Stimulation of nonshivering thermogenesis in the Syrian hamster by norepinephrine and β-selective adrenergic agents: A phenomenon of refractoriness

The ability of different adrenergic agents to stimulate nonshivering thermogenesis in Syrian hamsters was investigated. The hamsters were cold-acclimated to 6 °C and their thermogenic response was investigated in an open-circuit system at 24 °C. Both norepinephrine and the β₃-specific adrenergic agonist CGP-12177 induced a high rate of nonshivering thermogenesis. However, neither CGP-12177 nor other β₃-selective agonists (BRL-37344, ICI-D7114) could induce nonshivering thermogenesis fully to the extent induced by norepinephrine. It was further observed that an apparent “thermogenic refractoriness” was induced by certain adrenergic agents (isoprenaline, CGP-12177) but not by others (norepinephrine, BRL-37344, ICI-D7114). It is discussed whether the refractoriness could be secondary to effects of these agents on the vascular system. It is pointed out that the thermogenic response to adrenergic stimulation observed in the intact animal does not always fully correspond to what would be predicted from corresponding studies with isolated brown-fat cells.     

Energy and Water Turnover Rates of a Free-living and Captive Goanna,Varanus caudolineatus (Lacertilia: Varanidae)

The small, arboreal goanna, Varanus caudolineatus, has a field metabolic rate of approximately 0.46 mL CO₂ g⁻¹ hr⁻¹ and a daily water intake requirement of approximately 31.6 mL kg⁻¹ day⁻¹ measured during the summer. V. caudolineatus held in a controlled-temperature environment of 35°C have lower metabolic (0.25 mL CO₂ g⁻¹ hr⁻¹) and water flux (24.9 mL H₂O kg⁻¹d⁻¹) rates than those in the field. Body water content was approximately 80% for V. caudolineatus.     

Effects of fasting and aminophylline on norepinephrine-stimulated non-shivering thermogenesis

In an attempt to further elucidate the mechanisms of fasting-depressed maximum thermogenesis and cold tolerance, norepinephrine (NE)-stimulated non-shivering thermogenesis (NST) in cold-acclimated rats was used as a functional index of possible alterations in adrenergic efficacy after fasting. Fasting decreased the magnitude of maximum NE-Stimulated NST by 18.2% [6.87±0.47 Kcal (Kg^.75.min)^?1 well-fed vs. 5.81±0.39 Kcal (Kg^.75.min)^?1 fasted], but the apparent adrenergic binding affinity was not affected [Ke=0.43 μg NE min^?1 well-fed vs 0.55 μg NE min^?1 fasted]. Pretreatment with aminophylline [15 mg Kg^?1, i.p.], a phosphodiesterase inhibitor, restored the fasting-depressed NE-stimulated NST to the fed level. The results suggest that the depression of maximum thermogenesis after fasting is not due to changes in adrenergic binding characteristics but to alteration in cAMP production/degradation, resulting in decreased substrate mobilization for thermogenesis.     

Secretion by the mandibular gland of the red kangaroo (Macropus rufus) during isoprenaline infusion

Summary Intracarotid infusion of isoprenaline, either alone or in combination with acetylcholine infusion was used to stimulate salivation by the mandibular glands of anaesthetized red kangaroos. Isoprenaline alone (0.20–1.25 mol·kg^–1·min^–1) elicited flow rates ranging from 0.014 to 0.239 ml·min^–1 (1.21–28.1 l·g gland^–1·min^–1). Salivary concentrations of sodium, chloride, phosphate and urea were negatively correlated with flow, whereas potassium, calcium, magnesium, hydrogen ion, bicarbonate, protein, and osmolality were poorly correlated with flow. Relative to cholinergic saliva produced at equivalent flow rates, isoprenaline-evoked saliva had higher osmolality, saliva/plasma urea ratios and concentrations of protein, potassium, magnesium, bicarbonate, and phosphate, but lower sodium, chloride and hydrogen ion levels. At a steady salivary flow (0.5 ml·min^–1), superimposition of isoprenaline infusion (0.15 mol·kg^–1·min^–1) on a pre-existing acetylcholine infusion reduced the rate of acetylcholine administration necessary to maintain flow, increased osmolality and the concentrations of protein, urea, potassium, calcium, magnesium, bicarbonate and phosphate and decreased sodium, chloride and hydrogen ion in the saliva. Salivary amylase activity was low and highly variable and the amylase activity/protein ratio fell substantially during isoprenaline stimulation. These results support the conclusion that the enzyme is of extrinsic origin. The response of the kangaroo mandibular gland to isoprenaline stimulation was very similar to that reported for rat mandibular gland, suggesting that the same ion transport phenomena underlie mandibular secretion in both species and probably in therian mammals generally.     

