Nicotine inhibits the synthesis of prostacyclin in rabbit aorta and human peripheral veins and the hypoxia-induced release of prostacyclin from rabbit hearts

antagonized by a vascular vasopressin antagonist, which suggests a role for vasopressin in mediating some cardiovascular responses (2). The cardiovascular effects of oral snuff have been examined systematically in only one study (13). Changes in heart rate and blood pressure that are similar in magnitude to those of cigarette smoking were ob served. However, the time course appears to be slower than the response to cigarette smoking, with maximum effects observed at 5 to 10 minutes after a dose of oral tobacco. Similar findings, along with increased myocardial contractility and coronary, femoral, and renal blood flow, were also noted in anesthetized dogs after the administration of oral tobacco (13). Thus it appears that single doses of smokeless tobacco can produce hemodynamic effects that are similar to those of cigarette smoking. Whether such changes are sustained throughout the day with repeated daily doses remains to be established.