Characterization of dopamine receptors involved in central thermoregulation in rabbits.

Intracerebroventricularly administered dopamine produced dose dependent hyperthermia in rabbits. Haloperidol, a D1 receptor blocker produced consistent hypothermia, whereas D2 receptor blocker metoclopramide produced hyperthermia, pretreatment with haloperidol competitively blocked the hyperthermic response of dopamine. Pretreatment with metoclopramide augmented the onset and peak response of dopamine. It is suggested that D1 receptors are involved in producing hyperthermia and D2 receptors in hypothermia.     

Characterization of enzymes involved in the central metabolism of Gluconobacter oxydans

Gluconobacter oxydans is an industrially important bacterium that lacks a complete Embden–Meyerhof pathway (glycolysis). The organism instead uses the pentose phosphate pathway to oxidize sugars and their phosphorylated intermediates. However, the lack of glycolysis limits the amount of NADH as electron donor for electron transport phosphorylation. It has been suggested that the pentose phosphate pathway contributes to NADH production. Six enzymes predicted to play central roles in intracellular glucose and gluconate flux were heterologously overproduced in Escherichia coli and characterized to investigate the intracellular flow of glucose and gluconates into the pentose phosphate pathway and to explore the contribution of the pentose phosphate pathway to NADH generation. The key pentose phosphate enzymes glucose 6-phosphate dehydrogenase (Gox0145) and 6-phosphogluconate dehydrogenase (Gox1705) had dual cofactor specificities but were physiologically NADP- and NAD-dependent, respectively. Putative glucose dehydrogenase (Gox2015) was NADP-dependent and exhibited a preference for mannose over glucose, whereas a 2-ketogluconate reductase (Gox0417) displayed dual cofactor specificity for NAD(P)H. Furthermore, a putative gluconokinase and a putative glucokinase were identified. The gluconokinase displayed high activities with gluconate and is thought to shuttle intracellular gluconate into the pentose phosphate pathway. A model for the trafficking of glucose and gluconates into the pentose phosphate pathway and its role in NADH generation is presented. The role of NADPH in chemiosmotic energy conservation is also discussed.     

Characterization of postjunctional alpha-adrenoceptors in the isolated aorta of the snake Bothrops jararaca

1. To characterize the alpha-adrenoceptors present in Bothrops jararaca aorta, selective alpha-adrenoceptor agonists and antagonists were used.2. The relative order of potency of the tested agonists was noradrenaline > phenylephrine > clonicline.3. Prazosin was more potent than phentolamine and yohimbine in antagonizing noradrenaline response, since the PA₂ values were 9.91, 7.59 and 7.33, respectively.4. Yohimbine was also able to block the contraction produced by phenylephrine, an alpha-1 agonist.5. These results suggest the existence of an alpha-1 subtype of adrenoceptor in this preparation which, however, presents some different characteristics from those described for mammals.     

Amino acids as central synaptic transmitters or modulators in mammalian thermoregulation

Of the amino acids that affect the activity of central neurons, aspartate and glutamate (which exert generally excitatory influences) and glycine, taurine, and gamma-aminobutyric acid (GABA) (which generally exert inhibitory influences) are the strongest neurotransmitter candidates. As with other putative transmitter substances, their effects on body temperature when injected into the cerebral ventricles or the preoptic hypothalamus tend to vary within and between species. These effects are uninterpretable without accompanying information regarding effector activity changes and the influences of dose and ambient temperature. Observations necessary for analysis of apparent action have been made in studies of the effects of intracerebroventricular injections of these amino acids into sheep. Aspartate and glutamate have similar excitatory effects on the neural pathways that activate both heat production and heat loss effectors. Glycine appears to be without effect.     

The central effect of noradrenaline on thermoregulation in the neonatal guinea pig.

Noradrenaline (10 microgram) injected into the lateral cerebral ventricle of guinea pigs aged 2 to 12 days produced a rapid increase in oxygen consumption and in colonic temperature at an ambient temperature of 30 degrees C. The increase was most pronounced in the youngest animals and decreased with advancing age, but was still significant at 12 days of age. Species differences and the role of ambient temperature in the responses are discussed.     

The role of the cholinergic system in the central control of thermoregulation in rats

Systemic and central administration of methacholine (a synthetic choline derivative) both produced dose-dependent decreases in rectal temperature in rats at all the ambient temperatures studied. Both at room temperature (22 degrees C) and in the cold (8 degrees C), the hypothermia in response to methacholine application was brought about by both a decrease in metabolic heat production and an increase in cutaneous circulation. In the heat (29 degrees C), the hypothermia was due solely to an increase in respiratory evaporative heat loss. Furthermore, the methacholine-induced hypothermia was antagonized by central pretreatment of atropine (a selective blocker of cholinergic receptors), but not by the central administration of either 6-hydroxydopamine (a relative depletor of catecholaminergic nerve fibers) or 5,6-dihydroxytryptamine (predominately a serotonin depletor). The data indicate that activation of the cholinergic receptors within brain with methacholine decreases heat production and (or) increases heat loss which leads to hypothermia in rats.     

