Vasoactive intestinal polypeptide and the canine cerebral circulation

Area of Science:

• Neuroscience
• Vascular Biology
• Pharmacology

Background:

• Cerebrovascular nerves containing vasoactive intestinal polypeptide (VIP) may influence cerebral blood flow (CBF).
• The role of VIP in regulating CBF during physiological challenges like hypercapnia and hypoxia is not fully understood.

Purpose of the Study:

• To investigate the role of VIP in cerebrovascular regulation.
• To determine if VIP affects CBF during hypercapnia and hypoxia.
• To explore the mechanisms by which VIP influences cerebral circulation.

Main Methods:

• Measurements of CBF using cerebral venous outflow and microsphere methods in anesthetized dogs.
• Radioimmunoassay to measure plasma VIP concentrations.
• Intra-arterial and intraventricular administration of VIP to assess its effects on CBF and regional cerebral blood flow (rCBF).

Main Results:

• Hypercapnia and hypoxia increased cerebral venous outflow but did not alter VIP concentrations in arterial blood, cerebral venous blood, or cerebrospinal fluid (CSF).
• Intra-arterial VIP increased blood flow in the common carotid artery and temporalis muscle but had no effect on total or regional CBF.
• Unilateral intraventricular infusion of VIP significantly increased rCBF, suggesting a local effect within the brain.

Conclusions:

• Local release of VIP from perivascular nerve endings may influence CBF.
• The blood-brain barrier likely contributes to the unresponsiveness of canine cerebral vessels to blood-borne VIP.
• VIP does not appear to mediate CBF changes induced by hypercapnia or hypoxia.