The present study was designed to examine the influence of Escherichia coli endotoxin (LPS, lipopolysac- charide) on the concentration of gonadotrophin-releasing hormone (GnRH) in the hypothalamus and luteinizing hormone (LH) in the pituitary as well as LH, prolactin (PRL), Cortisol (CI), and sex steroids in blood plasma of prepurtal gilts. In the ovaries, LH/human chorionic gonadotropin (hCG) receptors content was also estimated. The experiment was performed on 10 prepubertal gilts (Large White x Landrace) at the age of 156 ± 2 days (body weight 65.7 ± 3.56 kg, mean + SD). The animals were randomly assigned to one of two groups: 1) treated with Escherichia coli endotoxin (serotype 055:B5; n = 5), and 2) control gilts receiving saline (n = 5). 2 mg of LPS was administered i.m., twice a day (at 08:05 and 20:05) for 4 days. Blood samples from the jugular vein were collected every hour for 12 h (08:00/time 0 - 20:00), for 4 days of the study and more frequently during 4 h (08:00/time 0 - 12:00) sampling periods every day of the experiment. All the gilts were slaughtered on the next day, after the last LPS or saline injections were performed and then, the ovaries, hypothalamus and pituitary were immediately dissected out. Plasma and tissue hormone concentrations were analysed by radioimmunoassay (RIA). During the experimental period, rectal temperature in LPS-treated gilts was higher (on the 1st' and 2nd day - P < 0.001, on the 3th and 4th day - P < 0.05) than that found in the controls. During the whole experiment mean concentrations of CI in the gilts treated with LPS were higher (P < 0.05 - P < 0.001) in comparison to those observed in the controls. In the gilts receiving LPS, plasma LH was lower (P < 0.01, P < 0.001) than that found in the control animals on days 1-4 of the study. Injections of LPS did not affect the frequency, amplitude or duration of LH peaks. In LPS-treated group, plasma PRL was decreased (P < 0.05, P < 0.01) on the 4th day of the experiment in comparison to that found in the control group. During the consecutive days of the study, the levels of androstenedione (A4), testosterone (T) and estradiol-17ß (E2) remained unchanged in both control and LPS-treated gilts and no significant differences between both groups were found. GnRH content in the hypothalamus and LH in the pituitary varied insignificantly between the groups showing tendency to a slight decrease in the gilts receiving LPS. In the ovaries of LPS-treated animals, the concentration of LH/hCG receptors slightly decreased as compared with that found in the control gilts. The results obtained indicate that administration of LPS to prepubertal gilts causes a decrease in plasma LH and PRL concentrations, an increase in Cortisol level and a slight decrease in numbers of LH/hCG receptors in the ovaries. These findings suggest also that pathological states altering secretion of the pituitary hormones can impair processes leading to puberty in a female.
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