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PubMed1992

Changes in plasma free and sulfoconjugated catecholamines before and after acute physical exercise: experimental and clinical studies.

To elucidate whether sulfoconjugated catecholamines in plasma, especially dopamine, serve as a source of free catecholamines, we examined the change in afterload on the deconjugating activity of catecholamines in isolated Langendorff perfused rat hearts. Dopamine-sulfate was administered under ordinary or high-work-load conditions. Free dopamine in the effluent was increased by the high-work-load of the hearts, whereas conjugated dopamine showed an apparent decrease. These results indicate the possibility that deconjugation of sulfoconjugated catecholamines is accelerated by a high-work-load. To obtain further evidence in humans, we also examined the changes in the plasma levels of free and sulfoconjugated catecholamines in healthy volunteers before and after marathon running. Free dopamine increased 1.99-fold from the baseline value after exercise, whereas conjugated dopamine decreased by 12%. Similarly, the plasma levels of free noradrenaline and adrenaline increased after exercise to 2.45- and 1.51-fold their respective baseline values, while conjugated noradrenaline and adrenaline both decreased. These clinical results, as well as those of the experimental studies, suggest that the increase in plasma free catecholamines after exercise is due not only to increased release from the sympathoadrenal system but also to accelerated conversion from sulfoconjugated catecholamines in the plasma.

Adolescent↗
PubMedDate not supplied

Effect of arginine vasopressin and oxytocin on acetylcholine-stimulation of corticosteroid and catecholamine secretion from the rat adrenal gland perfused in situ.

The effects of acetylcholine, arginine vasopressin (AVP) and oxytocin (OXT) on both catecholamine and steroid secretion have been investigated using the isolated rat adrenal gland perfused in situ. Significant stimulation of steroid (aldosterone and corticosterone) secretion occurred with 1 mumol/l acetylcholine; the ED50 was approximately 20-fold higher (circa 20 mumol/l) than that for catecholamine secretion. The highest concentration of acetylcholine used (100 mumol/l) stimulated aldosterone secretion eight-fold; corticosterone secretion four-fold; noradrenaline and adrenaline secretion three-fold. AVP at 100 nmol/l but not at 1 nmol/l significantly stimulated the secretion of both steroids and catecholamines. OXT had no significant effect on corticosteroid or catecholamine secretion at either concentration. The effects on aldosterone secretion of simultaneous administration of acetylcholine and AVP were additive. No similar effect was seen on corticosterone or catecholamine secretion where the degree of stimulation was the same as for acetylcholine alone. OXT (100 nmol/l) inhibited acetylcholine-stimulated aldosterone secretion but had no effect on acetylcholine-stimulated catecholamine secretion. Carbachol was equipotent with acetylcholine in stimulating steroid secretion from the perfused gland. Our results support the hypothesis that acetylcholine may play a role in the control of steroid secretion by the rat adrenal cortex. They fail to support a role for AVP and OXT in modulating catecholamine secretion by the adrenal medulla except at high concentrations.

Acetylcholine↗
PubMed1988

A differential effect of yohimbine on adrenal and neuronal catecholamine release during bilateral carotid occlusion in the dog.

