Endogenous prostaglandins and spontaneous contractions in the circular muscle of the guinea-pig stomach.

The physiological significance of endogenous prostaglandin (PG) on spontaneous contractions in isolated circular muscles of the guinea-pig stomach was investigated. Contents of the E and F types of PG were measured by radioimmunoassay as PGE2 and PGF2 alpha. The isolated circular muscles contained 17.04 +/- 2.12 ng PGE2/g tissue (n = 12) and 9.38 +/- 0.62 ng PGF2 alpha/g tissue (n = 12), and released 0.36 +/- 0.04 ng PGE2/g tissue/min (n = 10) and 0.14 +/- 0.01 ng PGF2 alpha/g tissue/min (n = 12) into the solution. These contents and releases of PGs were reduced by treatment with indomethacin (ID50 = 0.3 microgram/ml). Indomethacin (0.1-6 microgram/ml) increased the amplitude of spontaneous contractions dose-dependently, while high concentrations (20 microgram/ml) conversely depressed it. Physiological concentrations of exogenously applied PGE2 (0.03-0.35 ng/ml) markedly suppressed spontaneous contractions in the presence and absence of indomethacin (3 microgram/ml), while PGF2 alpha in concentrations of 0.35-3.54 ng/ml slightly increased them. Therefore, these results suggested that spontaneous contractions in circular muscles were largely influenced by the E type of endogenous PG, not by the F type. The indomethacin-induced increase in the amplitude of spontaneous contractions was not affected by intrinsic nerves and was accompanied by an increase in spike discharges on the slow wave and 45Ca uptake in the muscle cells. These observations suggested that the E type of endogenous PG in circular muscles might play a suppressive role in spontaneous contractions by inhibiting spike generation on the slow wave.