An Excitatory Adrenergic Alpha Receptor Mechanism of Terminal Guinea-Pig Ileum

Abstract

Segments of terminal guinea-pig ileum were studied utilizing differential alpha and beta adrenergic receptor site blocking techniques. Phenylephrine caused a contraction of this segment of guinea-pig intestine which resembled biphasic responses-which follow a pattern of alpha excitation followed by beta inhibition while isopro-terenol elicited a pure beta inhibitory action. The use of phenoxy-benzamine as an alpha blocking agent abolished all excitatory responses while augmenting beta actions. Propranolol, through beta adrenergic receptor site blockade, potentiated alpha excitatory actions. The results indicate the presence of a unique excitatory alpha adrenergic receptor mechanism in terminal guinea-pig ileum.