Cerebral ischemia: Changes in brain choline,acetylcholine, and other monoamines as related to energy metabolism

The relationship of cerebral neurotransmitters acetylcholine (ACh), noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT) to the energy state of the brain was examined in mice at various times following complete ischemia produced by decapitation, in gerbils submitted to transient global ischemia (10 min bilateral carotid artery occlusion, 5 or 30 min recirculation), and in rats 24 hr after irreversible microembolism. Ischemia caused significant reductions in brain monoamine concentrations. The alterations in NA, DA, and 5HT levels persisted during recirculation and were unrelated to energy restoration. They were accompanied by an increase in the concentrations of related metabolites, suggesting that synthesis was unable to compensate for the release of the transmitters at early post-ischemic time periods. As described for the catecholamines and 5HT, ischemia resulted in a significant decrease in ACh level, but recirculation was associated with a rapid increase in ACh concentration. Impaired synthesis and/or increased release of ACh can be responsible for the decrease in ACh concentration during ischemia. Early post-ischemic elevation of ACh may be related to the large increase in brain choline brought about by ischemia.     

Effect of intracerebroventricularly administered insulin on brain monoamines and acetylcholine in euglycaemic and alloxan-induced hyperglycaemic rats.

There is now conclusive evidence for the presence of insulin and insulin receptors in the mammalian CNS and it has been postulated that they can modulate peripheral glucose homeostasis. Since a number of central neurotransmitters are also known to influence glucose levels and it is likely that CNS insulin receptors act through neurotransmitter mediation, the present study was conducted to investigate the effect of intracerebroventricularly (icv) administered insulin on rat brain dopamine (DA), noradrenaline (NA), serotonin and acetylcholine (ACh) activity in normal and alloxan-induced hyperglycaemic animals. Insulin was administered in doses (50 and 100 microU) which induced minimal hypoglycaemia, so as to obviate the likely effects of hypoglycaemia on neurotransmitter function. DA was estimated in midbrain-diencephalon (MD) and caudate nucleus (CN), NA and serotonin in MD and pons-medulla (PM), while ACh was estimated in all the three areas, namely, MD, CN and PM. The regional brain concentrations of DA, NA and serotonin were more in the hyperglycaemic rats as compared to their euglycaemic counterparts. However, the reverse was noted in case of ACh. Insulin induced a decrease in rat brain DA and NA levels, which was more marked in the hyperglycaemic animals. Conversely, insulin induced an increase in rat brain serotonin concentration which was not significantly different in normal and hyperglycaemic rats. Insulin induced marked increase in rat brain ACh levels, which was accentuated in hyperglycaemic animals. The present study reports for the first time the likely interaction between CNS insulin receptors and brain monoamines, and ACh, in euglycaemic and hyperglycaemic states.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increasing synaptic noradrenaline, serotonin and histamine enhances in vivo binding of phosphodiesterase-4 inhibitor (R)-[11C]rolipram in rat brain, lung and heart

Phosphodiesterase-4 (PDE4) is one of the main enzymes that specifically terminate the action of cAMP, thereby contributing to intracellular signaling following stimulation of various G protein-coupled receptors. PDE4 expression and activity are modulated by agents affecting cAMP levels. The selective PDE4 inhibitor (R)-rolipram labeled with C-11 was tested in vivo in rats to analyze changes in PDE4 levels following drug treatments that increase synaptic noradrenaline (NA), serotonin (5HT), histamine (HA) and dopamine (DA) levels. We hypothesized that increasing synaptic neurotransmitter levels and subsequent cAMP-mediated signaling would significantly enhance (R)-[(11)C]rolipram retention and specific binding to PDE4 in vivo. Pre-treatments were performed 3 h prior to tracer injection, and rats were sacrificed 45 min later. Biodistribution studies revealed a dose-dependent increase in (R)-[(11)C]rolipram uptake following administration of the monoamine oxidase (MAO) inhibitor tranylcypromine, NA and 5HT reuptake inhibitors (desipramine [DMI], maprotiline; and fluoxetine, sertraline, respectively), and the HA H(3) receptor antagonist (thioperamide), but not with DA transporter blockers GBR 12909, cocaine or DA D(1) agonist SKF81297. Significant increases in rat brain and heart reflect changes in PDE4 specific binding (total-non-specific binding [coinjection with saturating dose of (R)-rolipram]). These results demonstrate that acute treatments elevating synaptic NA, 5HT and HA, but not DA levels, significantly enhance (R)-[(11)C]rolipram binding. Use of (R)-[(11)C]rolipram and positron emission tomography as an index of PDE4 activity could provide insight into understanding disease states with altered NA, 5HT and HA concentrations.     

