Effect of handling and forced immobilization on rat plasma levels of epinephrine, norepinephrine, and dopamine-beta-hydroxylase.

Forced immobilization of rats triggers activation of adrenal-medullary discharge of epinephrine (EPI) and sympathetic neuronal release of norepinephrine (NE). Plasma levels of EPI reach peak values, which are about 40-fold greater than in undisturbed rats, at about 20 min and then decline to about one-third the peak levels. Plasma levels of NE are increased about 6-fold throughout the immobilization interval. Decapitation produces an 80-fold increase in plasma levels of EPI and an 8-fold increase in NE. These striking decapitation-induced increases are potentiated about 3-fold by immobilization, presumably as a consequence of an immobilization-induced alteration in the "set" of responsivity of spinal cord mechanisms controlling sympathoadrenal medullary discharge. Even minor disturbances produce highly significant increases in plasma EPI and NE and special precautions must be observed when studies involving plasma catecholamines or their effects are performed in animals.

Effect of the anesthetic agent propofol on hormonal responses to ECT.

Propofol is a new anesthetic induction agent that reduces electroconvulsive therapy (ECT) seizure duration. To indirectly investigate the effect of propofol on ECT-induced acute central neurotransmitter changes, we studied neuroendocrine responses in 25 primary depressed subjects treated with ECT under either propofol or thiopentone anesthesia. Blood samples were taken prior to ECT, and then at regular intervals for 2 hr. Only the prolactin response correlated significantly with seizure duration (r = 0.52, p less than 0.01). Subjects given propofol had significantly reduced adrenocorticotropin (ACTH) (p less than 0.01) and cortisol (p less than 0.05) responses compared to thiopentone, which were independent of seizure duration. There was a trend towards a reduction in the prolactin response with propofol compared to thiopentone, but this was dependent upon the diminished seizure duration. The results indicate that propofol affects endocrine responses to ECT by two distinct mechanisms: decreasing prolactin by reducing the seizure duration and decreasing ACTH and cortisol by another process, possibly via a reduction in central noradrenergic activation.

Pharmacokinetic analysis of the time course of effect of atracurium.

OBJECTIVE: To examine the ability to determine clinically important pharmacokinetic and pharmacodynamic parameters of atracurium by the analysis of the time course of effect without the use of plasma concentration data. DESIGN: Neuromuscular transmission was monitored with train-of-four stimulation and electromyographic quantitation of the first (T1) and fourth (T4) responses in eight anesthetized patients undergoing elective surgery. The time course of onset and recovery of neuromuscular blockade by three successive bolus doses of atracurium was recorded. Equations describing the theoretic time course of concentrations in the effect compartment and the dose-response relationship were fitted simultaneously to these data; the parameters of these equations derived from the fit of two doses were used to predict the response to a third dose. Fitting the equations to all three doses was also performed to assess the accuracy of predictions for atracurium. RESULTS: From the depression of the first twitch after three consecutive doses in eight patients, the half-lives of uptake into and elimination from the effect compartment were 2.1 +/- 0.2 minutes (mean +/- SEM) and 25.8 +/- 2.3 minutes (n = 8). The doses producing 50% and 95% depression of the first twitch (ED50 and ED95) were 168 +/- 15 and 280 +/- 25 micrograms/kg, respectively, with a Hill coefficient of 6.1 +/- 0.5. The half-life of elimination estimated from the fourth twitch was similar to that from the first twitch. CONCLUSIONS: The analysis of high-resolution effect data is capable of giving pharmacokinetic and pharmacodynamic parameters with clinically acceptable accuracy within a short sampling time, without resorting to laboratory analysis. This method is specific for active drug and would be of value for individualization of administration for short-term treatment.

Changes of adrenal catecholamines and their synthesizing enzymes during ontogenesis and aging in rats.

