A potent vasoconstrictor in the rat submandibular gland.
We detected a novel vasoconstrictor in an arginine esterase fraction separated from fractions containing tonin and other esterases that were obtained from a rat submandibular gland extract. When tested on isolated rabbit aorta rings, the substance caused dose-related contractions that were slow in onset, long-lasting, and difficult to reverse by rinsing. The substance acts directly on vascular smooth muscle, since preincubation with plasma or intact endothelium is not required. The fact that the constrictor was destroyed by heat and incubation with pronase suggests that it is a protein. Molecular sieving indicates an estimated molecular weight of 24,000 Da. It has a neutral isoelectric point that is higher than the pI of tonin, from which it can be separated by anion exchange chromatography. A small amount of the vasoconstrictor was obtained by gel filtration and eluted from isoelectric focusing polyacrylamide gels. The purified substance showed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was a potent vasoconstrictor; an estimated concentration of 2.5 nM induced contraction of isolated rabbit aorta rings ranging from 15% to 40% of the maximum contraction obtained by 60 mM KCl. Contraction was completely blocked by 1 mM (p-amidinophenyl)methanesulfonyl fluoride, a serine protease inhibitor. Contractile activity was not affected by hirudin, a thrombin inhibitor, but was completely inhibited by soybean trypsin inhibitor and blunted by aprotinin; thus it may be a trypsin-like serine protease. Purified vasoconstrictor preparation showed hydrolyzing activity on Pro-Phe-Arg-methyl-coumarin amide, a kallikrein substrate. We conclude that a novel vasoconstrictor serine protease is present in the rat submandibular gland.
- Copyright © 1991 by American Heart Association