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PubMed2003

Amperometric detection of quantal catecholamine secretion from individual cells on micromachined silicon chips.

We have fabricated electrochemical electrodes in picolitersized wells for measuring catecholamine release from individual cells with millisecond resolution. Each well-electrode roughly conforms to the shape of the cell in order to capture a large fraction of released catecholamine with high time resolution. Using this device, we can resolve spikes in amperometric current corresponding to quantal catecholamine release via exocytosis. In addition, we have combined amperometric recording on the chip with patch-clamp recordings of membrane capacitance as an assay of exocytosis. A quantitative comparison of the two methods suggests that a large fraction of catecholamine release is oxidized on the surface of the well-electrode. This technology has applications in cell-based biosensor development, high-throughput screening of drugs, and basic science investigations.

Animals↗
PubMed1989

Steady-state catecholamine distribution in chromaffin granule preparations: a test of the pump-leak hypothesis of general anesthesia.

The molecular mechanism of general anesthesia is not understood. Possible modes of action include binding at a protein site, such as a receptor or channel, or physical effects on membrane lipid properties. The pump-leak hypothesis suggests that anesthetics perturb the bilayer of synaptic vesicles, thereby increasing ionic permeability. This results in decay of proton gradients required for transport and accumulation of neurotransmitters. The subsequent loss of neurotransmitters from synaptic vesicles reduces the efficiency of synaptic transmission and results in the anesthetized state. We have determined the effects of general anesthetics on certain parameters of enzyme activity and membrane permeability relevant to the pump-leak hypothesis. We used chromaffin granules as a convenient model system and focused on clinically relevant anesthetic concentrations (ED50), quantitative measurements of permeability changes, and the kinetics of gradient decay. General anesthetics at ED50 have little or no effect on the proton-transport ATPase activity, but do cause modest increments in proton permeability that change the catecholamine distribution in actively pumping chromaffin granule preparations. We found that pH gradients do not collapse entirely under these conditions and that only a fraction of total catecholamine is lost from the chromaffin granules. When total collapse is induced by other means, efflux of catecholamines occurs with a half-time near 30 min. These results suggest that if the pump-leak hypothesis is valid, then very small losses of catecholamines must be sufficient to induce anesthesia. We conclude that the weight of evidence favors other mechanisms, notably direct binding of anesthetics to sensitive proteins.

Adrenal Glands↗
PubMed2001

Effects of substitution at serine 40 of tyrosine hydroxylase on catecholamine binding.

Phosphorylation of Ser40 in the regulatory domain of tyrosine hydroxylase activates the enzyme by increasing the rate of dissociation of inhibitory catecholamines [Ramsey, A. J., and Fitzpatrick, P. F. (1998) Biochemistry 37, 8980-8986]. To probe the structural basis for this effect and to ascertain the ability of other amino acids to functionally replace serine and serine phosphate, the effects of replacement of Ser40 with other amino acids were determined. Only minor changes in the Vmax value and the Km values for tyrosine and tetrahydropterin were seen upon replacement of Ser40 with alanine, valine, threonine, aspartate, or glutamate, in line with the minor effects of phosphorylation on steady-state kinetic parameters. More significant effects were seen on the binding of dopamine and dihydroxyphenylalanine. The affinity of the S40T enzyme for either catecholamine was very similar to that of the wild-type enzyme, while the S40E enzyme was similar to the phosphorylated enzyme. The S40D enzyme had an affinity for DOPA comparable to the phosphorylated enzyme but a higher affinity for dopamine than the latter. With both catecholamines, the S40V and S40A enzymes showed intermediate levels of activation. The results suggest that the serine hydroxyl contributes to the stabilization of the catecholamine-inhibited enzyme. In addition, the S40E enzyme will be useful in further studies of the effects of multiple phosphorylation on tyrosine hydroxylase, while the alanine enzyme does not provide an accurate mimic of the unphosphorylated enzyme.