This study reports on the effects of yohimbine and clonidine on the release of adrenal and renal catecholamines (epinephrine, E; norepinephrine, NE; and dopamine, DA) in response to bilateral carotid occlusion (BCO, 3 min) in vagotomized dogs anesthetized with sodium pentobarbital. The model used allowed us to simultaneously compare adrenal catecholamine secretion with neuronal NE release in the kidney. In control dogs, the net output (ng/min/g tissue) of adrenal E (70.5 +/- 19.7), NE (22.2 +/- 5.9) and DA (2.6 +/- 0.8) increased markedly (P less than 0.01) during BCO to a maximum level of 265.1 +/- 87.9, 97.4 +/- 30.6 and 10.5 +/- 3.2, respectively. Similarly, the net output (ng/min/g tissue) of renal NE (0.66 +/- 0.06) and DA (0.09 +/- 0.02) increased significantly (P less than 0.01) to 1.00 +/- 0.11 and 0.15 +/- 0.04, respectively. Aortic systolic pressure (mm Hg) (140.8 +/- 8.0) and heart rate (beats/min) (162.7 +/- 5.1) also increased (P less than 0.01) to 212.5 +/- 19.3 and 179.5 +/- 5.4, respectively. In dogs treated with yohimbine (0.3 mg/kg, i.v.), the net increase in adrenal catecholamine output was diminished by approximately 47% (P less than 0.05). In contrast, the net increase in renal NE output was potentiated by 41% (P less than 0.05). The net increase in heart rate was also enhanced significantly (P less than 0.01) in the presence of yohimbine. In dogs receiving clonidine (15 micrograms/kg, i.v.) the increases in net output of both adrenal and renal catecholamine were abolished. Similarly, pressor and heart rate responses were abolished in the presence of clonidine. The results indicate that yohimbine exerted a differential effect on renal sympathetic nerves (increase) and adrenal medullae (decrease) in modulating catecholamine release in response to BCO, while clonidine abolished both neural NE release and adrenal catecholamine secretion. This study suggests that a presynaptic alpha 2-adrenoceptor-mediated mechanism, the blockade of which enhances neural NE release at peripheral sympathetic nerve terminals in many tissues, may not be involved in the modulation of adrenal catecholamine secretion during BCO.

Adrenal Glands↗
PubMed1992

Further studies on the relationship between tyrosine supply and catecholamine production in cultured adrenal chromaffin cells.

To elucidate a possible role of tyrosine supply as a factor modulating catecholamine biosynthesis in the adrenergic cell, the transport of [14C]tyrosine into cultured bovine adrenal chromaffin cells was first examined, and the relationship between [14C]tyrosine transport and [14C]catecholamine formation was then investigated. Under the conditions which were routinely employed to determine the rate of catecholamine biosynthesis, tyrosine was taken up into the cells in a manner independent of extracellular Na+ and Ca2+, and this uptake was also insensitive to ouabain and various metabolic inhibitors. The stimulation of these cells with high K+ and other secretagogues caused no significant alteration in the uptake. While, tyrosine transport was markedly inhibited by tyrosine analogues and other L-aromatic amino acids, and this inhibition was accompanied by the reduction of [14C]catecholamine formation. In contrast, tyrosine transport was markedly enhanced by flavone, and this enhancement was also accompanied by the augmentation of catecholamine production under the same experimental conditions. These results seem to indicate that the transport of tyrosine into the cells may be closely related to catecholamine formation within the cells, thus providing an evidence for a possible role of tyrosine supply as one of the factors affecting catecholamine production in the adrenal chromaffin cell.

Adrenal Medulla↗
PubMed1983

Catecholamine uptake into isolated adrenal chromaffin cells: inhibition of uptake by acetylcholine.

We have investigated the process of catecholamine uptake in guinea-pig chromaffin cells. Isolated guinea-pig chromaffin cells accumulate [3H]norepinephrine and [3H]epinephrine by a saturable transport system. Catecholamine uptake is dependent upon temperature, energy, and extracellular Na+. The apparent KmS for norepinephrine and epinephrine transport are approximately 1 and 3.5 microM, respectively; the transport maximum (Vmax) for both compounds is about 100 pmol/min/mg protein. The uptake of norepinephrine into chromaffin cells is inhibited by imipramine (Ki = 50 nM) and by desmethylimipramine (IC50 = 20 nM). In both its substrate specificity and its sensitivity to pharmacological inhibition, the catecholamine uptake system in chromaffin cells is similar to the catecholamine transport system previously described in sympathetic neurons. Decreasing external Na+ from 130 to 19 mM increases the apparent Km for norepinephrine to 2.8 microM. Decreasing external norepinephrine increases the Na+ concentration required for half-maximal transport. Agents that depolarize chromaffin cells, such as acetylcholine and veratridine, significantly inhibit [3H]norepinephrine uptake. This decrease in uptake is due to an increase in the apparent Km for norepinephrine. The inhibition of [3H]norepinephrine uptake by depolarizing agents cannot be accounted for by the preferential release of newly-accumulated [3H]norepinephrine, or by the competitive inhibition of [3H]norepinephrine uptake by secreted catecholamines. The inhibition of catecholamine uptake by depolarizing agents suggests that the transport system may be regulated by the membrane potential. Norepinephrine and epinephrine that are spontaneously released from the adrenal medulla may be recaptured in vivo. The inhibition of transport by acetylcholine may prevent the re-uptake of catecholamine released during the physiological stimulation of secretion.

