Abstract
Right atria from rats were incubated in Krebs-Ringer solution at 37°C for 20 minutes with H3-tyramine (1.4 x 10-7 M). At the end of the incubation period, atria were washed with fresh Krebs-Ringer solution for periods up to 16 minutes. H3-tyramine rapidly disappeared from the atria during the first four minutes of the wash period. The rate of decrease of 113-tyramine slowed markedly during the remainder of the wash period. The disappearance of H3-tyramine during the wash period was accounted for by its quantitative conversion to H3-p-hydroxyphenylacetic acid. The amount of H3-octopamine remained constant throughout the wash period. Both desmethylimipramine (0.2-60 mg/kg i.p., 1 hour before sacrifice) and cocaine ( 10-6-3 x 1O-4 M, added to the incubation flask 15 minutes before the H3-tyramine) decreased the retention of H3-tyramine and the synthesis of H3-octopamine and H3-p-hydroxyphenylacetic acid. The inhibition of H3-octopamine synthesis produced by both drugs was competitive. No H3-p-hydroxymandelic acid was synthesized by intact atria either in control experiments or in the presence of drugs. In addition, no H3-octopamine was detected in bathing or wash solutions at any time. These results indicate there are two intraneuronal pools of H3-tyramine within the atria: one which turns over rapidly and is converted to H3-p-hydroxy-phenylacetic acid and one which remains firmly bound within the atria. H3-octopamine is retained in a site which is inaccessible to intraneuronal monoamine oxidase. Both desmethylimipramine and cocaine competitively inhibit the neuronal uptake of H3-tyramine into adrenergic neurons of the atria.
Footnotes
- Received April 13, 1970.
- Accepted August 28, 1970.
- © 1971, by The Williams & Wilkins Company
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|