Effect of L-dopa on interleukin-1β-induced suppression of luteinizing hormone secretion in intact female rats

BACKGROUND The cytokine, interleukin-1β (IL-1β), increases during immune stress and is known to suppress the preovulatory luteinizing hormone (LH) surge in female rats by decreasing hypothalamic norepinephrine (NE). We hypothesized that IL-1β could produce this effect by decreasing NE biosynthesis. METHODS Female Sprague–Dawley rats were implanted with a push–pull cannula in the medial preoptic area (MPA) of the hypothalamus and a catheter in the jugular vein. They were treated i.p. with the vehicle or 5 µg of IL-1β, the NE precursor, L-dopa, or a combination of L-dopa and IL-1β at 1300 hours on the day of proestrus. They were subjected to push–pull perfusion and serial blood sampling. Perfusates were analyzed for NE levels and serum samples for LH. RESULTS IL-1β treatment blocked the increase in NE levels in the MPA and the LH surge. Treatment with L-dopa was able to partially restore both NE and LH levels during the afternoon of proestrus. IL-1β treatment caused failure of ovulation and this effect was also reversed by L-dopa. CONCLUSIONS These results suggest that IL-1β could decrease NE levels in the MPA to suppress reproductive functions and L-dopa can be used to counter this effect.