Alteration of extracellular matrix in dilated cardiomyopathic hamster heart

The purpose of this study was to characterize the collagen in hereditary dilated cardiomyopathic hamster hearts, and to examine the participation of the collagen in the occurrence and progression of cardiomyopathy.BIO 53.58 hamsters (5, 10, 20 weeks old) were used as the model of dilated cardiomyopathy. Flb hamsters were used as controls. The collagen content was almost constant at any age in the Flb hamsters, but increased with age in BIO 53.58 hamsters. Type III collagen increased significantly in BIO 53.58 hamsters at 10 weeks. The acetic acid solubility of collagen decreased in BIO 53.58 hamsters as the fibrosis progressed, but was unchanged in controls. Reducible crosslinks showed a tendency to decrease progressively in BIO 53.58 hamsters. There were no differences between Flb and BIO 53.58 hamsters at 5 weeks, but its expression in BIO 53.58 hamsters at 10 and 20 weeks of age increased compared to Flb controls.These findings indicate that in the early phase of cardiomyopathy the extracellular matrix of the myocardium is rich in type III collagen. In the later phase, the matrix resembles that of hard tissues, whose collagen is mainly of type I collagen and is insoluble. These data suggest that the increased collagen synthesis may impair the cardiac function in the development of cardiomyopathy.     

Left ventricular catecholamines during acute myocardial infarction in the dog

To determine whether changes in left ventricular catecholamine content occur during the first 30 to 90 min of acute myocardial infarction, myocardial catecholamine (radioenzymatic assay) over the interval was studied in the dog. In nine pentobarbital-anesthetized opened-chest dogs without coronary ligation, myocardial catecholamine at 2.5 h after pentobarbital (i) consisted mainly of norepinephrine (87% total catecholamine), (ii) showed a base to apex gradient in norepinephrine (1.44 +/- 0.10 vs. 1.03 +/- 0.10 micrograms/g, p less than 0.05) and dopamine (0.20 +/- 0.03 vs. 0.12 +/- 0.02 micrograms/g, p less than 0.05) but not epinephrine (0.017 vs. 0.016 micrograms/g), and (iii) showed no difference in norepinephrine, dopamine, or epinephrine across basal, mid, and apical left ventricular transverse planes spanning the vascular territories of the two coronary arteries. In 18 pentobarbital-anesthetized dogs with coronary ligation, (i) norepinephrine, measured in 14 regions across the mid left ventricle after 90 min ischemia in four dogs, was less in the ischemic center of the occluded bed than normal myocardium (1.01 +/- 0.04 vs. 1.29 +/- 0.04 micrograms/g, p less than 0.05), and (ii) norepinephrine was unchanged in normal myocardium of 14 dogs at 30, 60, 90 min, and 48 h but decreased in ischemic myocardium by 31% at 60 min (0.89 +/- 0.10 vs. 1.29 +/- 0.08 micrograms/g, p less than 0.025) and 79% at 48 h (0.27 +/- 0.04 vs. 1.26 +/- 0.08 micrograms/g, p less than 0.001). Thus, norepinephrine depletion from ischemic but not normal myocardium is detectable by 60 min during acute myocardial infarction.     

Analysis of plasma catecholamines by high-performance liquid chromatography with fluorescence detection: simple sample preparation for pre-column fluorescence derivatization

Analysis of plasma catecholamines (norepinephrine, epinephrine and dopamine) by high-performance liquid chromatography using 1,2-diphenylethylenediamine as a fluorescent reagent is described. We have developed an automatic catecholamine analyser, based on pre-column fluorescence derivatization and column switching. The analysis time for one assay was 15 min. The correlation coefficients of the linear regression equations were greater than 0.9996 in the range 10–10 000 pg/ml. The detection limit, at a signal-to-noise ratio of 3, was 2 pg/ml for dopamine. A new method of sample preparation for the pre-column fluorescence derivatization of plasma catecholamines was used. In order to protect the catecholamines from decomposition, an ion-pair complex between boric acid and the diol group in the catecholamine was formed at a weakly alkaline pH. The stabilities of plasma catecholamines were evaluated at several temperatures. After complex formation, the catecholamines were very stable at 17°C for 8 h, and the coefficients of variation for norepinephrine, epinephrine and dopamine were 1.2, 4.2 and 9.3%, respectively.     

