Low doses of lead

The effects of exposure to high doses of lead on reproduction and development have been established, but not so those caused by low lead doses or the influence that life stage at which contact with the metal takes place might have. The aim of this work was to study the effects of 200 and 400 ppm lead acetate in drinking water on reproduction and development as well as on renal and hepatic parameters of rats at different life stages, from gestation to 3 mo postweaning. The results indicate a dose-dependent effect on reproduction, with variations in the number of births and in pups' weight. Development was mostly affected at the weaning stage, with hemoglobin levels and erythrocyte numbers significantly decreased. The lead levels in tissues, blood, urine, and feces along with selected renal and hepatic parameters (blood urea nitrogen, creatinine, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase) were determined. There were histological, blood urea nitrogen, alanine aminotransferase, and alkaline phosphatase changes in the first month postweaning. After 3 mo, these changes are no longer evident, possibly because of metabolic adaptation.     

The Effects of Peritoneal Dialysis on the Physiological Disposition of Oxacillin,Ampicillin and Tetracycline in Patients with Renal Disease

Seven patients with acute or chronic renal failure who were receiving intermittent peritoneal dialysis and who required parenteral oxacillin, ampicillin or tetracycline were studied to determine the disposition of these antibiotics in severe renal disease and the effects of peritoneal dialysis. While severe renal impairment markedly prolongs persistence in the serum of ampicillin and tetracycline, there is little effect on oxacillin. Whereas required doses of ampicillin and tetracycline are lower in the presence of severe renal disease, oxacillin should be given in doses equivalent to those used for patients with normal renal function. Peritoneal dialysis does not alter these dosage requirements.Four patients receiving ampicillin or tetracycline in the infusing solution during peritoneal dialysis were studied to determine the amount of systemic absorption. Local prophylaxis alone is not achieved with this method of administration, since small amounts of both antibiotics are absorbed systemically from the infusing solution. The serum concentration of tetracycline attained is inadequate for treatment of systemic infections but is probably significant, with repeated use in intermittent dialysis, in causing adverse effects. Tetracycline should be abandoned in the local prophylaxis of peritonitis during peritoneal dialysis.     

Histochemical and cytochemical studies of alkaline phosphatase activity in the synapses of rat brain

Summary Although a number of studies have been carried out on alkaline phosphatase (Al-P), this enzyme has not definitely been detected in synapses at the electron-microscopic level. Recently, we have successfully demonstrated, by perfusing specimens with 1% glutaraldehyde for fixation for as short a time as 8–10 min, that Al-P activity is localized on the presynaptic and postsynaptic membranes of the rat central nervous system (CNS). There were four types of presynaptic membrane: (1) those with the activity only on the membrane, (2) those with the activity only on the synaptic vesicle membrane, (3) those with the activity on both the presynaptic membrane and the synaptic vesicle membrane, and (4) those entirely free of the activity. The postsynaptic membranes were classified into two varieties: (1) those with the activity in the postsynaptic membrane and the postsynaptic thickening, and (2) those entirely without the activity. Thus, the occurrence of the enzyme activity assumed various combinations of presynaptic and postsynaptic involvement. The incidence of synapses either with presynaptic or postsynaptic activity varied distinctly from site to site.     

Histochemical and cytochemical studies of alkaline phosphatase activity in the synapses of rat brain.

Although a number of studies have been carried out on alkaline phosphatase (A1-P), this enzyme has not definitely been detected in synapses at the electron-microscopic level. Recently, we have successfully demonstrated, by perfusing specimens with 1% glutaraldehyde for fixation for as short a time as 8-10 min, that A1-P activity is localized on the presynaptic and postsynaptic membranes of the rat central nervous system (CNS). There were four types of presynaptic membrane: (1) those with the activity only on the membrane, (2) those with the activity only on the synaptic vesicle membrane, (3) those with the activity on both the presynaptic membrane and the synaptic vesicle membrane, and (4) those entirely free of the activity. The postsynaptic membranes were classified into two varieties: (1) those with the activity in the postsynaptic membrane and the postsynaptic thickening, and (2) those entirely without the activity. Thus, the occurrence of the enzyme activity assumed various combinations of presynaptic and postsynaptic involvement. The incidence of synapses either with presynaptic or postsynaptic activity varied distinctly from site to site.     

