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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The potential role of adrenaline, both circulating and in the central nervous system, in the maintenance of high blood pressure was examined in stroke-prone spontaneously hypertensive rats (SHRSP). alpha-Monofluoromethyldopa, a long-lasting inhibitor of dopa decarboxylase, was used to induce rapid depletion of central and peripheral catecholamine stores. Subsequent inhibition of phenylethanolamine-N-methyltransferase (PNMT) allowed the gradual restoration of dopamine and noradrenaline but not adrenaline, resulting in a greater relative depletion of adrenaline. Adrenaline was almost totally depleted in the circulation and peripheral tissues. The resting level of blood pressure, however, was unaffected, excepting after administration of a vasopressin (AVP) antagonist. Moreover, there was no reduction in the magnitude of acute pressor responses to electrical stimulation of the rostral ventrolateral medulla oblongata (C1 area), despite extensive loss of adrenaline from the brainstem and spinal cord. The results suggest that adrenaline contributes to the resting level of blood pressure but that its loss can be offset by the pressor activity of AVP. Thus neither central nor peripheral adrenaline stores appear to be essential for the maintenance of hypertension or for centrally-evoked vasoconstriction in adult SHRSP.
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PMID:Effects of depleting central and peripheral adrenaline stores on blood pressure in stroke-prone spontaneously hypertensive rats. 194 21

Tyrosine is the precursor of catecholamines. Small doses of tyrosine produce tachycardia and hypertension while higher doses produce bradycardia and hypotension in anaesthetised rats. The mechanism of these effects has not been established. An increased synthesis and release of catecholamines has been suggested to be the mechanism. Various pretreatments were given to anaesthetised Wistar rats to study the influence of a blockade of L-tyrosine metabolism and thus a blockade of catecholamine synthesis, on these cardiovascular effects: valine, which inhibits tyrosine uptake into brain, alpha-methyl-p-tyrosine, which blocks the rate-limiting enzyme, tyrosine hydroxylase, carbidopa and benserazide, which both inhibit dopa decarboxylase, and desipramine, which blocks catecholamine re-uptake. Benserazide and alpha-methyl-p-tyrosine partially blocked the stimulatory effects of tyrosine. None of the pretreatments were able to block effectively the inhibitory effects of L-tyrosine. Therefore, the metabolism of tyrosine to form catecholamines may be involved in the stimulatory but not in the inhibitory cardiovascular effects of L-tyrosine. Valine pretreatment did not antagonize the depressant effects of tyrosine. Since valine blocks the uptake of L-tyrosine into the brain, the depressant effects of L-tyrosine might be peripheral rather than central in origin.
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PMID:Cardiovascular effects of L-tyrosine: influence of blockade of tyrosine metabolism. 256 1

Elevation of brain catecholamine levels by systemic administration of L-dopa in dogs pretreated with the dopa decarboxylase inhibitor carbidopa inhibits the secretion of vasopressin and adrenocorticotropic hormone (ACTH) and decreases arterial blood pressure. The aim of the present study was to determine whether the inhibition of vasopressin secretion is mediated by dopamine or norepinephrine, both of which have been implicated in the control of vasopressin secretion, and whether the decrease in vasopressin secretion contributes to the suppression of ACTH secretion and fall in blood pressure produced by L-dopa. This was accomplished by comparing the effects of dopamine and alpha-adrenergic receptor antagonists on vasopressin, ACTH, and blood pressure responses to L-dopa. The effect of a specific antagonist of the vasoconstrictor action of vasopressin also was studied. Injection of L-dopa (20 mg/kg i.v.) in dogs pretreated with carbidopa (20 mg/kg i.v.) caused reductions in plasma vasopressin concentration (from 16.0 +/- 4.8 to 3.8 +/- 0.9 pg/ml; p less than 0.05), plasma ACTH concentration (from 96.0 +/- 20.4 to 49.2 +/- 10.0 pg/ml; p less than 0.05), and mean arterial pressure (from 121 +/- 6 to 78 +/- 5 mm Hg; p less than 0.05). Pretreatment with pimozide (1 mg/kg i.p.) completely blocked the inhibition of vasopressin secretion by L-dopa but failed to block the suppression of ACTH secretion (57.6 +/- 11.8 to 34.0 +/- 5.1 pg/ml; p less than 0.05) or the decrease in mean arterial pressure (126 +/- 5 to 93 +/- 7 mm Hg; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Hypertension 1986 Oct
PMID:Role of dopamine in the inhibition of vasopressin secretion by L-dopa in carbidopa-treated dogs. 287 46

