EFFECTS OF SYNTHETIC OXYTOCIN WITH AND WITHOUT PRESERVATIVES UPON CORONARY BLOOD FLOW IN THE DOG

¹ Department of Pharmacology, University of Tennessee Medical Units, Memphis, Tennessee

These studies include evaluation in anesthetized dogs of the effects of preservative-free synthetic oxytocin, of the commercial preparation of synthetic oxytocin with ethanol and chlorobutanol as preservatives (Syntocinon) and of a synthetic oxytocin-chlorobutanol mixture. Also, the effects of the preservatives, ethanol and chiorobutanol, were investigated separately and in combination. Parameters recorded included phasic coronary blood flow, mean coronary blood flow, myocardial contractile force, heart rate and coronary perfusion pressure. Oxytocin alone in the dog directly constricted the coronary vasculature without modifying other cardiovascular parameters. A biphasic flow response was observed when the commercial preparation was administered. Also, when pure oxytocin was mixed with chlorobutanol, the preparation elicited a biphasic response essentially identical with that seen with the commercial preparation. The preservatives, when administered individually and in combination, were without effect on coronary blood flow. These findings indicate that preservative-free synthetic oxytocin is a coronary vasoconstrictor in the dog and suggest that an interaction occurs between oxytocin and chlorobutanol, the product of which produces a transient increase in coronary blood flow followed by a more prolonged decrease in flow.