Sudden bladder distention in a female rat

Abstract

We purchased a batch of 48 female Long-Evans rats, weighing 200–250 g, from an accredited animal supplier for studies on sexual behavior. The animals lived in groups of four in large wire-mesh cages in a colony room maintained on a reversed 12:12 h light/dark cycle at approximately 21o ± 2o C. The rats had ad libitum access to commercial rat feed and water.We anesthetized the females with a mix-ture of ketamine (50 mg/ml) and xylazine (4 mg/ml), mixed at a ratio of 4:3 respectively, and injected intraperitoneally in a volume of 1 ml/kg of body weight. The anesthetized females then underwent bilateral ovariec-tomy via a lumbar incision. We allowed the animals one week of post surgical recov-ery before copulatory trials, after which we induced sexual receptivity by subcutaneous injections of estradiol benzoate (10 µg) 48 hours and progesterone (500 µg) 4 hours before each test. All females underwent this hormonal treatment every four days during 10 copulatory sessions.Due to the hormonal injection schedule, we handled and checked all animals every two days. After nine copulatory sessions, we noticed one rat with an enlarged abdo-men, which we determined to be caused by severe bladder distention. This condition was not present two days before. On clini-cal examination, the rat was dehydrated, but we found no abnormalities in gait, postural reactions, or spinal reflexes. External exami-nation of the vagina did not reveal abnormal secretions either. Very gently, the examiner tried to void the bladder by compressing the anterior border, but it was not successful. Then, on closer examination of the vagina, the examiner found a tightly fitted sperm plug. He used a rat restrainer to hold the rat still and upside down and gently removed the plug with surgical tweezers. The exam-iner did not detect any abnormal vaginal secretions, but he did notice a foul odor. Once the plug was removed, the examiner voided the bladder very gently. He gave the rat saline subcutaneously to hydrate it and then returned the animal to its home cage. Two days later the same clinical signs were present (