The effects of xylazine on intrauterine pressure, uterine blood flow, maternal and fetal cardiovascular and pulmonary function in pregnant goats.

To investigate the effects of xylazine on pregnant goats, xylazine induced changes in heart rate (HR), arterial blood pressure (ABP) and arterial blood pH and gases in the mother and fetus, as well as changes in intrauterine pressure (IUP) and uterine blood flow (UBF), were studied using a chronic preparation model of pregnant goats. Intramuscular administration of xylazine (0.2 mg/kg b.w.) caused a marked decrease in HR and ABP of the mother, which remained significantly reduced up to 120 min. In the fetus, a significant decrease in HR and a significant increase in ABP were recorded after only 5 min. Significant decreases of maternal arterial blood pH and oxygen partial pressure (Po2) were observed up to 120 and 30 min after the injection, respectively. Fetal arterial blood pH and Po2 also decreased, but these changes were milder and less persistent than those of the mother. Within 2 to 5 min after the administration of xylazine, IUP began to increase and remained high for about 15 min. Thereafter, there was a frequent periodic increase in IUP. After 5 min, UBF decreased significantly and remained low up to 120 min. A fall in UBF was associated with a rise in IUP. These findings suggested that administration of xylazine to pregnant goats results in a decrease in UBF arising from the induction of uterine contractions, a decrease in circulating blood volume, hypoxemia and acidosis in the mother.