Amino Acid Substitution↗
PubMedDate not supplied

Phorbol ester facilitates 45Ca accumulation and catecholamine secretion by nicotine and excess K+ but not by muscarine in rat adrenal medulla.

Several investigators have shown that tumour promoter phorbol esters mimic the effects of endogenous diacylglycerol to activate a second messenger, protein kinase C. These phorbol esters have proved to be valuable tools for exploring the role of protein kinase C in many cellular functions. We demonstrate here that secretion of catecholamines evoked from the rat adrenal gland by stimulation of splanchnic nerves, excess potassium (K+) and nicotine is facilitated by phorbol 12,13-dibutyrate. An inhibitor of protein kinase C, polymixin B, produced concentration-dependent inhibition of the evoked secretion, and the effect was reversed by the phorbol ester. Furthermore, we show that an increase in the accumulation of radioactively labelled calcium (45Ca) obtained in the adrenal medulla after stimulation with nicotinic agonists and excess K+ is further enhanced by phorbol ester. Muscarine-evoked secretion of catecholamines, which depends on mobilization of intracellularly bound Ca2+, was not associated with an increase in 45Ca2+ uptake, and phorbol ester did not facilitate either catecholamine secretion or 45Ca2+ accumulation. We suggest that protein kinase C is involved in the exocytotic secretion of catecholamines by regulating the influx of Ca2+ through voltage-sensitive and nicotine receptor-linked Ca2+ channels of rat chromaffin cells.

Adrenal Medulla↗
PubMed1982

Effects of salt intake and renal denervation on catecholamine catabolism and excretion.

My study was designed to measure the effect of salt intake on secretion and catabolism of catecholamines by the kidney and renal nerve contributions to urinary catecholamine excretion. Rats with one chronically denervated (DEN) and one innervated (INN) kidney were fed either high salt (HS) or low salt (LS) diets for 5 to 14 days. Under Inactin anesthesia rats were expanded with isotonic saline while LS rats received 10% mannitol to produce the same urine flow rates. Epinephrine excretion was ten times greater from LS than from HS rats; however, epinephrine/inulin excretion was the same from INN and DEN kidneys. Norepinephrine/inulin excretion was 30% less from DEN than from INN kidneys in both HS and LS rats (P less than 0.01). Dopamine/inulin excretion was 20% less from the DEN kidney than from the INN kidney of HS rats (P less than 0.05), but the 5% lower dopamine/inulin excretion from DEN than from INN of LS rats was not significant. Norepinephrine and dopamine tubular secretions from the rats, estimated by microinjecting radioactive tracers beneath the renal capsule, were 21 and 65%, respectively. After the microinjection, 68% of radioactive norepinephrine and 65% of radioactive dopamine were secreted unchanged. Catecholamine secretion rates and catabolism were not altered by denervation or different salt intakes. Estimated neural NE release was 1 ng/min in INN kidneys of both HS and LS rats; dopamine release 0.6 ng/min in kidneys of HS rats. Thus, when anesthesized, renal nerves contribute 30% to urinary NE and up to 21% to urinary dopamine excretion. Salt intake did not influence NE release from renal nerves or catecholamine secretion and catabolism by the kidney, but salt depletion decreased the renal nerve contribution to urinary dopamine excretion.

Animals↗
PubMed1998

Catecholamine transport by the organic cation transporter type 1 (OCT1).