Correlation of behavioral and neurochemical effects of acute administration of cocaine in rats.

Effects of cocaine were investigated on spontaneous motor activity (SMA) and stereotypy as well as on the concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and acetylcholine (ACh) in the discrete brain areas, such as the caudate nucleus (CN), diencephalon-midbrain (DM) and pons-medulla (PM) in rats up to 90–120 min following its injection in single doses (15–20 mg/kg, i.p.). After cocaine administration, the SMA was increased usually reaching its peak between 10–20 min, and then decreased gradually. Stereotypy and its components gradually increased to their maximum at about 50–60 min and remained at that level during rest of 120 min sessions. NE levels slightly increased in the DM and PM at 10 min post-drug after which they were decreased at 20 min. DA levels in the CN and DM were increased markedly at 20 min post-drug and decreased at 40 min. 5-HT levels in DM and PM decreased gradually up to 20 min, then began to increase. ACh level in the CN was gradually increased at 40 min and then decreased. It appears that cocaine-induced hyperactivity and stereotypy followed release of NE and DA after their accumulation in the respective brain areas.     

Effect of piracetam, a nootropic agent, on rat brain monoamines and prostaglandins

Piracetam is the prototype of a new class of psychotropic drugs, the nootropic agents, which are claimed to selectively improve the higher telencephalic integrative activities. The effect of piracetam on rat brain monoamines and prostaglandins (PGs) was assessed so as to garner information on its mode of action. Two doses of the drug were used, a lower dose (20 mg/kg ip) and a higher dose (100 mg/kg, ip), the latter being known to exert a facilitatory effect on learning and memory. Piracetam produced a dose-related effect on rat brain serotonin (5HT) and noradrenaline (NA), with the lower dose inducing a decrease in 5HT levels and an increase in NA concentrations. The higher dose of piracetam produced the opposite effect. Dopamine (DA) levels were not significantly affected. The lower dose of the drug attenuated 5HT turnover and augmented that of NA, whereas the higher dose of piracetam produced the reverse effects, in clorgyline treated rats. The lower dose of piracetam produced a slight and statistically insignificant increase in rat brain PGE2 and PGF2 alpha. However, the higher dose of the drug produced marked increase in the levels of both the PGs. The observed biochemical effects may provide a basis for the nootropic effect of piracetam. However, they may also be due to the GA-BA-mimetic action of the drug, particularly those observed with the lower dose of piracetam.     

Long term effect of lithium on brain regional catecholamine metabolism

Administration of LiCl (2-4 mmol/kg/day, po) to adult male albino rats for 7 consecutive days increased the catabolism of dopamine (DA) in striatum (ST) and noradrenaline (NA) in hypothalamus (H). Extension of the period of treatment with LiCl (2-4 mmol/kg/day, po) to 14 consecutive days increased catabolism of DA in CX (cerebral cortex) and PM (pons-medulla) and NA in H, and decreased metabolism of DA in ST and NA in PM. Further prolongation of treatment with LiCl (2 or 4 mmol/kg/day, po) for 21 consecutive days greatly affected DA and NA metabolism in the respective brain regions. These results, thus suggest that LiCl produces region specific differential action depending on its dosage and duration of treatment in catecholaminergic activity in rat brain.     

Disruption of 5-hydroxytryptaminergic neuronal function blocks the action of morphine on tuberoinfundibular dopaminergic neurons

Subcutaneous injections of morphine to male rats reduced dopamine(DA) turnover (α-methyltyrosine-induced decline of DA concentrations) in the median eminence, and increased DA turnover in the striatum. Selective destruction of central 5-hydroxytryptamine(5HT)-neurons with intracerebroventricular injections of 5,7-dihydroxytryptamine, or the administration of metergoline, a putative 5HT antagonist, blocked the inhibitory effects of morphine on DA turnover in the median eminence. In the same experiments disruption of 5HT neurotransmission processes caused a similar but less dramatic antagonism of the stimulatory actions of morphine on DA turnover in the striatum. Thus, 5HT neurons play a role in mediating the effects of morphine on tuberoinfundibular and possibly on nigrostriatal DA neurons.     

