Enzymatic decarboxylation of L-threo-3,4-dihydroxyphenylserine in rat heart.

Decarboxylation of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) by the higher speed supernatant of the rat heart homogenate and the regional distribution of L-threo-DOPS decarboxylase activity were examined. Decarboxylation was demonstrated to occur specifically with L-isomer but not with D-isomer. Addition of pyrogallol was necessary for maximal recovery of norepinephrine. The optimal condition for decarboxylation of L-threo-DOPS by the rat heart enzyme was similar to conditions required with the enzymes from brain and kidney. Under the optimal conditions, Km and Vmax for L-threo-DOPS were 2.1 mM and 6.4 nmoles/mg protein/15 min, respectively. Decarboxylation of L-threo-DOPS was markedly inhibited by D-threo-DOPS and D-DOPA. The L-aromatic amino acid decarboxylase activity was highest in the right auricle followed by the atrial body, the left auricle, the right ventricle and the left ventricle.     

Intranasal l-threo-3,4,-dihydroxyphenylserine in Treating Diarrhea Associated With Familial Amyloidotic Polyneuropathy

We evaluated the absorption disturbance of the gastrointestinal tract in patients with familial amyloidotic polyneuropathy (FAP). Ursodeoxycholic acid (UDCA) 300 mg was administered orally to 10 patients with FAP and 11 control subjects. Serum levels of total bile acid were determined as an indicator of absorption. The patients had lower serum levels of total bile acid than controls, suggesting an absorption disorder. To attempt to treat the diarrhea commonly associated with FAP, l-threo-3,4-dihydroxyphenylserine (l-threo-DOPS), a synthetic precursor of norepinephrine, was administered 100 mg/dose by the oral and 8 mg/0.4 ml by the intranasal route and their effects on the elevation of serum norepinephrine levels were compared. The 3–0-monohemiphthalate salt of glycyrrhizinic acid and sodium ascorbate were used as vehicles for the intranasal preparation to enhance drug absorption and prevent oxidation. Increased serum levels of norepinephrine, the converted metabolite of l-threo-DOPS in serum, was observed 2 hours after intranasal administration, but not after administration of the oral preparation or vehicle alone. Intranasal administration of 8 mg 3 times/day for 1 week resulted in reduction of the daily frequency of diarrhea as well as a decrease in the severe orthostatic hypotension in three patients with FAP. Thus, an intranasal delivery system for l-threo-DOPS, which acts by stimulating adrenergic receptors, may be considered in treating patients with FAP with severe diarrhea.     

Characteristics of enzymic decarboxylation of L-threo-3,4-dihydroxyphenylserine using hog renal L-aromatic amino acid decarboxylase.

Decarboxylation of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) was examined in vitro using hog renal L-aromatic amino acid decarboxylase. Decarboxylation was measured by chemical assay of the reaction product, noradrenaline (NA), and was found to occur specifically with the L-isomer and not with the D-isomer. The maximum rate of decarboxylation of L-threo-DOPS was obtained in the presence of 10 μM pyridoxal phosphate (PALP) at 37° and pH 8.6. Under the optimal conditions, K_m and V_max for L-threo-DOPS were 4 × 10^?4 M and 2.80 nmoles NA/mg of protein/min respectively. Decarboxylation of L-threo-DOPS was competitively inhibited by L-3,4-dihydroxyphenylalanine (L-DOPA) and L-5-hydroxytryptophan (L-5-HTP). D-Threo-DOPS and D-DOPA at 0.125 mM inhibited the decarboxylation of L-threo-DOPS to about half that of the control. D-Erythro-DOPS at higher concentrations had a slight inhibitory effect on the decarboxylation of L-threo-DOPS, while D-5-HTP and D-tryptophan up to 1 mM had no effect whatever. The inhibition induced by D-threo-DOPS was competitive when the concentration of D-threo-DOPS was below that of L-threo-DOPS. When the concentration of the D-isomer was higher than that of the L-isomer, a noncompetitive inhibition was observed. Inhibition due to inactivation of PALP by interaction of PALP and D-isomer was ruled out. These results suggest that inhibition of decarboxylation of L-threo-DOPS by D-threo-DOPS is the result of the interaction of the D-isomer with the enzyme.     

