Adjustment behavior of adrenergic-induced vasoconstrictions in the intestinal circulation of the cat.

Adrenergic-induced vasoconstrictions are succeeded by an adjustment reaction (‘escape phenommenon’ or ‘autoregulatory escape’) and after the end of stimulation by a postconstrictive dilation (‘reactive hyperemia’)- These vascular reactions have been examined on the intact mesenteric circulation of the cat by performing frequency-response curves (5 and 10 V, 1 msec. 1–50 Hz). An electrotonic blockade and a local summation could be excluded as the cause of the escape within the physiological range. The maximum of the initial reaction was found at a stimulation strength between 12 and 16 V (10 Hz, 1 msec). The maximum of the escape reaction occurred at 5 V. Both vascular reactions were strongly dependent on the local concentration of noradrenaline (i.a. infusion); however, they reached their maximum at different concentrations. The escape reaction is apparently a persisting adjustment to a steady state. Despite a formal similarity, no correlation could be demonstrated between the postconstrictive dilation and the escape reaction. Both vascular adjustment reactions are of myogenic origin. It is concluded that the reason for the escape phenomenon can not be found in the local or propagated nerval response, in the transmitter release, or in its effect on the vascular smooth muscle. But it is suggested that the escape reaction is a form of myogenic, autonomic adjustment behavior.