Effect of Intrauterine Infusions of E. coli Endotoxin on Luteinizing Hormone Receptor Binding Capacity in Ovarian Follicles of Heifers: Exploratory Study

A study was conducted to determine whether follicles recovered from heifers treated with intrauterine infusions of E. coli endotoxin had altered LH binding capacities. Four Holstein heifers were synchronized (two PGF2 injections PG-1 and PG-2) and then super ovulated (with twice daily injections of FSH in decreasing doses for four days). On the third day luteolysis was induced with a third PGF2 injection (PG-3). Starting 24 h after PG-3, heifers received intrauterine infusions of either 5 cc sterile pyrogen-free water (CTR; n=2) or E. coli endotoxin at a dose of 5 μg/Kg bw (TRT; n=2), every 6 h for 7 treatments. An intensive blood sampling was carried out and plasma concentrations of LH, P4 and cortisol were determined by RIA's. All heifers were ovariectomized 64 h after PG-3 injection. Follicles were hystologicaly evaluated and classified as atretic or non-atretic. The concentrations of LH receptors in follicular wall were determined by one-point saturation analysis. A third of the follicles in TRT were classified as atretic versus a quarter in CTR heifers. Intrauterine infusions of endotoxin triggered only transitory, inconsistent rises in plasma cortisol. Treated animals had larger areas under the cortisol curve (5.9 and 7.71 v/s 4.66 and 4.13), but not significantly different from the controls (P>0.05). The concentrations of LH receptors were significantly lower (P<0.05) in TRT (1.9 ± 0.58 and 2.24 ± 0.2 fmol/mg) compared to CTR heifers (3.51 ± 0.53 and 3.72 ± 0.44 fmol/mg). In conclusion, E. coli endotoxin induced a significant reduction in the follicular concentrations of LH receptors in heifers. The mechanism whereby endotoxin affects follicular LH receptors is unknown.