The influence of superovulation preparations on the levels of catecholamines in eminentia mediana, the pituitary and pineal gland of the sheep.

The influence of hormonal superovulation preparations of FSH (450 IU) or PMSG (1500 IU), on the levels of catecholamines (dopamine, norepinephrine and epinephrine) was studied in the oestrus period using radioenzymatic methods. The administration of FSH caused a significant increase in the concentrations of norepinephrine (NE) and epinephrine (EPI) in eminentia mediana (EM) of sheep (p<0.001 and p<0.01, respectively). The pituitary gland exhibited an increase in the level of norepinephrine after administration PMSG while no marked changes were recorded for epinephrine and dopamine (DA). The administration of FSH affected the increase in pituitary epinephrine (p<0.01). The hormonal stimulation by FSH resulted in a marked decrease of dopamine (p<0.05) as well as in a significant increase of norepinephrine (p<0.05) and epinephrine (p<0.05) in the epiphysis. The comparison of the effect of hormonal preparations on the changes in catecholamine levels showed that the effect of FSH was observed mostly in eminentia mediana and the pituitary gland while that of PMSG was recorded in the epiphysis.     

Interactions of nimodipine and cocaine on endogenous catecholamines in the squirrel monkey

The effects of nimodipine on the cocaine-induced alterations in blood pressure, heart rate, and plasma catecholamines were studied in the squirrel monkey. Cocaine in intravenously administered doses of 0.5, 1, and 2 mg/kg produced significant increases in blood pressure and significant decreases in heart rate. These cardiovascular changes were associated with transient episodes of arrhythmias and with significant increases in plasma concentrations of dopamine, epinephrine, and norepinephrine. Nimodipine, 1 micrograms/kg/min for 5 min administered intravenously 5 min after cocaine, corrects the cardiovascular and plasma catecholamine concentration changes induced by this alkaloid. The same dose of nimodipine administered 5 min before cocaine prevents elevations of blood pressure. Plasma catecholamine increments are also prevented except for the highest dose of cocaine. Cardiovascular changes induced by cocaine administration in the squirrel monkey are temporally associated with significant increments in plasma catecholamines. Administration of nimodipine prevents or minimizes these endocrine and physiologic changes.     

Catecholamine concentrations in plasma and organs of the fetal guinea pig during normoxemia, hypoxemia, and asphyxia

To examine the responses of the sympatho-adrenal system to reduced oxygen supply we studied plasma and tissue concentrations of catecholamines during normoxemia, hypoxemia, and asphyxia in 22 fetal guinea pigs near term. Fetal blood was obtained by cardiopuncture in utero under ketamine/xylazine-anesthesia. Catecholamines were determined in plasma and tissue of 15 organs and 14 brain parts by HPLC-ECD. During normoxemia (SO2 54 +/- 4 (SE) %, pH 7.36 +/- 0.02, n = 5) plasma catecholamine levels were low (norepinephrine 447 +/- 53, epinephrine 42 +/- 12, dopamine 44 +/- 6 pg/ml). During hypoxemia (SO2 27 +/- 3%, pH 7.32 +/- 0.01, n = 6) and asphyxia (SO2 24 +/- 2%, pH 7.23 +/- 0.02, n = 11) tissue catecholamine concentrations changed with changing blood gases and with increasing plasma catecholamines. Norepinephrine concentrations increased in both skin and lung and decreased in liver, pancreas, and scalp; those of epinephrine increased in the heart, lung liver, and scalp and decreased in the adrenal. There were only minor changes in brain catecholamine concentrations except for a 50% reduction in dopamine in the caudate nucleus. Concentrations of dopamine catabolite 3,4-dihydroxyphenylacetic acid decreased in many brain parts, suggesting that cerebral catecholamine metabolism was affected by hypoxemia and asphyxia. We conclude that the sympatho-adrenal system of fetal guinea pigs near term is mature and that its stimulation by reduced fetal oxygen supply leads to changes in both plasma and tissue catecholamine concentrations.     