1. Liver and kidney extract adrenaline and noradrenaline from the circulation by a mechanism which does not seem to be one of the classical catecholamine transporters. The hypothesis that OCT1 is involved the organic cation transporter type 1 which exists in rat kidney and liver-was tested. 2. Based on human embryonic kidney cells (293), we constructed a cell line which stably expresses OCT1r (293OCT1r cells). Transfection with OCT1 resulted in a transport activity not only for prototypical known substrates of OCT1 such as 3H-1-methyl-4-phenylpyridinium and 14C-tetraethylammonium but also for the catecholamines 3H-adrenaline, 3H-noradrenaline (3H-NA) and 3H-dopamine (3H-DA), the indoleamine 3H-5-hydroxytryptamine (3H-5HT) as well as the indirect sympathomimetic 14C-tyramine. 3. For 3H-DA, 3H-5HT and 3H-NA, at non-saturating concentrations, the rate constants for inwardly directed substrate flux (kin) were 6.9+/-0.8, 3.1+/-0.2, and 1.2+/-0.1 microl min(-1) mg protein(-1). In wild type cells (293WT) the corresponding kin's were considerably lower, being 0.94+/-0.40, 0.47+/-0.08 and 0.23+/-0.05 microl min(-1) mg protein ' (n=12). The indirectly determined half-saturating concentrations of DA, 5HT, and NA were 1.1 (95% c.i.: 0.8, 1.4), 0.65 (0.49, 0.86), and 2.8 (2.1, 3.7) mmol l(-1) (n=3). 4. Specific 3H-DA uptake in 293OCT1r cells was resistant to cocaine (1 micromoll(-1)), 3H-5HT uptake was resistant to citalopram (300 nmol l(-1)) and 3H-NA uptake was resistant to desipramine (100 nmoll(-1)), corticosterone (1 micromol l(-1)), and reserpine (10 nmoll(-1)) which rules out the involvement of classical transporters for biogenic amines. 5. The findings demonstrate that OCTI efficiently transports catecholamines and other biogenic amines and support the hypothesis that OCT1 is responsible for hepatic and renal inactivation of circulating catecholamines.

Animals↗
PubMed2004

Long-term plasma catecholamines in patients with hypertension and left ventricular hypertrophy treated with losartan or atenolol: ICARUS, a LIFE substudy.

Hypertension is a major risk factor for morbidity and mortality. Plasma catecholamines are linked to the pathogenesis of hypertension. Pharmacological intervention, including treatment with beta-blockers, reduces cardiovascular mortality and morbidity. In the Losartan Intervention For Endpoint reduction in hypertension (LIFE) study, the angiotensin receptor blocker losartan significantly reduced cardiovascular end points compared to the beta-blocker atenolol. Thus, for the first time, one drug was shown to be superior to another in hypertension. The present substudy examined the effects of atenolol vs losartan treatment on plasma catecholamines at rest and during hyperinsulinaemia in a cohort of 86 LIFE patients. Plasma adrenaline increased significantly from placebo treatment at baseline to year 1 of treatment (P<0.0001), and also during hyperinsulinaemia (P<0.0001). Plasma noradrenaline did not change significantly from placebo treatment at baseline to year 1, but increased significantly during hyperinsulinaemia both at baseline and at year 1 (P<0.0001 for both). There were no differences in plasma catecholamines or the relative changes between the two treatment arms at any stage. In a subset of 42 patients examined also at years 2 and 3, these findings were confirmed during long-term treatment. Thus, losartan had an effect on plasma catecholamines comparable to that with the beta-blocker atenolol in patients with hypertension and left ventricular hypertrophy at rest and during hyperinsulinaemia. We find it unlikely that a difference in sympathetic activity explains the outcome benefits of losartan over atenolol in the LIFE study.

Aged↗
PubMed2006

Effect of pre-treatment with catecholamines on cold preservation and ischemia/reperfusion-injury in rats.