Effects of the potential neuroleptic peptide des-tyrosine1-γ-endorphin and haloperidol on apomorphine-induced behavioural syndromes in rats and mice

The effects of haloperidol and Des-Tyr¹-γ-endorphin (DTγE) were studied on climbing induced in mice by high doses of apomorphine and on the yawning syndrome induced in rats by low doses of apomorphine. Haloperidol in a dose of 0.0046 mg/kg s.c. potentiated climbing whereas at higher doses climbing was inhibited (ED₅₀=0.03 mg/kg). DTγE had no effect on climbing under normal conditions in doses up to 2 mg/kg s.c.. After three days of handling and saline pre-injections DTγE potentiated climbing in doses from 0.1 to 1 mg/kg.Haloperidol inhibited yawning induced by low doses of apomorphine (ED₅₀=0.01 mg/kg). DTγE, on the other hand, potentiated yawning induced by low apomorphine at doses of 0.02 and 0.04 mg/kg s.c.. From the point of view that low doses of apomorphine predominantly activate presynaptic dopamine autoreceptors while higher doses predominantly activate postsynaptic dopamine receptors the following tentative conclusions are drawn. 1) Haloperidol blocks presynaptic dopamine autoreceptors at low doses and postsynaptic dopamine receptors at higher doses. 2) DTγE sensitizes presynaptic dopamine autoreceptors at low doses, thereby strengthening the local feedback mechanism at the dopaminergic nerve ending, and sensitizes postsynaptic dopamine receptors at higher doses.     

Changes in presynaptic calcium signalling accompany age‐related deficits in hippocampal LTP and cognitive impairment

The loss of cognitive function accompanying healthy aging is not associated with extensive or characteristic patterns of cell death, suggesting it is caused by more subtle changes in synaptic properties. In the hippocampal CA1 region, long‐term potentiation requires stronger stimulation for induction in aged rats and mice and long‐term depression becomes more prevalent. An age‐dependent impairment of postsynaptic calcium homeostasis may underpin these effects. We have examined changes in presynaptic calcium signalling in aged mice using a transgenic mouse line (SyG37) that expresses a genetically encoded calcium sensor in presynaptic terminals. SyG37 mice showed an age‐dependent decline in cognitive abilities in behavioural tasks that require hippocampal processing including the Barnes maze, T‐maze and object location but not recognition tests. The incidence of LTP was significantly impaired in animals over 18 months of age. These effects of aging were accompanied by a persistent increase in resting presynaptic calcium, an increase in the presynaptic calcium signal following Schaffer collateral fibre stimulation, an increase in postsynaptic fEPSP slope and a reduction in paired‐pulse facilitation. These effects were not caused by synapse proliferation and were of presynaptic origin since they were evident in single presynaptic boutons. Aged synapses behaved like younger ones when the extracellular calcium concentration was reduced. Raising extracellular calcium had little effect on aged synapses but altered the properties of young synapses into those of their aged counterparts. These effects can be readily explained by an age‐dependent change in the properties or numbers of presynaptic calcium channels.     

Comparative characterization of reactions of skeletal muscle arterial and venous vessels to combined adrenergic effects

In experiments with the constant blood flow perfusion of the cat calf muscle and combined actions of adrenalin and noradrenaline were tested as to the blood flow resistance changes of the arterial and venous blood vessels. Separately applied the catecholamines evoked vascular resistance changes practically similar in value; combined effects of catecholamines realized in greater increase of arterial than venous resistance. In contrast to arterial vessels supramaximal stimuli resulted in much lesser constrictive effect as compared with reaction of intramural veins to separately applied catecholamines. Greater doses of catecholamines being combined, stability of effector system of skeletal muscle veins is decreased as compared to arteries.     