Acetylcholine↗
PubMedDate not supplied

Improved catecholamine histofluorescence in the developing brain based on the magnesium and aluminum (ALFA) perfusion techniques: methodology and anatomical observations.

Detailed protocols for the application of two different metal salt perfusion procedures are described for the production of superior catecholamine histofluorescence in the brains of immature rats up to 2 weeks of age. As in the adult, both magnesium and aluminum salts are highly advantageous for catecholamine histofluorescence in developing animals, and yield marked increases in sensitivity. In the magnesium-perfusion technique, animals are perfused in a simple one-step process using a hand-held syringe with cold buffer containing magnesium sulphate, formaldehyde and glyoxylic acid. The aluminum-perfusion (ALFA) technique provides even greater sensitivity and richness of detail, but requires a controlled-pressure perfusion system and a two-step perfusion process. Animals are first perfused with a room-temperature buffer containing magnesium sulphate and procain (to prevent vasoconstriction) followed by cold buffer containing aluminum sulphate and formaldehyde. In both methods, tissue pieces are subsequently freeze-dried, reacted with formaldehyde vapour and paraffin-sectioned according to the standard Falck-Hillarp procedure. Tissue pieces can also be taken from aluminum-perfused brains for simultaneous catecholamine assay using radioenzymatic methods, thereby permitting correlated histochemical and neurochemical analyses on the same brains. Many catecholamine terminal systems can be visualized in the rat brain even at birth with the ALFA procedure following pargyline pretreatment. However, the endogenous intraaxonal catecholamine concentration is so low in immature brains that the full anatomical extent of these systems cannot be reliably seen without recourse to pre-loading with an exogenously administered amine. For this purpose systemic injections of alpha-methyl-noradrenaline were extensively investigated. In combination with the ALFA procedure, such pretreatment was found to cause a dramatic increase in both the intensity and number of terminal and preterminal fibers throughout the brain. Control experiments with 6-hydroxydopamine and the catecholamine uptake blocker, nomifensine, indicate that this loading is specific for catecholamine systems. This approach has indicated that certain of the forebrain noradrenergic and dopaminergic systems are very extensive at birth, and in some regions an intermediate stage of hyperinnervation is a normal feature of ontogeny. Some of these findings are illustrated here and will also be presented in greater detail in further reports.

Aging↗
PubMedDate not supplied

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: VI. Catecholamine innervation of vasopressin and oxytocin neurons in the rhesus monkey hypothalamus.

The co-localization patterns of catecholamine varicosities and peptide-specific neuronal perikarya were assessed within the supraoptic and paraventricular nuclei in the rhesus monkey, Macaca mulatta. Formaldehyde-induced histofluorescence was coupled with the unlabelled antibody technique for the demonstration of neuropeptides. Hormone-specific neurophysin staining served to identify vasopressin and oxytocin-containing neurons in these hypothalamic nuclei. Catecholamine varicosities were seen in juxtaposition to vasopressin- and oxytocin-containing perikarya and proximal dendrites. The densest catecholamine innervation patterns were seen in the ventrolateral portion of the supraoptic nucleus; the dorsomedial portion of this nucleus received a considerably less dense innervation pattern. Oxytocin neurons were clustered in this relatively catecholamine poor region, whereas the vasopressin-containing neurons were more abundantly found in the catecholamine rich region. The paraventricular nucleus presented a considerably more complex pattern, perhaps reflecting the more diverse organization of this nucleus. Nevertheless, some separation of the oxytocin neurons, in a region less densely innervated by catecholamine varicosities, was noted. These observations confirm our earlier reports, in rat hypothalamus, that the norepinephrine innervation of the hypothalamic magnocellular neurons as seen with catecholamine histofluorescence favors the vasopressin-containing neurons over those located within the same nuclei which synthesize another neurohyphysial principal, oxytocin.

Animals↗
PubMed1987

Catecholamines bind to enkephalins, morphiceptin, and morphine.