Treatment of organ donors with catecholamines reduces acute rejection episodes and improves long-term graft survival after renal transplantation. The aim of this study was to investigate the effect of catecholamine pre-treatment on ischemia/reperfusion (I/R)- and cold preservation injury in rat kidneys. I/R-injury was induced by clamping the left kidney vessels for 60 min along with a contralateral nephrectomy. Cold preservation injury was induced by storage of the kidneys for 24 h at +4 degrees Celsius in University of Wisconsin solution, followed by syngeneic transplantation. Rats were pre-treated with either dopamine (DA), dobutamine (DB), or norepinephrine (2, 5, and 10 microg/kg/min, each group) intravenously via an osmotic minipump for 24 h before I/R- and cold preservation injury. Pre-treatment with DA (2 or 5 microg/kg/min) and DB (5 microg/kg/min) improved recovery of renal function after I/R-injury and dose dependently reduced mononuclear and major histocompatibility complex class II-positive cells infiltrating the kidney after I/R-injury. One day after I/R-injury, upregulation of transforming growth factor (TGF)-beta 1 and 2 and phosphorylation of p42/p44 mitogen-activated protein kinases was observed in kidneys of animals treated with DA or DB. DA (5 microg/kg/min) and DB (5 microg/kg/min) pre-treatment reduced endothelial cell damage after 24 h of cold preservation. Only DA pre-treatment improved renal function and reduced renal inflammation after 24 h of cold preservation and syngeneic transplantation. Our results demonstrate a protective effect of pre-treatment with catecholamines on renal inflammation and function after I/R- or cold preservation injury. This could help to explain the potent organoprotective effects of catecholamine pre-treatment observed in human kidney transplantation.

Animals↗
PubMed1966

The release of adenosine triphosphate catabolites during the secretion of catecholamines by bovine adrenal medulla.

1. AMP, adenosine, inosine and hypoxanthine were present in perfusates collected from bovine adrenal glands during periods when catecholamine secretion was evoked by injections of carbamoylcholine. 2. The molar ratio of catecholamines to ATP-catabolites present in the perfusates was similar to that of catecholamines to ATP in chromaffin granules. 3. ATP added to the perfusing medium was extensively degraded during passage through bovine adrenal glands. 4. The mechanism of catecholamine secretion is discussed.

Adenine Nucleotides↗
PubMed1970

The effect of a cross-bridging thiol reagent on the catecholamine fluxes of adrenal medulla vesicles.

The thiol groups of the vesicular protein of bovine adrenal medulla were allowed to react with the bifunctional thiol reagent bis-(N-maleimidomethyl) ether and with the monofunctional thiol reagent N-ethylmaleimide, and the ATP-dependent and -independent catecholamine fluxes of the modified preparations were studied. 1. During the initial phase of the reaction bis-(N-maleimidomethyl) ether blocks twice as many thiol groups as does N-ethylmaleimide at equimolar concentrations. 2. Labelling of the bis-(N-maleimidomethyl) ether-protein compound with [(14)C]-cysteine shows that 70-80% of the blocked thiol groups are interconnected by the bifunctional thiol reagent. 3. At a low extent of reaction (1.5mol of thiol groups/10(6)g of protein) the catecholamine efflux is diminished. If more than 2mol of thiol groups/10(6)g of protein are blocked, the efflux is enhanced whichever thiol reagent is applied. 4. If 2-4mol of thiol groups/10(6)g of protein are blocked the inhibition of the catecholamine influx increases linearly with the proportion of the thiol groups blocked. 5. ATP protects the catecholamine influx and the adenosine triphosphatase activity against bis-(N-maleimidomethyl) ether poisoning somewhat less effectively than against N-ethylmaleimide poisoning.

Adenosine Triphosphatases↗
PubMed2001

Role of catecholamine signaling in brain and nervous system functions: new insights from mouse molecular genetic study.

Catecholamines, including dopamine and norepinephrine, are the principal neurotransmitters that mediate a variety of the central nervous system functions, such as motor control, cognition, emotion, memory processing, and endocrine modulation. Dysfunctions in catecholamine neurotransmission are implicated in some neurologic and neuropsychiatric disorders. Recent mouse molecular genetic approaches provide genetic evidence for an important role of catecholamines in brain functions. In this paper, I describe the phenotype of mutant mice with impairments in dopamine or norepinephrine biosynthesis. Mice defective in dopamine biosynthesis exhibit severe motor dysfunctions characterized by a reduction in spontaneous locomotion and cataleptic behavior, and defects in drug-induced hyperactivity at the juvenile stage. They also exhibit defects in the acquisition of conditioned learning dependent on tone stimulus. These results indicate that dopamine is essential for motor control and emotional learning during postnatal development, possibly through nigrostriatal and mesolimbic neuronal pathways. On the other hand, mice carrying the mutation in the gene encoding tyrosine hydroxylase (the rate-limiting enzyme of catecholamine biosynthesis) display a reduction in norepinephrine biosynthesis. This leads to deficits in latent learning and long-term memory formation of different conditioned learning paradigms. The results indicate that norepinephrine is essential for the consolidation process of long-term memory, suggesting that norepinephrine may control the neuronal activity in the cerebral cortex or amygdala to maintain the memory process of conditioned learning.

