HR (22.01 +/- 1.9 vs 14.15 +/- 1.04% at 7th week) and BF of systolic blood pressure (15.6 +/- 1.1 vs 19.2 +/- 1.2% at 4th week); p < 0.07, showed a rapid decrease in parasympathetic tone and a early increase in sympathetic activity. Nevertheless, in steady state of this syndrome, parasympathetic tone returned to initial values (18.43 +/- 3.25% at 20th week). Insulinemia significantly increased from the 4th week (14.2 +/- 0.9 vs 25.3 +/- 2.2 microUI/mL at 20th week), but noradrenaline remained not modify (400 +/- 85 vs 312 +/- 45 pg/mL at 20th week). Spontaneous baroreflex efficiency also decreased from the 2nd week (35.5 +/- 5.5 vs 16.7 +/- 4.9 mmHg/ms at 20th week). This study shows that an hyperlipidic hypercaloric diet induces a decrease in both parasympathetic tone and spontaneous baroreflex efficiency, which could be the physiopathological link between obesity, hypertension and hyperinsulinism.

Effects of octreotide on experimental neurogenic orthostatic hypotension in anaesthetized dogs

This paper investigates the effects of octreotide (0.1 mg/kg, subcutaneous) on cardiovascular adaptation during head-up tilt test in an experimental model of neurogenic orthostatic hypotension (OH) obtained by chronic sinoaortic denervation in anaesthetized dogs. Blood pressure (BP), heart rate (HR), spectral variability (Fast Fourier transformation on 512 consecutive points, delta t: 2 Hz) and plasma catecholamine levels were measured in a double blind cross-over randomized study versus placebo, in supine position and during a head-up tilt test (80 degrees, 10 min) in six sinoaortic denervated and six control (normal) dogs. In normal dogs, head-up tilt test significantly increased HR and diastolic blood pressure (DBP). Plasma noradrenaline levels and energy of the low frequency band (40-150 mHz) of systolic blood pressure (SBP) significantly increased whereas the energy of the low frequency band of HR significantly decreased. Placebo and octreotide failed to modify supine and head-up tilt values of the measured parameters (except the value of low frequency band of SBP, which increased after octreotide). In sinoaortic denervated dogs, supine values of BP, HR and plasma noradrenaline levels were significantly higher than in controls whereas the energy of the low frequency spectral band of HR and SBP was similar to controls. Head-up tilt test induced a dramatic decrease in BP. HR, plasma noradrenaline levels and energy of the low frequency band of SBP and HR remained unchanged during head-up tilt tests. Neither supine nor head-up tilt values of these parameters were modified 45 min after octreotide or placebo administration. These results show that sinoaortic denervation is a reproducible model of OH characterized by a lack of activation of sympathetic efferent pathways during head-up tilt tests. Octreotide at the dose used remains ineffective to prevent the fall in BP under these experimental conditions.

A study of dopaminergic sensitivity in Parkinson's disease: comparison in "de novo" and levodopa-treated patients

The present study investigates dopaminergic sensitivity in Parkinson's disease (PD) through the measurement of neuroendocrine (growth hormone: GH, prolactin: PRL) and cardiovascular (blood pressure: BP, heart rate: HR) responses to low doses of apomorphine (5 micrograms/kg s.c.) in three groups of subjects: 13 normal volunteers (controls), 19 "de novo" never-treated PD patients, and 14 levodopa-treated PD patients. Apomorphine did not change BP and HR but significantly decreased PRL plasma levels in controls as well as in the two groups of PD patients. GH plasma levels significantly increased after apomorphine. There was no significant difference in the changes in neuroendocrine (GH, PRL) parameters in the two groups of PD patients in comparison with controls. However, "de novo" patients exhibited a significantly higher number of apomorphine-induced orthostatic symptoms (7 of 19) than did controls (0 of 13) or treated PD patients (2 of 14). These results show that hypothalamic dopaminergic sensitivity (studied through GH and PRL responses to apomorphine) is normal in PD. In contrast, because apomorphine-induced orthostatic hypotension is mainly due to the stimulation of peripheral dopaminergic receptors, our study suggests a peripheral dopaminergic hypersensitivity in some "de novo" never treated (but not in treated) PD patients.

