Neural mechanisms regulating neurohypophysial resistance arteries

Area of Science:

• Neuroscience
• Vascular Biology
• Neuroendocrinology

Background:

• The neurohypophysis receives arterial supply from both extracranial (inferior hypophysial artery) and intracranial (superior hypophysial artery) sources.
• Understanding the neural regulation of blood flow to the neurohypophysis is crucial for its physiological function.

Purpose of the Study:

• To define the extent of vasoactive intestinal polypeptide (VIP) and noradrenergic influences on neurohypophysial resistance arteries.
• To investigate the pharmacological and physiological responses of these vessels to neural stimulation.

Main Methods:

• Isolated 100- to 200-microns-diameter vessels from the neurohypophysis were used.
• Perivascular nerve innervation was assessed.
• Pharmacological sensitivity to VIP and norepinephrine was determined.
• Transmural nerve stimulation was employed to assess physiological responses (vasodilation and vasoconstriction).

Main Results:

• The inferior hypophysial artery showed noradrenergic and VIP-like innervation, while the superior hypophysial artery had primarily VIP-like innervation.
• Both arteries were sensitive to VIP, with the inferior hypophysial artery also responding to norepinephrine.
• Transmural nerve stimulation induced frequency-dependent vasodilation in both arteries, unaffected by atropine or propranolol.
• Vasoconstriction was observed in the inferior hypophysial artery, partially blocked by alpha-adrenergic antagonists and guanethidine.

Conclusions:

• Neurohypophysial resistance vessels possess regionally unique neural mechanisms for blood flow regulation.
• The inferior hypophysial artery demonstrates neural control for both dilator and constrictor activities, meeting anatomical, pharmacological, and physiological definitions.
• VIP plays a significant role in the vasodilation of neurohypophysial arteries.