Animals↗
PubMed2002

Ca(2+) -independent vesicular catecholamine release in PC12 cells by nanomolar concentrations of Pb(2+).

Effects of Pb(2+) on vesicular catecholamine release in intact and ionomycin-permeabilized PC12 cells were investigated using carbon fibre microelectrode amperometry. Changes in intracellular Pb(2+) and Ca(2+) were measured from indo-1 fluorescence by confocal laser scanning microscopy. Depolarization of intact cells and superfusion of permeabilized cells with saline containing > or = 100 microm Ca(2+) rapidly evokes quantal catecholamine release. Superfusion with up to 10 microm Pb(2+) -containing saline evokes release of similar catecholamine quanta after a concentration-dependent delay. Thresholds to induce exocytosis within 30 min of exposure are between 1 and 10 microm Pb(2+) in intact cells and between 10 and 30 nm Pb(2+) in permeabilized cells. Additional inhibition of exocytosis occurs in permeabilized cells exposed to 10 microm Pb(2+). Using membrane-impermeable and -permeable chelators it is demonstrated that intracellular Ca(2+) is not required for Pb(2+) -induced exocytosis. In indo- 1-loaded cells Pb(2+) reduces the fluorescence intensity after a concentration-dependent delay, whereas the fluorescence ratio, indicating intracellular Ca(2+) concentration, remains unchanged. The delay to detect an increase in free intracellular Pb(2+) (> or = 30 nm) is much longer than the delay to Pb(2+) -induced exocytosis, indicating that cytoplasmic components buffer Pb(2+) with high affinity. It is concluded that Pb(2+) acts as a high-affinity substitute for Ca(2+) to trigger essential steps leading to vesicular catecholamine release, which occurs when only approximately 20% of the intracellular high-affinity binding capacity ( approximately 2 attomol/cell) is saturated with Pb(2+).

Animals↗
PubMed1997

Cardiovascular and catecholamine responses to static exercise in partially curarized humans.

Neural control of the circulation was evaluated during static exercise in 19 subjects by the determination of heart rate (HR), mean arterial pressure (MAP), cardiac output (CO) and plasma catecholamines. Influence from central command was evaluated during contractions with weakened muscles following partial curarization and reflex influence from metaboreceptors was assessed by post-exercise muscle ischaemia. Static handgrip increased HR and more so MAP and CO and MAP remained elevated during post-exercise muscle ischaemia. With partial curarization plasma catecholamines were also increased (P < 0.05). Two-leg extension increased all variables and during post-exercise muscle ischaemia elevations of HR, MAP and CO were maintained (P < 0.05). With partial curarization HR, MAP and plasma noradrenaline were even greater during the contraction. With the involvement of both legs during static exercise, reflex influence from the muscles elevated blood pressure by way of HR and CO and the importance of central command was detectable for HR and MAP as plasma catecholamines became elevated. However, the results indicate a separation between a central command influence on HR and CO related to an increase in plasma catecholamines during a handgrip, while the reflex influence on blood pressure was directed towards total peripheral resistance.

Adult↗
PubMed1997

The effect of an intravenous infusion of IGF-I and insulin on IGFBP-1, IGFBP-3, acid labile subunit, free and bound IGF-I, catecholamines and potassium in normal volunteers during an amino acid and glucose clamp.

