Die Wirkung von Adrenalin auf die Aktivit�t der Nierennerven beim Frosch

Catecholamines increase urine formation in isolated toad (Bufo marinus) kidneys perfused at constant rate

Infusion of catecholamines into isolated kidneys of the toad (Bufo marinus) perfused at constant rate, produced increased arterial pressure accompanied by increased glomerular filtration rate, urine formation rate and sodium excretion. These parameters were all increased by arterial infusion of adrenaline or noradrenaline, or by infusion of adrenaline via the renal portal veins. Portal venous pressure increased slightly after arterial or portal infusion of adrenaline, but decreased after arterial infusion of noradrenaline. Estimation of segmental pressure gradients indicated that the efferent glomerular arterioles were selectively constricted by low concentrations of adrenaline or noradrenaline (3 X 10(-9), 3 X 10(-8) mol l(-1)). Higher concentrations of these amines constricted the preglomerular, as well as the postglomerular vasculature. These results demonstrate that the pericytes and/or endothelial cells which form the walls of the efferent arterioles in B. marinus are capable of active contraction.

Effects of renal nerve stimulation on vascular resistance in the toad kidney

Stimulation of the renal nerves to the perfused toad kidney produced an increase in intravascular pressure. This response was always abolished by bretylium, indicating that it was mediated by adrenergic nerves. The response was usually reduced by tubocurarine, indicating that some of the fibres in the renal nerve trunks were preganglionic. The vasoconstrictor response was abolished by treatment with yohimbine or phenoxybenzamine, but was only partially reduced by phentolamine. It is postulated that adrenaline released from nerve terminals acts primarily on "junctional" adrenoceptors which are not antagonised by phentolamine. However, part of the vasoconstrictor response appears to be due to occupation of nearby "extra-junctional" receptors by neurally-released adrenaline: only this part of the response can be antagonised by phentolamine. The vasoconstrictor response was enhanced by propranolol in both summer and winter. This indicates that neurally-released adrenaline can occupy beta-adrenoceptors, to antagonise the effects of alpha-receptor occupation, at both times of the year. In this respect, the beta-receptors mediating the effects of renal nerve stimulation are different from those acted upon by perfused adrenaline. A non-adrenergic vasodilatation was sometimes revealed after abolition of the vasoconstrictor response, but the nature of the nerve fibres mediating this response could not be determined.