The Antarctic notothenioid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis> is thermally flexible: acclimation changes oxygen consumption

Antarctic marine organisms are considered to have extremely limited ability to respond to environmental temperature change. However, here we show that the Antarctic notothenioid fish Pagothenia borchgrevinki is an exception to this theory. P. borchgrevinki was able to acclimate its resting metabolic rate and resting ventilation frequency after a 5°C rise in temperature. Acute exposure to 4°C resulted in an elevation in metabolic rate (57.8 ± 4.79 mg O₂ kg⁻¹ h⁻¹) and resting ventilation rate (40.38 ± 1.61 breaths min⁻¹) compared with fish at −1°C (metabolic rate 34.45 ± 3.12 mg O₂ kg⁻¹ h⁻¹; ventilation rate 29.88 ± 3.72 breaths min⁻¹). However, after a 1-month acclimation period, there was no significant difference in the metabolic rate (cold fish 29.52 ± 3.01; warm fish 31.13 ± 2.30 mg O₂ kg⁻¹ h⁻¹), or the resting ventilation rate (cold fish 28.75 ± 0.98; warm fish 34.25 ± 2.28 breaths min⁻¹) of cold and warm acclimated fish. Acclimation changes to the rate of oxygen consumption following exhaustive exercise were complex. The pattern of oxygen consumption during recovery from exhaustive exercise was not significantly different in either cold or warm acclimated fish.     

Metallobiochemistry of ultratrace levels of bismuth in the rat I. Metabolic patterns of 205+206Bi3+ in the blood

BackgroundThe number of the applications of bismuth (Bi) is rapidly and remarkably increasing, enhancing the chance to increase the levels to which humans are normally daily exposed. The interest to Bi comes also from the potential of Bi-based nanoparticles (BiNPs) for industrial and biomedical purposes. Like other metal-based NPs used in nanomedicine, BiNPs may release ultratrace amounts of Bi ions when injected. The metabolic fate and toxicity of these ions still needs to be evaluated. At present, knowledge of Bi metabolism in laboratory animals refers almost solely to studies under unnatural “extreme” exposures, i.e. pharmacologically relevant high-doses (up to thousand mg kg⁻¹) in relation to its medical use, or infinitesimal-doses (pg kg⁻¹ as non-carrier-added Bi radioisotopes) for radiobiology protection, diagnostic and radiotherapeutic purposes. No specific study exists on the “metabolic patterns” in animal models exposed to levels of Bi, i.e. at “environmental dose exposure” that reflect the human daily exposure (μg kg⁻¹).MethodologyRats were intraperitoneally injected with 0.8 μg Bi kg⁻¹ bw as ^205+206Bi(NO)₃ alone or in combination with ⁵⁹Fe for radiolabelling of iron proteins. The use of ^205+206Bi radiotracers allowed the detection and measurement down to pg fg⁻¹ of the element in the blood biochemical compartments and protein fractions as isolated by differential centrifugation, size exclusion- and ion exchange chromatography, electrophoresis, solvent extraction, precipitation and dialysis.Results24 h after the administration, the blood concentration of Bi was 0.18 ng mL⁻¹, with a repartition plasma/red blod cells (RBC) in a ratio of 2:1. Elution profiles of plasma from gel filtration on Sephadex G-150 showed four pools of Bi-binder proteins with different molecular sizes (> 300 kDa, 160 kDa, 70 kDa and < 6.5 kDa). In the 70 kDa fraction transferrin and albumin were identified as biomolecule carriers for Bi. In red blood cells, Bi was distributed between cytosol and membranes (ghosts) in a ratio of about 5:1. In the cytosol, low molecular components (LMWC) and the hemoglobin associated the Bi in a ratio of about 1.8:1. In the hemoglobin molecule, Bi was bound to the beta polypeptide chain of the globin. In the ghosts, Bi was detected at more than one site of the protein fraction, with no binding with lipids. Dialysis experiments and the consistently high recovery (80–90 %) of ²⁰⁶Bi from chromatography of ²⁰⁶Bi-containing biocomponents suggest that Bi was firmly complexed at physiological pH with a low degree of breaking during the applications of experimental protocols for the isolation of the ²⁰⁶Bi-biocomplexes. These latter were sensitive to acid buffer pH 5, and to the presence of complexing agents in the dialysis fluid.ConclusionsOn the basis of an environmental biochemical toxicology approach, we have undertaken a study on the metabolic patterns of Bi³⁺ ions in rats at tissue, subcellular and molecular level with the identification of cellular Bi-binding components. As a first part of the study the present work reports the results concerned with the metabolic fate of ultratrace levels of ^205+206Bi(NO)₃ in the blood.     