[Effects of octreotide on experimental orthostatic neurogenic hypotension]

The synthetic somatostatin analogue, octreotide, has recently been proposed for the treatment of both postprandial and orthostatic hypotension (OH) in humans with autonomic failure related to multiple system atrophy (MSA) or diabetes mellitus. However, pharmacodynamic data are not still available in experimental models of orthostatic hypotension. We investigated in a model of neurogenic orthostatic hypotension, obtained by chronic sinoaortic denervation (SAD) in chloralose-anaesthetized dogs, the effects of octreotide (0.1 mg/kg, subcutaneous route) during a double-blind cross-over study vs placebo. Blood pressure (BP) and heart rate (HR) average values, SBP and HR short-term variabilities (using fast Fourier transformation) in both low (LF: 50-150 mHz) and high frequency range (respiratory rate +/- 50 mHz) and plasma noradrenaline (NA) levels (HPLC) were measured in supine position and during head-up tilt test (HUT: 80 degrees, 10 min) before and 45 min after drug administration. In controls, as expected, head-up tilt test induced a significant increase in DBP (+14 +/- 8 mmHg), HR (+36 +/- 21 beat/min), NA (296 +/- 118 vs 141 +/- 63 pg/ml), SBP-LF (25 +/- 5 vs 14 +/- 3%) whereas HR-HF significantly decreased. The changes during head-up tilt test were not modified after placebo or octreotide administration. In SAD dogs, head-up tilt test elicited a dramatic fall in SBP (-74 +/- 39 mmHg), DBP (-20 +/- 15 mmHg) without any significant change in HR (-5 +/- 12 beat/min), NA (708 +/- 213 vs 606 +/- 331 pg/ml), SBP-LF (16 +/- 3 vs 16 +/- 3%), HR-HF (8 +/- 2 vs 7 +/- 1%). Octreotide or placebo failed to significantly modify any of the measured parameters during head-up tilt test performed 45 min after drug administration. At the dose used, octreotide elicited a 80% decrease in insulin plasma levels after 45 min in both normal and SAD dogs. These results suggest that 1) this experimental model of orthostatic hypotension in SAD dogs is reproductible and can be used to investigate the pharmacological effects of antihypotensive drugs, 2) cardiovascular and biochemical characteristics of the SAD model are similar to those observed in MSA and 3) octreotide, in these experimental conditions, is not able to correct the BP fall during head-up tilt test.

Effects of pentobarbital and etomidate on plasma catecholamine levels and spectral analysis of blood pressure and heart rate in dogs

The present paper investigates the effects of two anaesthetic drugs (pentobarbital and etomidate) on both short-term variabilities of systolic blood pressure (SBP) and heart rate (HR) using fast Fourier transformation and catecholamine plasma levels. HR and BP were continuously recorded through an arterial catheter and blood samples were taken from the jugular vein. Spectral analysis was performed first in the conscious state and six minutes after induction of anaesthesia on a series of 256 consecutive BP and HR values (delta t: 2 Hz). The area under the curve (AUC) was determined in the low-frequency component of the SBP (LF: 40-150 mHz), in the high-frequency band of HR (HF: respiratory frequency +/- 50 mHz) and in the total frequency spectra. Results were normalized by calculation of the ratio between AUC of LF and HF and the total AUC of the corresponding spectrum (TS). Etomidate (2 mg/kg i.v.) induced a significant increase in TS and LF without changing the LF/TS ratio or the HR variability when compared with the awake period. Catecholamine plasma levels did not change. In contrast, pentobarbital (30 mg/kg i.v.) decreased the values of LF, HF, LF/TS and HF/TS and catecholamine plasma levels. These results suggest that pentobarbital decreases the activity of the two components of the autonomic nervous system whereas etomidate induces only minimal changes.

Spectral analysis of blood pressure and heart rate, catecholamine and neuropeptide Y plasma levels in a new model of neurogenic orthostatic hypotension in dog

The aim of the study was to compare changes in blood pressure (BP) and heart rate (HR) variability, catecholamine and neuropeptide Y (NPY) plasma levels induced by passive head-up tilt in normal and sino-aortic denervated (SAD) chloralose-anaesthetized dogs. In controls, 80 degrees head-up tilt test failed to change BP and increased HR. Plasma noradrenaline and NPY levels (but not adrenaline) significantly rose. In SAD dogs, head-up tilt test induced a marked and reproducible decrease in BP without any change in HR or noradrenaline and NPY plasma levels. In SAD dogs, spectral analysis in supine position was characterized by reduced variability in the high frequency (HF) band of the HR spectrum without changes in low frequency (LF) bands of both HR and systolic blood pressure (SBP). Head-up tilt test increased the LF component of SBP variability and decreased the HF component of HR variability in controls but failed to modify HR and BP variabilities in SAD dogs. In conclusion, sino-aortic denervation in dogs elicits a reproducible postural fall in BP with impaired adaptation of sympathetic nervous system activity. This model may be of value in evaluating the pharmacological effects of drugs for the management of orthostatic hypotension.

