Abstract
Purpose: To determine the mechanism underlying the anti-hyperprolactinemia effects of Radix bupleuri extract (RBE) in rats. Methods: Rats were divided into six groups ( n =10 each group): healthy controls, untreated hyperprolactinemic rats, hyperprolactinemic rats treated with bromocriptine (0.6 mg/kg), and hyperprolactinemic rats treated with RBE (4.8, 9.6, or 19.2 g/kg). After 30 days, hypothalamic protein levels of dopamine D2 receptor, protein kinase A (PKA), and cyclic adenosine monophosphate (cAMP) were determined. Results: Dopamine D2 receptor levels were lower in untreated hyperprolactinemic rats than in healthy controls ( p < 0.01), but this decrease was attenuated by RBE ( p < 0.05). Elevated PKA levels in untreated hyperprolactinemic rats (0.61 ± 0.04 μg/ml, p < 0.01) were decreased by RBE (4.8 g/kg, 0.42 ± 0.03 μg/ml, p < 0.05; 9.6 g/kg, 0.33 ± 0.02 μg/ml, p < 0.01; 19.2 g/kg, 0.27 ± 0.03 μg/ml, p < 0.01). Similarly, elevated cAMP levels in hyperprolactinemic rats (2.4 ± 0.4 ng/ml) were decreased by RBE (4.8 g/kg, 1.8 ± 0.3 ng/ml, p < 0.05; 9.6 g/kg, 1.5 ± 0.3 ng/ml, p < 0.01; 19.2 g/kg, 1.2 ± 0.2 ng/ml, p < 0.01). Conclusions: RBE anti-hyperprolactinemia activity is mediated by dopamine D2 receptor signaling via the cAMP/PKA pathway. Keywords: Hyperprolactinemia, Radix bupleuri , Dopamine D2 receptor, cAMP/PKA
Highlights
Hyperprolactinemia is a heterogeneous disorder characterized by elevated blood prolactin level.This disorder of the hypothalamic-pituitary axis can have a physiological cause, pathological cause, or unknown cause
We found that Radix bupleuri extract (RBE) decreased prolactin levels in hyperprolactinemic mice [5]
We investigated the effects of RBE on protein levels of dopamine D2 receptor, protein kinase A (PKA), and cyclic adenosine monophosphate (cAMP) in the hypothalamus of hyperprolactinemic rats
Summary
Hyperprolactinemia is a heterogeneous disorder characterized by elevated blood prolactin level. The two most commonly prescribed drugs for the treatment of hyperprolactinemia are bromocriptine and cabergoline These medications are dopamine receptor agonists with similar characteristics and adverse effects (e.g., headache, nausea, and vomiting), but the frequency and severity of adverse effects appear to be lower for cabergoline. We investigated the effects of RBE on protein levels of dopamine D2 receptor, PKA, and cAMP in the hypothalamus of hyperprolactinemic rats. To determine hypothalamic dopamine D2 receptor protein levels after the 30-day treatment period, rat hypothalamus tissues were homogenized in RIPA buffer with protease inhibitor (cOmplete EDTA-free protease inhibitor cocktail tablets; Roche Applied Science, Mannheim, Germany) and centrifuged at 3000 × g for 15 min at 4 °C. To determine hypothalamic cAMP and PKA protein levels after the 30-day treatment, rat brains were stripped of membranes and blood vessels, homogenized, and centrifuged for 15 min at 3000 r·min-1. Data are expressed as mean ± SEM; p < 0.05 was considered statistically significant
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