[The effect of cocaine on uterine contractions in the rat].

The abuse of cocaine during pregnancy has become a major problem in substance abuse in the U.S.A. Although cocaine often induces preterm labor, little is known about the effect of this drug on uterine contractions. In 23 pregnant (P) and 23 nonpregnant (NP) rats, a carotid artery and jugular vein were catheterized, and a balloon catheter was inserted into the uterine cavity 24 hrs prior to the study. Arterial blood pressure, heart rate, intrauterine pressure were recorded throughout the study. Uterine contractions were expressed in Montevideo Units (M.V.U.). Cocaine (1.25-20 mg/kg) or saline was administered intravenously to test its toxicity and the effect on uterine contractions. A 1.25 or 2.5 mg/kg dose of cocaine did not produce toxic symptoms, but 2.5 mg/kg resulted in a marked increase in M.V.U. in both P and NP. In P, the maximum change in M.V.U. was as high as 250% from the baseline value, twice as much as that observed in NP. Mean arterial blood pressure increased 15% on the average and heart rate decreased 10%. This study indicates that a non-toxic dosage of cocaine stimulates uterine contractions, and pregnancy enhances this effect.