Enzymatic deconjugation of catecholamines in human and rat plasma and red blood cell lysate

We have developed a method for enzymatic hydrolysis of both sulfated and glucuronidated catecholamines in plasma and red blood cell lysate. Hydrolysis occurs in the course of the radioenzymatic assay for catecholamines. In human plasma, catecholamines are conjugated almost entirely with sulfate while, in rat plasma, glucuronides are the main conjugates of epinephrine and dopamine but not norepinephrine. Rat plasma contains less percent conjugated catecholamine than human plasma. Human red blood cell lysate contains less conjugated catecholamine than plasma, whereas free E in lysate exceeds that of plasma and free NE has same level both in plasma and lysate. This method is useful in detecting total (free + sulfated + glucuronidated) catecholamines and the nature of conjugated catecholamines.     

Estimation of catecholamines in human plasma by ion-exchange chromatography coupled with fluorimetry

Estimation of catecholamines in human plasma was made by ion-exchange chromatography coupled with fluorimetry.Catecholamines in deproteinized plasma were adsorbed onto Amberlite CG-50 (pH 6.5, buffered with 0.4 M phosphate buffer) and selectively eluted by 0.66 M boric acid. The catecholamine fraction was separated further on a column of Amberlite IRC-50 which was coupled with a device for the automated performance of the trihydroxyindole method (epinephrine and norepinephrine) or the 4-aminobenzoic acid—oxidation method (dopamine). One sample could be analysed within 25 min with either method. The lower detection limits were 0.02 ng for epinephrine and dopamine, and 0.04 ng for norepinephrine.Plasma catecholamine contents of healthy adults at rest were epinephrine 0.07 ± 0.01 ng/ml (n = 19), norepinephrine 0.27 ± 0.03 ng/ml (n = 19) and dopamine 0.22 ± 0.03 ng/ml (n = 26).The procedure of adsorption and elution of the plasma catecholamines by ion-exchange resin was simple, the simplicity contributing to constant recovery. The catecholamine fraction could be analysed without evaporation of the eluate. The analytical column could be used for the analysis of more than 1000 samples before excessive back-pressure developed. Our method of continuous measurement of plasma catecholamine fulfils clinical requirements.     

Catecholamines and uterine activity rhythms in the pregnant rhesus macaque.

This study was designed to examine the relationship between uterine contractile rhythms with maternal plasma and amniotic fluid catecholamine concentrations in the pregnant rhesus macaque. Six chronically catheterized rhesus macaques were maintained in a vest and tether system and exposed to a 12L:12D cycle. Continuous uterine activity recordings demonstrated a contractile pattern with peak activity at 2200 h (p less than 0.05). Paired maternal plasma and amniotic fluid samples were collected at 3-h intervals for 24 h between Days 131 and 148 of gestation. Samples were analyzed for norepinephrine, epinephrine, and dopamine by HPLC. Maximum plasma concentrations across the 24-h periods for norepinephrine (633 +/- 230; mean pg/ml +/- SEM) and dopamine (378 +/- 110) were observed at 2100 h and epinephrine (408 +/- 95) at 1200 h, but these values were not significant. The maximum amniotic fluid values were 378 +/- 126, 267 +/- 190, and 556 +/- 87 pg/ml for norepinephrine, epinephrine and dopamine, respectively. However, concentrations across 24 h did not differ. Neither maternal plasma nor amniotic fluid catecholamine concentrations were correlated with uterine activity rhythms. Therefore, we conclude that the nocturnal uterine activity in the rhesus macaque is not related to maternal arterial or amniotic fluid catecholamine concentrations.     

