Tissue Norepinephrine Levels Research Articles

Role of norepinephrine in the dorsomedial hypothalamic panic response: An in vivo microdialysis study

Blockade of gamma-aminobutyric acid-A (GABA A) receptors in the dorsomedial hypothalamus (DMH) elicits a panic-like response that includes increases in heart rate (HR), blood pressure (BP), respiration rate (RR), and anxiety. Norepinephrine (NE) has been postulated to be critical in regulating panic and anxiety responses. Therefore, the first study sought to determine changes in extracellular NE levels within the DMH following acute blockade of GABA A receptors in the DMH using in vivo microdialysis. Rats were implanted with femoral arterial catheters and microdialysis probes into the DMH. Following recovery, the DMH of conscious rats were perfused with 100, 150, or 200 μM solutions of the GABA A receptor antagonist bicuculline methiodide (BMI) via the microdialysis probe. HR and BP responses were recorded and the changes in extracellular levels of NE in the dialysate samples from the DMH were determined by HPLC. Rats receiving BMI injections showed dose-dependent increases in both the extracellular NE levels in the DMH as well as HR and BP. The second study was conducted to test the functional importance of NE in the DMH to the BMI-induced physiological responses. The effects of BMI microinjection into the DMH were measured at baseline and 10 days after local injection of either vehicle or two doses of 6-hydroxydopamine (6-OHDA), a neurotoxin known to lesion NE terminals. There was a significant loss of tissue NE levels as well as BMI-induced HR, BP and RR responses in the 6-OHDA-treated but not vehicle-treated rats. Thus, blockade of GABA A receptors in the DMH results in NE release and the presence of NE appears to be necessary for eliciting the physiological components of the panic-like responses in this region.

Norepinephrine turnover in peripheral tissues of rats with heart failure.

Experiments were performed to determine if there is regional heterogeneity in sympathetic neural activation of peripheral tissues in rats with chronic heart failure (HF; 6-8 wk after coronary artery ligation). Norepinephrine (NE) turnover, an index of sympathetic activation, was determined on the basis of the decline in tissue NE levels that occurs during the 8-h after tyrosine hydroxylase inhibition (alpha-methyl-DL-p-tyrosine, 300 mg/kg ip at 4-h intervals). Compared with sham-operated rats, NE turnover was increased in the cardiac left ventricle, skeletal muscle, duodenum, and kidney of rats with HF, but was unaltered in liver and spleen. The increased renal NE turnover in HF was largely a reflection of increased turnover in the cortex, with no change evident in the medulla. Blockade of sympathetic ganglionic traffic (hexamethonium, 2 mg/kg sc at 2-h intervals) eliminated the tissue-specific effects of HF on tissue NE levels measured 8-h after tyrosine hydroxylase inhibition. These data support the contention that chronic HF evokes a central nervous system-mediated increase in basal sympathetic tone that exhibits regional heterogeneity (both between and within organs), a phenomenon that likely contributes to the functional consequences of this pathophysiological state.

The role of NGF in pregnancy-induced degeneration and regeneration of sympathetic nerves in the guinea pig uterus

In the guinea pig, pregnancy is associated with a generalised depletion of noradrenaline in uterine sympathetic nerves and, in the areas of the uterus surrounding the foetus, by a complete degeneration of sympathetic nerve fibres. These pregnancy-induced changes have been interpreted as a selective effect of placental hormones on the system of short sympathetic fibres arising from the paracervical ganglia. An alternative explanation is that pregnancy affects the neurotrophic capacity of the uterus. We measured NGF-protein levels in the guinea pig uterine horn, tubal end and cervix at early pregnancy, late pregnancy and early postpartum, using a two-site enzyme-linked immunosorbent assay. For comparative purposes the distribution and relative density of noradrenaline-containing sympathetic nerve fibres were assessed histochemically, and tissue levels of noradrenaline were measured biochemically, using high-performance liquid chromatography with electrochemical detection. In all the uterine regions analysed, NGF-protein levels showed a decline at term pregnancy, but in no case was this change statistically significant. After delivery, NGF-protein levels showed a marked increase in the cervix as well as in both the fertile and empty horns. These results suggest that alterations in NGF-protein do not account for the impairment of uterine sympathetic innervation during pregnancy, but may contribute to their recovery after delivery.

