Neuropeptide Y inhibits chromaffin cell nicotinic receptor-stimulated tyrosine hydroxylase activity through a receptor-linked G protein-mediated process

Acetylcholine stimulation of bovine chromaffin cells results in increased norepinephrine and epinephrine secretion accompanied by a corresponding increase in synthesis. The addition of neuropeptide Y (NPY) to the culture medium prevents the increase in catecholamine synthesis but not secretion. Treatment of chromaffin cells with nicotine produces a concentration-dependent increase in tyrosine hydroxylase activity (IC50 = 1.2 microM) that is reduced if NPY is present during stimulation. Tyrosine hydroxylase activity decreases in a concentration-dependent fashion if increasing amounts of NPY are included in the culture medium, IC50 = 0.2 nM. Treatment with pertussis toxin completely prevents the effect of NPY. The rank order of potency for inhibition of tyrosine hydroxylase activity is NPY > or = [Leu31,Pro34]NPY > or = peptide YY > NPY2-36 > NPY13-36 > NPY18-36 > or = NPY26-36 >> NPY1-30, suggesting a NPY-Y1 receptor subtype. Examination of the effect of NPY on nicotine stimulation of chromaffin cell protein phosphorylation showed that NPY produces a concentration-dependent decrease in a 60-kDa protein, IC50 = 6.4 nM. The effect of NPY is pertussis toxin-sensitive. The rank order of potency is [Leu31,Pro34]NPY > or = NPY >> NPY18-36. Immunoprecipitation confirmed the identity of the 60-kDa protein as tyrosine hydroxylase.

Immunohistochemical localization of serotonin, galanin, cholecystokinin, and methionine-enkephalin in adrenal medullary cells of the chicken

The identification of adrenaline- (A) and noradrenaline- (NA) containing cells in the adrenal medulla of the chicken and colocalization of serotonin and neuropeptides with A or NA in medullary cells were investigated with the use of immunohistochemical methods. Antisera against tyrosine hydroxylase and phenylethanolamine-N-methyltransferase were used as markers for catecholamine- and A-synthesizing cells, respectively. About 70% of catecholamine-synthesizing cells also exhibited immunoreactivity for phenylethanolamine-N-methyltransferase antiserum. Therefore, these cells are A-containing ones and the rest of cells seem to be NA-containing cells. Immunoreactivity with serotonin antiserum was observed in almost all medullary cells. Galanin-immunoreactivity was also found throughout the adrenal medulla, but was stronger in A-containing cells than in NA-containing ones. Cholecystokinin-immunoreactivity was restricted to A-containing cells. Methionine-enkephalin-immunoreactivity was seen in both A- and NA-containing cells, but in about half of medullary cells. From these results, it is suggested that serotonin, galanin, cholecystokinin, and methionine-enkephalin may be co-released with A and/or NA from adrenal medullary cells of the chicken.

Sustained stimulation of rat adrenal chromaffin cell proliferation by reserpine

Chronic administration of reserpine is associated with the development of pheochromocytomas in rats. Short-term administration of reserpine to rats has been shown to stimulate chromaffin cell proliferation, leading to the hypothesis that reserpine causes pheochromocytomas indirectly by providing a proliferative backdrop on which genetic damage may occur. However, it is not known whether the proliferative effects of reserpine persist long enough for this model to be tenable. In the present investigation, the effects of reserpine on bromodeoxyuridine (BrdU) incorporation into epinephrine (E)- and norepinephrine (NE)-type chromaffin cells were studied after 1, 4, and 12 weeks of reserpine administration. Reserpine administered in the diet at 10 or 50 ppm was shown to result in a persistent mitogenic stimulation of the rat adrenal medulla. Cells that incorporated BrdU at all time points appeared to be typical E- and NE-type chromaffin cells, and the ratio of BrdU-labeled E cells to BrdU-labeled NE cells was not altered by reserpine. An additional observation was that the ratio of all E cells to all NE cells declined after Week 1 and that the decline could be accelerated by administration of reserpine. This finding suggests that neural stimulation of chromaffin cells might play a role in age-related functional changes of the adrenal medulla during early adult life. The present observations support the hypothesis that reserpine induces pheochromocytomas indirectly by increasing chromaffin cell proliferation. They also decrease the likelihood that rat pheochromocytomas arise from preferential stimulation of proliferation of a particular cell type.