Catecholamine and blood pressure regulation by gonadotropin-releasing hormone analogs in amphibians

Analogs of gonadotropin-releasing hormone (GnRH) occur in the brain, plasma, and sympathoadrenal system of anuran amphibians. The present experiments studied the effects of GnRH and [Trp7, Leu8]-GnRH on plasma catecholamines and cardiovascular function in conscious adult bullfrogs (Rana catesbeiana) and cane toads (Bufo marinus). Both GnRH analogs elicited dose-dependent (0.1-1 nmol.kg-1) increases in arterial norepinephrine, epinephrine, and blood pressure levels when injected intravenously into toads. In bullfrogs, [Trp7, Leu8]-GnRH (1 nmol.kg-1) increased arterial norepinephrine concentration approximately 10-fold without affecting the concentrations of norepinephrine sulfate, norepinephrine glucuronide, epinephrine, epinephrine sulfate, or epinephrine glucuronide. The noradrenergic response of bullfrogs to [Trp7, Leu8]-GnRH was specific to the neurohormone because it could be inhibited by [D-pGlu1, D-Phe2, D-Trp3,6]-GnRH. The sympathomimetic activities of the GnRH analogs did not depend on changes in temperature, which occur seasonally in natural habitats, because similar noradrenergic responses were observed at 4 and 22 degrees C. GnRH and [Trp7, Leu8]-GnRH (0.01-10 nmol.kg-1) did not raise arterial blood pressure in bullfrogs despite their pressor actions in toads. This interspecific difference was remarkable because cardiovascular responses to norepinephrine, angiotensin II, and vasotocin in bullfrogs were similar to those in toads. The parallels between catecholamine and blood pressure responses suggest that epinephrine is the principal mediator of the blood pressure response to native GnRH analogs in toads. In bullfrogs, [Trp7, Leu8]-GnRH mobilizes norepinephrine but not epinephrine, and the noradrenergic effect is insufficient to raise blood pressure. These observations are consistent with a physiological role for native GnRH analogs in the regulation of the sympathoadrenal system in anuran amphibians.     

Flux of catecholamines through chromaffin vesicles in cultured bovine adrenal medullary cells

Primary cultures of bovine adrenal medullary chromaffin cells were pulse-labeled with [3H]dopamine or [3H]norepinephrine and examined for radioactive and total catecholamine contents by high performance liquid chromatography after additional incubations of 15 min to 10 days. [3H]Dopamine was rapidly taken up by chromaffin vesicles in situ and converted to norepinephrine with a half-time of approximately 6 h. [3H] Norepinephrine taken up by the cells was metabolized in three phases. 1) During its brief transit through the cytoplasm, 20 to 35% of this amine was converted to [3H]epinephrine. 2) Following vesicular accumulation, 65 to 70% of the remaining [3H]norepinephrine was methylated to form [3H]epinephrine with a half-time of approximately 30 h, corresponding to the rate of vesicular catecholamine loss from reserpine-treated cells. 3) The residual [3H]norepinephrine decreased with a half-time of 5 days, probably representing loss from norepinephrine-storing cells. [3H]Epinephrine formed endogenously had a half-life in the cultures of approximately 15 days. These data suggest that leakage of norepinephrine from chromaffin vesicles into the cytoplasm limits the rate of dopamine conversion to epinephrine in the adrenal medulla. The kinetic data indicate that approximately 18% of the endogenous norepinephrine and 73% of the endogenous dopamine are present in epinephrine cells.     

Influence of age on orthostatic changes in plasma renin activity and urinary catecholamines in man.