Function of myocardial alpha-adrenoceptors

In addition to beta-adrenoceptors (beta ARs), cardiac myocytes of animals and man possess alpha 1ARs, but not alpha 2ARs. Norepinephrine and epinephrine have a higher affinity for myocardial alpha 1ARs than for beta ARs. Unlike beta AR stimulation, myocardial alpha 1AR stimulation does not increase the slow inward current. The alpha 1AR-mediated positive inotropic effect seen in isolated heart preparations appears to involve increased Ca sensitivity of myofibrils and production of inositol triphosphate (IP3) and diacylglycerol (DAG), but the functions of IP3 and DAG are not clear. Myocardial alpha 1AR stimulation reduces rate of isolated atria and Purkinje fibers and lengthens refractory period and action potential duration. Hypoxia increases alpha 1AR density in cardiomyocytes. alpha 1AR-mediated arrhythmias occur in isolated Purkinje fibers during hypoxia, following infarction, and in the presence of Ba2+ or high Ca2+. In animals, coronary artery occlusion and/or reperfusion increase myocardial alpha 1AR density and responsiveness, and alpha AR blocking drugs attenuate arrhythmias. However, an antiarrhythmic effect of alpha AR blocking drugs mediated by action on coronary vascular alpha ARs cannot be excluded. Presently available drugs do not differentiate between myocardial and vascular alpha ARs and thus affect the coronary and systemic circulations and, indirectly, the heart. Additional myocardial alpha 1AR-mediated effects include production of cardiac hypertrophy, stimulation of glucose uptake and phosphofructokinase and cyclic AMP phosphodiesterase activity, and release of atrial natriuretic peptide.     

Function of myocardial alpha-adrenoceptors

Myocardial α-adrenoceptors are similar to vascular α-adrenoceptors; therefore the drugs which are used to study myocardial α-adrenoceptors can affect the heart indirectly by acting on vascular α-adrenoceptors. High concentrations of α-adrenoceptor stimulant and α-adrenoceptor blocking drugs can exert cardiac effects that do not result from action on α-adrenoceptors; therefore relatively low concentrations of these drugs must be used to obtain specific effects.An α-adrenoceptor mediated positive inotropic effect has been observed in relatively slow beating isolated heart preparations; it is not associated with shortening of the duration of systole or an increase in myocardial cyclic AMP concentration and is probably accompanied by an increase in Ca²⁺ influx. Usually α-adrenoceptor stimulation has no effect on heart rate.Myocardial α-adrenoceptor mediated ventricular arrhythmias have been caused in animals by high concentrations of catecholamines, and a transient increase in α-adrenoceptor concentration has been found in ischemic myocardium. We do not know how myocardial α-adrenoceptor stimulation causes arrhythmias. In isolated heart preparations low concentrations of epinephrine and norepinephrine prolong refractory period and action potential duration by α-adrenoceptor stimulation, and higher concentrations of the catecholamines shorten refractory period and action potential duration by α-adrenoceptor stimulation. In isolated specialized conducting fibers low concentrations of catecholamines reduce automaticity by α-adrenoceptor stimulation and higher concentrations increase automaticity by β-adrenoceptor stimulation. In partially depolorized ventricle preparations α-adrenoceptor stimulation has been reported both to depress and to restore electrical and mechanical activity. Clearly, much remains to be done before we understand α-adrenoceptor mediated cardiac effects.     

Characterization of sediment bacteria involved in selenium reduction

Bacterial reduction of selenium (Se) oxyanions (Se[VI] and Se[IV]) to elemental Se (Se[0]) is one of the major biogeochemical processes removing Se from agricultural drainage water and depositing Se in the sediment. This study was conducted to characterize Se-reducing bacterial populations in Lost Hills evaporation pond sediment and to observe their response to Se(VI) and organic C amendments. Se(VI) was removed from the dissolved phase in the sediment slurries amended with organic C with a decrease in redox potential (Eh). Se(VI) concentrations decreased from 2137 to 79 microg L-1 after 9 days of incubation in a 5% soil slurry. Upon our screening process, 9 Se(VI)- and 14 Se(IV)-reducing bacteria were isolated from sediment slurries and identified by amplification and sequencing of 16S rDNA. Bacillus strains appeared to be dominant in the bacterial assemblages active in Se(VI) and Se(IV) reduction in the sediment. Halomonas pacifica and Staphylococcus warneri were also identified as Se(IV)-reducers. Indigenous bacteria have a significant role in the biogeochemical cycling of Se and may be stimulated by addition of a suitable organic source for Se reduction. The bacterial strains isolated from salt-affected and Se-contaminated Lost Hills evaporation pond sediment may have potential application in removing Se from high salt drainage water.     

Heterogeneity of vascular alpha-adrenoceptors in man

The knowledge on alpha-adrenoceptors has expanded enormously in the last decade, mostly as a result of in vitro and in vivo animal experiments. In the face of considerable species differences we have tested several of the newly developed concepts on alpha-adrenoceptors in the circulation of the human forearm. In this model we were able to show the presence of postsynaptic alpha 1- and alpha 2-adrenoceptors, both contributing to resting vascular tone. Although adrenaline and noradrenaline were shown to have affinity for each alpha-adrenoceptor subtype, noradrenaline seems to be the natural agonist for both receptors. Evidence is presented for an intrasynaptic location of the alpha 1-adrenoceptor and an extrasynaptic location of the alpha 2-adrenoceptor and also for a functional presynaptic alpha 2-adrenoceptor in the human forearm circulation. Selective hyperresponsiveness to alpha 1- or alpha 2-adrenoceptor stimulation in hypertensive patients could not be established. Calcium entry blockers were shown to attenuate the vasoconstriction induced by selective alpha 2-adrenoceptor stimulation but not by selective alpha 1-adrenoceptor stimulation. These data support the physiological and pharmacological relevance of the new concepts on alpha-adrenoceptors for the situation in man.