FORMATION OF DOPAMINE AND NORADRENALINE IN RAT VAS DEFERENS: COMPARISON WITH GUINEA‐PIG VAS DEFERENS

The formation of [14C]‐3,4‐dihydroxyphenylalanine (DOPA) from [14C]‐tyrosine, in the presence of the amino acid decarboxylase inhibitor, brocresine (3‐hydroxy‐4‐bromobenzyloxy‐amine dihydrogen phosphate), was greatly enhanced in rat vasa deferentia depolarized by a KCl‐enriched Krebs‐Henseleit solution (52 mM KCl) compared with tissues maintained in unmodified Krebs‐Henseleit solution.When the conversion of tyrosine was allowed to proceed as far as catecholamine (brocresine absent) no significant difference was observed between the accumulation of [14C]‐catecholamines (CA) in depolarized rat vasa deferentia and the accumulation in control (non‐depolarized) tissues.Endogenous CA levels in the depolarized rat vasa deferentia fell to 67% of the controls after a 1 h incubation period and to 53% at the end of 2 hours.Chromatographic separation on Amberlite CG‐120 columns of the newly synthesized CA and catechol metabolites from the rat vas deferens revealed that a very high proportion was present as dopamine. The percentage distribution after 1 h incubation in control Krebs‐Henseleit was: noradrenaline (NA): 30.6 ± 5.2; dopamine 56.9 ± 5.9; acid metabolites: 12.8 ± 1.1; and in KCl‐rich Krebs‐Henseleit, NA: 32; dopamine: 44.7 and acid metabolites 23.3. In contrast to the newly synthesized (14C‐labelled) CA, endogenous dopamine comprises only 10% of the endogenous CA stores in rat vas deferens.The distribution of newly synthesized NA and dopamine in rat vas deferens is strikingly different from that of guinea‐pig vas deferens where more than 80% of newly formed amine is present as NA. In the latter tissue depolarization with K+causes a striking increase in CA biosynthesis.