Adrenal Dopamine Research Articles

Revealing the biological mechanism of acupuncture in alleviating excessive inflammatory responses and organ damage in sepsis: a systematic review.

Sepsis is a systemic inflammation caused by a maladjusted host response to infection. In severe cases, it can cause multiple organ dysfunction syndrome (MODS) and even endanger life. Acupuncture is widely accepted and applied in the treatment of sepsis, and breakthroughs have been made regarding its mechanism of action in recent years. In this review, we systematically discuss the current clinical applications of acupuncture in the treatment of sepsis and focus on the mechanisms of acupuncture in animal models of systemic inflammation. In clinical research, acupuncture can not only effectively inhibit excessive inflammatory reactions but also improve the immunosuppressive state of patients with sepsis, thus maintaining immune homeostasis. Mechanistically, a change in the acupoint microenvironment is the initial response link for acupuncture to take effect, whereas PROKR2 neurons, high-threshold thin nerve fibres, cannabinoid CB2 receptor (CB2R) activation, and Ca2+ influx are the key material bases. The cholinergic anti-inflammatory pathway of the vagus nervous system, the adrenal dopamine anti-inflammatory pathway, and the sympathetic nervous system are key to the transmission of acupuncture information and the inhibition of systemic inflammation. In MODS, acupuncture protects against septic organ damage by inhibiting excessive inflammatory reactions, resisting oxidative stress, protecting mitochondrial function, and reducing apoptosis and tissue or organ damage.

Biological variations in adrenal gland response to immobilization and glucoprivation stressors in rats

The aim of the present study was to investigate the potential variation in adrenal gland response to two different types of acute stressors, immobilization and glucoprivation. Twenty-four adult male albino rats were randomly divided into three main groups (8 rats/group): a) control, i.e. non-stressed group, b) immobilized group (IS), and c) glucoprivated (GS) group. Plasma catecholamines (CAs), including epinephrine (E), norepinephrine (NE), dopamine (DA), adrenocorticotrophic hormone (ACTH), corticosterone (CORT), sodium, potassium, and glucose were measured. Adrenals weight, CAs levels, and nitric oxide (NO) content were also determined. Immobilized group of rats showed significantly higher plasma NE and DA levels along with asignificantly lower adrenal NE content than GS group. On the other hand, GS group was associated with significantly higher plasma E, ACTH, CORT, glucose, and Na+ levels as well as higher adrenal DA and NO levels along with significantly lower plasma K+ levels and adrenal E content in comparison with IS group. Stress response is unique according to the nature of the stressor. Adrenal glands play akey role in this stress-induced differentiated response probably via modulation of its adreno-medullary and/or adrenocortical hormone levels in order to assign the body cope with different types of stress challenges during the life.

Coping with Chronic Social Stress in Mice: Hypothalamic-Pituitary-Adrenal/ Sympathetic-Adrenal-Medullary Axis Activity, Behavioral Changes and Effects of Antalarmin Treatment: Implications for the Study of Stress-Related Psychopathologies

The aim of this study was to analyze the individual differences that lead to the development of psychopathological changes in response to chronic social stress. We also assessed the ability of an antagonist of the corticotrophin-releasing hormone (CRH) receptors to reverse the effects of stress. Male adult mice were exposed to repeated defeat experiences for 21 days using a sensorial contact model. After 18 days of defeat, two groups of subjects were established (active and passive), according to their behaviors during social confrontation. Antalarmin treatment was given for 4 and 6 days. The results corroborated previous data indicating that subjects who adopted a passive coping strategy had higher corticosterone levels after 21 days of defeat and decreased resting levels 3 days later. Moreover, they showed higher resting expression levels of hypothalamic CRH than their active counterparts. On day 24, the experimental animals were subjected to another social defeat to determine whether the stress response remained. The increase in corticosterone and hypothalamic CRH levels was similar for all of the stressed subjects, but the passive subjects also had a greater CRH response in the amygdala. Passive subjects had decreased levels of adrenal dopamine β-hydroxylase, tyrosine hydroxylase and plasma adrenaline compared to the active subjects, and lower plasma noradrenaline levels than manipulated controls. The passive profile of physiological changes in both the hypothalamic-pituitary-adrenal and sympathetic-adrenal-medullary (SAM) axes has been associated with changes related to mood disorders, such as posttraumatic stress disorder and depression. The active coping profile is characterized by similar corticosterone resting levels to controls and increased SAM activity. Both profiles showed alterations in the novel palatable and forced swimming tests, with the passive profile being the most vulnerable to the effects of stress in this last test. Pharmacological treatment with antalarmin failed to reverse the effects of stress.

