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Prostate ; 57(1): 51-6, 2003 Sep 15.
Article in English | MEDLINE | ID: mdl-12886523

ABSTRACT

BACKGROUND: Recent studies from our laboratory have demonstrated that androgen-induced basal norepinephrine (NE) release is responsible for the onset of proliferation in seminal vesicle smooth muscle (SVM) cells during early puberty. With subsequent sexual maturation, SVM was irreversibly differentiated to an androgen-resistant-amitotic state in which basal NE release remained elevated and resistant to androgen withdrawal or repletion. Based on these findings, we hypothesized that this irreversible elevation of basal NE release during pubertal development is caused, at least in part, by the down-regulation of pre-synaptic NE feedback inhibition, secondary to irreversible reduction in the expression of neuronal (pre-synaptic) alpha(2)-adrenoceptors. Functional alpha(2)-adrenoceptors are selectively localized to pre-synaptic sites in SVM. METHODS: To test this hypothesis, we employed ligand binding techniques with [(3)H]RX821002, an antagonist which labeled all alpha(2)-adrenoceptor sub-types. Initial experiments focused on analysis of competitor specificity to identify the predominant alpha(2)-adrenoceptor sub-type in SVM. Subsequently, we quantified the changes in the receptor concentration (B(max)) for [(3)H]RX821002 at the point of maximal dihydrotestosterone (DHT)-induced change in basal NE release. RESULTS: Based on competitor specificity for [(3)H]RX821002, the alpha(2D)-adrenoceptor sub-type predominated in SVM. We treated pre-pubertal castrate animals with DHT for 7 days, which was previously demonstrated to maximally induce basal NE release. This treatment reduced the pre-synaptic alpha(2)-adrenoceptor B(max) 4-fold. In animals which had been castrated as adults, the B(max) for [(3)H]RX821002 remained irreversibly suppressed. CONCLUSIONS: The DHT-dependent reduction in the alpha(2)-adrenoceptor concentration is consistent with the developmental pattern of increased basal NE release. These findings support the hypothesis that the down-regulation of pre-synaptic NE feedback is mechanistically involved in the irreversible elevation of basal NE release. NE mediates proliferation in SVM in early pubertal development. Thus, the androgen-dependent pubertal growth of smooth muscle cells may be indirectly controlled at the level of neurotransmission.


Subject(s)
Dihydrotestosterone/pharmacology , Muscle, Smooth/cytology , Norepinephrine/metabolism , Receptors, Adrenergic, alpha-2/metabolism , Seminal Vesicles/cytology , Adrenergic alpha-Antagonists/pharmacology , Animals , Binding, Competitive , Cell Division/drug effects , Cell Division/physiology , Guinea Pigs , Idazoxan/analogs & derivatives , Idazoxan/pharmacology , Male , Muscle, Smooth/drug effects , Muscle, Smooth/metabolism , Receptors, Presynaptic/metabolism , Seminal Vesicles/drug effects , Seminal Vesicles/metabolism , Sexual Maturation/physiology , Tritium
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