The aim of the study is to investigate the pathophysiological role of dopamine (DA) in the development of hypertension in DOCA-salt hypertensive rats and spontaneously hypertensive rats (SHRs). The augmentation of dopaminergic activity by chronic administration of bromocriptine, a DA agonist, suppressed the increase of blood pressure in DOCA-salt hypertensive rats. In contrast, suppression of dopaminergic activity by chronic administration of carbidopa, an inhibitor of dopa decarboxylase, accelerated the development of hypertension in SHRs, and this acceleration was also increased by salt loading. Increased urinary excretion of norepinephrine (NE) by DOCA-salt treatment was suppressed by the treatment of bromocriptine. In contrast, administration of carbidopa and salt loading in SHRs resulted in an increase in renal NE content and in urinary NE and epinephrine (E) excretion and a decrease in urinary sodium excretion. These results suggest that dopaminergic activity participate in the development of hypertension and decreased dopaminergic activity accelerates the development of hypertension in hypertensive rats mainly through the enhancement of peripheral sympathetic nerve activity.
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PMID:Pathophysiological role of dopamine on the development of hypertension in rats. 343 Jun 92

Kidneys form dopamine (DA) from L-dopa and serotonin from L-5-hydroxytryptophan (L-5-HTP) via aromatic L-amino acid decarboxylase. We compared the ability of isolated perfused kidneys from adult (20-week-old) spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) to form these biogenic amines. Renal vascular resistance (RVR) was greater in perfused kidneys from SHR (n = 10) than WKY (n = 8) (p less than 0.01). Slight decreases in RVR were observed during L-dopa infusion but these were unrelated to DA formation. L-Dopa infusion was associated with greater DA output in SHR than WKY in both the renal venous and urinary effluents although the latter did not achieve statistical significance. L-5-HTP increased RVR to a greater degree in SHR than WKY kidneys. This was associated with larger quantities of serotonin in the urinary and venous effluents and greater pressor responses to exogenous serotonin in SHR than WKY kidneys; however, either parameter alone was not significantly increased. Our findings do not support a deficiency of intrarenal DA formation as a pathogenic factor for hypertension in SHR. Biogenic amine formation is as great if not greater in SHR than WKY kidneys and appears to contribute largely to the greater increases in renal resistance seen in SHR kidneys on infusion of L-5-HTP. Enhanced renal serotonin formation may elevate blood pressure, whereas enhanced renal DA formation would favor blood pressure lowering, perhaps as a compensatory mechanism.
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PMID:Formation of biogenic amines by isolated kidneys of spontaneously hypertensive rats. 348 34

To clarify role of dopamine in the development of hypertension, the effect of a dopamine synthesis inhibitor on blood pressure and urinary output of catecholamines was investigated in spontaneously hypertensive rats (SHR) fed with high sodium diet. Rats were orally given carbidopa, an inhibitor of peripheral DOPA decarboxylase, or the vehicle for 4 weeks. Carbidopa administration accelerated significantly the development of hypertension as compared to the control SHRs with the vehicle. Carbidopa administration resulted in a significant decrease of urinary excreted sodium, urinary dopamine and renal content of dopamine. Conversely, carbidopa administration resulted in a significant increase of urinary excreted norepinephrine, urinary epinephrine and renal content of norepinephrine as compared with control SHRs. These results suggest that decreased dopamine synthesis in kidneys and probably other peripheral tissue accelerates the development of hypertension, mediated by a decrease of natriuresis and an enhancement of sympatho-adrenomedullary activity. Dopamine plays an important role in its protective action against the development of hypertension enhanced by salt loading, and decreased dopaminergic mechanisms accelerated hypertension in SHR.
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PMID:Effect of decreased dopamine synthesis on the development of hypertension induced by salt loading in spontaneously hypertensive rats. 362 32

