The neural and vascular effects of killed Su-Streptococcus pyogenes (OK-432) in preterm fetal sheep

Abstract

Fetal exposure to inflammatory mediators is associated with a greater risk of brain injury and may cause endothelial dysfunction; however, nearly all the evidence is derived from gram-negative bacteria. Intrapleural injections of OK-432, a killed Su-strain of Streptococcus pyogenes, has been used to treat fetal chylothorax. In this study, we evaluated the neural and cardiovascular effects of OK-432 in preterm fetal sheep (104 +/- 1 days, term 147 days). OK-432 (0.1 mg, n = 6) or saline vehicle (n = 7) was infused in the fetal pleura, and fetuses were monitored for 7 days. Blood samples were taken routinely for plasma nitrite measurement. Fetal brains were taken for histological assessment at the end of the experiment. Between 3 and 7 h postinjection, OK-432 administration was associated with transient suppression of fetal body and breathing movements and electtroencephalogram activity (P < 0.05), increased carotid and femoral vascular resistance (P < 0.05), but no change in blood pressure. Brain activity and behavior then returned to normal except in one fetus that developed seizures. OK-432 fetuses showed progressive, sustained vasodilatation (P < 0.05), with lower blood pressure after 4 days (P < 0.05), but normal heart rate. There were no changes in plasma nitrite levels. Histological studies showed bilateral infarction in the dorsal limb of the hippocampus of the fetus that developed seizures, but no injury in other fetuses. We conclude that a single low-dose injection of OK-432 can be associated with risk of focal cerebral injury in the preterm fetus and chronic central and peripheral vasodilatation that does not appear to be mediated by nitric oxide.

Fig. 1.

Time sequence changes in mean arterial blood pressure (MAP, top) and fetal heart rate (FHR, bottom) in the control group (○) and OK-432 group (●). Data are 1-h averages (means ± SE) from 12 h before injection (dotted line) until 168 h (7 days) after injection.

Fig. 2.

Time sequence changes in carotid blood flow (CaBF, top) and carotid vascular resistance (CaVR, bottom) in the control group (○) and OK-432 group (●). Data are means ± SE from 12 h before injection (dotted line) until 168 h (7 days) after injection. Bar denotes significance, P < 0.05 control vs. OK-432.

Fig. 3.

Time sequence changes in femoral blood flow (FBF, top) and femoral artery vascular resistance (FVR, bottom) in the control group (○) and OK-432 group (●). Data are means ± SE from 12 h before injection (dotted line) until 168 h (7 days) after injection. Bar denotes significance, P < 0.05 control vs. OK-432.

Fig. 4.

Time sequence changes in electrocorticogram (ECoG) amplitude (dB, top) and spectral edge (Hz, bottom) in the control group (○) and OK-432 group (●). Data are means ± SE from 12 h before injection (dotted line) until 168 h (7 days) after injection. Bar denotes significance, P < 0.005 control vs. OK-432.

Fig. 5.

Photomicrographs of the hippocampal region from the OK-432 treatment fetus with injury, an OK-432 treatment fetus without injury, and a control fetus. A: acid fuchsin/thionin (AF/T); note a large area of infarction indicated by an arrow. There is no injury in the other two groups. The arrow in the control fetus of A indicates the CA1 region. Isolectin B4 staining (IB4, B) indicates activated microglia in the area of the infarct, but no activated microglia in the other groups. Glial fibrillary acidic protein staining (GFAP, C) indicated that there was no increase in activated astrocytes 7 days after OK-432 infusion. Taken at ×10 magnification.