Increase in adrenal dopamine following 6-hydroxydopamine.

Increase in adrenal dopamine following 6-hydroxydopamine.

Catecholamine release and excretion in rats with immunologically induced preganglionic sympathectomy.

Plasma and urinary catecholamines were quantified to assess global sympathoadrenal function in rats with preganglionic lesions caused by antibodies to acetylcholinesterase (AChE). Rats were given intravenous injections of normal mouse IgG or murine monoclonal anti-acetylcholinesterase IgG (1.5 mg). Five or 16 days afterward, basal blood samples were taken through indwelling arterial cannulate. A few hours later, the rats were immobilized for 10 min in padded restrainers, and another blood sample was drawn. HPLC determinations showed low basal levels of norepinephrine and epinephrine (< 0.2 ng/ml in all rat plasma samples). In control rats, immobilization stress increased levels of plasma catecholamines up to 35-fold. In rats tested 5 days after injection of antibody, the norepinephrine response was much smaller (15% of control), and the epinephrine response was nearly abolished (5% of control). There was some recovery at 16 days after antibody treatment, but stress-induced catecholamine release was still markedly impaired. Reduced stress-induced release was not accompanied by major changes in tissue epinephrine or norepinephrine (heart, spleen, adrenal glands, and brain), although adrenal dopamine content dropped by 60%. Urinary excretion was studied in parallel experiments to gain insight into the effects of AChE antibodies on basal sympathoadrenal activity. Epinephrine, norepinephrine, dopamine, and selected metabolites were quantified in 24-h urine samples collected at frequent intervals for 30 days after antibody injection. No statistically significant changes were detected in the urinary output of dopamine, 3-methoxytyramine, normetanephrine, or 3-methoxy-4-hydroxyphenylglycol. On the other hand, epinephrine and norepinephrine output increased sharply at the time of antibody injection and then fell significantly below control levels. Norepinephrine output returned to normal after 2 weeks, but epinephrine output remained depressed. These results are consistent with previous evidence of widespread and persistent antibody-mediated damage to the preganglionic sympathetic system.

Effects of dopamine β-hydroxylase genotype and disulfiram inhibition on catecholamine homeostasis in mice

Dopamine beta-hydroxylase (DBH) converts dopamine (DA) to norepinephrine (NE), thus playing a critical role in catecholamine metabolism. We examined the effects of Dbh gene dosage and the DBH inhibitor disulfiram in mice with zero, one, or two null Dbh alleles (+/+, +/-, and-/- mice). DBH protein levels in adrenal and prefrontal cortex (PFC) and adrenal DBH activity were proportional to number of wild-type alleles. Adrenal DA was slightly increased in+/- mice and markedly increased (80-fold) in -/- mice compared to wild-type animals. While adrenal NE and epinephrine (EPI) were undetectable in -/- mice, adrenal concentrations of NE and EPI were similar in +/+ and +/- mice, suggesting that the increase in DA maintains the normal rate of beta-hydroxylation in Dbh +/- mice. Disulfiram had little effect on adrenal catecholamine levels, regardless of genotype or dose. NE was absent in the PFC of -/- mice, but only slightly reduced in +/- animals compared to wild-type animals. PFC DA was increased twofold in +/- mice and fivefold in -/- mice, and the NE to DA ratio was reduced ( approximately 35%) in +/- mice, compared to wild-type mice. Disulfiram significantly decreased PFC NE and increased DA in +/+ and +/- animals, with the disulfiram and genotype effects on the PFC NE to DA ratio apparently additive. The data reveal potentially important and apparently additive effects of Dbh genotype and disulfiram administration on PFC catecholamine metabolism. These effects may have implications for genetic control of DBH activity in humans and for understanding therapeutic effects of disulfiram.