L-DOPS-Accelerated recovery of locomotor function in rats subjected to sensorimotor cortex ablation injury: pharmacobehavioral studies.

Central norepinephrine (NE) has been shown to play a beneficial role in amphetamine-facilitated recovery of behavior. To give insight into understanding the mechanism, the present studies were conducted to examine (a) the effects of L-threo-3,4-dihydroxyphenylserine (L-DOPS) combined with benserazide (BSZ; a peripheral aromatic amino acid decarboxylase inhibitor) and L-3,4-dihydroxyphenylalanine (L-DOPA), precursors of NE and dopamine (DA), respectively, on the recovery from beam-walking performance deficits in rats subjected to unilateral sensorimotor cortex ablation injury, and (b) the relationships between the behavioral recovery and the frequency of postoperative training and the size of ablation injury. It was found that the combined treatments with L-DOPS and BSZ promoted the recovery of locomotor function as early as 24 hours after injury. L-DOPA alone, however, did not facilitate behavioral recovery. The results of assay for the tissue levels of NE and its major metabolite (3-methoxy-4-hydoxyphenylethylene glycol; MHPG) in the brain using high-pressure liquid chromotography showed MHPG, but not NE, significantly increased in the cerebellum and the hippocampus. The behavioral recovery was also significantly correlated with the frequency of training subsequent to injury, but inversely with the size of cortex ablation. These results suggest that NE is likely to modulate functional recovery in this rodent model.

Testosterone effects on renal norepinephrine content and release in rats with different Y chromosomes.

The Y chromosome in spontaneously hypertensive rats (SHR) and stroke-prone rats has been shown to contain a locus that contributes to the hypertensive effect; both the sympathetic nervous system and testosterone may be involved. The objective of this study was to look at the effects of testosterone on renal norepinephrine (NE) release and content in the isolated perfused kidney in different Y chromosome backgrounds. The study involved male SHR, Wistar-Kyoto rats (WKY), and 2 consomic strains with different Y chromosomes (n=5 to 8 per group). Adult animals were castrated, and implants containing testosterone propionate were placed at the base of the neck. Blood testosterone levels were measured by radioimmunoassay 2 weeks after castration. The left kidney was isolated and perfused with oxygenated Krebs solution at a constant flow and temperature with KCl and electrical stimulation of the renal nerves. Perfusate was collected and analyzed for NE by high-performance liquid chromatography. Lactate dehydrogenase analyses were performed as a marker for potential tissue damage. Renal perfusate and renal tissue NE levels were significantly elevated by testosterone. The average NE increase with a single testosterone implant was 13.2 ng/mL, and for a double testosterone implant it was 29.8 ng/mL. The Y chromosome from the SHR produced a significant increase in renal NE release compared with the WKY Y chromosome. Significance was shown between all groups: 1 versus 2 implants, P=0.0067; 1 versus sham implants, P=0.015; 2 versus sham implants, P<0.001. In conclusion, testosterone caused an enhanced renal NE release that was strain-specific, with the Y chromosome raising renal NE content and release.

Regional sympathetic activity in pre-hypertensive phase of spontaneously hypertensive rats

