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Apomorphine increases plasma oxytocin concentration in male rats
M R Melis1, A Argiolas, G L Gessa
1Department of Neurosciences, University of Cagliari, Italy.
Abstract:
The effect of systemic administration of the dopamine agonist apomorphine on plasma oxytocin concentration was studied in male rats by a specific radioimmunoassay. Apomorphine given subcutaneously in doses ranging from 80 to 480 micrograms/kg increased oxytocin levels in a dose-dependent manner. The minimal effective dose was found to be 80 micrograms/kg, which induced a 66% increase above basal values, while the maximal effect (210%) was seen with a dose of 240 micrograms/kg. The apomorphine effect was prevented by pretreatment with the DA D2-receptor blockers haloperidol (0.2 mg/kg i.p.) or (-) sulpiride (10 mg/kg i.p.) and, but only partially, with the DA D1-receptor blocker SCH 23390 (0.2 mg/kg s.c.). The present results suggest that hypothalamic dopamine has a facilitatory role on the release of oxytocin in male rats.
Insights
Dopamine agonist apomorphine administration significantly increased oxytocin levels in male rats. This dopamine-induced oxytocin release was primarily mediated by dopamine D2 receptors, suggesting a key role for dopamine in oxytocin regulation.
Area of Science:
- Neuroendocrinology
- Pharmacology
Background:
- Oxytocin plays a crucial role in social behavior and stress response.
- Dopamine is a key neurotransmitter involved in various physiological processes.
Purpose of the Study:
- To investigate the effect of the dopamine agonist apomorphine on plasma oxytocin concentration in male rats.
- To determine the role of dopamine receptors in mediating this effect.
Main Methods:
- Systemic administration of apomorphine in varying doses (80-480 µg/kg) to male rats.
- Measurement of plasma oxytocin concentration using radioimmunoassay.
- Pretreatment with dopamine receptor blockers (haloperidol, sulpiride, SCH 23390) to assess receptor involvement.
Main Results:
- Apomorphine dose-dependently increased plasma oxytocin levels, with significant effects observed at doses as low as 80 µg/kg.
- The minimal effective dose of 80 µg/kg resulted in a 66% increase in oxytocin, while 240 µg/kg caused a 210% increase.
- Pretreatment with D2 receptor antagonists (haloperidol, sulpiride) completely blocked the apomorphine-induced oxytocin increase, while a D1 antagonist (SCH 23390) only partially inhibited it.
Conclusions:
- Hypothalamic dopamine exerts a facilitatory influence on oxytocin release in male rats.
- Dopamine D2 receptors are predominantly involved in mediating the stimulatory effect of dopamine on oxytocin secretion.