The authors studied plasma renin activity (PRA), urinary epinephrine, norepinephrine and dopamine excretion and their mutual relationships in 54 healthy subjects under basal (recumbent) conditions and age-related orthostatic changes in these parameters. The test subjects were divided into six 10-years groups, according to their year of birth (1901-1910 to 1951-1960). In the oldest groups (1901-1910 and 1911-1920), both basal PRA values and norephrine and epinephrine excretion and their postural increase were smaller than in younger subjects. Conversely, urinary dopamine excretion and the dopamine/norepinephrine and epinephrine ratio rose with advancing age. There were no significant differences between the plasma sodium and potassium concentrations in the various groups. Urinary aldosterone excretion was slightly higher in the oldest group than in the others, but was still within the control value limits. The intravenous administration of Inderal reduced both resting PRA values and the orthostatic increase in the youngest age groups, so that their PRA approached the values in older subjects. Higher norepinephrine and epinephrine excretion and the lower dopamine/norepinephrine and epinephrine in young subjects may play a role in their higher PRA, especially in the orthostatic reaction. Diminution of sympathetic activity, with lower norepinephrine and epinephrine excretion and relatively high dopamine excretion, may have a direct bearing on the lower PRA values in older subjects. The diminished capacity of older subjects for catecholamine mobilization and raised renin secretion during an orthostatis stress may be related to the higher incidence of orthostatic forms of hypotension in old age.     

Effects of exercise on plasma catecholamine levels in the toad, Bufo paracnemis: role of the adrenals and neural control

Resting plasma epinephrine (E) and norepinephrine (N) concentrations for intact toads (Bufo paracnemis) were 5.57+/-1.0 and 0.88+/-0.38 ng/ml, respectively. Exercise induced a significant increase in heart rate, blood pressure and plasma epinephrine (about 4.3 times), whereas norepinephrine remained unchanged. The resting [E]/[N] ratio was 6.3 and increased to 32.9 during exercise. Adrenal denervation did not alter the basal plasma catecholamine or norepinephrine levels after exercise, but prevented the increase in epinephrine during exercise, suggesting that in the intact toad this increase is due to adrenal secretion whereas resting norepinephrine may be liberated by extra-adrenal chromaffin tissues. This also suggests that the adrenal glands can release selectively the two catecholamines. The increases in heart rate and blood pressure in denervated toads were not significantly different from those of intact animals, suggesting that during exercise the sympathetic nerves play the main role in inducing cardiovascular responses. Spinal transection induced a significant increase in basal norepinephrine levels, which remained elevated after exercise. Since spinal toads are unable to perform spontaneous movements it is possible that this increase may be caused by this stressful condition. The increases in heart rate and blood pressure observed in spinal toads during exercise may be due to direct mechanical effects of venous return on the heart.     

Adrenomedullary Secretion of DOPA, Catecholamines, Catechol Metabolites, and Neuropeptides

Abstract: Catecholamines and their metabolites have been proposed as markers of sympathetic nervous system stimulation. However, the adrenal medulla is a rich source of catecholamines and catecholamine metabolites and may play a significant role in plasma levels of these compounds. In addition to adrenal catecholamine metabolite efflux, the role of the catecholamine precursor 3,4-dihydroxyphenylalanine (DOPA) has not been fully evaluated. The simultaneous effluxes of catecholamines, metabolites, DOPA, and neuropeptides were measured in perfusates from isolated dog adrenals. The relative abundance of compounds detected consistently during unstimulated conditions was epinephrine ≫ norepinephrine > 3,4-dihydroxyphenylglycol > metanephrine > normetanephrine > dopamine > 3,4-dihydroxyphenylacetic acid > 3-methoxy-4-hydroxyphenylglycol ≥ DOPA ≫ [Met]enkephalin ≫ neuropeptide Y. Effluxes of analytes were not affected by cocaine and the ratios of catecholamines to metabolites increased dramatically with carbachol stimulation, consistent with negligible reuptake into adrenal cells. Thus, most of the 3,4-dihydroxyphenylglycol is expected to be derived from epinephrine and norepinephrine subsequent to translocation from chromaffin vesicles into the cytosol. The efflux of DOPA increased dramatically during stimulation with 30 µ M carbachol in a calcium-dependent manner. Efflux of DOPA during the initial stabilization period of the perfusion preparation declined exponentially, in parallel with the effluxes of the catecholamines and neuropeptides but not with metabolites. Evoked release of DOPA was Ca²⁺-dependent. These data suggest that DOPA can be stored and released exocytotically from chromaffin granules.     