Comparison of the effects of 2-deoxyglucose and immobilization on secretion and synthesis rate of catecholamines in the adrenal gland: a microdialysis study in conscious rats

Using microdialysis, extracellular 3,4-dihydroxyphenylalanine (DOPA), noradrenaline (NA) and adrenaline (AD) concentrations in the adrenal gland were monitored in conscious rats during and after 60 min of immobilization (IMM) as well as after injection of 500 mg kg(-1) 2-deoxyglucose (2-DG). IMM produced a rapid and transient increase in secretion of AD (20-fold), NA (13-fold) and DOPA (3.6-fold). This was accompanied by an increase in blood pressure (+18 mmHG) and heart rate (+146 b.p.m.). Repeated exposure to IMM (daily 60 min, for 5 days) had no influence on either catecholamine secretion of haemodynamic profiles, indicating the lack of habituation to stressful conditions. Unlike IMM, the stress of 2-DG-induced central neuroglucopenia stimulated the release of AD without affecting NA secretion. AD levels peaked (5.1-fold increase) 40-60 min after 2-DG injection and then slowly declined. 2-DG induced no changes in blood pressure but reduced the heart rate (-48 b.p.m.). In separate experiments, steady-state dialysate DOPA levels, reached during continuous infusion of decarboxylase inhibitor NSD 1015 into adrenal gland tissue through the dialysis probe, served as an index of adrenomedullary tyrosine hydroxylase (TH) activity. IMM evoked a marked response in TH activity (DOPA formation increased 2.7-fold), which remained elevated 60 min after the cessation of stress when AD and NA secretion had already fallen to baseline. After 2-DG, despite significant hormonal response, adrenal TH activity was unchanged. These results give clear evidence that IMM and 2-DG-induced neuroglucopenia may be considered as two different types of stressful stimuli.

Alteration of catecholamine phenotype in transgenic mice influences expression of adrenergic receptor subtypes

Agonist-induced regulation of adrenergic receptors (ARs) has an important role in controlling physiological functions in response to changes in catecholamine stimulation. We previously generated transgenic mice expressing phenylethanolamine N-methyltransferase (PNMT) under the control of a human dopamine beta-hydroxylase gene promoter to switch catecholamine specificity from the norepinephrine phenotype to the epinephrine phenotype. In the present study, we first examined changes in catecholamine metabolism in peripheral tissues innervated by sympathetic neurons of the transgenic mice. In the transgenic target tissues, a high-level expression of PNMT led to a dramatic increase in the epinephrine levels, whereas the norepinephrine levels were decreased to 48.6-87.9% of the nontransgenic control levels. Analysis of plasma catecholamines in adrenalectomized mice showed large amounts of epinephrine derived from sympathetic neurons in the transgenic mice. Subsequently, we performed radioligand binding assays with (-)-[125I]iodocyanopindolol to determine changes in binding sites of beta-AR subtypes. In transgenic mice, the number of beta 2-AR binding sites was 56.4-74.9% of their nontransgenic values in the lung, spleen, submaxillary gland, and kidney, whereas the beta 1-AR binding sites were regulated in a different fashion among these tissues. Moreover, northern blot analysis of total RNA from the lung tissues showed that down-regulation of beta 2 binding sites was accompanied by a significant decrease in steady-state levels of the receptor mRNA. These results strongly suggest that alteration of catecholamine specificity in the transgenic sympathetic neurons leads to regulated expression of the beta-AR subtypes in their target tissues.

Targeted disruption of the glucocorticoid receptor gene blocks adrenergic chromaffin cell development and severely retards lung maturation

The role of the glucocorticoid receptor (GR) in glucocorticoid physiology and during development was investigated by generation of GR-deficient mice by gene targeting. GR -/- mice die within a few hours after birth because of respiratory failure. The lungs at birth are severely atelectatic, and development is impaired from day 15.5 p.c. Newborn livers have a reduced capacity to activate genes for key gluconeogenic enzymes. Feedback regulation via the hypothalamic-pituitary-adrenal axis is severely impaired resulting in elevated levels of plasma adrenocorticotrophic hormone (15-fold) and plasma corticosterone (2.5-fold). Accordingly, adrenal glands are enlarged because of hypertrophy of the cortex, resulting in increased expression of key cortical steroid biosynthetic enzymes, such as side-chain cleavage enzyme, steroid 11 beta-hydroxylase, and aldosterone synthase. Adrenal glands lack a central medulla and synthesize no adrenaline. They contain no adrenergic chromaffin cells and only scattered noradrenergic chromaffin cells even when analyzed from the earliest stages of medulla development. These results suggest that the adrenal medulla may be formed from two different cell populations: adrenergic-specific cells that require glucocorticoids for proliferation and/or survival, and a smaller noradrenergic population that differentiates normally in the absence of glucocorticoid signaling.