A study of tolerance to apomorphine

1. The present study was designed to investigate tolerance to several pharmacological effects of apomorphine. 2. Changes in blood pressure, heart rate, plasma noradrenaline levels, rectal temperature, respiratory rate and retching plus vomiting were compared after administration of apomorphine (200 micrograms kg-1, i.v. as a bolus) or saline at different time intervals (30, 120 and 720 min) in four groups of chloralose-anaesthetized dogs. 3. The first administration of apomorphine induced a significant decrease in blood pressure and rectal temperature, a marked rise in heart rate with no change in noradrenaline plasma levels or respiratory rate. Emesis occurred in 71% of the animals. 4. A second administration of apomorphine 30 min later failed to modify blood pressure or heart rate. In contrast, the magnitude of apomorphine-induced changes in blood pressure and heart rate was similar to that observed after the first administration when apomorphine was given 120 or 720 min later. 5. The apomorphine-induced decrease in rectal temperature evoked by a second dose of apomorphine was less marked when given 30 and 120 min after the first dose and unchanged when given 720 min later. 6. The number of animals exhibiting retching and vomiting was lower when apomorphine was reinjected after 30 min than when the time between two successive injections of apomorphine was 120 or 720 min. 7. These results show that tolerance to apomorphine involves its cardiovascular, hypothermic and emetic effects. The time course of tolerance to repeated injections of apomorphine is longer for its hypothermic than for its hypotensive or emetic effects. This suggests a tissue-specific regulation of D2 dopamine receptors to repeated injections of apomorphine.

Central cardiovascular effects of acetylcholine in the conscious dog

1. The effects of central cholinomimetic drugs on cardiovascular and vasoactive hormonal responses (blood pressure, heart rate, catecholamines, vasopressin, atrial natriuretic factor, neuropeptide Y plasma levels and plasma renin activity) were investigated in conscious Beagle dogs. For this purpose a catheter was chronically implanted into each dog's cisterna magna to allow repeated central injections in the awake animals. 2. Intracisternal acetylcholine (20 micrograms kg-1) significantly increased systolic and diastolic blood pressure. These changes were accompanied by an initial short term tachycardia followed by a long lasting bradycardia. Intracisternal acetylcholine also increased noradrenaline, adrenaline and vasopressin plasma levels, decreased plasma renin activity but did not modify plasma levels of neuropeptide Y and atrial natriuretic factor. 3. The effects of acetylcholine were completely abolished by pretreatment with intracisternal injection of the muscarinic antagonist, atropine (5 micrograms kg-1) but not by the intracisternal injection of the nicotinic antagonist, mecamylamine (25 micrograms kg-1). 4. The present results demonstrate that there are qualitative and quantitative differences between the central cardiovascular effects of acetylcholine in conscious dogs compared to what we previously reported, using a comparable protocol, in anaesthetized dogs. Under both conditions, we observed a central cholinergically mediated increase in blood pressure secondary to an increase in sympathetic tone and vasopressin release but these responses were shorter (less than 10 min) in the conscious dogs than in anaesthetized dogs (more than 10 min). Moreover, we detected in the response to the central cholinergic stimulation in the conscious dogs a significant increase in plasma adrenaline levels and biphasic changes in heart rate which were not described previously in the anaesthetized dog.

Involvement of renal dopaminergic system in experimental neurogenic arterial hypertension

The effect of chronic salt loading (10 g of NaCl for a period of 7 days) on urinary dopamine release has been investigated in 3 groups of beagle dogs: normotensive dogs (group 1: n = 7), and 2 groups of dogs made hypertensive by chronic sinoaortic denervation [group 2: (n = 6) during the first 4 months after sinoaortic denervation i.e. a model of arterial hypertension with high levels of plasma catecholamines and group 3: (n = 6) one year after denervation i.e. a model of arterial hypertension with normal sympathetic tone]. In normal dogs (group 1), salt loading induced an increase in urinary dopamine excretion during the two first days after salt loading. The rise in urinary dopamine was blunted in group 2. It was not observed in group 3. Salt loading failed to change arterial pressure and heart rate in the three groups of animals. These data show an alteration of the renal dopaminergic system in hypertensive sinoaortic denervated dogs suggesting that a dopaminergic impairment can appear during the development of arterial neurogenic hypertension.

