Accumulation of ³H-Adrenaline by Rabbit Aorta

Abstract

The accumulation of (–)^-3H-adrenaline (³H-A) by rabbit isolated aorta was studied. In all experiments, monoamine oxidase and catechol-O-methyltransferase were inhibited by treatment with pargyline and 3’,4’-dihydroxy-2-methyl-propiophenone (U-0521), respectively. The relationship between the accumulation of ³H derived from ³H-A (10^–8 M) and the duration of incubation (0–3 h) was linear. The ³H-accumulation after 3 h incubation was 22.5 ml·g^-1. In reserpine-treated tissue, the ³H-accumulation levelled off after 30 min and was 8.5 ml·g^–1 after 3 h. The concentration of ³H-A or (–)^-3H-noradrenaline (³H-NA) and the ³H-accumulation (ml·g^–1) were inversely related. At 10^–8 M, the 1-hour accumulation of ³H derived from ³H-A and ³H-NA was 7.8 and 15.2 ml·g^–1, respectively. With increasing concentrations (3 × 10^–8–10^–4 M), the accumulation values approached each other. At 10^–4 M, the accumulation was 2.3 and 2.8 ml·g^-1 for ³H-A and ³H-NA, respectively. The accumulation of ³H derived from ³H-A (10^–8–10^–4 M) by reserpine-treated tissue also showed an inverse relationship with concentration: 5.4 ml·g^-1 (10^–8 M) and 2.6 ml·g^–1 (10–4 Af). The accumulation of ³H derived from ³H-A (10–8 M; 1 h) was dependent on the bath temperature (1–37 °C). The accumulation increased continuously from 1.1 ml·g^–1 (1 °C) to 11.1 ml·g^-1 (37 °C). Storage of tissue (0–5 days in salt solution without equilibration with 95% O₂/5% CO₂; 4 °C) did not affect the accumulation of ³H derived from ³H-A (10^–8 M; 1 h). Thereafter (7–14 days), the accumulation decreased. The inhibitory potency (IC_5o; –log M) of desimipramine, cocaine, (–)-propranolol, (–)-isoprenaline, and (±)-normetanephrine on accumulation of ³H derived from ³H-A (10^-8 M; 1 h) was found to be 8.26; 6.50; 5.48, 4.88, and 4.02, respectively. The maximal degree of inhibition was almost the same for these drugs, while that of clonidine and corticosterone was 50 and 20%, respectively. In the presence of desimipra-mine (10^–6 M), either clonidine (10^–5–10^–3 M), corticosterone (10^–6–10^–4 M) or (-)-isoprena-line (10^–5–10^–3 M) reduced the accumulation of ³H derived from ³H-A (10^–8 M; 1 h). Oua-bain (3 × 10^–4 M) and iodoacetic acid (10^–3 M), but not sodium cyanide (10^–3 M) and 2,4-dinitrophenol (10^–3 M), reduced the accumulation of ³H derived from ³H-A (10^–8 M; 1 h). Anoxia (95% N₂/5% CO₂; 37 °C; 1–24 h) did not alter the accumulation of ³H derived from ³H-A (10^–8 M; 1 h). D-(+)-Glucose deprivation alone or combined with anoxia markedly reduced the ³H-accumulation. These results suggest that adrenaline is transported into neu-ronal and extraneuronal sites via a carrier mechanism which is energy-dependent.