Catecholamines in human keratinocyte differentiation

Human keratinocytes have the capacity to synthesize catecholamines from L-tyrosine, which in turn is produced from L-phenylalanine via phenylalanine hydroxylase. This enzyme activity is controlled by the supply of the essential cofactor/electron donor (6R)5,6,7,8 tetrahydrobiopterin (6-BH4). Undifferentiated keratinocytes express high levels of the rate-limiting enzymes for the de novo synthesis of 6-BH4, i.e., GTP-cyclohydrolase-1, and for its recycling, i.e., 4a-hydroxytetrahydrobiopterin dehydratase. As a consequence of 6-BH4 synthesis, phenylalanine hydroxylase is activated, yielding L-tyrosine, which in the presence of excess 6-BH4 turns on the biosynthesis of catecholamines via the rate-limiting enzyme tyrosine hydroxylase. Therefore, undifferentiated keratinocytes contain high levels of the catecholamine system yielding sufficient levels of norepinephrine and epinephrine, required for the induction of beta-2-adrenoceptors. Stimulation of beta-2-adrenoceptors by epinephrine causes a rise in intracellular calcium via extracellular influx. This event corresponds with keratinocyte differentiation. In differentiated keratinocytes, all enzyme activities involved in 6-BH4, L-tyrosine, and epinephrine biosynthesis are decreased, resulting in significantly lower levels of epinephrine and a concomitant decrease in the expression of beta-2-adrenoceptors. These data strongly suggest a connection between catecholamine biosynthesis, beta-2-adrenoceptor expression, calcium flux, and the differentiation of keratinocytes in human epidermis.

Nonadrenal epinephrine-forming enzymes in humans. Characteristics, distribution, regulation, and relationship to epinephrine levels

Animal studies indicate that nonadrenal tissues may synthesize epinephrine (E). Here we demonstrate phenylethanolamine N-methyltransferase (PNMT) and/or nonspecific N-methyltransferase (NMT) enzymatic activity in human lung, kidney, heart, liver, spleen, and pancreas. There was a significant overall correlation (r = 0.34) between tissue PNMT and E. PNMT and NMT in human tissues differed in substrate and inhibitor specificity, thermal stability, and antigenicity. By these criteria, PNMT in human lung and in human bronchial epithelial cells were indistinguishable from adrenal PNMT. PNMT and/or NMT activity were present in red blood cells (RBCs), and cancer cell lines. Human kidney, lung, and pancreas showed immunohistochemical staining with an antibody to adrenal PNMT. RBC PNMT activity was lower in males than females and was increased in hyperthyroidism and decreased in hypothyroidism. PNMT activity in a human bronchial epithelial cell line was dramatically increased by incubation with dexamethasone. E and 3H-E levels in plasma and urine during an intravenous infusion of 3H-E into humans indicated that kidney may synthesize half of urinary E. We conclude that PNMT and NMT are widely distributed in human tissues, that they may synthesize E in vivo and are influenced by glucocorticoid and thyroid hormones.

Noradrenaline is essential for mouse fetal development

Catecholamines such as noradrenaline and adrenaline have been implicated in numerous physiological processes but, although catecholamine synthesis begins at mid-gestation, previous studies have provided little evidence for any role in early development. Furthermore, there are several case reports of humans with noradrenaline deficiency. To investigate this, we use gene targeting to produce mice lacking dopamine beta-hydroxylase and therefore unable to synthesize noradrenaline or adrenaline. We report here that in heterozygous mothers, most homozygous embryos died in utero, and only about 5% reached adulthood. Survival probably depends on catecholamine transfer across the placenta because, in homozygous mothers, all embryos die in utero. Mortality was due to lack of noradrenaline in utero because it could be prevented by treatment with dihydroxyphenylserine, a precursor that can be converted to noradrenaline in the absence of dopamine beta-hydroxylase. Mutant embryos had a histological phenotype similar to that of embryos deficient in tyrosine hydroxylase, suggesting that death might be due to cardiovascular failure.