Nuclear magnetic resonance spectroscopy, pH titration, and color reactions demonstrate that the catecholamines dopamine, epinephrine, and norepinephrine bind to the enkephalins. Binding constants are c. 6 X 10(3) per mole. Catecholamines also bound to the mu opiate receptor agonist morphiceptin (Tyr-Pro-Phe-Pro-NH2). Very little binding was found to enkephalin and morphiceptin fragments and analogues, indicating that the entire molecules are necessary. Serotonin binding peptides do not bind the catecholamines. Morphine and apomorphine, however, do bind these catecholamines (with a binding constant for morphine of c. 4 X 10(4) per mole). The opiate antagonist naloxone and a number of other drugs do not bind catecholamines. Morphine, morphiceptin, and the enkephalins also retard the formation of colored reaction products by catecholamines in vitro. These results may help to explain observations that the enkephalins are co-stored and co-transmitted with dopamine and norepinephrine, and may provide a basis for the elucidation of other known cases of peptide-monoamine co-transmission. Possible implications for understanding opiate effects on catecholamines during addiction and withdrawal are discussed, and suggestions concerning drug design are made.

Catecholamines↗
PubMed1991

Analysis of plasma catecholamines by high-performance liquid chromatography with fluorescence detection: simple sample preparation for pre-column fluorescence derivatization.

Analysis of plasma catecholamines (norepinephrine, epinephrine and dopamine) by high-performance liquid chromatography using 1,2-diphenylethylenediamine as a fluorescent reagent is described. We have developed an automatic catecholamine analyser, based on pre-column fluorescence derivatization and column switching. The analysis time for one assay was 15 min. The correlation coefficients of the linear regression equations were greater than 0.9996 in the range 10-10,000 pg/ml. The detection limit, at a signal-to-noise ratio of 3, was 2 pg/ml for dopamine. A new method of sample preparation for the pre-column fluorescence derivatization of plasma catecholamines was used. In order to protect the catecholamines from decomposition, an ion-pair complex between boric acid and the diol group in the catecholamine was formed at a weakly alkaline pH. The stabilities of plasma catecholamines were evaluated at several temperatures. After complex formation, the catecholamines were very stable at 17 degrees C for 8 h, and the coefficients of variation for norepinephrine, epinephrine and dopamine were 1.2, 4.2 and 9.3%, respectively.

Autoanalysis↗
PubMed1996

Oxidative damage caused by free radicals produced during catecholamine autoxidation: protective effects of O-methylation and melatonin.

Catecholamine autoxidation produces reactive oxygen species that have been implicated in the loss of dopaminergic neurons in the nigrostriatal region of the brain that occurs during normal aging and in Parkinson's disease. In the present study, the potential protective effects of catecholamine O-methylation and of melatonin against catecholamine autoxidation-induced protein damage were assessed in vitro using the oxygen radical absorbance capacity (ORAC) assay. The rate of oxidation of the fluorescent protein porphyridium cruentum beta-phycoerythrin (beta-PE) caused by the oxidizing agent CuSO4 was shown to be accelerated by addition of the catecholamines dopamine and L-dopa. Replacement of dopamine and L-dopa in the assay with their O-methylated metabolites 3-O-methyldopamine and 3-O-methyldopa significantly decreased the rate of beta-PE oxidation. When melatonin was added to the ORAC assay in combination with dopamine or L-dopa, the rate of beta-PE oxidation was decreased as well. These findings were consistent with the following interpretations: (1) O-methylated catecholamines are less susceptible to autoxidation than their nonmethylated precursors, and (2) melatonin, which has recently been shown to be a powerful antioxidant, is capable of scavenging free radicals produced during catecholamine autoxidation. These findings suggest that O-methylation and melatonin may be important components of the brain's antioxidant defenses against catecholamine autoxidation and may protect against consequent dopaminergic neurodegeneration.

Catecholamines↗
PubMed2004

Stress-mediated modulation of B(alpha)P-induced hepatic CYP1A1: role of catecholamines.

