Noradrenaline induced secretion of nonelectrolytes through frog skin

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Abstract
Addition of noradrenaline (4×10−5 m) to the inner bathing fluid in the skin of the frogRana esculenta results in increased unidirectional fluxes of urea, thiourea, N-methyl-thiourea, N-N′-dimethylthiourea and mannitol. Fluxes towards the external medium (Φ 0) undergo a much greater increase than those moving in the opposite direction (Φ i ). The effect of noradrenaline on (Φ 0) is higher for urea and thiourea than mannitol, while its effect on (Φ 0) thiourea derivatives is related to lipid solubility. This phenomenon does not occur for (Φ i ) of the same molecules. FCCP (10−6 m) pretreatment strongly inhibits the noradrenaline effect on (Φ 0). In skin pretreated whith colchicine (2×10−5 m) both urea fluxes are increased to the same extent by noradrenaline. Noradrenaline is concluded to exert two separate effects: (1) a change in permeability in both directions; (2) a secretion of nonelectrolytes towards the external fluid. Such secretion is most probably associated with the hormone-induced secretion of fluid and electrolytes, perhaps mediated by an exocytotic mechanism.