Increased Angiotensin II AT1 Receptor Expression in Paraventricular Nucleus and Hypothalamic-Pituitary-Adrenal Axis Stimulation in AT2 Receptor Gene Disrupted Mice

Angiotensin II AT₂ receptor gene-disrupted mice have increased blood pressure and response to angiotensin II, behavioral alterations, greater response to stress, and increased adrenal AT₁ receptors. We studied hypothalamic AT₁ receptor binding and mRNA by receptor autoradiography and in situ hybridization, adrenal catecholamines by HPLC, adrenal tyrosine hydroxylase mRNA by in situ hybridization and pituitary and adrenal hormones by RIA in AT₂ receptor-gene disrupted mice and wild-type controls.To confirm the role of adrenal AT₁ receptors, we treated wild-type C57 BL/6J mice with the AT₁ antagonist candesartan for 2 weeks, and measured adrenal hormones, catecholamines and tyrosine hydroxylase mRNA. In the absence of AT₂ receptor transcription, we found increased AT₁ receptor binding in brain areas involved in the regulation of the hypothalamic-pituitary-adrenal axis, the hypothalamic paraventricular nucleus and the median eminence, and increased adrenal catecholamine synthesis as shown by higher adrenomedullary tyrosine hydroxylase mRNA and higher adrenal dopamine, norepinephrine and epinephrine levels when compared to wild-type mice. In addition, in AT₂ receptor gene-disrupted mice there were higher plasma adrenocorticotropin (ACTH) and corticosterone levels and lower adrenal aldosterone content when compared to wild-type controls. Conversely, AT₁ receptor inhibition in CB57 BL/6J mice reduced adrenal tyrosine hydroxylase mRNA and catecholamine content and increased adrenal aldosterone content. These results can help to explain the enhanced response of AT₂ receptor gene-disrupted mice to exogenous angiotensin II, support the hypothesis of cross-talk between AT₁ and AT₂ receptors, indicate that the activity of the hypothalamic-pituitary-adrenal axis parallels the AT₁ receptor expression, and suggest that expression of AT₁ receptors can be dependent on AT₂ receptor expression. Our results provide an explanation for the increased sensitivity to stress in this model.

Copper Deficiency Alters Rat Dopamine β-Monooxygenase mRNA and Activity

Dopamine β-monooxygenase (DBM), a cuproenzyme, converts dopamine to norepinephrine in selected cells. Studies were conducted in albino rats to resolve the known paradox of DBM after copper deficiency in which metabolite analyses of tissues suggest lower activity, whereas direct assay of homogenates suggests enhanced activity. After 4 wk of postweanling copper deficiency, male Holtzman rats exhibited 1.4-fold higher adrenal DBM activity and 1.8-fold higher adrenal DBM mRNA levels than copper-adequate rats. Mixing experiments did not support the existence of endogenous activators or inhibitors. Adrenal catecholamine content indicated lower norepinephrine, higher dopamine and unaffected epinephrine content in copper-deficient compared with copper-adequate rats. Studies in 22-d-old male Sprague-Dawley offspring of dams started on copper deficiency at d 7 of gestation indicated similar results for adrenal DBM mRNA, a 1.75-fold increase compared with copper-adequate pups. Adrenal dopamine content was higher in female copper-deficient offspring compared with controls, but norepinephrine was not lower. Medulla oblongata/pons DBM mRNA concentration was higher in 22-d-old copper-deficient female but not male rats compared with controls. Six weeks of copper repletion to the 22-d-old rats restored adrenal DBM mRNA levels to control values. Enzyme assay and RNA results are consistent with enhanced formation of DBM in adrenal gland and noradrenergic cell bodies of copper-deficient rats. The molecular signal may not be solely lower norepinephrine content because adrenal DBM mRNA changes were evident in both nutritional models, whereas the norepinephrine content was altered only in the postnatal model.

Effect of cholinergic blockade on glucocorticoid regulation of NPY and catecholamines in the rat adrenal gland.