The demonstration of acceleration of hypertension was investigated in spontaneously hypertensive rats (SHR) treated with carbidopa, inhibitor of peripheral dopa decarboxylase. Oral administration of carbidopa to young SHR for 4 weeks accelerated significantly (P less than 0.05) development of hypertension as compared to SHR treated with vehicle. Urinary excretion of dopamine (DA) (P less than 0.01) and renal content of DA (P less than 0.02) were significantly decreased by carbidopa treatment. Urinary excretion of sodium (P less than 0.05) was significantly decreased and renal content of norepinephrine (NE) (P less than 0.01) was significantly increased by carbidopa. Urinary excretion of NE and epinephrine (E) did not change during the experimental period. Negative correlation between systolic blood pressure and urinary excretion of sodium (P less than 0.05) or dopamine (P less than 0.01) and positive correlation between systolic blood pressure and renal content of NE (P less than 0.05) were significantly observed in both groups of SHR treated with carbidopa and with vehicle for 4 weeks. These results suggest that decreased DA biosynthesis in peripheral tissues accelerates development of hypertension mediated by decrease of natriuresis and enhanced release of NE in the kidneys of SHR. DA plays an important role in regulation of blood pressure, and reduced dopaminergic mechanisms enhance blood pressure in SHR.
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PMID:Involvement of dopamine in development of hypertension in spontaneously hypertensive rat: effect of carbidopa, inhibitor of peripheral dopa decarboxylase. 367 44

Synthesis of dopamine (DA) was studied in cortical slices of Sprague-Dawley (SD) rat kidneys incubated with L-DOPA (10(-6) M). In morphological studies, formaldehyde-induced histofluorescent deposits were detected at the apical pole of the convoluted parts of the proximal tubules. Elsewhere along the nephron, no positive reaction appeared. DOPA decarboxylase inhibitors suppressed the advent of the deposits, but prior denervation did not. Biochemical studies showed: (a) slices produced 2.2 nmol mg-1 protein, glomeruli 0.2 and cytosol 43 nmol. In absence of L-DOPA or in presence of DOPA decarboxylase inhibitors, DA production was suppressed. Prior denervation did not influence DA production; (b) DA synthesis increased with sodium concentration of the milieu (range 95 to 152 mmol). Adult spontaneously hypertensive rats (SHR) produced less DA than SD or normotensive Wistar-Kyoto, at any sodium concentration from 95 to 142 mmol. This discrepancy could be related to the pathogenesis of hypertension.
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PMID:Extraneuronal production of dopamine by kidney slices in normo and hypertensive rats. 367 50

Concentrations of norepinephrine in lower brainstem and hypothalamus of genetically hypertensive rats are significantly lower than in control rats. There is a concomitant reduction (50 percent) in aromatic L-amino acid decarboxylase but not in tyrosine hydroxylase activity. A possible relation of this central catecholamine deficiency to the hypertension is discussed.
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PMID:Norepinephrine metabolism in brainstem of spontaneously hypertensive rats. 550 6

Intravenously infused L-dopa (0.3 mg/kg per min) produced hypertension and cardiac arrhythmias in halothane anesthetized dogs. Biochemical studies showed that the heart, kidney, and brain of these animals accumulated significant amounts of catecholamines formed from the administered precursor. Pretreatment of dogs with an extracerebral inhibitor of dopa decarboxylase [D,L-alpha-hydrazino-alpha-methyl-beta-(3.4-dihydroxyphenyl) propionic acid] prevented the development of hypertension and arrhythmias with infusion of L-dopa. Instead, these animals developed significant hypotension. The heart and kidney of these animals accumulated markedly reduced amounts of catecholamines formed from L-dopa compared with dogs receiving L-dopa alone: the amount of catecholamines accumulated in brain was unchanged. L-dopa, after extracerebral decarboxylase inhibition, appeared to produce hypotension by reducing peripheral vascular resistance without altering sympathetic nerve function. During hypotension, cardiac output was not altered and arterial pressure in perfused hindlimbs fell, even though flow was maintained. The pressor response to intravenous injections of norepinephrine and dopamine was unchanged. Hindlimb arterial pressure response to direct electrical stimulation of the lumbar sympathetic trunk was also unchanged. Pretreatment with a drug which inhibits brain as well as extracerebral dopa decarboxylase [D,L-seryl-2,3,4-trihydroxybenzylhydrazine hydrochloride] abolished all effects of L-dopa on blood pressure. In these animals, there was a marked reduction of catecholamine formation from L-dopa in the brain as well as the heart and kidney. It appears that L-dopa produces opposite effects on blood pressure depending on the site of accumulation of its metabolic products, dopamine and norepinephrine. If L-dopa is rapidly decarboxylated to catecholamines in peripheral organs, hypertension and cardiac arrhythmias occur. If peripheral dopa decarboxylase is selectively inhibited, a centrally mediated hypotensive effect, probably secondary to the accumulation of catecholamines in the brain, becomes apparent. If dopa decarboxylase is inhibited in the brain in addition to extracerebral organs, L-dopa has no effect on blood pressure.
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PMID:Modification of the cardiovascular effects of L-dopa by decarboxylase inhibitors. 557 36


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