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Ovarian venaus cannulation has been a frequently used technique to estimate the secretion rates of ovarian steroids ( 1-9). Estimates of flow rates as determined by the total collected volume have exhibited considerable variation (3-9 ml/hr), depending on the length of the bleeding time and the endocrine status of the animal. Continuous measurements of flow rates following cannulation are not available. Determination of intact flow rates by IVurtman (10) indicates that administration of luteinizing hormone ( L H ) results in ovarian hyperemia and that this is the result of release of a vasoactive substance by LH from the ovary rather than a direct effect of LH. Further evidence for such a vasoactive substance is provided by the studies of Szego and Gitin (11) and more recently by Lipner ( 1 2 ) .The present investigation was undertaken to determine, through continuous measurement, changes in ovarian blood flow following cannulation and to evaluate the effects of L H and antihistamine treatment on these changes.Materials and Methods. Mature female rats (Holtzman Co., Madison, WT), 60-70 days of age, were kept in 14 hr photoperiods ( 5 a. m. to 7 p.m.) at 24 t 0.5". Feed (Wayne Lab. Blox, Allied Mills, Chicago, IL.) and water were administered ad libitum. Daily vaginal smears were taken to establish cyclicity. Only animals in diestrus were used throughout the experiment.All animals were injected via tail vein with 0.8 ml of test solution 20 min prior to cannulation. Animals were grouped into four categories according to treatment as follows; (group 1 ) 0.9% saline solution only; (group 2 ) 50 pg/kg of NIH-LH-S15 in saline; (group 3 ) 50 pg/kg of NIH-LH-S15 and 4.0 mg/kg of promethazine hydrochloride 1 Supported by U S . Public Health Service Research Grant HD 04375-02.(Phenergan, LF'yeth Labs.) ; (group 4) 4.0 mg/kg of promethazine hydrochloride only.At the time oi cannulation, animals were anesthetized lightly with ether followed by 18-22 mg/kg of sodium pentobarbital (Abbot Labs.). Each animal also received 0.8 mg of heparin intravenously.Laparotomy was performed, and the left utero-ovarian vein was isolated. .4 23 gauge needle attached to YE-50 polyethylene tubing (0.584 mm i.d.) was inserted and tied securely with silk. The uterine branch was immediately ligated with silk placed in position prior to cannulation. The polyethylene end of the cannula was directed over a Narco Model 705-0014 drop flow counter which was attached to a Narco Model DMP-4A Physiograph. In order to determine if the effects of L H were specific with respect to the ovarian vein, in some animals the femoral vein was cannulated as described above. All cannulas were calibrated with blood immediately after use to determine the number of drops per milliliter.Flow rates were calculated on the basis of 3 min intervals and reported a t the middle of each 3 min interval as follows: 1.5, 4.5, 7.5, 10.5, 13.5, 16.5, and 19.5 min after the beginning of each bleeding. I n the case of femoral veins, the bleeding period was extended to 30 min. Due to var...

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