Noradrenaline uptake by non‐innervated smooth muscle

Summary1 Uptake of noradrenaline (NA) into the non‐innervated smooth muscle cells of the human umbilical artery and the chick amnion has been studied with the fluorescence histochemical technique for localizing monoamines. Comparison has been made with uptake into sympathetically innervated smooth muscle of the rabbit ear artery. 2 Accumulation of NA within non‐innervated smooth muscle cells is observed histochemically after exposure to much lower concentrations of NA (10 −7 g/ml) than in sympathetically innervated smooth muscle cells, where accumulation occurs with NA (10 −5 g/ml). 3 In contrast to innervated smooth muscle, uptake of NA (10 −4 g/ml) by non‐innervated smooth muscle is characterized by lack of inhibition by phenoxybenzamine, normetanephrine and cold, although some inhibition is apparent at lower NA concentrations. Retention of NA during prolonged washing in NA‐free Krebs demonstrates that it is strongly bound within the non‐innervated smooth muscle cells, particularly in the nucleus. 4 After inhibition of catechol‐ O ‐methyl transferase, the accumulation of NA in innervated smooth muscle closely resembles that in non‐innervated smooth muscle.