DMBA-induced Mammary Carcinogenesis, in Relaton to Rebound Increase of Serum Prolactin after Suppression with Bromocryptine in Pubescent Virgin Rats

Twenty six, 31 and 53 young female Sprague-Dawley rats in Groups A, C and E, respectively, were administered 10 mg/Kg Bromocryptine daily by intubation for 3 weeks from 31 to 51 days of age. Twenty five rats each in Groups B and D served as the controls. Tail blood was collected for radioimmunoassay of prolactin from only metaand di-estrus rats in Groups A, B and E around 10 am at the age of 51-58 days, and the sampling was not repeated in any animal. A rebound increase of serum prolactin level occurred within 3 days after the termination of Bromocryptine treatment. A single dose of 5mg/rat DMBA in Groups A and B and 2.5mg/rat in Groups C and D was given orally around 11 am at the age of 52 days, and the carcinogenesis with DMBA was evaluated 22 weeks after the single administration of carcinogen. Mammary adenocarcinoma developed in some animals, but no other tumors could be found. When a single weaker dose of DMBA was administered orally on the day after the cessation of the 3 week treatment with Bromocryptine, the chemical induction of mammary carcinogenesis was enhanced distinctly.