OBJECTIVES: To investigate the effects of IGF-I and insulin at doses equipotent with respect to hypoglycaemic effect on IGF-I concentrations (free and bound), IGF binding proteins, catecholamines and potassium levels. DESIGN: A glucose and amino acid clamp technique was used to investigate the effects of a 3 h intravenous infusion of either IGF-I 43.7 pmol/kg/min (20 micrograms/kg/h) or insulin 3.4 pmol/kg/min (0.5 mU/kg/min). MEASUREMENTS: Circulating levels of total IGF-I, free and bound IGF-I, Insulin, IGFBP-1, IGFBP-3, ALS, catecholamines and potassium were measured. PATIENTS: 6 normal human volunteers aged 21-49. RESULTS: During the IGF-I infusion, IGF-I levels increased (P < 0.01) (26.6 +/- 2.8-88.9 +/- 14.2 nmol/l) and insulin levels fell (P < 0.05) (16.7 +/- 2.9-7.2 +/- 1.6 mu/l). During the insulin infusion, insulin levels increased (P < 0.01) (11.7 +/- 1.6-56.7 +/- 16 mu/l) and there was no change in IGF-I. There was no significant change in IGFBP-3 or ALS during the IGF-I or insulin infusions. There was a significant (P < 0.05) fall in IGFBP-1 levels from 27.1 +/- 4.1-8.06 +/- 1.6 micrograms/l during the insulin infusion and a significant (P < 0.05) rise during the first 120 min of IGF-I infusion from 28.6 +/- 6.3-67.9 +/- 10.6 micrograms/l. There was a significant (P < 0.05) increase in free IGF-I and IGF-I bound to the 150 and 50 kD plasma fractions during the IGF-I infusion. At basal and the end of the IGF-I infusion adrenaline levels (pmol/l) were: 173 +/- 22 and 174 +/- 28; dopamine levels (pmol/l) were: 415 +/- 87 and 470 +/- 87; plasma potassium (mmol/l) was 4.2 +/- 0.06 and 3.56 +/- 0.13. At basal and the end of the insulin infusion adrenaline levels (pmol/l) were: 160 +/- 38 and 163 +/- 21; dopamine levels (pmol/l) were: 238 +/- 26 and 316 +/- 31; plasma potassium (mmol/l) was 4.2 +/- 0.07 and 3.92 +/- 0.17. There were no significant changes in plasma catecholamine concentrations with either infusion but potassium concentrations were significantly (P < 0.05) reduced during the IGF-I infusion. CONCLUSIONS: We conclude that an infusion of IGF-I resulted in increased levels of both free and bound IGF-I. IGF-I and insulin under conditions of adequate substrate supply have acute effects on IGFBP-1 and potassium physiology, but have little effect on IGFBP-3, ALS or catecholamines.

Adult↗
PubMed1999

Syndrome of body fat redistribution in HIV-1-infected patients: relationships to cortisol and catecholamines.

OBJECTIVE: Alterations of body fat distribution have been recently reported in HIV-infected patients. We aimed to investigate whether the hormones modulating adipose tissue metabolism could be implicated. SUBJECTS: We investigated twenty-eight HIV-infected patients who had developed abdominal fat, combined with peripheral lipodystrophy in 25 cases and 'buffalo hump' in 2 cases, but who had otherwise improved on antiretroviral therapies. Twelve patients with no change in body fat, matched for age, disease control and treatment, were studied as controls. MEASUREMENTS: Body composition was assessed by bioelectrical impedance analysis. Subcutaneous (SAT) and visceral (VAT) compartments of total abdominal adipose tissue (TAT) were measured by computed tomography. Resting metabolic rate (RMR) was assessed by indirect calorimetry. Endocrine investigations included plasma thyroid hormones, cortisol, testosterone, oestradiol and 24-hour urinary free cortisol (UFC) and catecholamines. RESULTS: Despite similar body mass index, the patients with body fat alterations showed significantly larger VAT and higher VAT:TAT ratio than controls (P = 0.002 and 0.0001, respectively). In these patients, RMR was significantly higher than estimated according to the Harris-Benedict formula (+ 19.7 +/- 11.6 %, P = 0.0001) and correlated with VAT (r = 0.58, P = 0.003) and 24-hour urinary output of catecholamines (r = 0.67, P = 0.002), that was significantly increased in comparison with controls (1737 +/- 1228 vs 476 +/- 292 nmol, P = 0.013). We also found a significant correlation between VAT and UFC (r = 0.41, P = 0.042) that was absent in controls, although levels of UFC were similar in the two groups. CONCLUSIONS: Our data suggest that body fat redistribution may involve cortisol and catecholamine actions. While high release of catecholamines may enhance RMR through increased lipolysis, cortisol may promote central fat storage. These effects might be related both to persistent hormonal responses to stress becoming inappropriate while disease control improved and to an increased sensitivity of visceral adipose tissue to cortisol in affected patients.