Effects of dopaminergic drugs on the sympathoadrenal system

Several studies have suggested that dopamine (DA) plays a major role in cardiovascular functions. Dopaminergic receptors have been found on sympathetic nerve terminals (DA2), kidney (DA1, DA2), vascular smooth muscle (DA1) as well as on sympathetic ganglia (DA1, DA2) and adrenal gland (DA1, DA2). Previous studies have shown that DA2 receptor stimulation by a specific DA2 agonist, quinpirole (1) elicits a peripheral depressor action (decreased blood pressure) and a central pressor component involving an increase in both sympathetic tone and vasopressin release and (2) does not affect under in vivo conditions adrenal catecholamine release. The present study investigates the effects of fenoldopam, a specific DA1 receptor agonist on both cardiovascular responses and catecholamine release from the adrenal medulla. In conscious normal dogs, fenoldopam (10, 20 and 40 micrograms/kg i.v.) elicited a decrease in blood pressure and a marked increase in heart rate associated with a rise in plasma catecholamine levels. The increase in heart rate is only due to baroreflex mechanism since fenoldopam (conversely to DA2 receptor agonists like quinpirole) does not exert a central excitatory component (as shown by the absence of cardiovascular effects after intracisternal injection). Moreover, in sinoaortic denervated dogs (i.e. animals deprived from baroreflex pathways), the decrease in arterial blood pressure was more important than in normal dogs. Heart rate was unchanged. In these animals, DA1 stimulation induced a decrease in sympathetic tone, as shown by the significant fall in plasma noradrenaline levels. These "in vivo" data clearly demonstrate the inhibitory role of ganglionic DA1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for activation of both adrenergic and cholinergic nervous pathways by yohimbine, an alpha 2-adrenoceptor antagonist

Adrenoceptors are involved in the control of the activity of the autonomic nervous system and especially the sympathetic nervous system. Activation of alpha 2-adrenoceptors decreases sympathetic tone whereas their blockade has an opposite effect. However, previous investigations have shown that yohimbine (a potent alpha 2-adrenoceptor antagonist) increases salivary secretion through activation of cholinergic pathways. The aim of the present experiment was to investigate the involvement of both the sympathetic and the parasympathetic system in several pharmacological effects of yohimbine. For this purpose, salivary secretion and various endocrino-metabolic parameters (noradrenaline and insulin secretions, lipomobilization) were evaluated in conscious fasting dogs before and after blockade of either the sympathetic (with the beta-adrenoceptor antagonist agent nadolol) or the parasympathetic (with the anticholinergic agent atropine) systems. Yohimbine alone (0.4 mg.kg-1, i.v.) increased within 5-15 minutes, plasma noradrenaline (600%), insulin levels (300%), free-fatty acids (79%) and salivary secretion (143%). Atropine (0.2 mg.kg-1, i.v.) suppressed yohimbine-induced salivary secretion (90%) but did not significantly modify the yohimbine induced changes in noradrenaline (312%), insulin (277%) and free-fatty acids (102%) plasma levels. Administration of nadolol (1 mg.kg-1, i.v.) did not change the magnitude of the increase in both noradrenaline plasma levels (550%) and salivary secretion (300%) induced by yohimbine. However, nadolol totally blunted the increase in insulin (15%) and free-fatty acids (4%) plasma levels. These results show that yohimbine-induced increase in salivary secretion is a cholinergic effect whereas the increase in insulin and free fatty acids can be explained by an increase in sympathetic tone.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ambulatory measurement of blood pressure and plasma catecholamines in the study of orthostatic hypotension]

The purpose of the study was to investigate the interest of ambulatory blood pressure (BP) monitoring (ABPM) and plasma catecholamines in the management of orthostatic hypotension (OH). Fifteen patients, 4 men, 11 females, 53.3 +/- 21.1 years old, with OH were included in the study: 7 with dysautonomia (G1) = multiple systemic atrophy, pure autonomic failure, OH in elderly people; 8 with OH from other origin (G2) = hypovolemia, neurodystonia, vaso-vagal syncope. ABPM and plasma catecholamines assays (HPLC) in lying then in standing position were carried out in all patients. BP was 131.2 +/- 31.9/78.1 +/- 12.0 mmHg in lying and 112.1 +/- 25.3/75.4 +/- 15.8 in standing position (n = 15). The systolic (S) standing-induced (delta) decrease in BP after 1 min and 10 min (delta SBP) correlated with standard-deviation and variation coefficient of mean SBP (r = 0.78, p < 0.01; r = 0.82, p < 0.01 for delta sBP 1 min and r = 0.80, p < 0.01; r = 0.81, p < 0.01 for delta sBP 10 min), but not with norepinephrine (NorE) or epinephrine levels. There was a significant correlation between diastolic nycthemeral BP variability expressed by mean night-time DBP/mean day-time DBP ratio/diastolic N/D) and standing-induced decrease in DBP after 1 min (r = 0.59, p < 0.05). delta SBP 1 min and 10 min, delta DBP 1 min (p = 0.02, p = 0.05, p = 0.01) and systolic and diastolic N/D (p = 0.02; p < 0.01) were significantly different in G1 and G2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of insulin on the release of neuropeptide Y, [Met5]enkephalin and catecholamines from dog adrenal medulla