Studies on the mechanism of postetorphine catalepsy. Effects of clotiapine, haloperidol and rompun on postetorphine changes in concentrations of dopamine and noradrenaline in central nervous system of rats

Changes in dopamine (DA) and noradrenaline (NA) concentrations in various central nervous system structures were compared in rats after administration of haloperidol, clotiapine and rompun with changes in these concentrations during etorphine-induced catalepsy. Besides that, these changes were compared with changes in DA and NA concentrations after etorphine administration during full action of haloperidol, clotiapine and rompun. Haloperidol, clotiapine and rompun prolonged the duration of etorphine-induced catalepsy in rats and modified significantly postetorphine changes in DA and NA concentrations in the investigated central nervous system structures. The action of haloperidol, clotiapine and rompun increasing the intensity of postetorphine catalepsy and the previously demonstrated anticataleptic and antietorphine action of agents stimulating the postsynaptic adrenergic structures in the central nervous system in rats may suggest that DA release from presynaptic structures is inhibited after etorphine.     

The effects of the perinatal treatment with 5-hydroxytryptophan or tranylcypromine on the peripheral and central serotonin homeostasis in adult rats

Serotonin (5HT) is a biologically active amine present in mammals in the brain and the peripheral tissues. Autism is a neurodevelopmental disorder in which 5HT homeostasis is disturbed both centrally and peripherally, but the relationship between the 5HT disturbances in the two compartments is not understood. In an attempt to explore the relationship between the disturbed peripheral 5HT homeostasis and central 5HT functioning, we exposed the developing rat brain to increased 5HT concentrations, by treatment of rats with subcutaneous injections of the immediate 5HT precursor 5-hydroxy-l-tryptophan (5HTP, 25 mg/kg), or the non-selective MAO inhibitor tranylcypromine (TCP, 2 mg/kg), during the period of the most intensive development of 5HT neurons - from gestational day 13 to post-natal day 21. The effects of the mentioned treatments on peripheral and central 5HT levels were then studied in adult rats. Platelet and plasma 5HT concentrations (measured by ELISA), as well as cortical and midbrain 5HT, tryptophan and 5-hydroxyindoleacetic acid levels (measured by HPLC) were determined in twelve 5HTP treated and eight TCP treated rats, and compared with the values measured in 10 control, saline treated rats. Treatment with 5HTP significantly raised peripheral but not central 5HT concentrations. At adult age, peripheral 5HT homeostasis was re-established, while modest decrease in 5HT concentration was observed in frontal cortex, presumably due to hyperserotonemia-induced loss of 5HT terminals during brain development. Treatment with TCP induced significant 5HT elevations in both compartments. At adult age, permanent changes in 5HT homeostasis were observed, both peripherally (as hyperserotonemia) and centrally (as altered 5HT metabolism with decreased 5HT concentrations). Further studies are planned in order to explore the nature of the different disturbances of 5HT homeostasis induced by the two compounds, and their results are expected to shed some light on the role of hyperserotonemia in autism.     

Effect of poly herbal formulation,EuMil, on neurochemical perturbations induced by chronic stress

EuMil, a polyherbal formulation consisting of standardised extracts of Withania somnifera (L) Dunal, Ocimum sanctum L, Asparagus racemosus Wilid and Emblica officinalis Gaertn., is used as an anti-stress agent to attenuate the various aspects of stress related disorders. In the present study, the neurochemical mechanisms underlying the anti-stress activity of EuMil were evaluated by measuring the rat brain monoamine neurotransmitter levels and tribulin activity. Chronic electroshock stress (14 days) significantly decreased the nor-adrenaline (NA) and dopamine (DA) levels in frontal Cortex, pons-medulla, hypothalamus, hippocampus and striatal, hypothalamal region, respectively, and increased the 5-hydroxytryptamine (5HT) level in frontal cortex, pons medulla, hypothalamus and hippocampus. Chronic stress, also increased the rat brain tribulin activity. EuMil (100 mg/kg, p.o., 14 days) treatment normalized the perturbed regional NA, DA, 5HT concentrations, induced by chronic stress. EuMil also significantly attenuated the stress-induced increase in the rat brain tribulin activity. The amelioration of chronic stress-induced neurochemical perturbations by EuMil explains the neurochemical mechanisms underlying the observed putative anti-stress activity of the product.     

