8-NH2-boldine, an antagonist of alpha1A and alpha1B adrenoceptors without affinity for the alpha1D subtype: structural requirements for aporphines at alpha1-adrenoceptor subtypes

Planta Med. 2005 Oct;71(10):897-903. doi: 10.1055/s-2005-871281.


Structure-activity analysis of 21 aporphine derivatives was performed by examining their affinities for cloned human alpha (1A), alpha (1B) and alpha (1D) adrenoceptors (AR) using membranes prepared from rat-1 fibroblasts stably expressing each alpha (1)-AR subtype. All the compounds tested competed for [ (125)I]-HEAT binding with steep and monophasic curves. The most interesting compound was 8-NH (2)-boldine, which retains the selective affinity for alpha(1A)-AR (pKi = 6.37 +/- 0.21) vs. alpha(1B)-AR (pKi = 5.53 +/- 0.11) exhibited by 1,2,9,10-tetraoxygenated aporphines, but shows low affinity for alpha(1D)-AR (pKi < 2.5). Binding studies on native adrenoceptors present in rat cerebral cortex confirms the results obtained for human cloned alpha (1)-AR subtypes. The compounds selective for the alpha (1A) subtype discriminate two binding sites in rat cerebral cortex confirming a mixed population of alpha (1A)- and alpha (1B)-AR in this tissue. All compounds are more selective as inhibitors of [ (3)H]-prazosin binding than of [ (3)H]-diltiazem binding to rat cerebral cortical membranes. A close relationship was found between affinities obtained for cloned alpha (1A)-AR and inhibitory potencies on noradrenaline-induced contraction or inositol phosphate accumulation in tail artery, confirming that there is a homogeneous functional population of alpha(1A)-AR in this vessel. On the contrary, a poor correlation seems to exist between the affinity of 8-NH (2)-boldine for cloned alpha (1D)-AR and its potency as an inhibitor of noradrenaline-induced contraction or inositol phosphate accumulation in rat aorta, which confirms that a heterogeneous population of alpha (1)-AR mediates the adrenergic response in this vessel.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic alpha-1 Receptor Antagonists*
  • Adrenergic alpha-Antagonists / administration & dosage
  • Adrenergic alpha-Antagonists / pharmacology*
  • Animals
  • Aorta, Thoracic / drug effects
  • Aporphines / administration & dosage
  • Aporphines / pharmacology*
  • Arteries / drug effects
  • Binding, Competitive / drug effects
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / physiology
  • Muscle Contraction / drug effects
  • Muscle, Smooth, Vascular / drug effects
  • Phytotherapy*
  • Plants, Medicinal*
  • Rats
  • Structure-Activity Relationship


  • Adrenergic alpha-1 Receptor Antagonists
  • Adrenergic alpha-Antagonists
  • Aporphines
  • boldine