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Molecular species of prostaglandins involved in modulating luteinising hormone pulses of female rats under infectious stress conditions

Mammalian reproductive function is controlled by the hypothalamic‐pituitary‐gonadal (HPG) axis, which is suppressed under infectious stress conditions. By analysing the pulsatility of luteinising hormone (LH), we have previously demonstrated that prostaglandins (PGs) in the central nervous system mediate infectious stress to suppress the activity of the HPG axis. The present study aimed to characterise the types of PGs responsible for suppression of the HPG axis. We focused on three major types of PGs: PGE2, PGD2 and PGF2α. We used female rats overiectomised bilaterally 1 week before the experiments. Lipopolysaccharide (100 μg kg–1) suppressed LH pulses at the same time as enhancing the concentration of all three PGs in the cerebrospinal fluid, which was restored by indomethacin (10 mg kg–1). Subsequently, we observed LH pulsatility after a single injection of each PG and after co‐injection of PGE2 with PGF2α into the third cerebral ventricle. A single injection of PGE2 dose‐dependently induced a transient increase in mean LH concentration and LH pulse amplitude, and PGD2 significantly increased the amplitude of LH pulses, wereas PGF2α did not affect LH pulsatility. On the other hand, co‐injection of PGE2 and PGF2α induced a significant suppression of both the frequency and amplitude of LH pulses. These results suggest that PGE2 and PGF2α can represent two of the mediators that suppress the HPG axis in situations of infectious stress. Moreover, the results imply that there are two contradictory effects of PGE2 on LH pulsatility: (i) enhancive when working alone and (ii) suppressive when working together with PGF2α.