Glucocorticoids and catecholamines as mediators of acute-phase proteins, especially rat alpha-macrofoetoprotein.

Adrenal hormones were studied as possible triggering substances of the synthesis of acute-phase reactants in rats. alpha-Macrofoetoprotein, which rises sharply in concentration during inflammation, was used to monitor the acute-phase reaction. In normal rats glucocorticoids and catecholamines induce alpha-macrofoetoprotein synthesis; glucocorticoids only increase alpha-macrofoetoprotein to moderate levels in plasma, but catecholamines enhance alpha-macrofoetoprotein synthesis to very high levels, comparable with those observed in the post-injury phase. However, catecholamines in vivo also activate the adrenal cortex, suggesting a synergistic effect of both kinds of adrenal hormones. Our study showed that in adrenalectomized rats, the effect of catecholamines on alpha-macrofoetoprotein synthesis is greatly diminished, whereas the moderate effect of glucocorticoids remains. Combination of glucocorticoids and catecholamines induces extremely high alpha-macrofoetoprotein levels in both adrenalectomized and normal rats. With crossed immunoelectrophoresis it was shown that other acute-phase reactants, such as haptoglobin and alpha 1-major acute-phase protein, are affected differently by the hormones. Contrary to glucocorticoids, catecholamines give a pattern comparable with that found after surgical injury.     

Ultrastructural localization of nitric oxide synthase immunoreactivity in the cat ventrobasal complex

This study describes the ultrastructural localization of nitric oxide synthase (NOS) immunoreactivity in the cat ventrobasal complex. NOS immunoreactivity was found in the cell bodies and dendrites of local circuit neurons and in vesicle-containing profiles. The vesicle-containing profiles could be divided into two classes, those of dendritic origin (presynaptic dendrite boutons) and those of axonal origin. The NOS labelled axon terminals varied in size and packing density and were principally located in the extra-glomerular neuropil. These boutons presented a range of morphologies and it was not possible to determine the probable source based on morphological criteria. The NOS immunoreactive presynaptic dendrite boutons were found both within and outside glomeruli and established both pre- and post-synaptic relationships with other elements. Post-embedding GABA immunocytochemistry showed that some NOS immunoreactive axonal boutons and presynaptic dendrites were also immunopositive for GABA. This finding suggests that some of the NOS labelled axonal boutons are of local circuit neuron origin. These results suggest that local circuit neurons in the cat ventrobasal complex might be involved in specific, short range interactions using GABA and longer, more global interactions using nitric oxide.     

O-Methylated and sulfoconjugated catecholamines: differential activities at human platelet alpha 2-adrenoceptors.

The physiological effects of the sulfoconjugates of epinephrine, norepinephrine, and the 3-O-methylated catecholamines, metanephrine, normetanephrine, and methoxytyramine were examined with regard to their alpha 2-adrenoceptor binding properties and aggregation activity in human platelets. Sulfoconjugation of catecholamines resulted in the loss of both their competitive potency for [3H]yohimbine binding and their influence on platelet aggregation. O-Methyl substituted catecholamines showed attenuation of their alpha 2-adrenoceptor binding affinities when compared with those of the corresponding non-esterified amines. Unlike the free amine epinephrine, which stimulated platelet aggregation, the O-methylated catecholamine derivatives inhibited aggregation. Inhibition was dose-dependent and restricted to the alpha 2-adrenoceptor mediated aggregation response stimulated by epinephrine (1 microM) or potentiated by subthreshold concentrations of epinephrine (30-300 nM) in the presence of subaggregatory doses of vasopressin (10-30 nM). Collagen- and ADP-induced platelet aggregation was not affected. The hydrophilic beta-antagonist CGP 12177 displayed no effects. However, high concentrations (0.1 mM) of both isomers of the strongly lipophilic beta-adrenoceptor antagonist propranolol inhibited the actions of all aggregators by stabilizing the membrane. Such a nonspecific membrane interaction of the methylated catecholamines could be excluded because of their low lipid solubility calculated in a n-octanol-phosphate buffer system at pH 7.4. We suggest therefore that methylated catecholamines are biological alpha 2-adrenoceptor antagonists acting on alpha 2-adrenoceptor stimulated reactions of human platelets. Whether this receptor antagonism is relevant to other human tissues needs clarification. Sulfated catecholamines, however, are wholly ineffective at this receptor site and may constitute a pathway to control the concentration of the active free catecholamines.     

