A comparison of leukotriene and prostaglandin binding to human myometrium

The binding of radiolabelled leukotriene (LT) C4 to 50,000 g membrane preparations of human myometrium was characterized and compared to the binding of prostaglandin (PG) E2 by the same tissue. 3H-LTC4 binding was temperature-sensitive, proportional to the amount of protein, reversible, specific (LTC4 greater than LTD4 greater than LTE4 much much greater than LTB4, PGE2, PGF2 alpha, arachidonic acid) and saturable (10 pmol/mg protein) with a Kd of 15 nM. These data were obtained in the presence of serine-borate to prevent the conversion of LTC4 to LTD4. The binding of PGE2 to the same membrane preparations was more stable, of lower capacity (200 fmol/mg protein) and of higher affinity (Kd 1 nM). The effect of LTs on the contractility of human myometrial strips in vitro and in comparison with the effect of PGs was studied. LTC4, LTD4 and LTE4 had no stimulatory effect in the dose range 0.05-1.25 microM, but a weak inhibitory effect was noted with 1.25 microM LTC4. As expected, PGF2 alpha stimulated and PGE2 inhibited contractility. In contrast to PGE2, the binding of LTC4 in human myometrium is unlikely to represent true receptors because LTs have little direct influence on myometrial contractility in vitro.