Male Wistar specific-pathogen-free rats aged 2, 7, 17, 30, 60, 120, 200, 360 and 600 days, all killed in experiment on the same day, were examined. The body weight significantly increased until the 200th day, the weight of adrenals until the 120th day and the adrenal protein content until the 30th day of life. The adrenaline content of the adrenals increased continuously during the 600 days studied. Adrenal noradrenaline content increased rapidly over the first 17 days, remained at a stable level until the 120th day, and rose to a higher level after 200 days. The activity of adrenal catecholamine-synthesizing enzymes also increased with age: tyrosine hydroxylase gradually increased until the 360th day, dopamine-beta-hydroxylase and phenylethanolamine-N-methyl transferase until the 200th day. Our results demonstrate that, in the rat, during development there is a gradual increase of adrenal weight, adrenaline content, tyrosine hydroxylase and phenylethanolamine-N-methyl transferase activity until maturation (120th day), whereas the adrenal noradrenaline content reaches the adult values earlier, around the 17th day. During aging, adrenal catecholamines significantly increase when compared to young-adult rats (120-day-old), probably due to the elevated activity of the adrenal catecholamine-synthesizing enzymes. The increased adrenal catecholamine levels in old animals might be connected with a higher incidence of cardiovascular diseases in aged.

Presynaptic and postsynaptic depressant effects of phenytoin sodium at the neuromuscular junction.

1. Phenytoin sodium, 10 micrograms/ml (3.6 x 10(-5) M), reduces the amplitude of endplate potentials in mouse sternomastoid neuromuscular junctions. 2. The reduction in amplitude is due to a reduction both in the quantal content of endplate potentials and in the amplitude of the voltage response to quanta of acetylcholine. 3. The reduction caused by phenytoin in the amplitude of spontaneous miniature end plate potentials was due to a reduction in the time constant of decay of miniature endplate currents. 4. It is concluded that phenytoin depresses neuromuscular transmission by reducing both the amount of acetylcholine secreted in response to an action potential and by reducing the lifetime of postsynaptic channels activated by acetylcholine.

The kinetics of effect of neuromuscular blocking drugs.

In attempts to derive pharmacokinetic constants from effect data three methods were explored, using non-depolarizing neuromuscular blocking drugs as the paradigm for obtaining effect data. The first method, based on the simple assumption that following two doses, the drug concentrations at times of equal effect during recovery, were equal. Provided that recovery took place in the log-linear drug elimination phase, the elimination rate constant (beta) could be calculated. This method proved rather inaccurate, a second method, again dependent on recovery in the log-linear phase yielded a constant which was the product of beta and the exponent of the Hill equation (s). This method yielded results within 20% of values calculated from plasma drug assays, and it was demonstrated that the time-effect curve could be described from knowledge of this constant. The third method, using non-linear curve fitting technique, derived values for the rate constants of plasma redistribution (alpha) and elimination (beta) as well as for the rate constant of elimination from an effect compartment (keo). If the values were derived from the effect of two doses of a drug, the intensity and duration of effect of a third dose could be predicted with reasonable accuracy. The dose dependent constants of the usual compartmental equations for the plasma concentration of a drug (A and B) could be derived in terms of the EC50. The method can be applied to any drug whose effect can be measured and whose maximal effect can be defined. We believe that the method may be useful in rapidly and inexpensively estimating population kinetic parameters, and in screening drugs.

Some advantages of the membrane oxygenator for open-heart surgery.

The Lande'-Edwards oxygenator has been used for clinical perfusions on 283 patients. Among these patients we have encountered the full range of congenital and acquired defects and a variance in age from 1 day to adulthood. Data are presented concerning the means and methods of perfusion, the defects involved, and the results of treatment. A comparison has been made between two groups of 20 adults each, one group perfused with a bubble oxygenator (Bently) and the other with the Lande'-Edwards membrane lung. This study showed that platelet function is better preserved by the membrane lung, that hemolysis is less severe, and that postoperative bleeding is reduced. Indirect evidence has been accumulated to suggest that pulmonary, cerebral, and renal function is also better preserved when the membrane lung is employed.

Enhanced phosphoinositide hydrolysis in the pineal gland of spontaneously hypertensive rats.