Insulin-induced hypoglycaemia is a well-known stimulating factor for the release of adrenaline from adrenal medulla. The present experiment investigates the co-release of catecholamines and neuropeptides (neuropeptide Y and [Met5]enkephalin) from the adrenal medulla in chloralose-anaesthetized dogs after intravenous administration of insulin (0.3 U/kg). The increases in noradrenaline, adrenaline and [Met5]enkephalin were 29.6-, 23.8-, and 27.9-fold basal values, respectively whereas the neuropeptide Y increase was only 1.6 times the baseline. These results show that adrenal [Met5]enkephalin and catecholamines exhibit the same pattern of co-release which is not the case for adrenal neuropeptide Y.

Relationship between arterial blood pressure disturbances and alpha adrenoceptor density

To investigate the influence of blood pressure disturbances on human platelet alpha 2-adrenoceptor density, we studied 7 normotensive Parkinsonians with orthostatic hypotension and 23 mild essential hypertensive patients. Plasma catecholamine levels were measured by HPLC and alpha 2-adrenoceptor number and affinity determined by [3H]-yohimbine binding. Alpha-adrenergic reactivity was investigated by blood pressure response to noradrenaline infusion in Parkinsonians and by adrenaline-induced platelet aggregation in hypertensive patients. In Parkinsonians with orthostatic hypotension, in comparison with Parkinsonians without orthostatic hypotension and normotensive control subjects age and sex matched, noradrenaline plasma levels were significantly lower (62 +/- 11, 195 +/- 14 and 219 +/- 13 pg. ml-1 respectively, p < 0.05), platelet alpha 2-adrenoceptor number was significantly higher (313 +/- 52, 168 +/- 9 and 174 +/- 4 fmol.mg-1 protein respectively, p < 0.05) and the noradrenaline dose required for a 25 mm Hg increase of systolic blood pressure significantly lower (0.19 +/- 0.03, 0.86 +/- 0.11 and 0.68 +/- 0.10 microgram.Kg-1 respectively, p < 0.05). In hypertensive patients, in comparison with normotensive control subjects age and sex matched, plasma noradrenaline levels remained unchanged (306 +/- 68 vs 246 +/- 28 pg.ml-1) whereas both platelet alpha 2-adrenoceptor number (137 +/- 15 vs 177 +/- 15 fmol.mg-1 protein, p < 0.05) and velocity of adrenaline-induced platelet aggregation were significantly decreased. These results indicate that platelet alpha 2-adrenoceptor density is related to blood pressure values. In Parkinsonians with orthostatic hypotension, the up-regulation of alpha 2-adrenoceptors was induced by the decrease of endogenous catecholamines. In contrast, in essential hypertension a down-regulation of alpha 2-adrenoceptors was observed in spite of no significant increase of catecholamine levels. These results suggest that only sustained abnormal plasma noradrenaline levels could allow the development of alpha 2-adrenoceptor regulatory mechanisms.

Effects of clonidine, dihydralazine and splanchnic nerve stimulation on the release of neuropeptide Y, MET-enkephalin and catecholamines from dog adrenal medulla

Various neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release (evaluated by adrenal vein plasma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkephaline (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)] from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of clonidine (10 micrograms/kg) and dihydralazine (1 mg/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. The increment in the release of catecholamines and neuropeptides was evaluated for dihydralazine and splanchnic nerve stimulation. Dihydralazine (at its maximal effect) induced a significant preferential increase in catecholamines (expressed as mean (SEM): NA: 17.3 (5.4) fold, A: 13.1 (2.6) fold) and ME (16.0 (7.1) fold) versus basal values. However, the significant increase in NPY-LI was only 2.0 (0.4) times the baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. When the stimulation frequency was increased from 1 Hz to 5 Hz, NA and A levels increased 17.9 (4.3) and 14.0 (2.2) fold, respectively and ME levels 14.1 (3.0) fold. By contrast, NPY-LI was increased only 2.3 (0.3) fold under the same conditions. Increasing the stimulation frequency from 5 Hz to 10 Hz resulted in similar elevations of NA, ME, and NPY-LI adrenal plasma levels (about 4 times) whereas A only increased twice. Clonidine decreased catecholamine and ME adrenal plasma levels (the maximal percent decrease when compared with control values was about 75%) whereas NPY adrenal plasma levels remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