Catecholamines and neuropeptide Y (NPY) levels were determined in the adrenals of rats treated for 2.5 days with chlorisondamine (6 mg/day), a nicotinic ganglionic blocking agent, metyrapone (66 mg/day), an inhibitor of the 11 beta-hydroxylase activity or both metyrapone and chlorisondamine. Chlorisondamine induced a significant increase in adrenal weight (31%) without significant rise in hypothalamic CRH content, plasma ACTH level and plasma corticosterone concentration. This drug was unable to affect significantly dopamine (DA), norepinephrine (NE) and epinephrine (E) content of the adrenals; in contrast, it induced a significant decrease (90%) of plasma NE and E levels. Chlorisondamine induced no change in adrenal NPY content as well as NPY mRNA level determined by Northern blot but significantly increased NPY plasma level. Metyrapone-treatment induced a significant drop of plasma corticosterone level and elicited a significant reduction of hypothalamic CRH content, a rise (460%) of the plasma ACTH concentration associated with a significant increase (18%) of the adrenal weight. A marked increase of DA (240%) and significant decrease of E (22%) in the adrenal gland were observed in response to metyrapone treatment. In addition, metyrapone induced a drop (23%) in plasma E level. In both the adrenals and the plasma, the ratio E/NE was significantly reduced by metyrapone treatment. Metyrapone elicited a significant increase of adrenal NPY content (88%) as well as of NPY mRNA revealed by Northern blot analysis but was unable to significantly affect NPY plasma level. The effects of chlorisondamine, given in combination with metyrapone on both hypothalamic CRH content and plasma ACTH level, were similar to those induced by metyrapone given alone. Chlorisondamine-mediated pharmacological ganglionic blockade increased metyrapone-induced adrenal hypertrophy and adrenal DA storage but prevented metyrapone-induced depletion of adrenal E as well as increase of the adrenal NPY mRNA level and NPY content. Chlorisondamine-induced elevation of plasma NPY level was not observed under metyrapone treatment. Present data suggest that the increase in adrenal NPY synthesis in response to metyrapone treatment is mediated by transsynaptic cholinergic activation and implies nicotinic receptors. On the other hand, adrenal TH may be regulated by additional or different mechanisms, which possibly involve nonnicotinic transmission. Present work also suggests that the suppression of the glucocorticoid feedback inhibition of hypothalamic CRH neurons could stimulate sympathoneuronal outflow and consequently elicit transsynaptic cholinergic activation of adrenal neuropeptide Y gene expression.

In vivo activity of tyrosine hydroxylase in rat adrenal glands following administration of quinpirole and dopamine

Using adrenal dopamine as indicator we have previously obtained evidence that quinpirole and several other agonists on dopamine D 2-like receptors acutely stimulate the synthesis of adrenal catecholamines. In the present study we measured the effect of quinpirole and dopamine on the hydroxylation of tyrosine in the adrenals, using the method of DOPA (3,4-dihydroxyphenylalanine) accumulation following the administration of the inhibitor of aromatic l-amino acid decarboxylase NSD 1015 (3-hydroxybenzylhydrazyne). In view of the large amounts of catecholamines in the adrenal tissue samples, this necessitated a modification of the method for analysing DOPA. Both quinpirole and dopamine significantly enhanced the rate of DOPA accumulation in the adrenals, indicating stimulation of adrenal tyrosine hydroxylase. The effect of dopamine was blocked by domperidone, a dopamine D 2 receptor antagonist that penetrates poorly into the central nervous system. Thus the effect of dopamine, which itself penetrates poorly into the central nervous system, was presumably mediated peripherally. Similarly epinine, i.e. the N-methyl derivative of dopamine, appeared to enhance adrenal catecholamine synthesis, as indicated by an elevated adrenal dopamine level. The data support the view that stimulation of peripherally located dopamine D 2-like receptors can enhance the rate of adrenal catecholamine synthesis by stimulating the activity of tyrosine hydroxylase.

Acute dopaminergic influence on plasma adrenaline levels in the rat

This study was aimed at in vivo characterisation of the possible role of dopamine receptors in the modulation of adrenaline release from the adrenal medulla in rats. Quinpirole (0.3, 1 and 3 mg/kg s.c., 30 min), an agonist at dopamine D 2-like receptors, induced a statistically significant increase not only in adrenal dopamine but also in plasma and heart adrenaline levels. The effects of the lowest dose of quinpirole were blocked by domperidone (5 mg/kg s.c., 150 min). Implantation of catheters followed by blood sampling appeared to be a stressful procedure, inducing itself an elevation of adrenal dopamine and of heart adrenaline by 100 and 250%, respectively. To explore the possibility of determining the plasma levels of adrenaline without blood sampling, regression modelling was performed by means of partial least squares regression (PLS) using treatment and levels of heart adrenaline and adrenal dopamine as predictor variables. The selected variables were found to be good predictors of plasma adrenaline levels. Accordingly, the increase in adrenal dopamine and heart adrenaline levels following administration of the dopamine autoreceptor agonist, talipexole, and the classical non-selective dopamine receptor agonist, apomorphine, were interpreted as indicators of the increased adrenomedullary adrenaline release. Neither of the dopamine D 2 receptor antagonists used, i.e. domperidone, supposed to have only peripheral effects, nor raclopride, had significant effects on adrenal dopamine and heart adrenaline. Our results support the presence of peripherally located dopamine D 2-like receptors, capable of acutely stimulating not only the synthesis of catecholamines, but also the release of adrenaline from adrenals in the conscious rat.

