Effects of Gram-positive bacterial pathogens in ewes: Peptidoglycan as a potential mediator of interruption of early pregnancy

Abstract

Bacterial cell walls contain peptidoglycan (PTG), which, among other actions, induces fever. The present experiment evaluated the effects of PTG treatment on early pregnancy and blood plasma concentrations of reproductive hormones. Ewes were injected i.v. with saline or 15, 30 or 60 μg kg-1 sonicated PTG (Streptococcus pyogenes) on day 5 after mating. Each dose of PTG induced fever. Pregnancy rate at day 25 was not related to incidence of fever but tended to differ among treatments (control, 100%; low, 100%; medium, 67%; high, 60%; P < 0.08). Combined pregnancy rate in ewes from control and low dose groups (100%) was greater than that in ewes from medium and high dose groups (64%, P < 0.01). Ewes with high 13, 14-dihydro-15-keto-prostaglandin F2α (PGFM) concentrations had lower pregnancy rates (6 of 10) than those with low concentrations of PGFM (11 of 11; P < 0.05). Mean cortisol concentrations were higher in treated (2.8 ± 0.28 μg dl-1) than in control (1.1 ± 0.03 μg dl-1) ewes (P < 0.01); the pattern of secretion was biphasic and increased in all treated ewes (P < 0.01). Neither means nor profiles of oestradiol differed with treatment. Mean concentrations and the pattern of concentrations of progesterone were reduced in all treated ewes, as indicated by the time by treatment and linear interaction with treatment (1.2 ± 0.1 versus 1.6 ± 0.1 ng ml-1, P < 0.01). Patterns of LH pulses did not differ from 0 to 4 h or 24 to 28 h after treatment; mean plasma LH concentration was lower in ewes treated with 0, 15 or 30 μg PTG kg-1 than with 60 μg PTG kg-1 (P < 0.01). Pregnancy status was not related to plasma concentrations or patterns of LH, oestradiol, progesterone or cortisol. Inflammatory mediators, such as PGF2α, may act directly on the embryo or uterus in ewes treated with PTG.