[Co-release of neuropeptides and catecholamines by adrenal medulla]

Different neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release of these neuropeptides [neuropeptide Y (NPY), met-enkephalin (ME)] and catecholamines (adrenaline and noradrenaline) from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of dihydralazine (1 mg/kg) and insulin (0.3 U/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. Baroreflex involvement or hypoglycemia induced a significant preferential increase in CA and ME versus basal values: around 16 fold for dihydralazine and 28 fold after insulin administration. In opposite, increase in NPY was only two times baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. At the lower frequencies (1 to 5 Hz), splanchnic nerve stimulation elicited a parallel increase in catecholamines and ME (13 to 17 fold basal values). By contrast, NPY increases 2 fold in the same conditions. At the higher frequencies (5 to 10 Hz), we observed a parallel (4 fold) increase in NA, ME and NPY adrenal plasma levels. In conclusion, the present data indicate that both adrenal ME and catecholamines (mainly NA) always exhibit a parallel fashion of corelease which is not the case for NPY and that different populations of chromaffin vesicles could be preferentially mobilized according to different physiological and pharmacological patterns.

Effects of yohimbine on plasma catecholamine levels in orthostatic hypotension related to Parkinson disease or multiple system atrophy

Different pathophysiological mechanisms may underly orthostatic hypotension (OH) observed in neurological degenerative disorders. The present study investigates the responses to the pharmacological activation of sympathetic pathways induced by yohimbine (0.2 mg/kg orally) through measurements of plasma catecholamine levels in parkinsonian patients with (n = 9) or without OH (n = 11), in patients with multiple system atrophy (MSA) plus OH (n = 9), and in controls (n = 6). Basal norepinephrine plasma levels in parkinsonian patients with OH (71 +/- 11 pg/ml) were significantly lower (p < 0.05) than in parkinsonian patients without OH (280 +/- 25 pg/ml) or in controls (259 +/- 48 pg/ml). In patients with MSA plus OH, basal catecholamine plasma levels were in the normal range (344 +/- 54 pg/ml). Yohimbine significantly increased norepinephrine (p < 0.05) but not epinephrine plasma levels in all groups. However, the increment obtained in parkinsonian patients with OH (+53 +/- 18 pg/ml) remained significantly lower (p < 0.05) than in parkinsonian patients without OH or in controls (+638 +/- 140 and +457 +/- 103 pg/ml, respectively) as well as in MSA plus OH (+633 +/- 142 pg/ml). Yohimbine failed to modify the blood pressure and heart rate at the dose used. The results suggest that the yohimbine test is useful to elucidate the site of the dysfunction of the efferent sympathetic pathways in these two conditions. In Parkinson disease with OH, the lesion is both central and postganglionnic, whereas in MSA it is only centrally located.

The effect of yohimbine on sympathetic responsiveness in essential hypertension

We have studied the sympathetic response to blockade of presynaptic alpha 2-adrenoceptors in essential hypertension by measuring plasma concentrations of noradrenaline after a single oral dose of yohimbine, an alpha 2-adrenoceptor antagonist. Mean baseline plasma noradrenaline and adrenaline concentrations were similar in the hypertensive and normotensive groups. Yohimbine (0.2 mg x kg-1 orally) caused a lesser increase in the plasma concentrations of noradrenaline in hypertensive patients (+67%) than in normotensive subjects (+178%) and a pressor response in hypertensive (but not in normotensive) patients. These results are consistent with an alteration in the balance of alpha-adrenoceptors (for example presynaptic alpha 2-adrenoceptor desensitization and post-synaptic alpha 1-adrenoceptor hyper-responsiveness) which would help to develop and/or maintain arterial hypertension.