Calcium alginate-Immobilized hepatic microsomes: Effect of NADPH cofactor on oxidation rates

An important function of the liver is detoxification of drugs, toxins and foreign compounds. Within the liver cell, the endoplasmic reticulum, isolated as the microsomal fraction, is especially active. Microsomal oxidation is the major oxidation pathway for many compounds, and the requirement for NADPH, an expensive cofactor, is an important consideration in bioreactor design. This paper presents design information for NADPH- and substrate-dependent oxidation rates for free and immobilized microsomes. The primary goal of this paper is determining NADPH requirements for oxidation. The effect of various initial levels of nicotinamide adenine dinucleotide phosphate (NADPH) on chlorpromazine oxidation rate has been studied for a crude hepatic microsomal fraction immobilized in calcium alginate gel. At an initial NADPH concentration of 600 nmoles/ml, immobilized microsomes accelerate to a maximal velocity of ≈ 240 nmoles min⁻¹ ml⁻¹ of oxygen consumption. In comparison, free microsomes reach a maximal velocity of approximately 150 nmoles min⁻¹ ml⁻¹ at an initial NADPH concentration of 220 nmoles/ml. By fitting the “initial” rate as a function of NADPH concentration to Michaelis-Menten kinetics, the apparent half-saturation coefficients (K_m)app are 3.5 nmole/ml for free microsomes and 134.4 nmole/ml for immobilized microsomes, however the maximum reaction velocity, V_max, for immobilized microsomes is calculated to be 322 nmoles min⁻¹ ml⁻¹ compared with 145 nmols min⁻¹ ml⁻¹ for free microsomes. Preliminary studies indicate that is is possible to obtain significant reaction rates using calcium alginate immobilized microsomes and that this system may offer advantages due to its simplicity and lower cost.     

Partitioning of oxygen consumption between “maintenance” and “growth” in developing herring Clupea harengus (L.) embryos

Growth and oxygen consumption was measured in developing herring Clupea harengus (L.) embryos. By considering the variations in oxygen consumption with embryonic size and growth rate, an attempt was made to partition oxygen consumption between growth related and growth unrelated (i.e., “maintenance”) processes. The metabolic cost of growth was estimated as ≈ 150 ng O₂ · μg dry wt tissue formed⁻¹. This estimate compares favourably with the biochemical estimate of the costs of transport and net biosynthesis. The “maintenance” component was proportional to embryonic mass (77 ng O₂ · μg⁻¹· d⁻¹). Over the entire embryonic period, growth processes were responsible for ≈ 25% of the cumulated oxygen consumption.     