Age-related changes in the chronotropic effect and the enzymic decarboxylation of L-threo-3,4-dihydroxyphenylserine in the rat heart

The cardiac effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) and the enzymatic decarboxylation of the drug by L-aromatic amino acid decarboxylase (AADC) were studied in atria isolated from rats ranging in age from newborn to adults and the findings compared with the cardiac effect of noradrenaline (NA). L-threo-DOPS produced dose-dependent, slow-onset and positive chronotropic effects in atria from rats of different ages. Its effect was inhibited in atria from benserazide-treated rats, suggesting that the effects are due to NA formed from L-threo-DOPS by enzymic decarboxylation rather than to the compound itself. Chronotropic sensitivity to L-threo-DOPS was highest in the newborn and decreased with age during the first 3 weeks of life. The development of cardiac response to it correlated well with the development of enzymic decarboxylation of the drug but did not correlate with the developments of chronotropic sensitivity to NA and of NA concentrations in the heart. These findings suggest that in newborn rats, L-threo-DOPS is effectively converted by AADC to NA which in turn acts on β-receptors in the pacemaker cell membrane.     

Pressor effect of L-threo-3,4-dihydroxyphenylserine in rats

The pressor effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) in rats and its decarboxylation in vivo have been examined. On i.v. administration, it produces a slow-onset and long-lasting pressor response, but no significant change in heart rate or e.c.g. The pressor effect was markedly reduced by inhibition of peripheral decarboxylase and by blockade of α-adrenoceptors. The slow-onset and long-acting pressor effect was also evident when the drug was given orally, while intracerebroventricular administration produced a long-lasting decrease in blood pressure. Noradrenaline (NA) concentrations in the plasma were significantly increased by both i.v. and oral administration of L-threo-DOPS. Elevation of plasma NA concentration by L-threo-DOPS given i.v. was suppressed by inhibition of decarboxylase. The plasma concentration of the drug was highest immediately after its i.v. administration. Its pressor effect was enhanced in rats made hypotensive by chemical sympathectomy with 6-hydroxydopamine (6-OHDA), compared with control rats, nevertheless, L-threo-DOPS produced the same increase in plasma NA concentrations in sympathectomized rats as in the controls. These results indicate that L-threo-DOPS is gradually converted to NA by L-aromatic amino acid decarboxylase in vivo. These findings suggest that L-threo-DOPS may be clinically useful as an oral pressor agent for the treatment of certain disorders related to hypotension.     

Pressor effect of L-threo-3,4-dihydroxyphenylserine in rats

The pressor effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) in rats and its decarboxylation in vivo have been examined. On i.v. administration, it produces a slow-onset and long-lasting pressor response, but no significant change in heart rate or e.c.g. The pressor effect was markedly reduced by inhibition of peripheral decarboxylase and by blockade of alpha-adrenoceptors. The slow-onset and long-acting pressor effect was also evident when the drug was given orally, while intracerebroventricular administration produced a long-lasting decrease in blood pressure. Noradrenaline (NA) concentrations in the plasma were significantly increased by both i.v. and oral administration of L-threo-DOPS. Elevation of plasma NA concentration by L-threo-DOPS given i.v. was suppressed by inhibition of decarboxylase. The plasma concentration of the drug was highest immediately after its i.v. administration. Its pressor effect was enhanced in rats made hypotensive by chemical sympathectomy with 6-hydroxydopamine (6-OHDA), compared with control rats, nevertheless, L-threo-DOPS produced the same increase in plasma NA concentrations in sympathectomized rats as in the controls. These results indicate that L-threo-DOPS is gradually converted to NA by L-aromatic amino acid decarboxylase in vivo. These findings suggest that L-threo-DOPS may be clinically useful as an oral pressor agent for the treatment of certain disorders related to hypotension.     