We studied the phosphoinositide (PI) turnover in the pineal gland of spontaneously hypertensive rats (SHR) and compared it to that in Wistar-Kyoto and Wistar rats. Both basal and norepinephrine-stimulated PI turnover were significantly higher in the SHR than in the other strains. Prazosin (1 mumol/L) completely blocked the norepinephrine-induced PI hydrolysis in all groups. However, prazosin failed to lower the enhanced basal PI turnover in SHR. Pineal response to the cholinergic agonist carbachol was similar in all groups. These results suggest enhanced membrane phospholipid turnover in the pineal gland of SHR. Moreover, signaling via the alpha 1-adrenoceptor might be sensitized in the SHR.

Increased beta 2-adrenoceptor number in peripheral sympathetic ganglia of spontaneously hypertensive rats.

We determined beta-adrenoceptor concentrations in sympathetic ganglia from adult Spontaneously Hypertensive Rats (SHR) and Wistar-Kyoto (WKY) control rats by quantitative autoradiography. Adjacent tissue sections were incubated with [125I]iodocyanopindolol, with or without excess of unlabeled (-)-propranolol, the beta 1-antagonist CGP 20712A or the beta 2-antagonist ICI 118,551. Most beta-adrenoceptors were of the beta 2-type. Their concentration was higher in the superior cervical and stellate ganglia of SHR when compared to normotensive WKY. Our results indicate that beta 2-adrenoceptor stimulation may be enhanced in sympathetic ganglia of SHR, and could play a role in the maintenance of their increased sympathetic activity.

Alcohol, corticosteroids, energy utilization, and hippocampal endangerment.

The cellular weakening or cytoxic consequences of CAC are intertwined in the most fundamental sense with energy intake, production, storage, and mobilization. The impact of CAC on the HPA axis to increase GCs makes this energy regulatory hormone along with pancreatic hormones a potential major player in the site-specific organ pathologies associated with CAC. Although little is known about the mechanism of CAC neurotoxicity, the hippocampal endangerment model which relies heavily on the cellular weakening, site-specific effect of continuous or chronic, intermittent (withdrawal, binge drinking) elevation of GCs, even less is known about the mechanism of neurotoxicity of activating the ethanol-inducible CYP2E1 system. It is likely that components of both models contribute to the site-specific, CNS neurotoxicity associated with CAC, but this remains largely unresolved.

Adrenergic regulation of [3H]ketanserin binding sites during immobilization stress in the rat frontal cortex.

Acute immobilization stress increased serotonin and 5-hydroxyindoleacetic acid levels, the 5-hydroxyindoleacetic/serotonin ratio, and the number of [3H]ketanserin binding sites, representing serotonin-2 type receptors, in the rat frontal cortex. Peripheral administration of propranolol or central administration of 6-hydroxydopamine abolished the stress induced elevation of [3H]ketanserin binding sites. Treatment with 6-hydroxydopamine did not affect the increase in serotonin and 5-hydroxyindoleacetic acid levels, and enhanced the increase in the 5-hydroxyindoleacetic acid/serotonin ratio produced by stress. Conversely, chemical serotoninergic denervation with 5,7-dihydroxytryptamine had no influence on the stress-induced elevation of [3H]ketanserin binding sites, but abolished the serotonin and 5-hydroxyindoleacetic acid increase produced by stress. These results suggest that an intact serotoninergic system is not essential for serotonin-2 type receptor regulation during stress. Instead, the noradrenergic system, most probably through stimulation of beta-adrenoreceptors, may control the regulation of [3H]ketanserin binding sites in the rat frontal cortex during acute stress.

Mepacrine treatment prevents immobilization-induced desensitization of beta-adrenergic receptors in rat hypothalamus and brain stem.