Dose-dependent inhibitory and non-inhibitory action of somatostatin on insulin release in rats

The dose-dependent effect of intravenously infused synthetic somatostatin-14 on basal and postprandial insulin and gastrin release was assessed in anesthetized rats.Infusion of 1 ng · kg^?1 · min^?1 elicited a significant reduction of basal and postprandial insulin levels compared to the saline control group. At 15 ng · kg^?1 · min^?1 basal insulin was not affected but postprandial insulin levels were still significantly reduced. At 30 ng · kg^?1 · min^?1 neither basal nor stimulated insulin levels were affected. At the highest concentration of 120 ng · kg^?1 · min^?1 basal and postprandial insulin levels were suppressed similar to the lowest infusion rate of 1 ng · kg^?1 · min^?1. Basal gastrin levels were significantly reduced only at the highest rate of 120 ng · kg^?1 · min^?1. A significant reduction of postprandial gastrin levels was observed at 15 ng · kg^?1 · min^?1 and all higher infusion rates employed. Measurements of plasma somatostatin-like immunoreactivity (SLI) demonstrated that plasma SLI levels during the lowest infusion rate of 1 ng · kg^?1 · min^?1 were not different from the controls. No significant rise of plasma SLI levels was observed in response to the test meal. The higher infusion rates elicited a dose-dependent increase in plasma SLI levels. These data demonstrate that in rats somatostatin exerts a biological effect on insulin release at very low doses while certain greater infusion rates have no suppressive effect. Gastrin secretion is inhibited in a more linear pattern.     

Pyrogenic effects of cytokines (IL-1β, IL- 6, TNF-α) and their mode of action on thermoregulatory centers and functions

The objective of this study was to compare the thermoregulatory responses of rabbits to fever-inducing doses of various cytokines (IL-1β, IL-6, TNF-α) injected peripherally (i.v.), or centrally (i.h.).TNF-α (1 μg kg⁻¹), when applied i.v. at thermoneutral conditions, induced a long lasting increase in hypothalamic temperature, which reached maximal values within 50 min and then persisted for at least 3 h. This monophasic fever-like response was due to extensive and long lasting attenuation of panting and due to transient vasoconstriction. Metabolic rate tended to increase during the early phase of the fever, only. On the other hand, IL-6 when applied i.v. in the same dose (1 μg kg⁻¹) and IL-1β, in a much lower dose (60 ng kg⁻¹), induced a short lasting monophasic hyperthermia due to transient attenuation of panting and due to transient vasoconstriction. No significant increase in metabolic rate was observed. The immediate attenuation of panting and induction of vasoconstriction rather resembled reflex (shock) responses than specific thermoregulatory reactions. Thirty minutes after i.v. administration of TNF-α, temperature thresholds for induction of cold thermogenesis, panting and vasomotion were shifted to higher body temperatures and remained elevated for at least 3 h. In case of IL-1β the increased temperature thresholds were observed 30 min after i.v. administration, only. I.v. applied IL-6 did not influence the thresholds neither 30 or 180 min after injection. Thus, peripheral IL-6 rather induced hyperthermia than fever.When injected i.h. all cytokines studied induced a long lasting increase in body temperature similar to that after i.v. injection of LPS. Temperature thresholds for induction of all thermoregulatory outputs were increased and remained increased for at least 3 h. No changes in hypothalamic thermosensitivity were observed. Data indicate a nonspecific effect of central cytokines on body temperature control.IL-1β appeared to be the most potent fever inducer. Nanogram doses of IL-1β injected i.v. induced a similar febrile response as microgram doses of other cytokines. On the other hand, TNF-α induced a longer lasting fever than other cytokines.     