I. c. v. dopamine fails to alter adrenomedullary function in rats.

Intracerebroventricularly (i.c.v.) administered dopamine (50-400 micrograms/kg, 30 min; 400 micrograms/kg, 2 and 4 h) did not induce statistically significant changes in heart adrenaline (presumed to represent the adrenaline release from the adrenals). Only the highest dose (400 micrograms/kg, 30 min) brought about significant increase in adrenal dopamine (reflecting the catecholamine synthesis), accompanied by increase in heart dopamine, indicating leakage of dopamine into the peripheral circulation. The results did not support involvement of the central dopamine receptors in the short-term control of the adrenomedullary function in rats.

Effects of MPP+ on catecholamine levels in adrenal glands and heart of rats.

The effects of MPP+ (2.5-20 mg/kg) on the adrenal glands and heart were investigated in rats. At various periods after s.c. drug administration the rats were decapitated and tissue catecholamine levels were determined by means of HPLC with electrochemical detection. Adrenal dopamine (DA) levels were reduced at 2-8 h after MPP+ administration, but this decrease was followed by an elevation after 16 h and return to the control values after one week. Three successive injections of MPP+ caused a statistically significant elevation in adrenal DA, one day, with a tendency to elevation four and seven days after the last injection, whereas a severe (up to 96%) decrease in heart noradrenaline (NA) was found one day after the last injection. Seven days after the last injection a 50% depletion of NA in the heart was still observed. Pretreatment with GBR 12909 (30 mg/kg, 4h) blocked the MPP+ (10 mg/kg, 2 h) induced reduction of adrenal DA levels, but at the same time GBR 12909 failed to block the effects of MPP+ in the heart. One day after three successive daily injections of MPP+ (10 mg/kg each), the DA-uptake inhibitor GBR 12909 (30 mg/kg, 6 h) could still induce an increase in adrenal DA. MPP+ appears to lack persistent cytotoxic action in the adrenal medulla but rather to cause a transient inhibition of DA synthesis followed by a compensatory stimulation. The inhibition can be blocked by specific inhibitor of the DA-uptake mechanism, suggesting a direct effect of MPP+ taken up by adrenomedullary cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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 D 2 receptor agonists and that this effect could be blocked by the DA D 2 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 16hr. 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. Domperidone (3 mg/kg, 3 hr) blocked the increasing effect of d-amphetamine (2.5 mg/kg, l hr) on adrenal DA, suggesting a peripheral site of action. The data indicate a complex involvement of dopaminergic mechanisms in adrenomedullary function.

Adrenal medullary adaptations and cardiovascular regulation after 6-hydroxydopamine treatment in rats

Experiments were conducted to assess the pattern of activation of adrenal medullary adrenaline (ADR) and noradrenaline (NA) chromaffin cells following damage to sympathetic neurons with 6-hydroxydopamine (6-HDA, 100 mg/kg per day for 7 days, s.c.). 6-HDA treatment resulted in a sustained elevation in urinary ADR excretion, suggesting that the adrenal medulla was continuously stimulated. Further evidence of neural stimulation of the adrenal medulla was demonstrated by a persistent elevation of adrenal medullary dopamine (DA) content, an indicator of catecholamine synthesis. The increase in synthetic rate was associated with a significantly augmented medullary NA and ADR content. However, NA content was elevated after only 1 day of treatment, whereas, ADR became elevated after the second day, a finding that suggests a differential activation of the two populations of chromaffin cells. Cardiac and kidney NA contents were reduced by 97 and 87%, respectively, and BP increments to stimulation of the thoracolumbar spinal cord of pithed rats (0.5 to 16 Hz) were attenuated by more than 75% by 6-HDA. Moreover, the residual BP responses were abolished by adrenalectomy. Thus the results indicate that the changes in adrenal CA disposition may be related to a greater reliance upon the adrenal medulla to maintain blood pressure (BP) following damage to sympathetic neurons, and further, the findings are consistent with the possibility that ADR and NA chromaffin cells are separately controlled.

Repeated immobilization stress increases the binding of c-Fos-like proteins to a rat dopamine beta-hydroxylase promoter enhancer sequence.

Repeated immobilization stress elicits a large elevation in adrenal dopamine beta-hydroxylase (DBH) mRNA levels. This study attempts to analyze the molecular mechanism of increased DBH gene expression in stress. Adrenomedullary nuclear proteins were prepared from controls and rats exposed to various intervals of immobilization stress. Electrophoretic mobility shift assays showed that repeated stress led to increased binding of adrenomedullary nuclear factors to a cis-acting regulatory element in the rat DBH promoter (DBH-1). One of the partners in the DNA-protein complex is c-Fos or a Fos-related protein. There was a correlation between promoter binding activity and elevated steady-state levels of DBH mRNA. Our data indicate that this cis regulatory element in the rat DBH promoter is functional in vivo, and increased binding of AP1-like transcription factors to this motif is induced by immobilization stress.

