Smnmary. Both hind legs of anaesthetized cats were perfused with the animals own blood at constant flow. From the perfusion-pressure curves, registrated under stimulating the sympathetic trunc at L 3, quantitative statements on the dynamics of the vascular muscles in situ could be made.
The observed variations of the perfusion-pressure (APD) were regarded as beeing representative for the strength of vasoconstriction, and for the concentration of transmitter until saturation within the muscular end-organs. The maximum velocity of the rise of the perfusion-pressure (max. dPD/sec) was taken as a relative measure for both, velocity of muscular contraction, and velocity of the accumuIation of the transmitter concentration in the nearest neighbourhood of the vascular muscles.
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Within a range of 2 to 100 stimuli per second a temporary summation of the vasoconstrictory effect could be observed: When the frequency was raised the final concentration of tile transmitter, and the velocity of its accumulation increased. The maximum of contraction, and therefore the saturation point of the concentration of the transmitter was reached at frequencies between 10 and 20 per second while the velocity could be raised up to a frequency of 100 per second.
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Stimulation with frequencies between 100 and 1000 per second lead to an inhibition of the nervous conduction (Wedensky-type) : A spatial summation of the vasoconstrictory effect appears as a sequence of an increasing blockade of efferent nerve fibres.
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Using different voltages of stimulation a similar effect could be shown consisting in a shortage of conducting nerve fibres at low voltage.
These results lead to the conclusion t h a t a postganglionie fibre m a y supply a circumscript vascular area only, whereby the possibility is given to use singular districts of the perfused vessel area for vasoconstriction. By the spatial summation no changes were produced within the activated end-organ in regard to the final concentration and the velocity of accumulation of the transmitter substance. An essential convergence of the efferent postganglionic vasoconstrictor nerve fibres on the vascular muscles could not be found either.
Z u s a m m e n f a s s u n g . An Katzen wurden die hinteren Extremiti~ten volumenkonstant mit Eigenblut durchstrSmt. Der Ver]auf der Perfusionsdruckkurve bei Grenzstrangreizung in HOhe yon L 3 er]aubt quantitative Aussagen fiber den Kontraktionsablauf der Gef/itmuskulatur in situ.
Die tt5he der Perfusionsdruck/~nderung (zJPD) wird als Ma$ ffir die St/irke der Vasoconstriction and, bis zur S/ittigungskonzentration, als ~a $ ffir die HShe der :Pflfigers Arch. ges. PhysioL, Bd. 286