Biochemical and Pharmacological Characteristics of Conjugated Catecholamines in the Rat Brain

Mass-fragmentographic methods are described that enable the simultaneous measurement of total, free, and conjugated catecholamines in brain tissues. These methods were used to assess the distribution, kinetics, and pharmacological characteristics of total, free, and conjugated catecholamines in the hypothalamus, caudate nucleus, hippocampus, and septum. Conjugated norepi-nephrine (NE) represents ?20% of total NE in the hypothalamus, septum, and hippocampus, whereas the percentage is ? 50% in the caudate nucleus. The percentages of conjugated dopamine (DA) in these brain areas are consistently less than those of NE (?13%). Although in the hypothalamus the steady-state concentrations of total, free, and conjugated NE are over four times higher than those of the corresponding total, free, and conjugated DA, the turnover rates of this DA are comparable with those of the corresponding NE. Further, the ratios of conjugated NE or DA turnover rates to those of the total amines are higher than the corresponding ratios of their steady-state concentrations. Treatments with pargyline (75 mg/kg, i.p.; rats killed 30 and 60 min later) failed to change the contents of conjugated catecholamines in the hypothalamus and the caudate nucleus significantly. Pharmacological manipulation with a number of proto-typic drugs revealed that although the assay of conjugated catecholamines might shed additional light on the effects of drugs on central catecholamines, the assessment of total or free amines are on the whole equally informative. In conclusion, a detailed assessment of brain conjugated catecholamines is reported. The information provided, fills a gap in our knowledge that has up to now not been adequately addressed.     

The sphincter of the efferent filament artery in teleost gills: II. Sympathetic innervation

In addition to the cholinergic innervation described in the sphincter of the efferent filament arteries (Bailly and Dunel-Erb, ′86), an aminergic component has been demonstrated by specific techniques. The Falck fluorescence technique reveals a network of nerve fibers displaying a green fluorescence characteristic of catecholamines. At the ultrastructural level two types of fibers are present, one with clear vesicles and another with densecored vesicles. Axo-axonal synaptic relationships exist between the two types. Results of 5- and 6-OHDA (hydroxydopamine) treatments confirm the presence of an aminergic component. These observations support the notion of a dual innervation: cholinergic and adrenergic of, respectively, parasympathetic and sympathetic origin. The presence of presynaptic modulation is suggested. The aminergic component could inhibit or reduce the release of acetylcholine from cholinergic nerve endings. These results suggest that the sympathetic innervation modulates the vasoconstriction effect of the parasympathetic component.     

Phosphatases modulate transmission and serotonin facilitation at synapses: studies with the inhibitor okadaic acid.

We examined the role of phosphatases in synaptic transmission using the permeant phosphatase inhibitor okadaic acid (OA). In the crayfish neuromuscular junction (NMJ), postsynaptic effects including increases in input resistance occurred at doses greater than 5 microM OA. At lower doses (0.5-5 microM) the effects were solely presynaptic and transmitter release increased over three-fold despite small reductions in amplitude and duration of presynaptic action potentials. Potentiating effects of serotonin on transmitter release, which depend on phosphorylation, were increased by OA. Frequency facilitation was reduced but its decay was not affected. In frog NMJs, OA increased spontaneous and evoked release two-fold through presynaptic mechanisms. An inactive analog of OA, OA tetra-acetate, had no effect on transmitter release at frog and crayfish NMJ. Therefore, phosphatases have a strong modulating influence on synaptic transmission.     

Catecholamines-crafty weapons in the inflammatory arsenal of immune/inflammatory cells or opening pandora's box?