Metabolic and hormonal responses during exercise at 20°, 0° and −20°C

This study was designed to clarify the effects of cold air exposure on metabolic and hormonal responses during progressive incremental exercise. Eight healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions in a climatic chamber in which the temperature was 20°, 0° or –20°C with relative humidity at 60%±1%. Exercise tests were conducted on an electrically braked ergocycle, and consisted of a propressive incremental maximal exercise. Respiratory parameters were continuously monitored by an automated open-circuit sampling system Exercise blood lactate (LA), free fatty acids (FFA), glucose levels, bicarbonate concentration (HCO ₃ ^– ), acidbase balance, plasma epinephrine (E) and norepinephrine (NE) were determined from venous blood samples obtained through an indwelling brachial catheter. Maximal oxygen uptake was significantly different between conditions: 72.0±5.4 ml kg^–1 min^–1 at 20°C; 68.9±5.1 ml kg^–1 min^–1 at 0°C and 68.5±4.6 ml kg^–1 min^–1 at –20°C. Workload, time to exhaustion, glucose levels and rectal Catecholamines and lactate values were not significantly altered by thermal conditions after maximal exercise but the catecholamines were decreased during rest. Bicarbonate, respiratory quotient, lactate and ventilatory thresholds increased significantly at –20°C. The data support the contention that metabolic and hormonal responses following progressive incremental exercise are altered by cold exposure and they indicate a marked decrease in maximal oxygen uptake, time to exhaustion and workload.This study was supported by grants from CSR, Univesité du Québec; FIR, Université du Québec à Trois-Rivières and NATO no, 86.0435.     

GLP-1(32–36)amide,a novel pentapeptide cleavage product of GLP-1, modulates whole body glucose metabolism in dogs

We have previously demonstrated in human subjects who under euglycemic clamp conditions GLP-1(9–36)amide infusions inhibit endogenous glucose production without substantial insulinotropic effects. An earlier report indicates that GLP-1(9–36)amide is cleaved to a nonapeptide, GLP-1(28–36)amide and a pentapeptide GLP-1(32–36)amide (LVKGR amide). Here we study the effects of the pentapeptide on whole body glucose disposal during hyperglycemic clamp studies. Five dogs underwent indwelling catheterizations. Following recovery, the dogs underwent a 180 min hyperglycemic clamp (basal glucose +98 mg/dl) in a cross-over design. Saline or pentapeptide (30 pmol kg⁻¹ min⁻¹) was infused during the last 120 min after commencement of the hyperglycemic clamp in a primed continuous manner. During the last 30 min of the pentapeptide infusion, glucose utilization (M) significantly increased to 21.4 ± 2.9 mg kg⁻¹ min⁻¹compared to M of 14.3 ± 1.1 mg kg⁻¹ min⁻¹ during the saline infusion (P = 0.026, paired t-test; P = 0.062, Mann–Whitney U test). During this interval, no significant differences in insulin (26.6 ± 3.2 vs. 23.7 ± 2.5 μU/ml, P = NS) or glucagon secretion (34.0 ± 2.1 vs. 31.7 ± 1.8 pg/ml, P = NS) were observed. These findings demonstrate that under hyperglycemic clamp studies the pentapeptide modulates glucose metabolism by a stimulation of whole-body glucose disposal. Further, the findings suggest that the metabolic benefits previously observed during GLP-1(9–36)amide infusions in humans might be due, at least in part, to the metabolic effects of the pentapeptide that is cleaved from the pro-peptide, GLP-1(9–36)amide in the circulation.     