Acute effects of ethanol on brain,plasma and adrenal monoamine concentrations in virgin and pregnant rats and their fetuses

The dose-response relationship in brain, plasma, and adrenal monoamine changes after acute oral ethanol administration (1, 2, 4 g/kg body wt) was studied in virgin rats to determine whether the response to the highest dose differed in 21-day pregnant animals, and to assess the potential consequences of ethanol on the neurotransmitter systems of their fetuses. Blood ethanol and acetaldehyde concentrations in blood increased progressively with the ethanol dose in virgin rats, and values in pregnant animals were very similar. Ethanol concentration in fetal blood and amniotic fluid did not differ from that in mother's blood whereas fetal acetaldehyde concentrations were negligible. In a dose-related manner, ethanol decreased brain DA, DOPAC and 5HT concentrations did not affect those of NA and 5HIAA, or adrenal A and NA concentrations, whereas it enhanced plasma NA levels. Basal levels of monoamines and their changes after ethanol intake did not differ in pregnant and virgin rats. Monoamine and metabolite concentrations were much lower in fetal than in maternal brains whereas plasma and adrenal catecholamine concentrations were very similar and maternal ethanol intake did not modify these fetal parameters in the fetus. Results are in agreement with the known similar metabolic response to ethanol in fed pregnant and virgin rats. The lack of fetal monoamine response to maternal ethanol intake may be a consequence of the incapacity of fetal liver to form acetaldehyde and the ability of the placenta to oxidize maternal acetaldehyde which protects the fetus from maternal alcohol intake at late gestation.     

Monoamine Synthesis and Concentration in Neonatal Rat Brain During Hypercapnia and Recovery

One-day-old rats were exposed to a gas mixture of 15% CO2-21% O2-64% N2 for a 30-min period. Monoamine synthesis in whole brain was measured during, and at various intervals after, hypercapnia by estimating the accumulation of dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) after inhibition of aromatic L-amino-acid decarboxylase with NSD 1015. Endogenous concentrations of tyrosine, dopamine (DA), noradrenaline (NA), tryptophan, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured at the same intervals. Exposure to CO2 induced an increased synthesis of catecholamines and 5-HT. Further, an increase in DA concentration was seen during hypercapnia, while NA and 5-HT were unchanged. After the CO2 exposure the increased in vivo synthesis rates of catecholamines and 5-HT were rapidly normalized, as was the endogenous DA concentration. A slight increase in 5-HT and 5-HIAA concentrations was seen immediately after CO2 exposure. These results indicate that in neonatal animals, hypercapnia induces changes in central monoamine neurons, primarily an increased synthesis. These alterations may be relevant to some physiological changes seen during CO2 exposure, such as the alteration in central respiratory performance.     

Fighting and Stinging Responses are Affected by a Dopamine Receptor Blocker Flupenthixol in Honey Bee Virgin Queens

Fighting and aggression are important tasks for self-preservation in animals. In honey bees, virgin queens fight against each other for survival in a monogynous colony. Because the virgin queens have higher levels of dopamine (DA) in the brain than do mated queens with low aggressiveness, DA may promote fighting and aggression behaviours of virgin queens. In the present study, we investigated the effect of DA on the fighting and stinging response of honey bee virgin queens. We injected two concentrations (10^?3 M and 10^?2 M) of DA and the DA receptor blocker flupenthixol into the abdomen of one-day-old virgin queens and observed fighting and stinging responses. DA injection did not affect fighting and stinging. Injections of 10^?3 M flupenthixol decreased the winning rate significantly, whereas 10^?2 M flupenthixol increased the winning rate, indicating the opposite effects on fighting responses depending on the degrees of blockade of DA signalling. In terms of the stinging response, 10^?2 M flupenthixol-injected virgin queens stung significantly more often than control and 10^?3 M flupenthixol-injected virgin queens. These results suggest an involvement of DA signalling in the regulation of fighting and aggression in virgin queens, although a blockade of DA does not always inhibit these behaviours.     