It is well established that catecholamines (CAs), which regulate immune and inflammatory responses, derive from the adrenal medulla and from presynaptic neurons. Recent studies reveal that T cells also can synthesize and release catecholamines which then can regulate T cell function. We have shown recently that macrophages and neutrophils, when stimulated, can generate and release catecholamines de novo which, then, in an autocrine/paracrine manner, regulate mediator release from these phagocytes via engagement of adrenergic receptors. Moreover, regulation of catecholamine-generating enzymes as well as degrading enzymes clearly alter the inflammatory response of phagocytes, such as the release of proinflammatory mediators. Accordingly, it appears that phagocytic cells and lymphocytes may represent a major, newly recognized source of catecholamines that regulate inflammatory responses.     

Catecholamines and the sleep-wake cycle I. EEG and behavioral arousal

The exact role of catecholamines (CA) on the sleep-wake cycle is still controversial. Critical analysis of lesion studies tends to suggest a neuromodulatory role for both dopamine (DA) and norepinephrine (NE) on EEG and behavioral arousal. Support for this view is provided by pharmacological studies in which catecholaminergic systems are activated or inhibited. Taken together they show that disturbances in the dynamic balance between neurochemical systems may alter the conditions for wake-triggering mechanisms to express at optimal levels. Large electrolytic or neurotoxic lesions which affect noradrenergic and dopaminergic structures are associated with marked and prolonged EEG changes and decreased behavioral arousal, respectively. In contrast, specific and circumscribed damage restricted to these systems is followed by a transient decrease in waking activity. Thus, results observed after large central lesions are most probably related to destruction of non-catecholaminergic neurons. Inhibition of brain CA synthesis causes behavioral sedation and a decrease in waking activity. Selective pharmacological stimulation of presynaptic alpha-adrenergic (∝ 2) receptors tends to decrease waking, while opposite effects result from ∝2-receptor blockade. Drugs with agonistic activity at postsynaptic alpha-adrenergic (∝1) sites increase EEG desynchronization, but specific blockade of ∝1-receptor does not result in marked decreases of waking EEG. In contrast, treatments which simultaneously block NE and DA receptors significantly affect waking. Beta-adrenergic receptor blockers show no conclusive effects on waking or sleep. Selective DA-receptor agonists induce biphasic effects, with low doses decreasing and large doses increasing cortical desynchronization and motility. Opposite effects are observed in laboratory animals after injection of specific DA-receptor blockers.     

Is the platelet phenolsulfotransferase involved in the sulfoconjugation of plasma catecholamines?

Catecholamines are predominantly present in the sulfoconjugated forms in human plasma. Phenolsulfotransferase (EC 2.8.2.1), which catalyses the sulfation of phenolic compounds, is widely distributed in human tissues. In blood, a phenolsulfotransferase, more specific for catecholamine sulfation is found exclusively in platelets. Free and sulfoconjugated catecholamines were measured in plasma and platelets of healthy volunteers and compared with those present in patients with uremia or pheochromocytoma to determine the ability of platelet phenolsulfotransferase to sulfurylate plasma catecholamines. In patients with pheochromocytoma, the rise in free and sulfoconjugated plasma catecholamines is accompanied by a simultaneous rise of these molecules in platelets. In uremia, where the level of plasma catecholamines is normal, the rise in the sulfoconjugates is not accompanied by a concomitant increase in either free or sulfoconjugated catecholamines in platelets. Platelet phenolsulfotransferase activity remains unchanged in pheochromocytoma and uremia. These data indicate that the platelet phenolsulfotransferase is involved in the sulfation of the catecholamines present in platelets, but its contribution, if any, to the high level of sulfoconjugated catecholamines found in plasma is negligible. This assertion is confirmed by our observations in thrombocytopenic patients. Indeed, despite the very low number of platelets and the absence of plasma phenolsulfotransferase activity, thrombocytopenic patients have normal plasma levels of free and sulfoconjugated catecholamines.     