Imbalances in central and peripheral sympathetic nervous system (SNS) activity have been observed in essential and experimental hypertension. This study was carried out in order to evaluate SNS activity in two distinct tissue types of spontaneously hypertensive rats (SHR), compared to Wistar-Kyoto normotensive (WKY) rats, in the pre-hypertensive phase (4–5 weeks of age). Interstitial concentrations of norepinephrine (NE) and other catecholamines were measured by microdialysis in striated muscle, whose tone is controlled by baroreflexes, and in the subcutaneous adipose tissue where sympathetic output mainly controls metabolism. Two groups of SHR and WKY male rats were studied, aged 4–5 weeks, with a mean body weight of 92 and 86 g respectively. Systolic blood pressure (SBP, tailcuff) values were 113 mm Hg (SD ± 6.2) in SHR and 108 mm Hg (SD ± 7.3) in WKY rats (p = 0.28, t test). Two microdialysis probes were positioned in the subcutaneous fatty tissue and in the striated muscle of the parascapular region and perfused with Ringers' solution. The dialysate was collected every thirty minutes for 3 hours and analyzed in HPLC-ED to determine the content of NE and other catecholamines. Interstitial levels of NE were higher in SH than in WKY rats in both tissues. Mean NE values from subcutaneous adipose tissue in 4–5 week-old SHR were 1162 ± 193 pg/ml compared to 496 ± 188 pg/ml in WKY rats (p < 0.001, t test). Muscle tissue NE levels in SHR were 1241 ± 337 pg/ml vs. 521 ± 138 pg/ml in WKY rats (p < 0.001, t test). Plasma NE concentrations (279 ± 61 pg/ml in SHR vs 246 ± 69 pg/ml in WKY P = 0.65, t test) were not significantly different between the two strains at this young age. These findings suggest SNS hyperactivity in young SHR, though still normotensive, possibly dissociated from regional components of regulation (baroreceptor control in striated muscle and metabolic control in subcutaneous adipose tissue).

Effluxes of 3,4-dihydroxyphenylalanine, 3,4-dihydroxyphenylglycol, and norepinephrine from four blood vessels during basal conditions and during nerve stimulation.

Effluxes of 3,4-dihydroxyphenylalanine, 3,4-dihydroxyphenyglycol, and norepinephrine from four superfused canine blood vessels (saphenous and portal veins and mesenteric and pulmonary arteries) were studied under basal conditions and during nerve stimulation. From quantification of the compounds a series of indices of activities at neuroeffector junctions are proposed. These are (a) basal overflow of 3,4-dihydroxyphenylglycol as an index of vesicular-cytoplasmic translocation of norepinephrine, (b) the increase in 3,4-dihydroxyphenyglycol overflow attributable to nerve stimulation as an index of neuronal reuptake of norepinephrine released by stimulation, (c) the sum of the increases in overflows of norepinephrine and 3,4-dihydroxyphenylglycol attributable to nerve stimulation as an index of evoked release of norepinephrine, and (d) the efflux of 3,4-dihydroxyphenylalanine as an index of the activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of norepinephrine. There were clear differences between these indices in the vessels. Correlation coefficients of the indices among vessels indicated that a high tissue norepinephrine level was associated with high biosynthetic capacity and high vesicular-cytoplasmic exchange but not with high release. There was no evidence suggesting feedback inhibition of synthesis by neuroplasmic norepinephrine--whether arising from vesicular-cytoplasmic translocation or from reuptake from the junctional cleft. The major value of these indices will probably be in determining the integrated effects of pharmacologic agents at neuroeffector junctions in different blood vessels.

Growth of the rat prostate gland is facilitated by the autonomic nervous system.

Many factors are implicated in the development of prostatic growth: androgens, growth factors, and stromo-epithelial interaction. This study examines the role of the sympathetic and parasympathetic branches of the autonomic nervous system control of different aspects of rat prostate growth and atrophy. Unilateral sympathectomy leads to decreases in ventral prostate weight, DNA, and protein content in the lesioned side. Unilateral parasympathectomy leads to increases in ventral prostate weight, DNA, and protein content in the intact side. The separate effects of sympathectomy and parasympathectomy are maintained across a diverse combination of neural manipulations. Significant re-innervation does not occur by 60 days after manipulation as assessed by tissue norepinephrine levels. There appears to be a differential effect of the autonomic nervous system on growth and maintenance of the ventral prostate. The mechanism of contralateral hyperplasia and ipsilateral atrophy has potential significance in understanding human abnormal prostate growth.