Catecholamine concentration in discrete brain areas following the withdrawal of barbital dependent rats

Noradrenaline (NA) and dopamine (DA) concentrations were measured in 5 discrete brain areas of barbital dependent rats following 0, 1 or 2 days of drug withdrawal. Statistically significant decreases in NA concentration were observed in the cerebral cortex and the thalamus of 1 day withdrawn rats while NA concentration in the hypothalamus was significantly reduced during the second day of withdrawal. The concentration of DA was significantly elevated in barbital dependent rats but declined following barbital withdrawal. Compared to control or nonwithdrawn rats, the concentration of DA in the thalamus was elevated by the second day of withdrawal. The changes in catecholamine concentration presumably reflect underlying effects of chronic barbital consumption or subsequent withdrawal on the synthesis, metabolism or utilization of these neurohumors.     

A short-term diabetes induced changes of catecholamines and p38-MAPK in discrete areas of rat brain

Chronic diabetes is associated with the alteration of second messengers and CNS disorders. We have recently identified that protein kinases (CaMKII and PKC-alpha) and brain neurotransmitters are altered during diabetes as well as in hyperglycemic and acidotic conditions. In this study, we investigated the effects of acute diabetes on the levels of dopamine (DA), norepinephrine (NE), epinephrine (E) and p38-Mitogen-Activated Protein Kinase (p38-MAPK) in striatum (ST), hippocampus (HC), hypothalamus (HT), midbrain (MB), pons medulla (PM), cerebellum (CB) and cerebral cortex (CCX). Alloxan (45 mg/kg) diabetic untreated rats that showed hyperglycemia (>260 mg%), revealed significant increases of DA level in ST (1.5 fold), HC (2.2 fold) and PM (2.0 fold) and the E level also found to be increased significantly in HT (2.4 fold), whereas the NE level was decreased in CB (0.5 fold), after 7 days of diabetes. Immunoblotting study of p38-MAPK expression under identical conditions showed significant alterations in ST, HC, HT and PM (p<0.05) correlated with the changes of catecholamines (DA and E). On the other hand, the above changes were reversed in insulin-treated diabetic rats maintained under normal glucose level (80 -110 mg %). These results suggest that p38-MAPK may regulate the rate of either the synthesis or release of DA and E in corresponding brain areas, but not NE, under these conditions.     

Role of monoamine oxidase-B in medroxyprogesterone acetate (17-acetoxy-6 alpha-methyl-4-pregnene-3, 20-dione) induced changes in brain dopamine levels of rats

The effect of medroxyprogesterone acetate (MPA) on brain monoamine levels and monoamine oxidase (MAO) activity was studied in adult, healthy, non-pregnant female rats. MpA was injected in a single dose of 100 mg/kg i.m. Dopamine (DA), noradrenaline (NA), 5-hydroxytryptamine (5-HT) levels and MAO activity were estimated fluorometrically in rat brian. No change in DA, NA, 5-HT or MAO activity was observed after 7 days of MPA treatment while a significant decrease in DA levels along with a significant increase in MAO activity was observed after 21 days of MPA treatment. However, there was no change in NA and 5-HT levels after 21 days of MPA administration. The selective reduction of DA by MPA could be due to an increase in MAO-B activity. MPA does not appear to increase MAO-A activity because neither of the specific substrates (NA and 5-HT) of MAO-A was found to be decreased inspite of the increase in MAO activity as estimated by the kynuramine method. These findings suggest the importance of MAO-B also in DA metabolism in rat brain.     

