Catecholamines in blood

Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levels

Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.

Influence of crying on plasma renin activity and aldosterone concentration

Infants and toddlers often start crying at venopuncture and the stress of crying has been known to increase the levels of plasma renin activity (PRA) and plasma aldosterone concentration (PAC), but no precise information is available. We measured the levels of PRA and PAC in blood samples taken from 30 infants and toddlers within 1 min after the onset of crying, as induced by venopuncture, and 3 and 5 min after continuation of crying (PRA1.0, PRA3.0, PRA5.0, and PAC1.0, PAC3.0, PAC5.0). The age of these subjects ranged from 1 to 30 months (median 16 months). PRA1.0, PRA3.0 and PRA5.0 were 4.0 +/- 1.8 ng/ml per hour, 5.5 +/- 2.7 ng/ml per hour, and 7.8 +/- 4.2 ng/ml per hour, respectively. PAC1.0, PAC3.0 and PAC5.0 were 210 +/- 110 pg/ml, 231 +/- 118 pg/ml and 269 +/- 145 pg/ml, respectively. Both PRA and PAC increased with elapsing time. The increase in PRA was marked after a short episode of crying, but that in PAC was of a mild degree.

Endogenous renal dopamine and control of blood pressure

Activation of specific receptors for dopamine in the renal vasculature and tubules leads to increases in glomerular filtration, and to diuresis and natriuresis. There is evidence for intrarenal production and release of dopamine, which may originate from two sources: tubular decarboxylation of plasma l-DOPA and a population of dopaminergic sympathetic neurons that innervate the renal cortex. Studies of plasma and urinary catecholamine levels indicate that dopamine is released within the kidney in response to sodium loading and to activation of sensory pathways related to nociception and chemoreception. There is also evidence for deficient renal release of dopamine in patients with renovascular or essential hypertension. Collectively, the available data suggest that intrarenal dopamine has a physiological function in control of blood volume and blood pressure, and that defects in this control may be implicated in the aetiology of some hypertensive states.

Vesicular storage of 3,4-dihydroxyphenylethylamine and noradrenaline in terminal sympathetic nerves of dog spleen and kidney

The subcellular distribution of 3,4-dihydroxyphenylethylamine (DA, dopamine) and noradrenaline was examined in preparations of dog spleen and renal cortex following ultracentrifugation on a discontinuous sucrose gradient. In both tissues, only half the total tissue DA was localized to the soluble phase, and 30-50% was found in association with noradrenaline in the large vesicular fraction, suggesting that both catecholamines may be stored together and released by nerve stimulation. The vesicular fraction from renal cortex contained more DA than could be attributed to its presence in noradrenergic axons alone, supporting other evidence for the existence of dopaminergic renal nerves.

Excretion of catecholamines and their metabolites in transplantable rat phaeochromocytoma

The urinary excretion pattern of catecholamines and their metabolites was studied in rats bearing a subcutaneous transplantable phaeochromocytoma. Compared with normal rats, tumour-bearing animals showed a markedly raised excretion of dopamine, noradrenaline and adrenaline, together with certain of their major acidic and alcoholic metabolites. No evidence of increased octopamine production could be obtained. There was a significant correlation between the output of dopamine and its metabolites, allowing accurate assessment of dopamine turnover rates which were comparable with those observed in human phaeochromocytoma. Tumour development, as determined by tumour weight, also correlated significantly with urinary excretion of noradrenaline and dopamine. Rat phaeochromocytoma appears to be a useful model for the human tumour.

Release of noradrenaline and dopamine by nerve stimulation in the guinea-pig and rat vas deferens