Effects of long-term right ventricular apical pacing on left ventricular perfusion, innervation, function and histology

Objectives. The purpose of this study was to better understand the effects of long-term right ventricular pacing on left ventricular perfusion, innervation, function and histology.Background. Long-term right ventricular apical pacing is associated with increased congestive heart failure and mortality compared with atrial pacing. The exact mechanism for these changes is unknown. In this study, left ventricular perfusion, sympathetic innervation, function and histologic appearance after long-term pacing were studied in dogs in an attempt to see whether basic changes might be present that might ultimately be associated with the adverse clinical outcome.Methods. A total of 24 dogs were studied. Sixteen underwent radiofrequency ablation of the atrioventricular (AV) junction to produce complete AV block. Seven of these underwent long-term pacing from the right ventricular apex (ventricular paced group), and nine had atrial and right ventricular apical pacing with AV synchrony (dual-chamber paced group). A control group of eight dogs had sham ablations with normal AV conduction. These dogs had atrial pacing only. Regional perfusion and sympathetic innervation were studied in all dogs by imaging with thallium-201 and [I123]metaiodobenzylguanidine, respectively. The degree of innervation was also determined by assay of tissue norepinephrine levels. Left ventricular function was assessed by radionuclide ventriculography. Cardiac histology was studied with both light and electron microscopy.Results. Mismatching of perfusion and innervation in the ventricular paced group was noted, with perfusion abnormalities of both the septum and free wall. Regional [I123]metaiodobenzylguanidine distribution was homogeneous. Tissue norepinephrine levels were elevated in both the ventricular and dualchamber paced groups compared with the control group. No light or electron microscopic findings were noted in any groups. In the dual-chamber paced group, diastolic dysfunction was noted, with normal systolic function.Conclusions. Ventricular pacing resulted in regional changes in tissue perfusion and heterogeneity between perfusion and sympathetic innervation. Both ventricular and dual-chamber pacing were associated with an increase in tissue catecholamine activity. The abnormal activation of the ventricles via right ventricular apical pacing may result in multiple abnormalities of cardiac function, which may ultimately affect clinical outcome.

Abnormalities of cardiac sympathetic function in pacing-induced heart failure as assessed by [123I]metaiodobenzylguanidine scintigraphy.

Increased activity of the sympathetic nervous system contributes significantly to the pathophysiology of heart failure. However, cardiac efferent sympathetic function has not been well characterized in this disorder. In this study, we evaluated cardiac sympathetic innervation using [123I]metaiodobenzylguanidine (MIBG) and compared this with left ventricular (LV) tissue norepinephrine concentration and myocardial perfusion, assessed by 201Tl, in a canine model of heart failure. Planar and tomographic cardiac imaging was performed for MIBG and 201Tl in 23 dogs: 8 normal dogs (group 1) and 15 dogs with heart failure induced by right ventricular pacing at 250 beats per minute either continuously for 3 weeks (group 2) or intermittently for 7 weeks (group 3). Plasma and LV tissue norepinephrine concentrations were also measured. Scintigraphic studies in group 2 demonstrated reduced cardiac MIBG activity at heart failure (0.17 +/- 0.04 versus 0.29 +/- 0.05 counts per megabecquerel per pixel at baseline, mean +/- SD; P = .0001), whereas thallium activity was unchanged from baseline. This reduction in cardiac MIBG activity with heart failure was associated with increased intraimage variability in the distribution of MIBG activity (21 +/- 8% versus 13 +/- 7% at baseline, mean +/- SD; P = .0001). The MIBG heart-to-lung ratio was calculated for all groups to control for the inhibitory effect that plasma norepinephrine has on the neuronal uptake of MIBG. There was a positive correlation between LV tissue norepinephrine and the MIBG heart-to-lung ratio (r = .67; P < .001; n = 22), for which the group 2 heart failure animals had the lowest values. No relation existed between plasma norepinephrine concentration and the MIBG heart-to-lung ratio. In addition, regional LV tissue norepinephrine concentration and MIBG activity were both lowest at the apex in normal (group 1) and heart failure (group 2) dogs. The MIBG heart-to-lung ratio also correlated inversely with cardiac filling pressure (r = -.59; P < .05) and heart rate (r = -.65; P < .01) and positively with cardiac output (r = .53; P < .05). Heart failure is associated with severe cardiac adrenergic dysfunction manifested by reduced MIBG activity and increased heterogeneity in the LV distribution of MIBG. Furthermore, MIBG scintigraphy is a simple noninvasive method for assessing global and regional LV tissue norepinephrine levels.

