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Growth and Food Intake of Prematurely Weaned Rats: Effect of Cortisone and Thyroxine Injection During the Suckling Period¹

Roy Lerman and Otakar Koldovsk

Department of Pediatrics, University of Pennsylvania, and Joseph Stokes Research Institute of Children's Hospital of Philadelphia, Pennsylvania 19104

In the first days after weaning, prematurely weaned (PW) rats consume little or no solid food and lose weight. Immaturity of food intake mechanisms and digestive processes were considered as one of the contributing factors. Food intake and weight gain were studied in PW rats untreated or pretreated in the suckling period with hormones of known maturative action cortisone or thyroxine. In experiment 1, (PW rats fed stock diet on postnatal day 15) the weight of untreated animals returned to weaning weight within 3.4 ± 0.13 days. Animals pretreated with cortisone acetate (5 mg/100 g body weight injected on postnatal day 11) regained weaning weight within 2.7 ± 0.14 days. In experiment 2, (performed 2 years later, rats PW on day 16) untreated animals fed stock diet or sucrose diet regained weaning weight within 3.9 ± 0.18 or 2.6 ± 0.07 days, respectively. PW animals pretreated with L-thyroxine (200 µg/100 g body weight, injected daily between days 11 to 15), fed stock diet, regained weaning weight within 2.9 ± 0.2 days. When identically pretreated PW rats were fed a sucrose diet, no halt in weight gain occurred, and food consumption began sooner than in untreated rats. PW untreated rats fed intragastrically on the first day after weaning, with free access to sucrose diet, recovered weaning weight within 1.7 ± 0.55 days. The same result was obtained when PW untreated rats were only sham fed. Our studies demonstrate a relationship between weight loss after premature weaning and immaturity of food intake mechanisms and digestive processes.

KEY WORDS: • food intake • growth • premature weaning • cortisone • thyroxine • incisors • rat

¹ Supported by Grant AM14531, NIH, Bethesda, Maryland.

Manuscript received 26 June 1978.