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Effect of prazosin on norepinephrine concentration and turnover in rat brain and heart
Abstract:
Prazosin hydrochloride injected i.p. into rats markedly increased MOPEG sulfate (3-methoxy-4-hydroxy-phenylethylene glycol sulfate) concentration in brain and the rate of MOPEG sulfate accumulation after probenecid. The increase in MOPEG sulfate was dose-related over a 5-40 mg/kg dose range. After a 20 mg/kg dose of prazosin, the increase in MOPEG sulfate was greater than after the same dose of phenoxybenzamine and persisted for up to 24 hr. The rate of metaraminol disappearance from rat brain after alpha-methyl-m-tyrosine injection and the decline in brain norepinephrine after inhibition of its synthesis by alpha-methyltyrosine injection were increased in rats pretreated with prazosin. These findings indicate that prazosin increased brain norepinephrine turnover, probably via compensation to central alpha adrenoceptor blockade. Prazosin increased sertonin and 5-hydroxy-indoleacetic acid concentration and slightly decreased 3,4-dihydroxy-phenylacetic acid in rat brain. Although prazosin had little effect on brain norepinephrine concentration, heart norepinephrine was depleted for up to 16 hr after a 20 mg/kg dose of prazosin, and the depletion at 4 hr was dose-related down to 2 mg/kg of prazosin. These biochemical changes may all result from prazosin's block of alpha adrenergic receptors.
Insights
Prazosin significantly increases brain and heart norepinephrine turnover in rats by blocking alpha-adrenergic receptors. This effect is dose-dependent and long-lasting, impacting neurotransmitter levels.
Area of Science:
- Neuropharmacology
- Adrenergic Receptor Research
Background:
- Prazosin is an alpha-adrenergic blocker used clinically.
- Understanding its central and peripheral effects on neurotransmitter turnover is crucial.
Purpose of the Study:
- To investigate the effects of prazosin on central and peripheral neurotransmitter levels and turnover in rats.
- To elucidate the role of alpha-adrenergic blockade in mediating these changes.
Main Methods:
- Rats were administered varying doses of prazosin hydrochloride intraperitoneally.
- Brain and heart tissues were analyzed for concentrations of norepinephrine, MOPEG sulfate, serotonin, and other metabolites.
- Neurotransmitter turnover rates were assessed using specific pharmacological challenges.
Main Results:
- Prazosin markedly and dose-dependently increased brain MOPEG sulfate concentration and accumulation, indicating increased norepinephrine turnover.
- Prazosin enhanced the disappearance of metaraminol and the decline of norepinephrine in the brain.
- Significant depletion of heart norepinephrine was observed, which was dose-related and persisted for up to 16 hours.
- Central serotonin and 5-hydroxyindoleacetic acid levels increased, while dopamine metabolites slightly decreased.
Conclusions:
- Prazosin increases central and peripheral norepinephrine turnover, likely as a compensatory response to alpha-adrenergic receptor blockade.
- These findings highlight the significant impact of prazosin on adrenergic and serotonergic systems.