Forced immobilization is a severe stress in rats which diminishes levels of epinephrine in specific nuclei in the hypothalamus and brain stem, suggesting that release of epinephrine is stimulated to a rate which exceeds the rate of its replacement. In the pineal gland, frog erythrocytes, C6 astrocytoma cells and rat brain, beta-adrenoceptor agonists appear to regulate the number of their receptors. Exposure to high concentrations of an agonist leads to apparent decrease in receptors reflected by a decrease in maximal specific binding of antagonists. The apparent decreases in receptors have been shown to be attended by decreases in physiologic responsiveness. In C6 astrocytoma cells, beta-agonists stimulate methylation of phosphatidylethanolamine to increase formation of membrane phosphatidylcholine which in turn appears to enhance activation of adenyl cyclase. Interference with the metabolism of phospholipids by exposure to phospholipase A2 inhibitor, mepacrine (quinacrine), prevents agonist-induced desensitization of beta-adrenoceptors in astrocytoma cells. In the present study repeated immobilization stress has been found to decrease significantly the number of beta-adrenoceptors in hypothalamus and brain stem while increasing the number of alpha 2-adrenoceptors. The desensitization of beta-adrenoceptors was prevented by treatment with mepacrine.

Increased beta 2-adrenoceptors in the superior cervical ganglia of genetically hypertensive rats.

[125I]Iodocyanopindolol binding sites were characterized by autoradiography in the superior cervical ganglia of Wistar-Kyoto (WKY) rats. A high concentration of (-)-[125I]iodocyanopindolol binding sites, characterized as beta-adrenoceptors by (-)-propranolol displacement, was distributed throughout the ganglia and in the postganglionic (internal carotid) nerve. ICI 118,551, a beta 2-selective antagonist, displaced more than 85% of the binding sites, whereas CGP 20712A, a beta 1-selective antagonist, displaced less than 10% of the binding sites, indicating that the beta-adrenoceptors were primarily of the beta 2-subtype. Emulsion autoradiography demonstrated that at least part of the binding sites were associated with principal ganglion cells. Unilateral deafferentation did not modify the number of binding sites in the superior cervical ganglia of WKY or spontaneously hypertensive rat (SHR). These results suggest that at least part of these receptors may correspond to prejunctional beta 2-adrenoceptors originated in principal ganglion cells. The concentration of beta 2-receptors was increased in the superior cervical ganglia of young and adult SHR when compared to age-matched WKY rats (49% and 39%, respectively). There were no differences in beta 2-adrenoceptor number in the stellate ganglia of young and adult WKY and SHR. These results suggest that beta 2-adrenoceptor stimulation may be selectively enhanced in some peripheral sympathetic ganglia in SHR and this could play a role in the development and maintenance of the increased sympathetic activity in this strain.

Distribution of phenylethanolamine-N-methyltransferase in the rat heart: effect of 6-hydroxydopamine.

The distribution of phenylethanolamine-N-methyltransferase (PNMT), the epinephrine-forming enzyme in the adult rat heart atria and ventricles was studied. The activity of the enzyme in the hearts of adult rats is very low; a significantly higher activity was found in the atria than in the ventricles. A significant increase in PNMT activity was found in all heart areas examined in 6-hydroxydopamine-treated rats compared to vehicle-treated rats. The increased PNMT activity might reflect compensatory or adaptation processes secondary to the destruction of the peripheral sympathetic nerve terminals.

Effect of indomethacin on cardiac beta-adrenergic receptors.

Treatment of rats with indomethacin, 1.5 mg/kg per day, for one week, significantly reduced the number of beta-adrenoceptors in the heart without altering their affinity for the specific beta-adrenergic ligand. In indomethacin-treated rats there was a reduction in the cardiac response to epinephrine in vivo as indicated by a shift to the right of the epinephrine dose-heart rate response curve. These results support a possible interference by indomethacin in beta-adrenoceptor-mediated effects.

Cholinergic stimulation of phosphoinositide hydrolysis in the rat pineal gland.

Carbachol induced a dose-dependent accumulation of inositol monophosphates in the Wistar rat pineal gland. The relative potency of muscarinic antagonists (atropine greater than pirenzepine much greater than gallamine) in blocking this response suggests the involvement of muscarinic M1 receptors. Following bilateral superior cervical ganglionectomy, the carbachol-induced phosphoinositide response was similar to that seen in sham-operated controls, while adrenergic response was enhanced by 50%. The results indicate that the pineal has functional muscarinic receptors which are not affected by removal of the sympathetic innervation to the gland.