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.

Catecholamine secretory vesicles. Augmented chromogranins and amines in secondary hypertension.

Chromogranins A and B are major soluble proteins in chromaffin granules. Their adrenomedullary content is increased in the spontaneously (genetic) hypertensive rat. Is augmented catecholamine vesicular storage of the chromogranins a specific feature of genetic hypertension? To explore this question, we measured chromogranin A immunoreactivity, using a novel, synthetic peptide radioimmunoassay, in rat adrenal medullas 4-6 weeks after induction of the two-kidney, one clip Goldblatt model of renovascular hypertension and in unmanipulated control animals. We also measured messenger RNAs of chromogranins A and B and dopamine beta-hydroxylase by Northern blot. Immunoreactive adrenal chromogranin A was 3.3-fold higher (p < 0.01) in clipped rat adrenals. Adrenal catecholamine concentrations and phenylethanolamine-N-methyltransferase activity were also higher in clipped rats. Adrenal dopamine beta-hydroxylase activity (both membrane-bound and soluble forms) and corticosterone (glucocorticoid) concentration did not significantly differ between the groups. Adrenal medullary chromogranin A messenger RNA levels in clipped rats were 3.2-fold higher (p = 0.029) than those in the control group, and chromogranin B messenger RNA levels were 4.6-fold higher (p = 0.05). Dopamine beta-hydroxylase messenger RNA levels were 2.9-fold higher (p = 0.038). Thus, augmented synthesis and storage of adrenomedullary chromogranins A and B, catecholamines, and their biosynthetic enzymes appear to be characteristic of both acquired and genetic hypertension.

Dopamine and the Kidney: Ten Years on

Ten years ago the Editorial Board of Clinical Science invited me to write an Editorial Review on dopamine and the kidney. The result was published in 1982 in Volume 62 [1]. It was my hope that it would serve to stimulate other investigators to take up this area of renal physiology and pharmacology and to help to solve some of the problems left unanswered at that time. Since 1982 much has happened: there have been major successes, such as the delineation of the renal and adrenal dopamine receptors, and some relative failures, such as the lack of development of clinically useful peripheral dopamine agonists for use in hypertension and congestive cardiac failure. Nevertheless, continuous progress has been made and it is my task in this Review to try to describe this general advance while not omitting remaining areas of uncertainty. The areas which I will undertake to describe are: 1. The renal receptors for dopamine. 2. The source of dopamine in the urine and its formation in the kidney. 3. The actions of dopamine upon the kidney. 4. The interaction of renal dopamine with other substances. 5. Dopamine formation in hypertensive and oedematous states. 6. The search for specific peripheral dopaminergic agonists of therapeutic utility. 7. Final conclusions and unanswered questions.

Selective activation of norepinephrine- and epinephrine-secreting chromaffin cells in rat adrenal medulla.

The differential effects of insulin-induced hypoglycemia and cold exposure on adrenal medullary epinephrine (Epi) and norepinephrine (NE) cells were investigated in male Sprague-Dawley rats. In rats fasted overnight, insulin produced a marked hypoglycemia that resulted in a 70% decrease in adrenal medullary Epi content 3 h after the insulin was administered. No change in NE content was observed. Plasma Epi concentration was increased markedly after insulin, with a smaller increment in NE. In contrast, exposure to a 4 degrees C environment selectively reduced adrenal NE content, with the effect reaching statistical significance at 18 h. Cold exposure also led to a significant rise in plasma NE but not Epi. Both insulin-induced hypoglycemia and cold exposure significantly elevated adrenal dopamine, indicating that catecholamine synthesis was stimulated. Further evidence of enhanced catecholamine formation was the observation that inhibition of synthesis with alpha-methyl-p-tyrosine (AMT) greatly augmented the ability of insulin-induced hypoglycemia to selectively reduce adrenal medullary Epi content. Similarly, in cold-exposed animals, AMT pretreatment accelerated the NE depletion so that a significant decline was observed at 3 h. These results support the conclusion that the two major populations of adrenal catecholamine-secreting cells may be preferentially stimulated by different stressors. Moreover, augmented synthetic activity functions to maintain catecholamine stores in both Epi- and NE-secreting cells.