The present study investigated the involvement of catecholamines in stress-mediated alterations in CYP1A1 induction by benzo(alpha)pyrene (B(alpha)P) in Wistar rats. This was achieved by measuring EROD activity and CYP1A1 mRNA levels in liver tissue from rats exposed to restraint stress and B(alpha)P coupled with pharmacological modulation of peripheral and central catecholamine levels and different adrenoceptors. In a state of reserpine-induced central and peripheral catecholamine depletion, stress strongly suppressed EROD induction. Peripheral catecholamines do not appear to play a critical role in the stress-mediated modulation of EROD inducibility by B(alpha)P. Stress did not alter EROD inducibility by B(alpha)P when peripheral catecholamines were either depleted by guanethidine or supplemented by peripheral adrenaline administration. On the other hand, central noradrenergic systems appear to have a role in the stress-mediated changes in B(alpha)P-induced EROD activity and Cyp1A1 gene expression. Stimulation or blockade of noradrenaline release with atipamezole and dexmedetomidine, respectively, significantly modified the up-regulating effect of stress. Alpha1 adrenoceptors also appear to participate in the effect of stress on EROD inducibility. Alpha1-blockade with prazosin potentiated the up-regulating effect of stress, possibly preventing the down-regulating effect of noradrenaline. Beta adrenoceptors also seem to be involved directly or indirectly in the stress-mediated modulation of Cyp1A1, as propranolol (beta-antagonist) blocked the down-regulating effect of stress on B(alpha)P-induced Cyp1A1 gene expression. Plasma corticosterone alterations after stress were not related to alterations in the B(alpha)P-induced EROD activity and Cyp1A1 gene expression. In conclusion, stress appears to interfere in the regulation of B(alpha)P-induced hepatic CYP1A1 in an unpredictable manner and via signalling pathways not always directly related to catecholamines. In particular, whenever drug treatment disrupts noradrenergic neurotransmission, other stress-stimulated factors appear to modify the induction of CYP1A1. In summary, regulation of induction of hepatic CYP1A1 during stress appears to involve various components of the stress system, including central and peripheral catecholamines, which interact in a complex manner, yet to be elucidated.

Adrenergic Uptake Inhibitors↗
PubMed2003

Effects of tryptophan depletion and catecholamine depletion on immune parameters in patients with seasonal affective disorder in remission with light therapy.

BACKGROUND: Altered immunologic parameters are found in symptomatic depressed patients relative to remitted depressed patients and healthy controls. We investigated whether tryptophan depletion and catecholamine depletion induce alterations in immunologic parameters in patients with seasonal affective disorder remitted on light therapy, and whether these changes are associated with changes in mood. METHODS: Remitted patients with seasonal affective disorder underwent tryptophan depletion, catecholamine depletion, and sham depletion in a prospective randomized, double-blind crossover design. Measures of depression, plasma levels of tryptophan and catecholamine metabolites, and plasma levels of cytokines (sIL-4, IL-6, neopterin, sTNF-R1 and sTNF-R2) were obtained at baseline, and 7, 24, and 30 hours after monoamine depletion. RESULTS: Tryptophan depletion decreased plasma total and free tryptophan levels; catecholamine depletion decreased plasma 3-methoxy-4-hydroxyphenylethyleneglycol and homovanillic acid levels. Tryptophan depletion and catecholamine depletion, but not sham depletion, induced a transient exacerbation of depressive symptoms (p <.001); plasma neopterin levels increased during tryptophan depletion and catecholamine depletion (p <.05). Tryptophan depletion and catecholamine depletion induced a transient reduction of plasma sIL-4 levels (p <.05). A significant correlation was found between sIL-4R levels and depression ratings after tryptophan depletion (r = -.61, p <.05). CONCLUSIONS: The monoamine depletion-induced alterations of humoral and cellular immunity suggest a potential role of immunologic parameters in the pathophysiology of seasonal affective disorder; however, the results must be considered preliminary and require further study.

Adult↗
PubMed1997

Apamin-sensitive SK(Ca) channels modulate adrenal catecholamine release in anesthetized dogs.

