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Reduction by propranolol of raised urinary output of MHPG in hyperactive rats
Abstract:
Prolonged isolation of rats resulted in hyperactivity in the open field and a significant increase in 24 hr urinary excretion of MHPG (3-methoxy-4-hydroxyphenylglycol). Exploratory activity of group-housed rats in open field was not associated with raised MHPG excretion, compared with that of rats remaining in home cages. Exposure of group-housed rats to 4 degrees C for 2 hr also increased urinary excretion of MHPG. Pretreatment of isolated rats with dl-, d-propranolol or practolol abolished hyperactivity of isolated rats and reduced MHPG output in these rats and in rats exposed to cold. dl-Propranolol did not reduce activity of group-housed rats in open field or their urinary excretion of MHPG. It is suggested that propranolol may have a selective inhibitory effect on stress-induced increases in noradrenaline turnover.
Insights
Prolonged isolation in rats increased hyperactivity and stress hormone MHPG (3-methoxy-4-hydroxyphenylglycol) excretion. Propranolol treatment reduced these stress responses, suggesting a selective effect on noradrenaline turnover.
Area of Science:
- Neuroscience
- Behavioral Science
- Pharmacology
Background:
- Prolonged isolation stress in rodents can lead to behavioral changes and altered neurochemical profiles.
- Urinary MHPG (3-methoxy-4-hydroxyphenylglycol) is a metabolite reflecting central noradrenaline turnover, a key neurotransmitter in stress response.
Purpose of the Study:
- To investigate the relationship between isolation-induced hyperactivity and MHPG excretion in rats.
- To evaluate the effects of beta-adrenergic antagonists, propranolol and practolol, on stress-induced behavioral and biochemical changes.
Main Methods:
- Rats were subjected to prolonged isolation or acute cold exposure.
- Open-field behavior and 24-hour urinary MHPG levels were measured.
- The effects of dl-propranolol, d-propranolol, and practolol were assessed in stressed and non-stressed rats.
Main Results:
- Isolation stress significantly increased hyperactivity and urinary MHPG excretion.
- Acute cold exposure also elevated MHPG levels.
- Pretreatment with propranolol or practolol attenuated isolation-induced hyperactivity and reduced MHPG excretion.
- dl-Propranolol did not affect activity or MHPG levels in non-stressed, group-housed rats.
Conclusions:
- Isolation stress in rats is associated with increased noradrenaline turnover, indicated by elevated MHPG.
- Beta-adrenergic antagonists, particularly propranolol, may selectively inhibit stress-induced increases in noradrenaline turnover and associated hyperactivity.