H2-receptors in the human ocular surface.

Area of Science:

• Ophthalmology
• Pharmacology
• Histamine Receptor Research

Background:

• The ocular surface is a complex interface with various physiological functions.
• Histamine receptors play roles in ocular inflammation and sensation.
• The specific role of H2-receptors in the human ocular surface was not well-defined.

Purpose of the Study:

• To investigate the presence and function of histamine H2-receptors on the human ocular surface.
• To determine if H2-receptor activation causes ocular vasodilation.
• To differentiate the roles of H1 and H2 receptors in ocular responses.

Main Methods:

• A two-part study involving ten healthy human volunteers.
• Administration of a selective H2-receptor agonist, dimethylaminopropylisothiourea (dimaprit dihydrochloride).
• Pretreatment with H2-receptor antagonist (cimetidine) and H1-receptor antagonist (antazoline phosphate) to assess receptor involvement.

Main Results:

• Dimethylaminopropylisothiourea induced vasodilation on the ocular surface without causing itch.
• Cimetidine significantly blocked the vasodilatory effect of dimethylaminopropylisothiourea.
• Antazoline phosphate did not inhibit the vasodilatory response, indicating H1-receptors are not primarily involved.

Conclusions:

• Histamine H2-receptors are demonstrably present in the human ocular surface.
• Activation of ocular H2-receptors leads to vasodilation.
• These findings suggest a specific role for H2-receptors in regulating ocular vascular tone.