Compensatory changes of in vivo acetylcholine and noradrenaline release in the hippocampus after partial deafferentation, as monitored by microdialysis

Lesions of the fimbria-fornix pathways are known to induce a partial cholinergic and noradrenergic denervation of the hippocampal formation, which is followed by a slow and protracted collateral sprouting by the spared afferents. Using the intracerebral microdialysis technique, compensatory changes in extracellular levels of acetylcholine (ACh) and noradrenaline (NA) have been monitored over time in the partially denervated hippocampus of awake unrestrained rats subjected to an unilateral fimbria-fornix (FF) transection. One week after the lesion, baseline ACh output was reduced by 90% and 80% in the dorsal and ventral hippocampus, respectively, and it remained depressed still by 6 months after lesion. KCl-evoked and atropine-stimulated ACh efflux were equally reduced by 1 week after lesion, remained depressed at 3 months, but showed a significant recovery by 6 months post-lesion. Tissue choline acetyltransferase (ChAT) activity levels, initially reduced by 92% and 86%, in the dorsal and ventral hippocampus, respectively, recovered significantly by 3 months and remained unchanged at 6 months. Baseline NA output was significantly reduced (-80%) in the dorsal hippocampus by 1 week after the lesion and showed a partial recovery over time (to 50% of normal), whereas the ventral part was not significantly affected by the FF lesion. The significant FF lesion-induced reduction in KCl- or desipramine (DMI)-stimulated NA release observed in the dorsal hippocampus at 1 week after the lesion remained unchanged during the subsequent months. By contrast, in the ventral hippocampus, the initial 65-70% reduction in KCl- and DMI-stimulated NA release significantly recovered to normal levels within 3 months post-lesion. The NA tissue levels were significantly reduced by 4 weeks after lesion, in the dorsal hippocampus and did not show any significant recovery over time. In the ventral hippocampus, these levels were significantly reduced only at 4 weeks. Transmitter turnover, expressed as the ratio between dialysate levels and tissue ChAT or NA content, showed a 3-fold increase in the dorsal hippocampus at 4 weeks after lesion, but not at later time points. This indicates that the spared noradrenergic and cholinergic afferents respond to the partial denervation by a transient increase in transmitter turnover, evident as early as 4 weeks post-lesion in the region of maximal denervation. This was followed by a long-term increase in evoked transmitter release which may result from a slowly progressing compensatory sprouting of the spared afferents.

Noradrenaline content of the tissue and nerve in the rabbit ear after freezing injury

The aim of this study was to investigate the development of the demarcation line in the rabbit ear upon injury by experimental freezing and thawing. For this purpose the sequential changes in noradrenaline (NA) content in the tissue and nerve of the ear were determined by liquid chromatography. Frostbite was inflicted with a glass bottle filled with liquid nitrogen and specimens were taken from the injured area, the probable demarcation line area and the healthy area 1, 3, and 7 days after frostbite. Control samples were taken from the normal contralateral ear. Tissue NA levels in the injured area and the probable demarcation line area were significantly lower than those in corresponding areas of the control ear after 1 day. Day 3 NA levels in the demarcation line area were 90% higher than those on Day 1 in this area and were not significantly different from Day 3 levels in the control ear. By Day 7, NA levels in the demarcation line area were down to 70% of the Day 3 levels. NA levels in the central nerve at the probable demarcation line were much higher than those in the control ear nerve and also showed a peak on Day 3. In conclusion, the results suggest that NA is released from the adrenergic nerves and the reaction at the probable demarcation line is strongest on the third day.