Characterization of beta 1- and beta 2-adrenoceptor subtypes in the rat sinoatrial node and stellate ganglia by quantitative autoradiography.

We characterized beta-adrenoceptors in rat sinoatrial node (SA) and stellate ganglia by incubating consecutive tissue sections with [125I]iodocyanopindolol, with or without the beta 1-selective (CGP 20712A) or the beta 2-selective (ICI 118,551) antagonists, followed by quantitative autoradiography. In the stellate ganglia, ICI 118,551 displaced more than 90%, and CGP 20712A less than 5%, of the binding sites. CGP 20712A displaced about 50% of the binding sites in the SA, and about 65% in the rat atria. The SA has a high percentage of beta 2-adrenoceptors and the stellate ganglia contains almost exclusively beta 2-adrenoceptor binding sites, implicating beta 2-adrenoceptors in the control of heart rate in the rat.

Changes of plasma and adrenal catecholamines and corticosterone in stressed rats with septal lesions.

The effect of septal lesions on plasma catecholamine and corticosterone (B) levels has been studied in rats during single and 7 times repeated immobilization stress (IMO). Blood samples were obtained via a catheter in the tail artery or by decapitation. The increased circulating epinephrine (EPI) and norepinephrine (NE) levels observed in the initial phase of acute stress as well as the elevated baseline EPI level after six times repeated IMO are indicative of an enhanced response of the sympathetic adrenomedullary system after lesions of the septum. After decapitation of rats with septal lesions there was a significant increase in plasma NE one day after the sixth IMO and a block of EPI increase after the seventh IMO compared to sham-operated rats. The adrenocortical system was similarly found to be activated after septal lesions, exhibiting increased baseline plasma B levels. It has been suggested that the septal region affects the studied systems by exerting an inhibitory tonus. The removal of this inhibitory system results in an increase of adrenocortical and sympathetic-adrenomedullary activities.

Presynaptic noradrenergic regulation during depression and antidepressant drug treatment.

A specific testable hypothesis in which supersensitive alpha-2-adrenoreceptors play an important role in the etiology and maintenance of affective illness is presented based on the following observations: (1) published findings of changes in adrenergic receptors in the periphery and brains of rats in response to antidepressant regimens; (2) new studies of the monoamine oxidase type A-inhibiting antidepressant clorgyline, specifically relating to adaptation in the alpha-adrenergic presynaptic negative feedback system; (3) human peripheral alpha-adrenergic receptor changes from studies of patients with affective illness; and (4) observations from animals and humans experiencing stress and withdrawal from chronic amphetamine and opiate administration, suggesting that the development of supersensitive alpha-2-adrenoreceptors may lead to affective illness in vulnerable individuals. Old and new pharmacologic treatments are then discussed in terms of their capacity to specifically alter adrenergic receptor state.

In-vitro interaction between H2 antagonists and vecuronium.

The interaction between histamine H2 antagonists and the neuromuscular blocking drug vecuronium was investigated in the rat phrenic nerve-hemidiaphragm preparation. Cimetidine alone, in the concentration range 800-4000 microM produced between 14 and 74% neuromuscular paralysis with an EC50 (mean +/- s.e.) of 2900 +/- 100 microM. Ranitidine augmented the indirectly-evoked muscle response at concentrations between 30 and 160 microM but at higher concentrations, between 300 and 1800 microM, produced neuromuscular paralysis. Famotidine produced negligible and statistically insignificant (0-5%) neuromuscular paralysis at concentrations between 0.3 and 300 microM. Cimetidine (800 microM) shifted the neuromuscular concentration-effect curve of vecuronium to the left in a parallel manner, while ranitidine (160 microM) shifted it to the right. The potentiation ratio was 1.90 +/- 0.14 for cimetidine and 0.62 +/- 0.05 for ranitidine. Famotidine (30 microM) did not alter the response to vecuronium. These data indicate that higher than clinically relevant concentrations of cimetidine and ranitidine produce neuromuscular paralysis and may potentiate the action of vecuronium. Low concentrations of ranitidine may antagonize the action of vecuronium. Famotidine, in contrast, lacks significant neuromuscular effects.