Adipose Tissue↗
PubMed1999

Myosin light chain kinase inhibitors and calmodulin antagonist inhibit Ca(2+)- and ATP-dependent catecholamine secretion from bovine adrenal chromaffin cells.

We have used stage-specific assays for ATP-dependent priming and for Ca(2+)-activated triggering in the absence of ATP to examine the effects of myosin light chain kinase (MLCK) inhibitors, ML-9 and ML-7, and calmodulin antagonists, W-7 and trifluoperazine (TFP), on regulated exocytosis in beta-escin-permeabilized bovine adrenal chromaffin cells. Ca2+ (0.1-30 microM) induced a significantly greater secretion of catecholamines in the presence of MgATP (2 mM) than in the absence of MgATP. ML-9 (30 and 100 microM), ML-7 (30 and 100 microM), W-7 (30 and 100 microM) and TFP (10 and 30 microM) inhibited the Ca(2+)-induced catecholamine secretion in the presence of MgATP, but did not affect the catecholamine response to Ca2+ in the absence of MgATP. In intact cells all these compounds inhibited catecholamine secretion in responses to acetylcholine (100 microM) and high K+ (40 mM). The results obtained in permeabilized cells suggest that the calmodulin-MLCK system plays an essential role in the ATP-requiring priming stage but not in the Ca2(+)-triggered fusion step in the exocytotic process in bovine adrenal chromaffin cells.

Acetylcholine↗
PubMed1996

Involvement of medullary catecholamine cells in neuroendocrine responses to systemic cholecystokinin.

Systemic administration of cholecystokinin (CCK) stimulates neurosecretory oxytocin (OT) and tuberoinfundibular corticotrophin releasing factor (CRF) cells of the hypothalamus. Data from previous studies suggest that A2 noradrengeric neurons of the dorsomedial medulla contribute to the OT cell response, but the role of other medullary catecholamine cells remains unclear. Using c-fos expression as a marker for cellular activity, we have found that CCK (100 micrograms/kg, i.p.) activates substantial populations of tyrosine hydroxylase and phenyl-N-methyl-transferase immunoreactive cells in the medulla, consistent with recruitment of overlapped noradrenergic and adrenergic cell populations in both the ventrolateral and dorsomedial medulla. In the ventrolateral medulla there was a particularly prominent activation of C1 adrenergic neurons at the level of the obex. To directly test the contribution of VLM catecholamine cells to hypothalamic neuroendocrine cell responses to CCK, animals were prepared with unilateral VLM lesions corresponding to those areas that had displayed the most marked response to CCK. VLM lesioned animals treated with CCK displayed a significant although small reduction in paraventricular nucleus (PVN) OT cell c-fos expression ipsilateral to the lesion, but no change in the responses of supraoptic nucleus OT cells or in cells of the medial parvocellular PVN, many of which are CRF cells. These findings indicate that VLM catecholamine cells make little contribution to hypothalamic neuroendocrine cell responses to CCK and thus serve to further highlight the role of dorsomedial catecholamine cells. However, it is now apparent that, in addition to A2 noradrenergic cells, CCK treatment also recruits C2 adrenergic cells of the dorsomedial medulla, many of which have previously been shown to project to the PVN.

Animals↗
PubMed2003

In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis.

Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.

2-Methoxyestradiol↗