Triple immunohistochemical staining for bromodeoxyuridine and catecholamine biosynthetic enzymes using microwave antigen retrieval

A method was developed for detection of bromodeoxyuridine (BrdU) in conjunction with other antigens in formalin-fixed paraffin sections with microwave antigen retrieval. The method was applied to rat adrenal medulla to demonstrate S-phase nuclei in epinephrine-producing cells stained for immunoreactive phenylethanolamine-N-methyltransferase and in norepinephrine-producing cells stained for immunoreactive tyrosine hydroxylase. The quality of staining for all three antigens was comparable to or better than that previously obtained with other techniques. This method provides an efficient tool for studying turnover of subpopulations of adrenal chromaffin cells. It should also be widely applicable to other cells and tissues.

Discrepancy between PNMT presence and relative lack of adrenaline production in extra-adrenal pheochromocytoma

Among catecholamine synthesizing enzymes, phenylethanolamine-N-methyltransferase (PNMT) exists only in adrenal and extra-adrenal pheochromocytoma has been believed not to produce adrenaline. However, adrenaline production is clinically active in some extra-adrenal cases. To investigate this controversy, the localization of catecholamine synthesizing enzymes was studied by immunohistochemical staining in extra-adrenal and adrenal cases. The results showed that PNMT was expressed not only in many cases of adrenal pheochromocytoma, but also in extra-adrenal pheochromocytoma. It is suspected that little adrenaline production in extra-adrenal cases is attributable to a lack of a good environment for the activation of PNMT by a high concentration of glucocorticoids.

Influence of GBR 12909 and d-amphetamine on indices of catecholamine synthesis and release in rat adrenal glands

Our previous results have shown that dopamine (DA) levels in rat adrenal glands could be increased by DA D2 receptor agonists and that this effect could be blocked by the DA D2 antagonists domperidone (supposed to be only peripherally active) and raclopride. The data now presented are aiming to characterize the effects of two indirect DA agonists, GBR 12909 and d-amphetamine, on adrenal DA levels (taken as an index of adrenal catecholamine synthesis rate), and on adrenaline (Ad) levels in the heart (assumed to reflect the Ad release from the adrenal medulla). After various periods of s.c. drug administration the rats were decapitated and tissue catecholamine levels were determined in adrenal glands, hearts and forebrains according to standard techniques by high performance liquid chromatography (HPLC) with electrochemical detection. GBR 12909 (15 and 3 mg/kg), a highly selective DA-uptake inhibitor, induced a pronounced dose dependent increase in adrenal DA and heart Ad, though not until 4 hr after administration; this effect persisted for at least 16 hr. However, a statistically significant decrease in forebrain DOPAC was observed already after 30 min. The GBR 12909 effects on adrenal DA and heart Ad were blocked by raclopride, but not by domperidone, suggesting a central site of action. d-Amphetamine, in both doses used (2.5 and 5 mg/kg) induced a statistically significant decrease in forebrain DOPAC between 30 min and 2 hr, and an increase in adrenal DA. Heart Ad was not significantly changed.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammalian adrenal chromaffin cells coexpress the epinephrine-synthesizing enzyme and neuronal properties in vivo and in vitro

Adrenal chromaffin cells and neurons of the sympathetic ganglia are derived from common precursors in the neural crest. The phenotype of the sympathoadrenal progenitor cell is unknown, but adult chromaffin cells are distinguished by the expression of phenylethanolamine-N-methyltransferase (PNMT) and the lack of neurofilament (NF) and neuritic processes. Mature neurons have processes and express NF, but are PNMT-. We hypothesize that embryonic adrenal cells are multipotential. This implies that the cells can coactivate all the traits characteristic of mature sympathetic neurons and chromaffin cells and then selectively extinguish expression of either the chromaffin or the neuronal traits, depending on the environment. We further asked whether this repression is plastic and can be environmentally modified in adult chromaffin cells. We demonstrate that, in vivo, embryonic (e-) rat adrenal cells coexpress PNMT and the intermediate- and high-molecular-weight neurofilaments at e-15.5 (21%), e-16.5 (40%), and e-20.5 (23%). When cultured in complete or glucocorticoid-depleted media for 5 to 14 days, 20% of adult bovine chromaffin cells which remain PNMT+ reexpress NF and extend NF+ and PNMT+ processes. Both the expression of NF and the extension of neurites are inhibited by the addition of 10(-7) M dexamethasone to complete media. We conclude that the embryonic adrenal medullary cells simultaneously express traits of mature chromaffin cells and neurons and that the phenotypes remain labile in the adult mammalian chromaffin cell. In addition, coexpression of PNMT, NF, and neurite extension are not mutually exclusive in either the embryonic or adult adrenal chromaffin cell.