Activation of angiotensin II receptors in brain potentiates the stimulating effect of endogenous opioid neurons on central sympathetic outflow

Endogenous opioid peptides appear to have neurotransmitter or neuromodulator functions in brain mediating a wide variety of effects. We have reported that intracisternal administration of synthetic human beta-endorphin increases plasma concentration of catecholamines, apparently by acting at unknown brain sites to increase sympathetic outflow to the adrenal medulla and sympathetic nerves. In the present study we examined the possibility that angiotensin II, acting in brain, modulates endorphin-induced catecholamine secretion. Simultaneous intracisternal administration of angiotensin II 1.0 nmol together with synthetic human beta-endorphin 1.45 nmol potentiated the plasma epinephrine, norepinephrine and dopamine responses to intracisternal beta-endorphin. In contrast, simultaneous intracisternal administration of the angiotensin II antagonist, [Sar1, Val5, Ala8]-angiotensin II (saralasin), 1.1 nmol together with beta-endorphin, blunted the plasma epinephrine, norepinephrine and dopamine responses to beta-endorphin. These data are consistent with the hypothesis that activation of angiotensin II receptors in brain potentiates the endorphin-induced stimulation of central sympathetic outflow. It remains to be demonstrated whether angiotensin II acting in brain to modulate activity of opioid neurons is synthesized in brain or is derived peripherally.     

Catecholamines, cocaine toxicity, and their antidotes in the rat.

Acute lethal cocaine intoxication in the rat induces significant increases of plasma dopamine, norepinephrine, and epinephrine concentrations associated with cardiac functional and morphologic changes. Nitrendipine (a calcium channel antagonist) administered 5 min following cocaine administration lowers catecholamine concentration and restores cardiovascular function to normal, while preventing lethality, and so does enalaprilat (an enzyme-converting inhibitor) administration with diazepam. Cocaine cardiac toxicity in the rat appears to be associated with a significant stimulation of the sympathoadrenal and a sustained elevated plasma concentration of epinephrine. The renin angiotensin system also appears to be activated.     

Alteration of Catecholamine Phenotype in Transgenic Mice Influences Expression of Adrenergic Receptor Subtypes

Abstract: Agonist-induced regulation of adrenergic receptors (ARs) has an important role in controlling physiological functions in response to changes in catecholamine stimulation. We previously generated transgenic mice expressing phenylethanolamine N -methyltransferase (PNMT) under the control of a human dopamine β-hydroxylase gene promoter to switch catecholamine specificity from the norepinephrine phenotype to the epinephrine phenotype. In the present study, we first examined changes in catecholamine metabolism in peripheral tissues innervated by sympathetic neurons of the transgenic mice. In the transgenic target tissues, a high-level expression of PNMT led to a dramatic increase in the epinephrine levels, whereas the norepinephrine levels were decreased to 48.6–87.9% of the nontransgenic control levels. Analysis of plasma catecholamines in adrenalectomized mice showed large amounts of epinephrine derived from sympathetic neurons in the transgenic mice. Subsequently, we performed radioligand binding assays with (−)-[¹²⁵I]iodocyanopindolol to determine changes in binding sites of β-AR subtypes. In transgenic mice, the number of β2-AR binding sites was 56.4–74.9% of their nontransgenic values in the lung, spleen, submaxillary gland, and kidney, whereas the β1-AR binding sites were regulated in a different fashion among these tissues. Moreover, northern blot analysis of total RNA from the lung tissues showed that down-regulation of β2 binding sites was accompanied by a significant decrease in steady-state levels of the receptor mRNA. These results strongly suggest that alteration of catecholamine specificity in the transgenic sympathetic neurons leads to regulated expression of the β-AR subtypes in their target tissues.     