Formation of noradrenaline in the rat brain from the four stereoisomers of 3,4-dihydroxyphenylserine

Summary Intraperitoneal injection of the (+)-erythro isomer of 3,4-dihydroxyphenylserine (DOPS) to rats markedly increased the concentration of cerebral noradrenaline (NA) which probably corresponds to the unnatural (+) form. In contrast, the other 3 stereoisomers of DOPS caused only a minor rise of NA. This difference is likely to be connected with the configuration of the stereoisomers at the and carbon which determines the rate of decarboxylation and possibly of penetration into the brain.     

Diuretic effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) in anesthetized rats

A synthetic amino acid, L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS), can be converted to (-)-norepinephrine (NE) by aromatic L-amino acid decarboxylase (AADC) in various mammalian tissues. Recent studies have indicated the pressor and diuretic effects of L-threo-DOPS. In this study, we examined the effects of L-threo-DOPS on renal hemodynamics and function in anesthetized rats, and evaluated possible mechanisms of the diuresis. Intravenous infusion of L-threo-DOPS at 120 micrograms/kg/min exerted a significant increase in mean arterial pressure (MAP). There was a slight but nonsignificant decrease in renal blood flow (RBF). Although the glomerular filtration rate (GFR) remained at a constant level, urine flow (UF) and urinary sodium excretion (UNaV) increased significantly during the drug infusion. Pretreatment with AADC inhibitor, benserazide, completely blocked both the pressor and diuretic effects of L-threo-DOPS. When the renal perfusion pressure was protected from the pressor effect of the drug by using a Blalock clamp, the drug-induced diuresis was abolished. The diuretic effect of L-threo-DOPS was markedly attenuated by the administration of phentolamine. There was a positive correlation between plasma NE concentration and UF during the infusion of L-threo-DOPS. Intrarenal arterial infusion of L-threo-DOPS at 20 micrograms/kg/min was without effect on renal function. These results indicate that diuresis and natriuresis induced by L-threo-DOPS are dependent on the pressor effect of NE via peripheral alpha-adrenoceptor activation.     

Synthesis of norepinephrine from 3,4-dihydroxyphenylserine by L-aromatic amino acid decarboxylase of the rat brain and kidneys]

The enzymic decarboxylation of stereoisomers of DOPS was examined using rat brain and kidney decarboxylase. Optimal assay conditions for racemic threo- and racemic erythro-DOPS decarboxylation were determined by the experiments concerning 1) time course, linear for 20 min, 2) optimal pH, pH 8.2, 3) optimal temperature, 37 degrees C except racemic L-threo-DOPS decarboxylation by kidney enzyme and 4) protein concentration, 1 to 5 mg in incubation medium. Under the optimal assay condition, Km of brain enzyme for L-threo-DOPS was 1.43 X 10(-3)M and Vmax, 2.22 nmoles NE/mg/15min, and Km for racemic erythro-DOPS was 10(-3)M and Vmas, 4.3 nmoles NE/mg/15min. Km of kidney enzyme for L-threo-DOPS was 1.37 X 10(-3)M and Vmax 21 nmoles NE/mg/15min, and Km for racemic erythro-DOPS was 8.7 X 10(-4)M and Vmax, 16.7 nmoles NE/mg/15min. On the other hand, D-threo and D-erythro-DOPS were scarcely decarboxylated. Decarboxylation of L-threo-DOPS in kidney enzyme was markedly inhibited by D-threo-DOPS. Kinetic analysis revealed that the type of inhibition was non-competitive. In helically-cut strips of isolated rabbit aorta, the contractile response to NE (10(-8)g/ml) formed from L-threo-DOPS was 95% that of 1-NE (10(-8)g/ml) while the response to NE (10(-8)g/ml) formed from racemic erythro-DOPS was not detectable. These results suggest that L-threo-DOPS is a more effective precursor of natural 1-NE than racemic threo-DOPS.     

Memory effect of dl-threo-3,4-dihydroxyphenylserine (DOPS) in human Korsakoff's disease

A group of amnesic patients with Korsakoff's disease were treated with a single 1 g dose of dl-threo-3,4-dihydroxyphenylserine (DOPS) and placebo (lactose) in a double-blind crossover study. Three hours following administration, patients were given a battery of psychometric tests to determine the effects of the treatment on memory functions. Administration of DOPS had a significant effect on performance on the Memory Passages test but not on any of the other measures of memory. The effect of DOPS on Memory Passages is similar to the response observed following administration of clonidine in Korsakoff patients. Blood pressure and pulse, measured before and every 2 h after treatment, were unaffected by DOPS.     