Spontaneous and nerve stimulated release of noradrenaline and dopamine from rat and guinea-pig vas deferens have been measured electrochemically after separation by high performance liquid chromatography (h.p.l.c.). In the absence of nerve stimulation both noradrenaline (NA) and dopamine were released into the bathing fluid in the rat but in the guinea-pig only noradrenaline could be detected. Drugs which block neuronal and extraneuronal uptake of catecholamines had little effect on spontaneous overflow but both tetraethylammonium and phenoxybenzamine increased overflow. Transmural nerve stimulation (5-10 Hz) increased catecholamine overflow in both species and dopamine release was now measurable from the guinea-pig vas. In the rat, the proportion of dopamine to NA was unchanged from that released spontaneously. The release of both amines was little affected by drugs that block neuronal and extraneuronal uptake and a monoamine oxidase inhibitor, but was inhibited by tetrodotoxin 0.2 microgram ml-1. In the guinea-pig tetraethylammonium 10 mM doubled overflow and phenoxybenzamine 10(-5)M increased it by five times but the dopamine percentage remained constant and equal to the control. Following nerve stimulation the amount of dopamine released expressed as a percentage of total catecholamine release was 6% for the rat and 1.3% for the guinea-pig. These values were considerably higher than the comparable figures for dopamine: NA content of the two tissues (2% and 0.5% respectively). Repeated periods of stimulation depleted these tissue stores and the depletion of dopamine was significantly greater than that of NA. 6 Our interpretation of these results is that both dopamine and NA are released from a common store during normal noradrenergic transmission. While all or most of the axonal dopamine is contained in this releasable pool, most of the axonal NA lies in a second, less readily released pool.

Active and passive coping under different degrees of stress; effects on urinary and plasma catecholamines and ECG T-wave

Cardiac sympathetic, urinary and plasma catecholamine effects of active and passive coping were investigated during both low and high stress. Stress intensity was manipulated by varying the work load on a bicycle ergometer. As predicted, T-wave flattening of the ECG - an index of cardiac sympathetic activity - was significantly more pronounced during active coping than during passive coping. This effect did not depend upon the degree of stress. A significant increase in both adrenaline and noradrenaline levels depended upon the combined effects of active coping and high stress. Because high concentrations of circulating catecholamines are thought to be related to cardiovascular pathology, the results suggest that active coping during high stress might involve the highest cardiovascular risks.

Strain differences in sympathetic-adrenal medullary responsiveness and behavior

Three experiments confirmed and extended previous findings from this laboratory regarding strain differences in physiological and behavioral responses of rats to stressful stimulation. In the first experiment, adult male Wistar-Kyoto (WKY) rats had greater plasma levels of norepinephrine and epinephrine and higher mean arterial pressures following 5 min of intermittent footshock (2.0 mA, 0.5-sec duration, every 6 sec) compared to adult male Brown-Norway (B-N) rats. In contrast, basal plasma levels of both catecholamines and resting values of mean arterial pressure and heart rate did not differ between strains when rats were undisturbed in their home cages. The second experiment involved a behavioral comparison of adult male and female WKY and B-N rats during 3 consecutive daily tests in an open field arena. B-N males and females were dramatically more active and reared more frequently during each open field test compared to WKY rats. For the third experiment, adult male and female rats of the two strains were trained in a one-trial passive avoidance task and median crossover latencies were similar for all strain-sex comparisons. However, median 24-hr retention latencies were much greater for WKY male and female rats. These findings indicate that strain differences in the physiological and behavioral responses of WKY and B-N rats are consistent across sexes. Moreover, our studies with these inbred strains of rats provide a convenient model for examining the relationship between sympathetic-adrenal medullary activity and behavioral responses to stressful stimulation.

Evaluation of sympathetic nervous system and adrenomedullary activity in normal children

In 22 healthy children heart rate, blood pressure and plasma levels of epinephrine (E) and norepinephrine (NE) were evaluated under basal conditions and in response to standing (5 min). Basal plasma E and NE levels found in these children were (means +/- S.E.M.) 139 +/- 17.9 pg/ml and 236 +/- 31.0 pg/ml respectively. Ten out of the 22 children reported dizziness and discomfort by the end of the 5 min standing period. These children showed not only a greater decrease in both systolic and diastolic blood pressure but also a lower basal heart rate, a tendency to higher basal NE levels and a blunted plasma NE response (23 +/- 7%) when compared with children not reporting symptoms (60 +/- 9%, P less than 0.01). Plasma E levels also showed an increment although a wide range of individual responses was observed in both groups.

Catecholamines in head and body blood of eels and rats

1. When compared with other vertebrates, the circulating titers of norepinephrine and epinephrine of the yellow eel are very low. 2. The ratio of the catecholamine titers in the eel differs from that reported for other vertebrates. 3. Following decapitation, the titers of the catecholamines are higher in head blood than in body blood of both unanesthetized and anesthetized eels. In decapitated rats, only the dopamine titer is higher in head blood. 4. As in the lamprey, agitation stress causes a drop of circulating catecholamines. However, other forms of stress cause the expected increase. 5. It appears that many data on catecholamines in both brain and circulation of vertebrates in general have been influenced by stress effects.

