Drug-induced changes in the release of ( 3 H)-noradrenaline from field stimulated rat iris

Br J Pharmacol. 1971 Sep;43(1):97-106. doi: 10.1111/j.1476-5381.1971.tb07160.x.


1. Isolated rat irides were incubated with [(3)H]-noradrenaline [(3)H-NA] (10(-7)M), superfused with buffer and then stimulated by an electrical field. The effect of desipramine, clonidine, phentolamine, phenoxybenzamine, GD131, normetanephrine and 4-tropolone-acetamide on the stimulation-induced overflow of [(3)H]-NA was tested by adding the drug to the superfusing buffer. The effect of pretreatment with phentolamine or phenoxybenzamine on the stimulation-induced overflow of [(3)H]-NA was also studied.2. The effect of desipramine, clonidine, phentolamine, phenoxybenzamine and GD131 on uptake of [(3)H]-NA in isolated irides was determined.3. Desipramine moderately increased the stimulation-induced overflow at concentrations which almost completely inhibited neuronal uptake. It was calculated that in the isolated rat iris 30-40% of the released [(3)H]-NA is inactivated by reuptake into the nerve terminal. This figure may represent the true reuptake percentage in this preparation. Desipramine-induced inhibition of [(3)H]-NA release from the nerve terminal, possibly via a negative feed-back mechanism, may also contribute to this low figure.4. Phentolamine and phenoxybenzamine, in concentrations or doses which did not inhibit neuronal uptake of [(3)H]-NA, consistently increased the stimulation-induced overflow. This increase was further augmented when neuronal uptake was inhibited.5. The alpha-adrenoceptor stimulating drug clonidine decreased the stimulation-induced overflow.6. GD131, normetanephrine and 4-tropolone-acetamide did not greatly affect the stimulation-induced overflow of [(3)H-NA].7. It is concluded that the increased [(3)H]-NA overflow obtained after alpha-adrenoceptor blockade is due to an increased [(3)H]-NA release from the nerve terminals.

MeSH terms

  • Acetamides / pharmacology
  • Aniline Compounds / pharmacology
  • Animals
  • Desipramine / pharmacology
  • Electric Stimulation
  • Ethylamines / pharmacology
  • Feedback
  • Female
  • Imidazoles / pharmacology
  • In Vitro Techniques
  • Iris / drug effects*
  • Iris / metabolism
  • Norepinephrine / metabolism*
  • Normetanephrine / pharmacology
  • Phenoxybenzamine / pharmacology
  • Phentolamine / pharmacology
  • Rats
  • Tritium


  • Acetamides
  • Aniline Compounds
  • Ethylamines
  • Imidazoles
  • Normetanephrine
  • Phenoxybenzamine
  • Tritium
  • Desipramine
  • Norepinephrine
  • Phentolamine