A study on the neuronal and non-neuronal stores of dopamine in rat and rabbit kidney

The present study has examined the effects of 6-hydroxydopamine (6-OHDA) alone and in combination with pargyline, desipramine and GBR 12909 and denervation as induced by occlusion of the renal artery (RAO) on the endogenous dopamine (DA) and noradrenaline (NA) contents in rat and rabbit renal tissues; the effects of chemical denervation on catecholamine levels in the left ventricle were also studied. In rat and rabbit renal medulla and rat renal cortex, 6-OHDA and pargyline plus 6-OHDA selectively reduced NA (85-92% reduction) without a parallel decrease in DA tissue content (19-27% reduction). This 6-OHDA- and pargyline plus 6-OHDA-insensitive DA pool was found to be resistant to denervation as induced by RAO. The NA-depleting effect of 6-OHDA in these renal areas was found to be prevented by the previous administration of desipramine, but not with that of GBR 12909. In the rabbit renal cortex, 6-OHDA selectively reduced NA (90% reduction) without a parallel depletion of DA (20% reduction); previous treatment with pargyline abolished this selectivity. Again, only desipramine, but not GBR 12909, was found to prevent the NA and DA depleting effect of 6-OHDA in the rabbit renal cortex. Denervation induced by RAO was also found to produce a parallel depletion of DA and NA tissue levels in this renal area. In the left ventricle, 6-OHDA alone or in combination with pargyline produced a parallel depletion of DA and NA tissue levels (79-88% reduction) in both species. These results provide evidence against the presence of independent dopaminergic neurones in rat and rabbit kidney and suggest that in rat and rabbit renal medulla and rat renal cortex most of DA is stored in a non-neuronal compartment; in rabbit renal cortex some of the DA appears to be located in noradrenergic neurones, in a store different from that which contains NA.

The effect of neonatal treatment of rats with nerve growth factor on the blood pressure and structure of the mesenteric arteries.

Newborn male Wistar rats were treated with nerve growth factor daily by subcutaneous injection for 2 weeks, and control rats were treated with either cytochrome c or buffered saline. Average body weight of the treated animals was lower than that of the controls during the 2 weeks of treatment, but became similar to that of the controls thereafter. Tissue levels of norepinephrine were elevated in the brain, adrenal glands, mesenteric arteries, and vas deferens of the treated animals immediately after the treatment, but became similar in the three groups 2 weeks after the termination of the treatment. Blood pressure and heart rate were measured beginning at 4 weeks of age until 28 weeks, when the rats were sacrificed and the mesenteric arteries sampled for morphometric measurements of vessel wall dimensions. Pretreatment with nerve growth factor did not affect blood pressure, nor heart rate. Structural alteration of the three types of mesenteric arteries was also absent in the treated animals. We conclude that even though neonatal treatment of normal Wistar rats with nerve growth factor for 2 weeks induced an elevation of the norepinephrine levels in several tissues at the end of the treatment period, it was not sufficient to produce hypertension and structural alterations in the blood vessels.

Effects of pentylenetetrazol-induced seizures on dopamine and norepinephrine levels and on glucose utilization in various brain regions of the developing rat

Levels of dopamine and norepinephrine were measured in seven brain areas after 60 min of sustained seizure activity induced by intraperitoneal repetitive timed administrations of pentylenetetrazol in rats at 10, 14, 17 and 21 days of postnatal life. The tissue levels of norepinephrine were markedly reduced in the majority of brain structures, except for striatum at 10 and 14 days. Conversely, dopamine concentrations increased in many areas and at various ages, except in cerebral cortex at 10 and 14 days and in midbrain between 14 and 21 days. PTZ seizures induced marked increases over control levels in the rates of glucose utilization, measured by the quantitative autoradiographic [14C]2-deoxyglucose method, in all dopamine- and norepinephrine-innervated areas studied at 10 and 14 days, except in cerebellar cortex at both ages and in frontal cortex and anteroventral thalamus at 14 days. At 17 and 21 days, glucose utilization remained increased over control levels in some areas, mainly in catecholaminergic cell groupings such as substantia nigra, ventral tegmental area and locus coeruleus, but was significantly reduced in cortex, caudate nucleus and thalamus, and similar to control rates in other regions.The present results suggest that pentylenetetrazol-induced seizures lead to a simultaneous increase in functional activity of norepinephrine neurons and an inhibition of dopaminergic-mediated neurons. They also confirm the maturation of connections, of metabolic activity and of neurotransmitter interaction within the brain, occurring mainly during the third week of postnatal life, paralleled by an increased selective vulnerability of some regions to this kind of insult.