The neurochemical control of aggression and submission]

Neurochemical mechanisms of agonistic behaviour in different models of aggression are discussed. The effects of aggression and submission experience in 10 mice intermale confrontations under conditions of sensory contact on the levels of brain neurotransmitters and their metabolites were investigated in 7 brain areas. The values obtained in aggressive and control, or submissive and control, animals were compared. In this comparison neurochemical alterations specific for aggressive or submissive behaviours, or nonspecific became apparent. The long experience of victories leads to activation of dopaminergic system through DA catabolism which leads to DOPAC formation. The long experience of defeats increases the 5HT metabolism and decreases NA level in some brain areas. The dopaminergic system of Nucleus accumbens and midbrain are nonspecifically activated in both aggressive and submissive animals. The investigation of values obtained in animals with conversion of behavioural type (after defeat of previously aggressive animals and/or display of aggressive reaction by previously submissive mice) allowed to find many significant differences between aggressive, submissive and "converted" males; in particular the amygdala is the site of opposite changes in 5HT system during inversion of aggressive or submissive behaviours. The above data evidence for the specific role of transmitter systems and brain structures in maintaining or inversion of different types of agonistic behaviour.     

Loss of noradrenaline transporter sites in frontal cortex of rats with acute (ischemic) liver failure

There is increasing evidence that central noradrenaline (NA) transport mechanisms are implicated in the central nervous system complications of acute liver failure. In order to assess this possibility, binding sites for the high affinity NA transporter ligand [3H]-nisoxetine were measured by quantitative receptor autoradiography in the brains of rats with acute liver failure resulting from hepatic devascularization and in appropriate controls. In vivo microdialysis was used to measure extracellular brain concentrations of NA. Severe encephalopathy resulted in a significant loss of [3H]-nisoxetine sites in frontal cortex and a concomitant increase in extracellular brain concentrations of NA in rats with acute liver failure. A loss of transporter sites was also observed in thalamus of rats with acute liver failure. This loss of NA transporter sites could result from depletion of central NA stores due to a reserpine-like effect of ammonia which is known to accumulate to millimolar concentrations in brain in ischemic liver failure. Impaired NA transport and the consequent increase in synaptic concentrations and increased stimulation of neuronal and astrocytic noradrenergic receptors could be implicated in the pathogenesis of the encephalopathy and brain edema characteristic of acute liver failure.     

Decreased monoamine release in the median preoptic area following ventricular treatment with the angiotensin II antagonist saralasin in normotensive and spontaneously hypertensive rats

Previous findings have shown that some of the neurons in the median preoptic nucleus (MnPO) receive both catecholaminergic inputs from the brainstem and angiotensinergic inputs from the subfornical organ (SFO), and that alterations in the function of the brain renin-ANG system are implicated in hypertension, especially in spontaneous hypertensive rats (SHR). In an attempt to clarify the action of these inputs on MnPO neurons and to find the difference in the action between normotensive Wistar-Kyoto (WKY) rats and SHR, we used microdialysis to investigate the effects of injections of saralasin (Sar), an angiotensin II (ANG II) antagonist, into the third ventricle (3V) on monoamine release in the MnPO area of awake WKY and SHR. The content of noradrenaline (NA) in the MnPO area was significantly higher in SHR. No significant differences were observed between WKY and SHR in the concentrations of dopamine (DA) and of its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In both WKY and SHR, Sar (Sar, 5 microg in 1 microl, three injections at 2-h intervals) injected into the 3V significantly decreased the extracellular concentrations of NA, DOPAC and HVA in the MnPO area. The decreases were much greater in SHR than in WKY rats. Similar injections of saline vehicle had no significant effect on the extracellular levels of NA, DA and the metabolites. These results suggest that central angiotensinergic circuits may serve to increase NA and DA release in the MnPO area, and support that a disorder in the ANG system may contribute, in part, to the elevated blood pressure of SHR.     

Tissue catecholamine concentrations in spontaneously hypertensive rats

Tissue concentrations of noradrenaline (NA), dopamine (DA) and adrenaline (A) were compared in spontaneously hypertensive (SHR) and normotensive (NCR) rats, aged 1, 3, 8, 14 and 24 weeks The organs analyzed included the brain, subdivided into prosencephalon and rhombencephalon, heart, adrenal glands and kidney. Brain catecholamines were significantly lower in SHR than in NCR, and the difference appeared already at the age of 3 weeks. Concomitant increase was found in the adrenal NA and A concentrations of the SHR. Concentration of NA in the heart decreased in the SHR following onset of hypertension. It is concluded that the diminished NA, DA and A concentrations in the brain as well as the augmented adrenal NA and A levels in the SHR may be causally related to the development of hypertension, while the heart NA level reflects the secondary, hypertension -- related changes.