Effects of handling during infancy on the sympathetic-adrenal medullary system of rats

We examined the effects of daily handling and maternal separation (5 min per day) on the responsiveness of the sympathetic-adrenal medullary system of Sprague-Dawley rats before weaning and in adulthood. Plasma levels of norepinephrine (derived primarily from sympathetic nerves) and epinephrine (released from the adrenal medulla) were elevated in handled pups compared to unhandled controls at 14 and 18 days of age but not at 6 and 10 days of age. When tested in adulthood, previously handled and control rats did not differ with respect to basal or stress-induced increments in plasma levels of norepinephrine and epinephrine. These results indicate that brief daily episodes of handling and maternal separation are attended by an increase in sympathetic-adrenal medullary tone in 14-18-day-old rats. However, the enhanced response of the sympathetic-adrenal medullary system of separated rats may not persist into adulthood.

Changes in plasma noradrenaline and adrenaline associated with central and peripheral thermal stimuli in the pig

1. The role of catecholamines in thermogenesis has been investigated in trained young pigs in various situations which increases heat production. Plasma noradrenaline and adrenaline concentrations were estimated by radioenzymic assay of samples taken from an indwelling jugular catheter to prevent disturbance and stress. 2. During 3 hr at ambient temperatures of between 25 and -5 degrees C, there was curvilinear increase in noradrenaline concentrations as temperature decreased, but adrenaline did not change. After 1-3 days at 5 or 1 degrees C, the concentrations of both amines were similar to those found at thermal neutrality. 3. Cooling the cervical region of the spinal cord resulted in a large increase in plasma noradrenaline whereas local cooling of the hypothalamus was associated with a small increase in the hormone. When cooling either region of the central nervous system, plasma adrenaline concentrations did not change. 4. During exposure to 45 degrees C, rectal temperature increased to 43 degrees C. Concentrations of catecholamines remained low or declined until the rectal temperature was above 41.5 degrees C when the concentrations increased in most animals. 5. Induced physical activity lasting 40 min was associated with an increase in both noradrenaline and adrenaline concentrations. 6. Blood samples from the inferior vena cava, just cephalad to the outlet of the adrenal veins, had much higher concentrations of noradrenaline during cold exposure than those taken simultaneously from the jugular vein. Therefore, at least part of the increase in noradrenaline concentrations reported above may have been due to release of the hormone from the adrenal medulla. 7. It is concluded that during short-term exposure to cold, and in exercise, there is a rapid catecholamine response, producing concentrations in the blood which could be high enough to stimulate thermogenesis. During longer-term cold exposure, catecholamine output is low and other factors must be of greater importance in maintaining thermogenic processes. Further, catecholamine output may result from thermal stimuli not only from outside the external surface of the animal but also from within the central nervous system.

An analysis of the mechanism of 5-hydroxytryptamine-induced vasopressor responses in ganglion-blocked anaesthetized dogs

5-Hydroxytryptamine (5-HT) administered intravenously (i.v., 1--30 micrograms kg-1) to ganglion-blocked anaesthetized dogs produced dose-related increases in diastolic blood pressure and we have analysed the mechanism involved. Cyproheptadine and methysergide (10--100 micrograms kg-1 i.v.) were potent and specific antagonists of the 5-HT induced rise in blood pressure, while the alpha-adrenoceptor blocking agent phentolamine (0.3--3 mg kg-1 i.v.) also caused dose-related inhibition. Syrosingopine pretreatment converted the vasopressor action of 5-HT to a vasodepressor action and acute bilateral adrenalectomy caused a marked reduction in the 5-HT-induced rise in blood pressure. In two dogs, 5-HT (30 micrograms kg-1 i.v.) markedly increased the venous plasma concentrations of noradrenaline and adrenaline. We concluded that the 5-HT-induced rise in diastolic pressure in the ganglion blocked anaesthetized dog is due largely to the release of catecholamines of which a substantial component is from the adrenal gland. The rise in diastolic blood pressure is specifically blocked by low doses of cyproheptadine and methysergide suggesting that the release of catecholamines is mediated by specific 5-HT receptors located mainly within the adrenal medulla.

