Abstract

A hypotensive, smooth muscle-contracting factor extracted from the rabbit fetal placenta has been described. The placental factor is dialyzable, relatively stable to heat and acid, unstable to alkali, and soluble in water and in some organic solvents such as butanol and ethanol. It migrates as a single compound ionophoretically and on paper chromatography using several solvent systems. The placental factor has an isoelectric point near pH 4. The placental factor is of low molecular weight and preparations of the partially purified factor liberate amino acids upon acid hydrolysis.

The placental factor causes contraction of guinea pig ileum, rabbit and rat uterus and intestine but not of rabbit aorta. Immature rat uterus and uterus from the virgin rabbit are more sensitive to the factor than estrogenized uterus or uterus from pregnant rabbits. The placental factor increases capillary permeability when injected intradermally.

Inhibition studies show that the placental factor is inhibited by epinephrine, norepinephrine, benactyzine and chlorpromazine but not by atropine, diphenhydramine, cocaine, decamethonium and d-tubocurarine.