Respiratory and cardiovascular responses resulting from intravenous injection of sheep hydatid cyst fluid to dogs

Effects of intravenous injection of sheep hydatid cyst fluid on respiratory and cardiovascular systems were studied in sodium pentobarbital-anesthetized dogs. Under sterile conditions, the fluid was drawn from the liver and lung hydatid cysts of sheep, and centrifuged for 20 min at 500g. The supernatant fluid was used as the test solution. In a majority of animals, administration of 5 ml of the cyst fluid caused a sharp fall in arterial blood pressure, with or without respiratory changes. The latter, when present, included temporary cessation of respiration followed by rapid shallow breathing. There was usually an increase in the heart rate as the arterial blood pressure dropped. Atropine, 0.5 mg/kg body wt, given subcutaneously prior to the cyst fluid administration, did not block the responses. Cardiovascular responses produced by intravenous injection of cyst fluid were similar in dogs with positive pressure breathing and with spontaneous breathing. In 7 out of 10 responsive dogs, pretreatment with the antihistamine, chlorpheniramine, abolished the respiratory and cardiovascular responses.