Plasma dopamine: source, regulation, and significance

Plasma dopamine is present in free form in a concentration approximately equivalent to that of epinephrine and about 25% that of norepinephrine. It originates in a variety of tissues including sympathetic nerves and adrenal, and the percentage originating from the various sources remains unknown. Events that are associated with increases in sympathetic activity such as stress, exercise, standing, or hypovolemia are associated with increases in plasma dopamine concentration, although the responses may be of considerably smaller magnitude than those for plasma norepinephrine and epinephrine. The functional importance of dopamine in the periphery and of changes in circulating dopamine remain only poorly defined. These include possible roles in neurotransmission in sympathetic ganglia, altering renal vascular bed, modulation of aldosterone secretion and sodium excretion, mediation of certain stress responses, and others yet to be revealed.

Sympathomimetic amines

The autonomic nervous system may play an important role in tissue autoregulation as the neurohumoral transmission process has been shown to constitute the final common pathway by which the effects of many physiological and pharmacological substances are mediated. The effects of the administration of a sympathomimetic amine cannot be accurately predicted in a subject. Choice of which sympathomimetic amine to use should be determined on the basis of data obtained in relevant clinical circumstances, but the dose should always be titrated against the effect in each individual. It is interesting that adrenaline, "the original autonomic drug" with its "venerable history", is still a first line drug in many of the situations for which it was being prescribed in 1907. It is the drug of first choice in anaphylactic reactions and for severe allergic bronchospasm, and is widely used as a vasoconstrictor in surgery and with local anaesthetic agents. Adrenaline in "physiological" doses is a satisfactory and cheap alternative to other available drugs for use in septic shock and in emergence from cardiopulmonary bypass.

Effects of work and acute beta-receptor blockade on myocardial noradrenaline release in congestive cardiomyopathy

Systemic hemodynamic changes and noradrenaline concentrations in coronary sinus blood were studied at rest and during work before and after acute beta-receptor blockade. Patients with congestive cardiomyopathy were compared to patients with primary valvular diseases and to healthy subjects. Noradrenaline concentrations were higher in coronary sinus blood than in arterial blood and increased after beta blockade and during work. Noradrenaline concentrations were more increased in patients with more pronounced myocardial failure and did not seem to separate patients with congestive cardiomyopathy from those with valvular disease. Patients with congestive cardiomyopathy showed a good hemodynamic tolerance toward acute beta blockade.

Comparative assessment of stimuli that release neuronal and adrenomedullary catecholamines in man

We assessed the release of neuronal and adrenomedullary catecholamines in response to various stimuli of the sympathetic nervous system in normal subjects. Plasma catecholamines and their urinary metabolites, normetanephrine and metanephrine, were measured. Sodium restriction increased supine plasma norepinephrine by 37% and ambulatory plasma norepinephrine by 22%, with urinary normetanephrine excretion increased 29%. The sodium restriction did not elevate plasma epinephrine or urinary metanephrine. The most potent stimuli of norepinephrine were treadmill exercise, orthostasis, caffeine, the cold pressor test, sodium restriction and handgrip exercise, in descending order. Plasma epinephrine was increased by caffeine, treadmill exercise, the cold pressor test, handgrip exercise and the Valsalva maneuver, in that order. Syncope resulted in profound changes in plasma epinephrine but only modest changes in plasma norepinephrine. We conclude that in man, there is frequent dissociation between the effects of different stimuli on neuronal and adrenomedullary catecholamine release.

Plasma adrenaline, noradrenaline and dopamine in man and different animal species

1. The catecholamines adrenaline (A), noradrenaline (NA) and dopamine (DA) were determined in plasma samples of man and various animal species using a highly sensitive radioenzymatic method.2. Basal values were determined under conditions producing virtually no physical or psychic stress in blood obtained through acutely inserted venous catheters in human volunteers, rabbits and cows, through chronic indwelling catheters in cats and rats, and by cubital venipuncture in trained dogs.3. Basal values (pg/ml.) for A, NA, and DA were respectively 64, 203 and 98 in man, 73, 609 and 276 in cats, 166, 392 and 216 in rabbits, 56, 152 and 91 in cows, 204, 376 and 173 in dogs, and 175, 509, and 84 in SPF rats. The NA concentrations were always higher than those of A and DA.4. Gentle handling of rats for 30 sec greatly increased the levels of all catecholamines, especially of A. Even more marked rises were observed during and up to 5 min after restraint stress.5. Blood from the trunk of decapitated rats contained about 20 times more A and 3-4 times more DA and NA than venous blood from catheters in the absence of handling.6. Basal values of plasma catecholamines in small animals can only be obtained through indwelling catheters and in the absence of handling. Most of the previously reported values are too high and are experimental artifacts.