The effect of silage additives containing formaldehyde on the fermentation of ryegrass ensiled at different dry matter levels and on the nutritive value of direct-cut silage

Ryegrass, harvested at the pre-ear emergence stage of growth, was ensiled in laboratory silos, either fresh (175 g dry matter kg^?1) or wilted to five DM levels ranging from 216–432 g DM kg^?1, with and without additive treatment. The additives used were “Sylade” containing sulphuric acid (15%) and formaldehyde (23%) applied at 4.6 l t^?1 and an “ADD-F” $\text{(85\%}\text{formic acid}\text{)}\text{formalin}$ mixture (7:3 by volume) applied at a similar rate (4.8 l t^?1). An additional treatment included application of the mixture at a constant rate related to the DM content of the ensiled crop (25 l t^?1 DM).In the untreated silages, the water-soluble carbohydrates (WSC) varied, respectively (over the DM range 175–432), from 0–32 g kg^?1 DM compared with 197-6 g kg^?1 DM for the “Sylade” treated silages and 256-50 g kg^?1 DM for the formic acid/formalin silages treated at an additive rate of 4.8 l t^?1. Corresponding ranges of protein N for the control and treatments (expressed as g kg^?1 total N) were 302–447, 624-502 and 620-505, respectively. When the formic acid/formalin additive was applied at a constant level related to the DM content of the crop, although the WSC content decreased with increasing DM (247-158 g kg^?1 DM), the protein N content (612 g kg^?1 total N) remained constant.Grass from the same field was ensiled fresh, treated with “ADD-F” at the rate of 3.4 l t^?1 fresh grass, $\text{“}\text{ADD-F}\text{”}\text{formalin}$ at the rate of 4.8 l t^?1 fresh grass and “Sylade” at the rate of 4.6 l t^?1 fresh grass. The silages were given to Suffolk-cross wether lambs in digestibility and intake trials. Digestibility coefficients of DM and energy of the silage treated with “Sylade” were significantly lower (P < 0.05) than those of the other three silages. The DM intakes of all the silages were high, ranging from 27.7 g kg^?1 live weight for the “Sylade” silage to 30.7 g kg^?1 live weight for the silage treated with $\text{“}\text{ADD-F}\text{”}\text{formalin}$. Live weight gains ranged from 200 g/day for the control silage to 267 g/day for the $\text{“}\text{ADD-F}\text{”}\text{formalin}$ silage.     

In vivo pharmacokinetics and in vitro production of cocaethylene in pregnant guinea pigs

Simultaneous exposure to cocaine and ethanol results in the formation of cocaethylene, an active metabolite of cocaine. The concurrent abuse of both cocaine and ethanol is common during human pregnancy, but the kinetics of elimination and formation of this ethyl ester of cocaine have not been studied during pregnancy in any species. In the late gestation guinea pig (61 to 63 days), cocaethylene, at doses of 2 to 4 mg · kg⁻¹, is rapidly eliminated with a half-life of 29 min and a total body clearance of 77 ml · min⁻¹ · kg⁻¹. It is formed enzymatically by hepatic microsomal preparations from fetal, neonatal and maternal guinea pigs. The maximum rate of cocaethylene production (apparent V_max) when either ethanol or cocaine are varied while the other substrate is held constant, increases with age, from the late fetal period (65 days gestation, term 70 days) to adulthood. However, the Michaelis-Menten constant (apparent K_M) does not change with age. The rapid elimination of cocaethylene, coupled with the slow rate of formation (apparent V_max of 140 pmol · min⁻¹ · mg microsomal protein⁻¹) and the small amount of plasma analyzed most likely explains the inability to detect cocaethylene in vivo after concomitant cocaine and ethanol administration.     

Regulation of adenylate cyclase in cultured cardiocytes from neonatal rats by adenosine and other agonists