Bulbospinal neuropeptide Y-immunoreactive neurons in the rat: comparison with adrenaline-synthesising neurons

Immunohistochemistry and retrograde tracing using cholera toxin B subunit colloidal gold (CTB-gold) has been used to identify neurons in the medulla that contain neuropeptide Y and project to the area of the intermediolateral cell column in either the upper (T2-T4) or the lower (T8-T9) thoracic spinal cord. The rostrocaudal distributions of neuropeptide Y neurons and neuropeptide Y/CTB-gold neurons have been compared with the distributions of adrenaline-synthesising, phenylethanolamine N-methyltransferase-containing neurons and phenylethanolamine N-methyltransferase/CTB-gold neurons visualised in adjacent sections. In particular areas of the rostral medulla similarities in the numbers and distributions of neuropeptide Y neurons and phenylethanolamine N-methyltransferase neurons suggested a coexistence of the peptide within the catecholamine neurons. However, at the most rostral levels of the rostral ventral medulla, the large numbers of phenylethanolamine N-methyltransferase neurons were not matched by similar numbers of neuropeptide Y neurons, so that the phenylethanolamine N-methyltransferase neurons in this area could not all contain neuropeptide Y. In the rostral ventral medulla fewer neuropeptide Y/CTB-gold neurons than phenylethanolamine N-methyltransferase/CTB-gold neurons were observed, so that these bulbospinal peptide neurons might define a subset of the phenylethanolamine N-methyltransferase/CTB-gold neurons, accounting for 25% of the total phenylethanolamine N-methyltransferase bulbospinal projection from the rostral ventral medulla. Other neuropeptide Y/CTB-gold neurons in the dorsal medulla are also likely to contain phenylethanolamine N-methyltransferase. Finally, a population of neuropeptide Y/CTB-gold neurons was identified in the caudal ventral medulla, these neurons appear not to contain catecholamine synthesising enzymes.

Activities of acetylcholinesterase, choline acetyltransferase, and catecholamine production in the spinal cord of the axolotl Ambystoma mexicanum during forelimb regeneration

Amputation of an axolotl limb causes severance of the brachial nerves, followed by their regeneration into a blastema. It is known that these nerves provide a neurotrophic factor to blastemal cells. To approach the problem of the response of spinal cord nerve centers to forelimb amputation, we have studied biosynthetic activities in the nerve centers involved in axonal injury during limb regeneration. We report that the acetylcholinesterase (AChE) activity in the spinal cord is elevated 2 days (+69%) and 7 days (+28%) after limb amputation compared with levels in unamputated control animals, but is not significantly elevated at 3 h or 15 days. The percentages of slow (3.6S and 6.0S) and fast (18S) sedimenting forms of AChE progressively decrease 2 and 7 days after amputation, while those of intermediate sedimenting forms (10.5S and 14.0S) increase. Fifteen days after amputation, lower molecular weight forms return to the control level, but the heavy molecular weight form of AChE is absent as at 7 days; consequently intermediate molecular weight forms are in a greater proportion than the other two forms. Choline acetyltransferase activity was measured only 2 days after amputation (when AChE was at its highest level). It increases by about 34% with regard to the controls. Adrenaline is higher than controls 2 days after amputation, while noradrenaline is not significantly modified. The metabolic changes observed in the spinal cord during limb regeneration probably are the result of a general reaction to the stress of amputation (transection of brachial nerves) and regeneration of nerve fibers, since similar metabolic activities were observed after a simple denervation of the two unamputated forelimbs.