[Differential regulation of the release of norepinephrine and neuropeptide Y]

The release of catecholamines and their co-neurotransmitter neuropeptide Y was investigated in conscious dogs with neurogenic arterial hypertension elicited by sinoaortic denervation. One month after denervation, an elevation of catecholamine levels (measured by HPLC) without elevation of neuropeptide Y levels in plasma (evaluated by RIA) has been found. This dissociation could be explained by a transient release of neuropeptide Y during the first weeks after surgery; a depletion of neuronal neuropeptide Y due to the permanent sympathetic stimulation; or an insufficient increase in sympathetic tone. To test these three hypotheses, we investigated the time courses of catecholamine and neuropeptide Y levels in arterial plasma during the first five weeks after sinoaortic denervation; and the responses to yohimbine (an alpha 2 antagonist which enhances transmitter release). Resting neuropeptide Y levels in plasma remained normal during the first five weeks after sinoaortic denervation. In normal dogs, a high dose of yohimbine (0.5 mg/kg i.v.) elevated both catecholamine (6-fold) and neuropeptide Y levels (1.5-fold), whereas a lower dose (0.05 mg/kg i.v.) induced a two fold elevation of catecholamine levels without changing neuropeptide Y concentrations. In sinoaortically denervated dogs, yohimbine elicited elevation of both catecholamines and neuropeptide Y whatever the dose used. Thus, neurogenic arterial hypertension in dogs seams to involve catecholamines but not neuropeptide Y. Moreover, the present work suggests that a high level of sympathetic stimulation is required for a co-release of catecholamines and neuropeptide Y.

[Is there any desensitization of presynaptic alpha 2-adrenergic receptors in hypertension? Experimental and clinical studies]

Several authors have discussed an alteration of adrenergic receptivity in arterial hypertension. De Champlain (Hypertension 1990; 8: S77-S85) suggested that postsynaptic alpha 1-adrenergic functions became dominant while beta-adrenergic functions are attenuated in arterial hypertension. However, the status of presynaptic alpha 2-adrenoceptors remains unknown. The present study investigates presynaptic alpha 2-adrenoceptors in hypertension through the measurement of plasma levels of noradrenaline after administration of yohimbine, an alpha 2-adrenoceptor antagonist, in essential hypertension. Yohimbine (0.2 mg/kg per os) induced a 73% increase of plasma levels of noradrenaline in hypertensive patients (n = 12) and a 178% one in normotensive subjects (n = 6, p < 0.05). A similar significant difference was found in experimental neurogenic hypertension observed in awake dogs 3 weeks after sinoaortic denervation: the increase in plasma concentrations of noradrenaline after yohimbine (0.5 mg/kg i.v.) was +279% in hypertensive versus +642% in normotensive dogs (p < 0.05). The results show that the magnitude of the yohimbine-induced sympathetic activation is lower in hypertensives than in normotensives. They suggest the existence of a presynaptic alpha 2-adrenoceptor desensitization in arterial hypertension. The abnormality of this presynaptic inhibitory mechanism can increase the sympathetic tone and help to develop and maintain arterial hypertension.

Is neuropeptide Y co-released with catecholamines in experimental arterial hypertension following sinoaortic denervation?

The release of catecholamines and their coneurotransmitter neuropeptide Y (NPY) was investigated in conscious dogs with neurogenic arterial hypertension elicited by sinoaortic denervation. One month after denervation, an elevation of catecholamine levels (measured by HPLC) without elevation of NPY-like immunoreactivity (NPY-LI) levels in plasma (evaluated by RIA) has been found. This dissociation could be explained by 1) a transient release of NPY during the first weeks after surgery, 2) a depletion of neuronal NPY due to the permanent sympathetic stimulation, or 3) an insufficient increase in sympathetic tone. To test these hypotheses, we investigated the time courses of catecholamine and NPY-LI levels in arterial plasma during the first five weeks after sinoaortic denervation and responses to yohimbine (an alpha 2 antagonist which enhances transmitter release). Resting NPY-LI levels in plasma remained normal during the first five weeks after sinoaortic denervation. In normal dogs, a high dose of yohimbine (0.5 mg/kg i.v.) elevated both catecholamine (6-fold) and NPY-LI levels (1.5-fold), whereas a lower dose (0.05 mg/kg i.v.) induced a two fold elevation of catecholamine levels without changing NPY-LI concentrations. In sinoaortically denervated dogs, yohimbine elicited elevation of both catecholamines and NPY-LI whatever the dose used. Thus, neurogenic arterial hypertension in dogs seems to involve catecholamines but not NPY. Moreover, the present work suggests that a high level of sympathetic stimulation is required for a co-release of catecholamines and NPY.