The presence of adenosine receptors coupled to adenylate cyclase in cultured cardiocytes from atria and ventricles from neonatal rats is demonstrated in these studies. N-Ethylcarboxamideadenosine (NECA), l-N⁶-phenylisopropyladenosine (PIA), and 2-chloroadenosine (2-cl-Ado) stimulated adenylate cyclase in a concentration-dependent manner in both cultured atrial and ventricular cells. The order of potency of stimulation was NECA > PIA > 2-cl-Ado. The stimulation of adenylate cyclase by NECA was enhanced by guanine nucleotides and was blocked by 3-isobutyl-1-methylxanthine in both these cells. Other agonists such as epinephrine, norepinephrine, dopamine, F^?, and forskolin were also able to stimulate adenylate cyclase, although the extent of stimulation by these agents was higher in ventricular than in atrial cells. The stimulation of adenylate cyclase by epinephrine and norepinephrine was inhibited by propranolol but not by phentolamine. On the other hand, phentolamine, propranolol, and haloperidol inhibited dopamine-stimulated adenylate cyclase activity to the same extent. Forskolin, at its maximal concentration, potentiated the stimulatory effect of epinephrine, norepinephrine, and dopamine on adenylate cyclase in both atrial and ventricular cardiocytes, but the interaction of NECA with epinephrine, norepinephrine, or dopamine was different in atrial and ventricular cells. The stimulation by an optimal concentration of NECA was additive with maximal stimulation by the catecholamines in atrial cells but not in ventricular cells. The data suggest the existence of adenosine “Ra” and catecholamine receptors in cultured atrial and ventricular cardiocytes. It can be postulated that adenosine in addition to its role as a potent vasodilator might regulate cardiac performance through its interaction with “Ra” receptors associated with adenylate cyclase. The difference in the mode of interaction of adenosine with catecholamines in atrial and ventricular cells suggests that the mechanism by which these agents activate adenylate cyclase may be different in these cells.     

The ventilation mechanism of the Pacific hagfish Eptatretus stoutii

We made anatomical and physiological observations of the breathing mechanisms in Pacific hagfish Eptatretus stoutii, with measurements of nostril flow and pressure, mouth and pharyngo-cutaneous duct (PCD) pressure and velum and heart impedance and observations of dye flow patterns. Resting animals frequently exhibit spontaneous apnea. During normal breathing, water flow is continuous at a high rate (~125 ml kg⁻¹ min⁻¹ at 12°C) powered by a two-phase unidirectional pumping system with a fast suction pump (the velum, ~22 min⁻¹) for inhalation through the single nostril and a much slower force pump (gill pouches and PCD ~4.4 min⁻¹) for exhalation. The mouth joins the pharynx posterior to the velum and plays no role in ventilation at rest or during swimming. Increases in flow up to >400 ml kg⁻¹ min⁻¹ can be achieved by increases in both velum frequency and stroke volume and the ventilatory index (product of frequency x nostril pressure amplitude) provides a useful proxy for ventilatory flow rate. Two types of coughing (flow reversals) are described. During spontaneous swimming, ventilatory pressure and flow pulsatility becomes synchronised with rhythmic body undulations.     

Characterization of receptors for α2-macroglobulin-trypsin complex in rat hepatocytes

High-affinity receptors for α₂-macroglobulin-trypsin complex were demonstrated in rat hepatocytes at 4°C. The dissociation rate constant for the labelled complex was very small at low receptor occupancies, approx. 4·10⁻⁴ min⁻¹. Dissociation was biphasic at high receptor occupancies with a rate constant for the rapid phase of about 2·10⁻² min⁻¹. At near-equilibrium, half of the receptors were saturated at a complex concentration of 150 pM, and the Scatchard plot was concave upwards. Thus, the binding shows complex kinetics with the probable involvement of negative cooperativity. Binding of the labelled complex was not influenced by galactose, mannose, mannose phosphate or fucoidin, whereas it was abolished in the absence of extracellular Ca²⁺ and inhibited by bacitracin. Approx. 70% of the labelled complex bound at 4°C was rapidly internalized (k_int about 3·10⁻¹ min⁻¹) after being warmed to 37°C. Radioactivity released from the cells at 37°C comprised intact labelled complex and iodide. The complex was initially released at a rapid rate (k₋₁ about 1·10⁻¹ min⁻¹) from about 25% of the cell-bound pool. This probably represents dissociation from the receptors. A slow phase of release followed, so that half of the bound pool was finally released as intact complex. Iodide release followed a sigmoidal curve after a 20 min lag period. Thus, specific high-affinity receptors mediate the internalization and eventual degradation of α₂-macroglobulin-proteinase complex into hepatocytes.     