An association of primary aldosteronism and adrenaline-secreting phaeochromocytoma

1. Two patients with adrenaline-only secreting phaeochromocytomas and primary aldosteronism were studied. 2. Urinary adrenaline levels were raised and plasma adrenaline was not suppressed normally following administration of clonidine. Plasma aldosterone to plasma renin activity ratios were repeatedly elevated. 3. Both had large intra-adrenal phaeochromocytomas visible on computerized tomography (CT) scanning. Surrounding adrenal cortical tissue contained an adenoma in one and nodular hyperplasia in the other. 4. Following removal of the adrenal gland containing the phaeochromocytoma, plasma and urinary adrenaline levels, and plasma aldosterone to plasma renin activity ratios returned to normal. 5. Adrenaline-only secreting phaeochromocytomas and primary aldosteronism have been rarely diagnosed even as separate entities, but reliable screening tests are now available. 6. Simultaneous presence of these two conditions of hormone excess is probably a chance occurrence. Alternatively, there may be a genetic predisposition to endocrine dysplasia, or an interaction between the contiguous medullary and cortical tissues, particularly after the normal architecture has been disturbed by an enlarging phaeochromocytoma.

Kinetics of adrenal medullary cells

The adrenal medulla of mammals has a heterogeneous population of cells. In adults most are epithelial cells containing a particular type of cytoplasmic granule. Based on a variety of cytochemical and ultrastructural studies it is now accepted that 2 different adrenal medullary chromaffin cell types can be distinguished, i.e. noradrenaline (NA) and adrenaline (A) synthesising and storing cells. Other cell types present in the adrenal medulla include neuronal elements comprising either cell bodies or nerve fibres entering from outside the gland (extrinsic innervation). It is assumed that adrenal medullary cells have a limited life span, i.e. they are replaced after a certain period. Data on this replacement process are scarce. Recently, we initiated an investigation into this question using cytochemical procedures that enable the detection of DNA duplication to measure mitotic activity in individual cells. Female Sprague-Dawley rats aged 22-36 wk received a single i.p. injection of BrdU or BrdU was administered continuously via an implanted mini-osmotic pump. Cell nuclei that had incorporated BrdU were demonstrated using an indirect immunoperoxidase staining technique. At 1 h after a single injection, 0.46 +/- 0.07% of the adrenal medullary (chromaffin) cells were labelled. This increased to 0.77 +/- 0.08% after 12 h with no further increase during the next 7-8 d. With continuous infusion of BrdU the fraction of labelled cells increased gradually to about 40% after 73 d (the longest period studied). These results show that in adult rats adrenal medullary cells are able to divide, although at a slow rate (renewal rate of about 1%/day).

Adrenal cortical and medullary responses to acetylcholine and vasoactive intestinal peptide in conscious calves

1. Adrenal responses to intra-aortic infusions of acetylcholine and vasoactive intestinal peptide (VIP) have been investigated in functionally hypophysectomized calves given exogenous adrenocorticotrophic hormone (ACTH, 2 ng min-1 kg-1 I.V.). 2. Infusions of VIP at a dose of 0.13 micrograms min-1 kg-1 caused a small, but significant increase in adrenaline and noradrenaline output which was, however, far below the level recorded previously in response to acetylcholine (0.7 micrograms min-1 kg-1). In contrast, these doses of the two agonists produced closely similar rises in adrenal cortisol output. 3. The steroidogenic effects of acetylcholine and VIP were found to be strictly additive and no evidence of potentiation was obtained in relation to either cortical or medullary responses or in the case of any of the cardiovascular responses which were monitored. 4. Intra-aortic infusions of VIP, at a dose which produced a substantial increase in adrenal steroidogenesis (0.065 micrograms min-1 kg-1), had no effect on the output of catecholamines, enkephalin-like immunoreactivity or corticotrophin-releasing factor, either in the presence or absence of acetylcholine. 5. It is concluded that VIP is unlikely to modulate adrenal medullary responses to muscarinic stimulation in this species as it has been claimed to do in the rat and does not potentiate adrenal steroidogenesis in response to acetylcholine as it does to ACTH.

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.

Evidence for an increased catecholamine synthesis in rat adrenal glands following stimulation of peripheral dopamine receptors