Adrenergic-cholinergic interactions in left atria. II. Comparison of the antagonism of inotropic responses to alpha- and beta-adrenoceptor stimulation and BAY K 8644 by carbachol, D-600, and nifedipine

The muscarinic agonist carbachol has previously been shown to reverse positive inotropic responses of rabbit left atrial strips to equiactive doses of the beta-adrenoceptor agonist isoproterenol and to the alpha-adrenoceptor agonist phenylephrine. Responses to phenylephrine were measured in the presence of the beta-blocker timolol. However, carbachol was not able to reverse the increase in tension produced by elevating the extracellular Ca2+ concentration. To gain more information about the nature of the functional interaction of carbachol with alpha- and beta-receptor stimulants in left atria, the interaction of carbachol with these agonists, as well as with elevated Ca2+ and the Ca2+ activator compound BAY K 8644, was compared with that of the Ca2+ antagonists D-600 and nifedipine. The results demonstrate that the Ca2+ antagonists exhibit a selectivity similar to that of carbachol, in that responses to both isoproterenol and phenylephrine plus timolol were blocked by low concentrations of D-600 and nifedipine, which had no effect on positive inotropic responses to elevated Ca2+. Higher concentrations of these antagonists shifted the Ca2+ dose-response curve to the right. In addition, although phenylephrine and BAY K 8644 increased tension to a similar extent, responses to phenylephrine were more sensitive than responses to BAY K 8644 to inhibition by both carbachol and D-600. These similarities between the effects of low concentrations of D-600 and nifedipine and those of carbachol are consistent with the hypothesis that carbachol antagonizes responses to alpha- and beta-receptor stimulation in left atria primarily by blocking increases in Ca2+ influx produced by these agonists.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of apomorphine and haldol on PCP induced behavioral and motor abnormalities in the rat

Behavioral abnormalities and motor dysfunctions induced by the administration of PCP to rats is antagonized by both the dopamine agonist apomorphite and the dopamine antagonist haloperidol. In the test situation used, however, the antagonistic effects of apomorphine were much more rapid than those of haloperidol. These results suggest that PCP may be acting on specific presynaptic dopamine receptors and that this reaction is effectively antagonized by low doses of apomorphine in a manner similar to its effects in reducing schizophrenic symptoms and choreiform movement disorders.     

Phosphatases modulate transmission and serotonin facilitation at synapses: Studies with the inhibitor okadaic acid

We examined the role of phosphatases in synaptic transmission using the permeant phosphatase inhibitor okadaic acid (OA). In the crayfish neuromuscular junction (NMJ), postsynaptic effects including increases in input resistance occurred at doses greater than 5 μM OA. At lower doses (0.5–5 μM) the effects were solely presynaptic and transmitter release increased over three-fold despite small reductions in amplitude and duration of presynaptic action potentials. Potentiating effects of serotonin on transmitter release, Which depend on phosphorylation, were increased by OA. Frequency facilitation was reduced but its decay was not affected. In frog NMJs, OA increased spontaneous and evoked release two-fold through presynaptic mechanisms. An inactive analog of OA, OA tetra-acetate, had no effect on transmitter release at frog and crayfish NMJ. Therefore, phosphatases have a strong modulating influence on synaptic transmission.     

Effects of verapamil on sympathetic tone in normal and chronic sinoaortic-denervated conscious dogs

Previous studies have shown that calcium channel blockers from the dihydropyridine group (such as nicardipine) induce an increase in sympathetic tone from a central origin in chronic sinoaortic-denervated (SAD) dogs. In the present study, we investigated to see if verapamil possesses such properties. The effects of acute injection of verapamil (0.2 mg/kg i.v.) were compared in normal and SAD conscious dogs. Verapamil induced a decrease in blood pressure in the two groups of animals, and an increase in heart rate and plasma catecholamines (noradrenaline and adrenaline) in normal but not in SAD dogs. Contrary to the dihydropyridine studies (nicardipine), we did not find any evidence for a centrally mediated sympathoexcitatory effect of verapamil in conscious SAD dogs.