A potent vasoconstrictor in the rat submandibular gland

Area of Science:

• Biochemistry
• Physiology
• Enzymology

Background:

• The rat submandibular gland is known to contain various esterases, including tonin.
• The physiological roles of many glandular enzymes remain incompletely understood.

Purpose of the Study:

• To identify and characterize novel vasoactive substances in rat submandibular gland extracts.
• To determine the biochemical nature and functional properties of a newly detected vasoconstrictor.

Main Methods:

• Fractionation of rat submandibular gland extract using chromatography (anion exchange, gel filtration).
• Assay of vasoconstrictor activity on isolated rabbit aorta rings.
• Biochemical characterization including heat stability, protease sensitivity, molecular sieving, isoelectric focusing, and SDS-PAGE.
• Enzyme inhibition studies using specific protease inhibitors.
• Substrate hydrolysis assay using a kallikrein substrate.

Main Results:

• A novel vasoconstrictor protein, distinct from tonin, was isolated from rat submandibular gland.
• The substance induced slow-onset, long-lasting contractions in rabbit aorta rings, acting directly on vascular smooth muscle.
• It is a serine protease with an estimated molecular weight of 24,000 Da and a neutral isoelectric point.
• The vasoconstrictor demonstrated potent activity, with 2.5 nM causing significant contraction.
• Activity was inhibited by serine protease inhibitors (soybean trypsin inhibitor, aprotinin) and showed hydrolyzing activity on a kallikrein substrate.

Conclusions:

• A novel vasoconstrictor serine protease is present in the rat submandibular gland.
• This enzyme directly affects vascular smooth muscle, suggesting a potential role in regulating vascular tone.
• Further research is warranted to elucidate its specific physiological function and contribution to blood pressure regulation.