Cardiovascular and metabolic responses to noradrenaline in men acclimatized to cold baths

The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 g·kg^–1·min^–1 (2–23 g·min^–1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15°Q baths of 30–60 min followed by rapid rewarming in hot (38–42°C) water, and was confirmed by tests of the subjects responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 g·kg^–1·min^–1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P<0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays.     

Norepinephrine in Goal-Directed Fluid Therapy During General Anesthesia in Elderly Patients Undergoing Spinal Operation: Determining Effective Infusion Rate to Enhance Postoperative Functions

Background and ObjectiveIntraoperative hypotension is a common complication in general anesthesia that could result in different serious complications particularly in elderly patients. This Randomized Clinical Trial (RCT) aims to determine effective continuous infusion rate of norepinephrine to prevent intraoperative hypotension during spinal surgery under general anesthesia in elderly patients.MethodsThis RCT was conducted on elderly patients (n= 108) undergoing general anesthesia for posterior lumbar spinal fusion. The patients were randomly divided into 0.030, 0.060, and 0.090 μg.kg-1.min-1 groups of norepinephrine infusion rates. The outcomes were assessed at entrance to operation room (T0), 15 mins after anesthesia induction (T1), 60 mins following surgery (T2), and immediately after surgery (T3). The intraoperative and postoperative complications and rehabilitation outcomes were comparatively assessed.ResultsAll three groups significantly reduced the incidence of delayed wound healing (0.030 vs. 0.060 vs. 0.090 μg.kg^-1.min^-1; 33.3% vs. 10% vs. 10%, P=0.024) and wound infection (26.7% vs. 6.7% vs. 6.7%, P=0.031). Intraoperative total fluid volume and colloids volume in the 0.030 group were significantly higher than 0.060 and 0.090 groups (P=0.005, P=0.003, and P=0.01, respectively). The 0.060 and 0.090 groups significantly increased mean-arterial-pressure than the 0.030 group at T2 and T3. Both 0.060 and 0.090 infusion rates significantly reduced intraoperative hypotension than 0.030 dosage (P=0.01 and P=0.003, respectively). The bradycardia incidence in the 0.090 group was significantly higher than the 0.030 (P=0.026) and 0.060 groups (P=0.038). The 0.060 group decreased the first intake by 1.4 hours (P=0.008) and first flatus by 1.1 hours (P=0.004) and postoperative hospital stay by 1 day (P=0.066).ConclusionThe 0.060 µg·kg^-1·min^-1 norepinephrine infusion combined with goal-directed fluid therapy exhibited adequate intraoperative management and postoperative outcomes.Clinical Trial Registration www.chictr.org.cn, identifier ChiCTR-1900021309.     

Determination of the retinobenzoic acid derivative Am580 in rat plasma by high-performance liquid chromatography

A specific liquid chromatographic method for the determination of 4-[[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)carbonyl]amino]benzoic acid (Am580) in rat plasma is described. The procedure includes one-step isolation of the compound and the internal standard (naphtol AS) from protein precipitated with acetonitrile, resolution on a reversed-phase column (Supelcosil LC18-DB, 5 μm) with water-acetonitrile-methanol-n-butanol (45:40:14:1, v/v) containing 65 mM ammonium acetate as elution system and UV absorbance detection at 280 nm. The assay was linear over a wide range (25–5000 ng ml⁻¹) and the limit of quantitation was 25 ng ml⁻¹ using 0.2 ml of plasma. It was precise and reproducible enough for pharmacokinetic studies. Application to a preliminary disposition study in the rat indicated that Am580 was characterized by a relatively large apparent volume of distribution (1.1–1.5 l kg⁻¹) and small clearance (8.8–9.7 ml min⁻¹ kg⁻¹). Its pharmacokinetic behaviour was linear within the dose range considered (2 and 10 mg kg⁻¹, i.p.).