In studies on peripheral dopamine (DA) turnover in our department evidence has accumulated that changes in adrenal DA levels induced by varying degrees of neurogenic stimulation roughly reflect changes in the catecholamine (CA) synthesis rate. The question arises if changes in DA levels in rat adrenals induced by different DA D-2 receptor agonists and previously reported from our laboratory, also indicate changes in CA synthesis. After various periods of drug administration rats were killed by decapitation and tissue CA levels in adrenals and forebrain were determined by HPLC-EC. The potent inhibitor of DA-beta-hydroxylase FLA 63 (40 mg/kg i.p.) increased adrenal DA by 186% after 1 h and by 423% after 3 h. The DA D-2 agonist quinpirole (0.2 mg/kg s.c., 30 min) itself increased adrenal DA by 55-60% compared to control. In FLA 63 pretreated rats quinpirole increased adrenal DA levels by further 127% (FLA 63-1 h), resp. 122% (FLA 63-3 h) than did FLA 63 itself. The DA D-2 receptor antagonist domperidone (3 mg/kg s.c., 150 min) blocked the quinpirole effect both in saline and FLA 63 (3 h) pretreated rats. Adrenal DOPAC was changed in similar manner as adrenal DA in FLA 63 pretreated rats. No significant changes either in adrenal NA or A were observed after FLA 63 pretreatment. Under the present experimental conditions adrenal DA may thus mainly be looked upon as an intermediate in the synthesis of NA and A, and the elevation of DA induced by DA D-2 receptor stimulation as a consequence of increased catecholamine synthesis.

Hypertension and a tumor of the glomus jugulare region. Evidence for epinephrine biosynthesis

Glomus jugulare tumors have been reported to secrete norepinephrine and cause severe hypertension with features similar to pheochromocytoma. In contrast, epinephrine secretion has not been observed in these neoplasms. This has been attributed to the absence of the norepinephrine-methylating enzyme, phenylethanolamine-N-methyltransferase (PNMT), required for epinephrine synthesis. We report a patient with severe hypertension caused by a glomus tumor that secreted norepinephrine and epinephrine. Following selective venous sampling, catecholamines were quantified by radioenzymatic assay. Marked elevations in norepinephrine and epinephrine release were localized to the glomus tumor. The enzymes involved in catecholamine biosynthesis, including PNMT and tyrosine hydroxylase, were identified immunocytochemically in the tumor. The glomus tumor had staining patterns identical to those observed within normal rat glomus cell. Hypertension resolved with resection of the functioning tumor. This is the first report of PNMT in a functioning paraganglioma of the glomus jugulare region. The factors that determine why functional activity is expressed only rarely by paraganglioma remain undefined.

Loss of C1 and C3 epinephrine-synthesizing neurons in the medulla oblongata in Parkinson's disease

We used immunohistochemical analysis to determine whether medulla oblongata neurons containing phenylethanolamine N-methyltransferase (PNMT) are affected in patients who died with idiopathic Parkinson's disease (n = 7) compared with age-matched control subjects who died with nonneurological diseases (n = 8). Transverse sections (50 microns) of medulla were prepared either for conventional neuropathological examination or for the immunohistochemical demonstration of PNMT. Immunopositive neurons at approximately 30 rostrocaudal levels, evenly spaced throughout the whole medulla, were mapped and cells in each section were counted with a camera lucida system linked to a computer. In the ventrolateral medulla, from the level of the obex to 11 mm rostral to the obex where the C1 group of neurons is located, there were 7,631 +/- 844 PNMT-positive neurons in control brains and 3,604 +/- 1,051 in brains affected by Parkinson's disease (47% of control). Many PNMT-positive neurons contained Lewy bodies. We observed a previously undescribed midline (C3) group of PNMT-positive neurons in normal brains, and this group was also severely affected (12% of control) in parkinsonian brains. Neither the C2 group nor the small PNMT-positive neurons in the nucleus tractus solitarii were significantly reduced in numbers but there was a reduction in the numbers of melanin-pigmented cells in both the ventrolateral (50% of control) and the dorsomedial (79% of control) region. Our results demonstrate a selective loss of C1 and C3 PNMT-positive neurons, providing the first quantitative evidence for damage to these presumed brainstem sympathetic premotor neurons in Parkinson's disease. These changes may underlie some of the autonomic symptoms occurring in this condition.

Production of catecholamines in the human epidermis

Cell-free extracts from human full thickness skin (i.e., epidermis and dermis), suction blister roofs (i.e., epidermis) and from human keratinocytes express biopterin-dependent tyrosine hydroxylase a well as phenylethanolamine-N-methyl transferase, both representing key enzymes for the biosynthesis of epinephrine. These enzyme activities could not be detected in cell extracts from human melanocytes and human fibroblasts. Since keratinocytes in the human epidermis, and in cell cultures, express a high density of beta-2-adrenoceptors, and this signal transduction system regulates intracellular calcium homeostasis, it can be concluded that epinephrine production in the epidermis activates calcium transport via the beta-2-adrenoceptor system. Our results show for the first time that the human epidermis has the capacity to independently produce epinephrine.