Beneficial attenuating effect of L-threo-3,4-dihydroxyphenylserine on postural hypotension in anesthetized rats

The effects of L-threo-DOPS (L-threo-3,4-dihydroxyphenylserine), a non-physiologic precursor amino acid of the natural form of norepinephrine, on postural hypotension were assessed in anesthetized rats. Rats were pretreated with DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine), a norepinephrine-decreasing agent acting on central and peripheral tissues, or hexamethonium, a ganglion-blocking agent. Postural hypotension was induced by 60 degrees head-up tilt for 4 min. L-Threo-DOPS (1-10 mg/kg, i.v.) produced an increase in basal blood pressure and attenuation of the postural hypotension, which persisted in a dose-related manner in rats pretreated with DSP-4 (50 mg/kg, i.p. 24 h prior to the tilt-experiment). Hexamethonium (5 mg/kg, i.v.)-induced postural hypotension was also attenuated dose-dependently by i.p. (3-30 mg/kg)- or p.o. (30 and 100 mg/kg)-administered L-threo-DOPS, associated with an increase in basal blood pressure. Neither attenuation of postural hypotension nor increase in basal blood pressure was observed after L-threo-DOPS (30 mg/kg i.p.) in rats pre-injected with carbidopa (20 mg/kg i.v.), a peripheral aromatic L-amino acid decarboxylase inhibitor, under the hexamethonium pretreatment. The effects of L-threo-DOPS administered by cumulative i.v. infusion (12.5-50 micrograms/kg/min) on the pressor responses to either spinal sympathetic nerve stimulation (1-10 Hz) or i.v. bolus-injected tyramine were also examined. L-Threo-DOPS dose-relatedly potentiated the pressor response to nerve stimulation in rats either untreated or pretreated with DSP-4 and the pressor response to tyramine in rats pretreated with DSP-4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-related changes in the chronotropic effect and the enzymic decarboxylation of L-threo-3,4-dihydroxphenylserine in the rat heart

The cardiac effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) and the enzymatic decarboxylation of the drug by L-aromatic amino acid decarboxylase (AADC) were studied in atria isolated from rats ranging in age from newborn to adults and the findings compared with the cardiac effect of noradrenaline (NA). L-threo-DOPS produced dose-dependent, slow-onset and positive chronotropic effects in atria from rats of different ages. Its effect was inhibited in atria from benserazide-treated rats, suggesting that the effects are due to NA formed from L-threo-DOPS by enzymic decarboxylation rather than to the compound itself. Chronotropic sensitivity to L-threo-DOPS was highest in the newborn and decreased with age during the first 3 weeks of life. The development of cardiac response to it correlated well with the development of enzymic decarboxylation of the drug that did not correlated with the developments of chronotropic sensitivity to NA and of NA concentrations in the heart. These findings suggest that in newborn rats, L-threo-DOPS is effectively converted by AADC to NA which in turn acts on beta-receptors in the pacemaker cell membrane.     

L-dopa-like regulatory actions of L-threo-3,4-dihydroxyphenylserine on the release of endogenous noradrenaline via presynaptic receptors in rat hypothalamic slices.

Effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on the spontaneous release and the stimulus(2 Hz)-evoked release of endogenous noradrenaline were studied in rat hypothalamic slices with functioning L-aromatic amino acid decarboxylase (AADC) and with AADC inhibition. In non-inhibited slices, spontaneous release was not modified by L-threo-DOPS at 1 pM-100 nM, tended to increase at 1-10 microM and increased at 100 microM. Noradrenaline tissue content slightly increased at 100 microM. Stimulated release was concentration-dependently facilitated at 1-1000 pM and tended to decrease gradually from a maximum at 10 nM-10 microM. Under AADC inhibition, spontaneous release concentration-dependently increased at 10-100 microM by 60% of the increase seen in slices without AADC inhibition. Increase in noradrenaline tissue content was abolished. L-threo-DOPS produced a triphasic pattern on stimulated release; concentration-dependent facilitation at 1-1000 pM similar to that seen in slices with functional AADC, no facilitation at 10-1000 nM, and a concentration-dependent increment at 10-100 microM. The facilitation at 1 nM was stereoselective and was antagonized by (-)-propranolol 10 nM, and no facilitation at 100 nM was restored to the maximum by yohimbine 10 nM, DG-5128 10 nM or S-sulpiride 1 nM. Furthermore, L-threo-DOPS (1-1000 pM)-induced facilitation was competitively antagonized by L-dopa methyl ester, a competitive antagonist for L-dopa, with a pA2 value of 13.6, whereas it was noncompetitively antagonized by (-)-propranolol.     

Deamination of newly-formed dopamine in rat renal tissues.

1. The present study has examined the formation of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in slices of the rat renal cortex and the renal medulla loaded with exogenous L-beta-3,4-dihydroxyphenylalanine (L-DOPA). The effects of pargyline and of two selective inhibitors of monoamine oxidase (MAO) types A and B, respectively Ro 41-1049 and Ro 19-6327, on the deamination of newly-synthesized dopamine in kidney slices incubated with exogenous L-DOPA were also tested. The assay of L-DOPA, dopamine, noradrenaline and DOPAC was performed by means of h.p.l.c. with electrochemical detection. 2. Incubation of renal slices with exogenous L-DOPA resulted in a concentration-dependent accumulation of dopamine and DOPAC; the tissue levels of newly-formed dopamine and DOPAC in slices of the renal medulla were 6-8% of those in cortical slices. 3. Pargyline (0.1 mM) produced a marked decrease (84% reduction) in the formation of DOPAC in kidney slices loaded with 1.0 mM L-DOPA; this effect was accompanied by a 17% increase in the accumulation of dopamine. Similar effects were obtained at higher concentrations of pargyline (0.5 and 1.0 mM). At 5.0 and 10.0 mM pargyline, a marked decrease (46 and 76% reduction) in the accumulation of newly-formed dopamine was observed. 4. The accumulation of dopamine and DOPAC was found to be time-dependent in experiments in which tissues were incubated with 5 and 10 microM L-DOPA for 5, 10, 20 and 30 min. Pargyline (0.1 mM) produced an increase in the accumulation of dopamine at all incubation periods and decreased the formation of DOPAC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diuretic effect of L-threo-3,4-dihydroxyphenylserine, a noradrenaline precursor, in rats and mice

L-Threo-DOPS, a noradrenaline (NA) precursor, produced a dose-dependent increase in the volume of urine in mice and rats. It also increased the total output of sodium and chloride ions, but not the excretion of potassium ion. Treatment with peripheral decarboxylase inhibitors antagonized not only the diuretic action, but also the increase in the concentration of kidney NA produced by L-threo-DOPS. These results suggest that the diuretic action of L-threo-DOPS might not be due to its direct action, but largely to NA formed by its decarboxylation in the kidney.     

Effect of infused L-threo-3,4-dihydroxyphenylserine on adrenergic activity in patients with familial amyloid polyneuropathy

Summary L-threo-3,4-dihydroxyphenylserine (DOPS), an immediate precursor amino acid of (-)-norepinephrine, was used as a pharmacological tool to investigate the pathophysiology of the peripheral sympathetic nervous system in Type 1 familial amyloid polyneuropathy. Patients with the well-established disorder showed an enhanced pressor reponse to L-threo-DOPS under conditions that produced no change in normal subjects. While octopamine induced a brisk pressor response, L-threo-DOPS produced a slow and prolonged change in blood pressure, with a marked concomitant increase in urinary excretion of norepinephrine. A slight increase in urinary excretion of total metanephrine was observed in both groups, but there was no significant increase in serum dopamine--hydroxylase activity. Since infusion of dilute norepinephrine into patients also produced a markedly hypersensitive response, the characteristic pressor response to L-threo-DOPS was indicative of denervation supersensitivity of adrenergic receptors to norepinephrine formed enzymatically from L-threo-DOPS.