Inhibition of phospholipase A2 modulates fecundity in the primitive insect Thermobia domestica (Thysanura)

Phospholipase A2 (PLA2) activity was tested in the seminal receptacle of the firebrat female during an ovarian cycle and in relation to insemination. The PLA2 activity was weak up to the time of insemination, while a strong increase of the enzyme activity occurred at the end of the ovarian cycle in both inseminated and non-inseminated females, indicating that PLA2 is an endogenous enzyme not transferred by the spermatophore. Females received various drugs whose anti-PLA2 effects were checked on the seminal receptacle tissues. The effects of the drugs were investigated on ovarian maturation and on the number of eggs layed by inseminated females. Dose-response relationships provide crucial indications that PLA2 inhibition interferes with the firebrat fecundity. The emergent picture is that oocyte maturation is insensitive to PLA2 activity, but that the treatments which reduce the release of arachidonic acid from cellular phospholipids interrupt some physiological link leading to egg deposition. The arachidonate metabolites are designated as the primer of the ovulation mechanisms; the possible role of development hormones in PLA2 regulation is discussed.