Angiotensin II receptor binding sites in brain microvessels

Area of Science:

• Neuroscience
• Pharmacology
• Cardiovascular Science

Background:

• Angiotensin II (Ang II) plays a crucial role in regulating blood pressure and fluid balance.
• The presence and function of Ang II receptors in the brain's microvasculature are not fully understood.

Purpose of the Study:

• To investigate the specific binding of Ang II to microvessels and particulate fractions of the canine cerebral cortex and cerebellum.
• To determine the characteristics and biological relevance of Ang II receptors in brain microvessels.

Main Methods:

• Radioligand binding assays using 125I-labeled Ang II.
• Isolation of microvessels and particulate fractions from canine cerebral cortex and cerebellum.
• Competition binding studies with Ang II analogues.

Main Results:

• 125I-Ang II demonstrated specific, saturable, and reversible binding to cerebral and cerebellar microvessels with high affinity (Kd ≈ 1 nM).
• Maximal binding of 125I-Ang II was significantly higher in brain microvessels compared to particulate fractions of the cerebral cortex and cerebellum.
• The rank order of displacement by Ang II analogues correlated with their known pharmacological activities, confirming receptor specificity.

Conclusions:

• Specific Angiotensin II receptor binding sites are present in canine brain microvessels.
• These Ang II receptors in the brain microvasculature may play a significant role in regulating cerebral blood flow.