We investigated the role of high conductance (BK(Ca)) and small conductance Ca2(+)-activated K+ (SK(Ca)) channels in adrenal catecholamine release in response to splanchnic nerve stimulation, acetylcholine, the nicotinic receptor stimulant 1,1-dimethyl-4-phenyl-piperazinium (DMPP), and muscarine in anesthetized dogs. The selective SK(Ca) channel blocker apamin and the selective BK(Ca) channel blocker charybdotoxin were infused into the adrenal gland through the phrenicoabdominal artery, and the cholinergic agonists were injected into the same artery. Splanchnic nerve stimulation (1, 2, 3 and 10 Hz), acetylcholine (0.75, 1.5 and 3 microg), DMPP (0.1, 0.2 and 0.4 microg) and muscarine (0.5, 1 and 2 microg) produced frequency- or dose-dependent increases in catecholamine output as measured in adrenal venous blood. Apamin infusion (1, 3 and 10 ng/min) enhanced the acetylcholine-, DMPP- and muscarine-induced increases in catecholamine output in a dose-dependent manner, but it did not affect the splanchnic nerve stimulation-induced catecholamine response. Charybdotoxin infusion (10, 30 and 100 ng/min) did not affect the increases in catecholamine output induced by the agonists and splanchnic nerve stimulation. Neither apamin nor charybdotoxin affected basal catecholamine output. These results suggest that apamin-sensitive SK(Ca) channels located in adrenal medullary cells may play an inhibitory role in the regulation of adrenal catecholamine release mediated by extrasynaptic nicotinic and muscarinic receptors.

Acetylcholine↗
PubMed1997

Potentiation of histamine-induced catecholamine secretion by ouabain in cultured bovine adrenal chromaffin cells is dependent on calcium and sodium influx.

The effects of histamine on catecholamine secretion from cultured bovine adrenal chromaffin cells were studied in the presence of ouabain, an inhibitor of Na+-K+ ATPase. The purpose of this study was to determine whether Na+, as well as Ca2+, was involved in histamine receptor-mediated catecholamine secretion. Histamine (10(-8)-10(-5) M)-induced catecholamine secretion was markedly potentiated by addition of ouabain (10(-5) M) and was inhibited by a histamine-H1 receptor antagonist or incubation in a Ca2+-free medium. Histamine-induced 45Ca2+ influx was also potentiated by addition of ouabain. Ouabain alone or in the presence of histamine increased 22Na+ influx into the cells. In an additional set of experiments, cells were preincubated in the presence or absence of Na+ for 30 min (+/- histamine and ouabain), washed and then catecholamine secretion was measured following exposure to 2.2 mM Ca2+ for 15 min. Preincubation with histamine alone with or without Na+ had no effect of Ca2+-induced secretion of catecholamine. Preincubation with ouabain alone or with ouabain plus histamine produced a slight stimulation of catecholamine secretion in Na+-free medium and a large stimulation in Na+-containing medium. These results suggested that stimulation of the histamine-H1 receptor and inhibition of the Na+ pump both increase intracellular Na+ levels, resulting in increases in Ca2+ influx and catecholamine secretion.

Adrenal Medulla↗
PubMed1997

A study of the cellular mechanism by which lead affects catecholamine secretion.

Our purpose was to determine the role of protein kinases in the mediation of the stimulatory effects of lead on catecholamine secretion. Pheochromocytoma cells were incubated for 90 minutes with W-7 (calmodulin antagonist), calphostin C (protein kinase C inhibitor), Sp-cAMPS (cAMP agonist), Rp-cAMPS (cAMP antagonist), forskolin (activator of adenylyl cyclase), or lead nitrate. Catecholamines were measured by liquid chromatography. Lead had a stimulatory effect on catecholamine secretion, whereas W-7 was inhibitory. In the presence of both lead and W-7, the response was markedly decreased compared to that seen with lead alone. Calphostin C suppressed the secretion of catecholamines; however, in the presence of lead and calphostin C, the secretion was similar to that seen with lead alone. Compared to control, Sp-cAMPS was stimulatory. Co-incubation of Sp-cAMPS and lead had a slight synergistic effect. Rp-cAMPS decreased catecholamine secretion, but co-incubation of Rp-cAMPS and lead resulted in a slight reduction compared to lead alone. Forskolin markedly increased the secretion of catecholamines, and co-incubation of lead and forskolin resulted in a synergistic increase. In the absence of calcium, lead had no effect. We conclude that lead stimulates catecholamine secretion by acting through the calcium/calmodulin-dependent protein kinase II system and not through the protein kinase C or protein kinase A system, and requires the presence of calcium for its action.