Presynaptic effects of melatonin on norepinephrine release and uptake in rat pineal gland

The effect of melatonin injection on norepinephrine (NE) turnover rate in rat pineal gland was estimated from the decline of tissue NE levels after the injection of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine. The administration of a single injection of 300 micrograms/Kg of melatonin at the beginning of the scotophase induced, 3 hr later, a significant decrease of pineal NE turnover. The possible direct effect of melatonin on pineal NE release was examined in vitro. Exposure of rat pineal explants previously loaded with 3H-NE to 10(-8)-10(-6) M melatonin decreased significantly 3H-NE release triggered by 60 mM K+. This activity of melatonin was revealed only in pineals excised at night (0000 and 0400, i.e., at the fourth or eighth hours of darkness) and not in those excised in the middle (1400) or late light phase of the daily photoperiod (2000). Melatonin did not modify the spontaneous pineal 3H-NE efflux. Melatonin decreased 3H-NE uptake at a low NE concentration (0.5 microM) in a dose-dependent manner (IC50 identical to 10(-10) M). A kinetic analysis of the pineal NE uptake process indicated that melatonin augmented both Vmax and Km of transmitter uptake. These results suggest that endogenously released melatonin may be a regulatory signal for rat pineal sympathetic synapses.

Relationship between myocardial tissue norepinephrine and coronary flow heterogeneity

The purpose of this study was to investigate the hypothesis that heterogeneity of myocardial tissue norepinephrine content exists and is one of the controllers of flow heterogeneity in the canine myocardium. Tissue norepinephrine content was measured simultaneously with coronary blood flow in multiple sections of the left ventricle of eight anesthetized open-chest dogs. Radioactive microspheres were used for the measurement of blood flow during baseline and sympathetic stimulation. The left ventricle was cut into 15 subepicardial and 15 subendocardial sections. Norepinephrine levels of these same tissue sections were measured using high-pressure liquid chromatography. The average control coronary blood flow was 92.4 ± 19.5 ml/min/100 g. Ansa subclavia stimulation (10-msec duration, 18–24 V, 10 impulses/sec) increased coronary blood flow to 127.9 ± 21.9 ml/min/100 g. The average of the norepinephrine levels was 2480 ± 573 ng/g wet wt and the biological variation was almost four times the method variation. The within-animal coefficient of variation was 32.9%. No significant regional differences were found in flow or norepinephrine content. Regression analysis between the percentage of mean norepinephrine (PNE) and the percentage of mean control flow (Pflow) produced the equation: Pflow = 0.29 (PNE) + 70.4 ( r = 0.44, P < .0001). The equation for PNE vs percentage of stimulated flow is Pflow = 0.24 (PNE) + 76.2 ( r = 0.48, P < .0001). Thus, significant heterogeneity of tissue norepinephrine levels exists in the heart. There also appears to be a direct linear relationship between tissue norepinephrine content and coronary blood flow distribution in the canine myocardium.

