[Effect of phentolamine on the reflex increase in arterial pressure]

Experiments were carried out in anaesthetized and curarized cats to study the effects of the alpha-blocker phentolamine on arterial pressor response to stimulation of group I afferent fibers from gastrocnemius-soleus muscles. It has been found that increasing doses of phentolamine given i.v. cause a decreasing pressor response until complete disappearance occurs at 2.5 mg/Kg. It is concluded that pressor response is present only when the adrenergic control system is effective and, therefore, it is due mainly to an increase in peripheral vascular resistances.