The poor reactivity of retinal vessels to systemic administration of vasoactive agents in pentobarbital anesthetized...

The responsiveness of retinal vasculature to i.v. administration of several potent vasoactive agents was studied in pentobarbital anesthetized rats by taking fundus photographs. Since cerebral vasculature had been claimed to react in a similar manner but less liably than retinal vessels to some vasoactive substances, the findings were applied to the problem of reactivity of brain vessels. Sublethal doses of noradrenaline, adrenaline, 5-hydroxytryptamine, angiotensin amide and arginine orlysine vasopressin caused no marked acute ( less than or equal to 2 min) vasoconstriction in retinal vessels. Nor did any of these agents or bradykinin elicit vasodilatation. The late vasoconstriction (greater than 2 min) found in succumbing animals was most likely unspecific, since it did not occur until severe toxic symptoms appeared. The findings support the concept that intracerebral vessels are quite resistant to the direct action of many vasoactive agents given i.v.