Adenylyl Cyclases↗
PubMed2003

Leptin administration to normal rats does not alter catecholamine responsiveness to insulin-induced hypoglycemia.

We previously showed, through direct neural recording in conscious rats, that hypoglycemia increases adrenal sympathetic nerve activity (SNA) both acutely and 24 hours following the second of 2 daily antecedent hypoglycemic episodes. Nonetheless, antecedent hypoglycemia impaired catecholamine responsiveness to subsequent acute hypoglycemia. Here we hypothesized that antecedent, nonhypoglycemic adrenal sympathetic stimulation by leptin would impair acute adrenal catecholamine responsiveness to subsequent hypoglycemia. We also hypothesized that acute leptin administration (after 2 days of antecedent hypoglycemia) would enhance adrenal SNA and thereby enhance catecholamine responsiveness to concurrent hypoglycemia. Leptin or saline was administered to normal rats in repeated subcutaneous injections for 2 days prior to acute insulin-induced hypoglycemia. In contrast to our hypothesis, antecedent leptin did not change catecholamine responsiveness or glycemic change in response to subsequent acute insulin administration. In additional studies, intravenous leptin or saline was acutely administered beginning 1 hour before insulin-induced hypoglycemia. All rats had been exposed to antecedent hypoglycemia. In these experiments, acute leptin did not alter catecholamine responses to insulin or glycemic change during or after termination of insulin. We conclude that antecedent nonhypoglycemic sympathetic stimulation by leptin does not alter subsequent catecholamine or glycemic responses to insulin. Moreover, concurrent leptin does not enhance catecholamine responses to insulin in rats exposed to antecedent hypoglycemia.

Adrenal Glands↗
PubMed1984

The effect of nerve growth factor (NGF) on the catecholamine contents of two human pheochromocytomas in tissue culture.

Two further cases of human pheochromocytomas were kept in tissue culture for three months. The cultures were parted into two groups: one group was treated with nerve growth factor (NGF), the other group served as the control. The catecholamines in the medium were determined radioenzymatically (Da Prada). NGF-treatment led to lower contents of adrenaline, noradrenaline and dopamine. Cultures without NGF had higher levels. Electron micrographs showed catecholamine granula during the whole culture period. NGF treated cultures contained more catecholamine granula than the untreated cultures. Though the number of catecholamine granula was increased by the NGF-treatment, the medium contained less catecholamines than in untreated cultures. It may be concluded that NGF influences the liberation of adrenaline, noradrenaline and dopamine in tissue culture: though NGF treated cells contained more catecholamine granula, the catecholamines were retained in the pheochromocytoma cells.

Aged↗
PubMed1977

Catecholamine release from the adrenal medulla.

Chromaffin cells in the adrenal medulla are specialized for the synthesis, storage, and secretion of catecholamines. These cells are innervated by preganglionic sympathetic neurons in the splanchnic nerves, and, because of their unique blood supply, are exposed to unusually high concentrations of glucocorticoids in the venous drainage from the adrenal cortex. Splanchnic nerve stimulation appears to be the most important determinant of adrenomedullary function. Chromaffin cells synthesize catecholamines from tyrosine. Splanchnic nerve stimulation leads to an increase in the activity of several of the catecholamine biosynthetic enzymes, and to an increase in the rate of catecholamine biosynthesis. Glucocorticoids cause the induction of the enzyme noradrenaline N-methyltransferase, and so are particularly important for the synthesis of epinephrine. Catecholamines are stored, together with ATP, Ca2+, and protein, in secretory vesicles known as chromaffin granules. Splanchnic nerve stimulation is the physiological stimulus for catecholamine secretion. Stimulation of the splanchnic nerves results in the release of ACh from nerve endings in the adrenal medulla. ACh causes an increase in the permeability of the chromaffin cells to Ca2+, and thereby leads to the entry of Ca2+ into the cells. Ca2+ then causes the secretion of catecholamines and of other chromaffin granule constituents from the chromaffin cells by exocytosis. The biochemical mechanisms of exocytosis, and the mechanism by which Ca2+ stimulates this process, are still unknown.

Acetylcholine↗