Levels of noradrenaline in plasma during thermogenesis induced by cold-exposure or by noradrenaline infusion in warm- and in cold-acclimated rats

Oxygen consumption and concentration of noradrenaline (NA) in arterial plasma have been measured in warm-acclimated (WA) and in cold-acclimated (CA) rats during exposure to cold and in barbital-sedated WA or CA rats receiving intravenous infusions of NA at various doses at room temperature. In WA and in CA rats in the cold, NA in plasma increased rapidly from a resting level of 0.1 to 0.2 ng/ml at thermoneutrality to values 5 to 10 times greater at -19 degrees C. The increases were directly related to the degree of cold exposure and were maintained throughout exposure. In barbital-sedated WA or CA rats infused with NA the plasma levels of NA which stimulated calorigenesis were approximately 10 times greater than those resulting from overflow of NA into the blood during intense cold exposure and were in the range found by others to be effective in stimulating O2 consumption in isolated brown adipocytes.

Increased plasma adrenaline concentrations in benign essential hypertension

Plasma adrenaline, noradrenaline, and dopamine concentrations and plasma renin activity were measured in the supine position and after standing for 10 minutes in 14 patients with sustained benign essential hypertension and in five patients with labile hypertension. Results were compared with values obtained in 11 normotensive control subjects. In controls plasma noradrenaline concentrations increased with age, while plasma adrenaline values tended to decrease with age. No significant difference in mean plasma noradrenaline was found between hypertensive and control subjects, but plasma noradrenaline seemed slightly increased in a proportion of hypertensive patients aged less than 50. Plasma adrenaline was considerably raised in both supine and standing positions in eight patients with sustained hypertension and in two with labile hypertension. Dopamine concentrations and plasma renin activity were similar in all groups studied. The finding of significantly raised plasma adrenaline concentrations in a large proportion of hypertensive patients supports the hypothesis that the activity of the sympathetic nervous system is increased in essential hypertension. Measurement of plasma adrenaline seems to be a more sensitive index of this activity than that of plasma noradrenaline.

A sensitive radioenzymatic assay for adrenaline and noradrenaline in plasma

1 An existing radioenzymatic assay for plasma catecholamines using catechol-o-methyl transferase and [3H]-S-adenosyl-methionine has been modified resulting in a more sensitive assay for the measurement of plasma adrenaline and noradrenaline. 2 The lower limit of sensitivity for this method is 25 pg for adrenaline and 30 pg for noradrenaline/ml of plasma. 3 Resting supine (60 min) plasma adrenaline concentration was (mean +/- s.d.) 124 +/- 76 pg/ml(n=11) in males and 130 +/- 71 pg/ml (n=7) in females; plasma noradrenaline concentrations were respectively 444 +/- 129 pg/ml and 550 +/- 87 pg/ml. 4 The changes in plasma catecholamine concentrations in response to 40 degrees head-up tilt have been determined in a group of healthy normal subjects and have been shown to be related to changes in blood pressure and heart rate.

Is dopamine a neurohormone of the adrenal medulla? Studies with morphine stimulation

Dopamine (da) concentrations in rat adrenals, plasma and brain were variably elevated 1 h after a large parenteral dose of morphine. In adrenals, unlabelled DA increased 2-fold and labelled DA, synthesized from 3H-tyrosine, increased more than 4-fold. The increases could be prevented by inhibition of DA-synthesizing enzymes and spinal cord transection, respectively. Labelled DA in plasma increased 2.7-fold after morphine in intact rats but did not increase in those with spinal cord transection. It is concluded that: (1) morphine stimulates the adrenal by increasing nerve impulse flow, (2) increased nerve impulse flow increases DA synthesis and levels, and (3) the increased DA levels result in increased release of DA into the bloodstream.