Study of salivary catecholamines using fully automated column-switching high-performance liquid chromatography

Cortisol and catecholamines are major physiological markers of human stress. In order to establish a fully automated assay system for both cortisol and catecholamines in saliva, which can be sampled without imposing stress, the previously developed system for salivary cortisol [Okumura et al., J. Chromatogr. B, 670 (1995) 11] was modified. The practical sensitivity was around 0.1 pmol ml⁻¹ for norepinephrine and epinephrine and 0.5 pmol ml⁻¹ for dopamine. The established assay procedure provided R.S.D. values of 2∼3% and recoveries of 96∼104% at 0.5 pmol ml⁻¹. Measurement of salivary catecholamines in more than 300 samples taken from about 50 healthy volunteers indicated that the normal values of norepinephrine and dopamine were very low, about 0.1 pmol ml⁻¹ each. In contrast to cortisol, salivary catecholamine levels did not parallel those in plasma. Nevertheless, since levels of salivary catecholamines may reflect the sympathetic nerve activity in the salivary gland, they were assayed in volunteers making a scientific presentation before a large audience. Four out of eleven volunteers reported strong feelings of fear or anxiety, and their salivary catecholamine levels were about ten times higher than normal.     

Effect of dietary proteins and carbohydrates on urinary and sympathoadrenal catecholamines

We previously observed that administration of tyrosine to rats or humans elevated urinary dopamine, norepinephrine and epinephrine levels. The present studies examine the effects on these urinary catecholamines of varying the ratio of protein to carbohydrate in the diets.Rats consumed diets containing 0, 18 or 40% protein (76, 58 and 36% carbohydrate respectively) for 8 days. The stress of consuming the protein-free food was associated with a 16% weight reduction, and with significantly lower serum, heart and brain tyrosine levels than those noted in rats eating the 18 or 40% protein diets. Absence of protein from the diet also decreased urinary levels of dopamine and DOPA but increased urinary norepinephrine and epinephrine, probably by increasing sympathoadrenal discharge; it also increased the excretion of DOPA in animals pretreated with carbidopa, a DOPA decarboxylase inhibitor. Carbidopa administration decreased urinary dopamine, norepinephrine and epinephrine as expected; however, among carbidopa-treated rats urinary norepinephrine and epinephrine concentrations were highest for animals consuming the protein-free diet, again suggesting enhanced release of stored catecholamines from sympathoadrenal cells. The changes in urinary catecholamines observed in animals eating the protein-free diet were similar to those seen in rats fasted for 5 days: dopamine levels fell sharply while norepinephrine and epinephrine increased.These data indicate that the effects of varying dietary protein and carbohydrate contents on dopamine secretion from peripheral structures differ from its effects on structures secreting the other two catecholamines. Protein consumption increases dopamine synthesis and release probably by making more of its precursor, tyrosine, available to peripheral dopamine-producing cells; it decreases urinary norepinephrine and epinephrine compared with that seen in protein-deprived animals, probably by diminishing the firing of sympathetic neurons and adrenal chromaffin cells.     

Catecholamine binding to plasma membrane enriched fractions of heart and skeletal muscle.

Binding of [3H]epinephrine to plasma membrane enriched fractions from guinea pig heart and rabbit skeletal muscle was investigated using the micropore filtration technique. [3H]Epinephrine and [3H]norepinephrine were found to be degraded rapidly in aqueous buffer at pH 7.6 and 37 degrees C. Deterioration of the compounds could be prevented by low concentrations of dithiothreitol. Binding of [3H]epinephrine to both membrane preparations was a slow process requiring 60 min to approach equilibrium in the case of cardiac membranes at 37 degrees C, and 20 min for skeletal muscle membranes at O degrees C. Binding was antagonized by the unlabeled beta-agonists, isopropylnorepinephrine, epinephrine, and norepinephrine but all were equipotent. A variety of catechol compounds were as effective antagonists of binding as the catecholamines. The beta-adrenergic antagonists propranolol, pronethalol, and dichloroisoproterenol were not effective in inhibiting binding to either membrane preparation. D-Norepinephrine and L-norepinephrine were equi-effective in antagonizing binding of [3H]norephinephrine to skeletal muscle membranes. It was concluded that binding of labeled catecholamine to isolated tissue membranes using the micropore filtration technique does not represent interaction with the specific beta-adrenergic receptor, but more likely reflects a less specific binding of compounds having one or more hydroxyl groups on a ring.