Altered Responsiveness of Saphenous Vein Grafts to Norepinephrine and Tyramine

This study was designed to investigate early changes in reactivity in relation to the adrenergic innervation of venous grafts. Saphenous vein grafts were implanted into the carotid artery by the end-to-end technique in mongrel dogs. After 1 week, the grafts were harvested and dose-response curves to norepinephrine and tyramine were determined and compared with those of nongrafted saphenous veins and carotid arteries. Tissue norepinephrine levels of the blood vessels were measured by HPLC with electrochemical detection. Grafted vessels demonstrated an enhanced sensitivity to norepinephrine and a significant attenuation to tyramine. Additionally, grafted saphenous veins exhibited a significant depletion of norepinephrine content when compared to nongrafted veins. These differences suggest that denervation of the saphenous vein produces a supersensitivity to catecholamines that could account for enhanced vascular reactivity observed following implantation of saphenous vein grafts.

Determination of Norepinephrine Levels in the Adult Human Prostate

Tissue levels of norepinephrine were measured in prostate tissue from 24 men ranging in age between 41 and 83 years. Prostatic tissue was obtained from men with subtle palpable prostate nodules undergoing transperineal needle biopsy. None of the patients were shown to have histologic evidence of adenocarcinoma. The severity of the symptoms of prostatism was evaluated prospectively using a standardized micturition symptom score questionnaire. Norepinephrine levels were quantified using a sensitive radioenzymatic assay (REA). Overall, the prostates contained relatively high levels of norepinephrine (1666 ± 124ng./gm.). Inverse correlations were observed between tissue norepinephrine levels and severity of symptoms of prostatism (r = −0.58; p = 0.003); age (r = −0.53; p =.008); and prostate size (r = −0.48; p =.02). Norepinephrine levels were also measured in tissue specimens obtained from men undergoing enucleation prostatectomy and transurethral resection of the prostate (TURP). The level of norepinephrine in these prostatectomy specimens (115ng./gm.) was only 14% the level of the prostate biopsy specimens. The relatively low level of norepinephrine in the specimens obtained from patients with symptoms necessitating prostatectomy provides further evidence that norepinephrine levels are inversely related to the degree of symptomatic bladder outlet obstruction. (J. Urol., 144: 1263–1266, 1990)

The Effects of Estradiol and Progesterone on Reproductive Tract Atrophy and Tissue Adrenergic Indices in Diabetic C57BL/KsJ Mice

The diabetes-associated changes in tissue norepinephrine (NE) concentrations and related adrenergic receptor types were correlated with changes in blood glucose and serum insulin levels in 8- to 16-week-old C57BL/KsJ-db/db mice relative to corresponding age-matched control (+/?) parameters. In addition, the ability of estradiol and progesterone treatments to modify the diabetes-related adrenergic imbalance was investigated. Tissue (i.e., ovarian, uterine, pancreatic, and adrenal) NE levels were determined by high-performance liquid chromatography and compared with the associated changes in tissue alpha 1,2 and beta-adrenergic membrane receptor populations. All db/db mice exhibited overt hyperglycemia, hyperinsulinemia, and obesity relative to controls between 8 and 16 weeks of age. Tissue NE levels in diabetics were either similar to, or elevated, as compared with those of age-matched controls. Although the alpha 1 and beta receptor populations (except liver) were similar in 16-week-old groups, alpha 2 receptor populations in db/db mice were elevated relative to controls. Chronic estradiol therapy effectively counteracted the diabetes-induced elevations in tissue NE and influenced all adrenergic receptor populations, normalizing both parameters to control levels as well as modifying the hyperglycemia, but not the hyperinsulinemic component, of the diabetes-obesity syndrome in this species. Chronic progesterone treatment was found to be less effective in modulating these systemic and adrenergic parameters in diabetics relative to oil- or estradiol-treated mice. These data demonstrate that a marked modification in tissue adrenergic parameters occur in association with the overt expression of the diabetes mutation in this species. The ability of estradiol treatment to normalize both blood glucose levels and tissue adrenergic parameters in C57BL/KsJ-db/db mice indicates that a direct association between systemic and cellular counter-regulating influences, relative to the severity of the Type II diabetic condition, exists in this species. The therapeutic correction of these metabolic problems by ovarian steroid hormones suggests the existence of a causal relationship between cellular glucose homeostasis and steroid action in the diabetic model.