Nanomolar concentrations of prostaglandin F2 alpha potentiate cholinergic contractions of rabbit isolated tracheal muscle.

The effects of prostaglandin F2 alpha (PGF2 alpha) on stimulation- or acetylcholine-evoked contractions were studied in isolated airway muscle preparations from rabbits, guinea-pigs and humans. Low concentrations of PGF2 alpha (10(-9) to 9 X 10(-8) mol/1) produced a dose-related (10-300%) increase in the contractile responses of the rabbit trachealis muscle to electrical stimulation at 2 Hz. This effect was inversely related to the rate of stimulation. In seven out of forty two preparations the resting muscle tone was also increased by 1.1 X 10(-8) mol/1 or higher concentrations of PGF2 alpha. This substance enhanced the contractile responses to acetylcholine (1-2.7 X 10(-8) mol/1) to the same extent as those to electrical stimulation. The potentiation produced by PGF2 alpha was not affected by indomethacin, mepyramine, methysergide or phenoxybenzamine. Electrically evoked contractions of isolated tracheal strips of guinea-pig or segments of human bronchial muscles were not changed significantly in the presence of 0.1-5 X 10(-8) mol/1 of PGF2 alpha. These results suggest that PGF2 alpha may modulate airway muscle tone by enhancing the postsynaptic stimulatory effect of acetylcholine released from the pulmonary cholinergic nerve endings. This modulation seems to be species-dependent.