Release of neuropeptide Y and noradrenaline during afferent nerve stimulation

The present study was carried out to investigate the possibility that noradrenaline (NA) and neuropeptide Y (NPY) are co-released after afferent vagal or saphenous stimulation (1, 5, 10 and 20 Hz) in chloralose-anaesthetized dogs. Electrical stimulation of the vagus elicited an increase in plasma NA levels for the 5, 10 and 20 (but not 1) Hz frequencies. Blood pressure only increased after a 20-Hz stimulation. In contrast, no change in plasma NPY levels was observed whatever the frequency of stimulation. Electrical stimulation of the saphenous nerve failed to change plasma NA and NPY levels. The present data suggest that (1) the release of NA varies according to the frequency of stimulation of nociceptive fibres, (2) NPY release does not seem to be involved in the pressor effect elicited by the stimulation of nociceptive-sensitive fibres, and (3) NPY and NA release are not necessarily linked.

Myocardial hypertrophy, cardiac beta-adrenoceptors and adenylate cyclase activity during sinoaortic denervation in dogs

1. The long-term effects of sinoaortic denervation on the development of left ventricular hypertrophy (assessed by the measurement of the ratio (R): heart weight/total body weight and LVT: left ventricular thickness), myocardial beta-adrenergic receptivity (measured by [125I]-cyanopindolol binding and adenylate cyclase activity) and plasma catecholamine levels (measured by h.p.l.c.) were investigated in three groups of dogs: normotensive controls (group 1), dogs made hypertensive by sinoaortic denervation and evaluated 1 (group 2) and 18 months (group 3) later. 2. Noradrenaline (NA) and adrenaline (A) plasma levels were 461 +/- 54 and 85 +/- 45 pg ml-1 in controls, 861 +/- 185 and 191 +/- 23 pg ml-1 in group 2 (P less than 0.05). They were normal in group 3 (426 +/- 132 and 110 +/- 16 pg ml-1). 3. R and LVT values were significantly (P less than 0.05) higher in sinoaortic denervated dogs (R = 7.7 +/- 0.1 and 7.8 +/- 0.2; LVT = 13.6 +/- 1.3 and 14.2 +/- 0.9 mm in groups 2 and 3 respectively) than in normotensive dogs (group 1: R = 6.7 +/- 0.1, LVT = 9.3 +/- 0.8 mm). 4. In group 1, the total number of beta-adrenoceptors (Bmax) was 37 +/- 11 and 29 +/- 6 fmol mg-1 protein in the left ventricle (LV) and right auricle (RA) respectively. In group 2, Bmax was significantly lower (10 +/- 3 in LV and 13 +/- 2 fmol mg-1 protein in RA, P less than 0.05) than in group 1. There was no difference between group 1 and group 3 (37 +/- 3 fmol mg-1 prot in LV and 31 +/- 3 fmol mg-1 protein in RA). 5. The percentage of beta 1-adrenoceptors was 82 +/- 4 in LV and 75 +/- 5 in RA in group 1. It was significantly lower (P less than 0.05) in groups 2 (LV: 33 +/- 6 and RA: 33 +/- 5) and 3 (LV: 59 +/- 3 and RA: 55 +/- 4). 6. Basal values of adenylate cyclase activity in LV significantly decreased after sinoaortic denervation.7. These data show that sinoaortic denervation is associated with left ventricular hypertrophy which appears early (1 month) and persists until 18 months despite the normalization of plasma catecholamine levels. The total number of myocardial beta-adrenoceptors is closely related to catecholamine levels but a selective decrease in beta 1-adrenoceptors is observed during cardiac hypertrophy. The fall in basal adenylate cyclase activity suggests that cardiac hypertrophy is associated with an impairment of transmembrane signalling.

Changes in plasma catecholamine and neuropeptide Y levels after sympathetic activation in dogs

1. Plasma levels of noradrenaline (NA) and neuropeptide Y (NPY) were evaluated in two experimental models associated with an increase in sympathetic tone: conscious dogs which were subject to either sinoaortic denervation or acute administration of the alpha 2-adrenoceptor antagonist yohimbine. 2. Dogs that had undergone sinoaortic denervation exhibited a two fold increase in plasma NA without any change in NPY levels. 3. Yohimbine (0.05 mg kg-1 i.v. as a bolus) produced similar effects. A higher dose of yohimbine (0.5 mg kg-1 i.v.) increased both plasma NA (7 fold) and NPY (6.5 fold) levels. 4. The present results indicate that changes in plasma catecholamines and NPY are not always concomitant. They suggest that the simultaneous release of NA and NPY is only observed under in vivo conditions for a marked increase in sympathetic tone.