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Roles of the Lactogens and Somatogens in Perinatal and Postnatal Metabolism and Growth: Studies of a Novel Mouse Model Combining Lactogen Resistance and Growth Hormone Deficiency

Division of Pediatric Endocrinology and Diabetes (D.F., J.O., S.W., J.K., M.F.), Duke University Medical Center, Durham North Carolina 27710; Institut National de la Santé et de la Recherche Médicale Unité 584-Hormone Targets (P.A.K., S.A., M.P.), Faculte de Medecine Necker, Paris, France 75015; and Musculoskeletal Diseases Center (S.M.), Jerry L. Pettis Veterans Affairs Medical Center, Loma Linda, California 92357

Address all correspondence and requests for reprints to: Dr. Michael Freemark, Division of Pediatric Endocrinology and Diabetes, Box 3080, Duke University Medical Center, Durham, North Carolina 27710. E-mail: freem001{at}mc.duke.edu.

To delineate the roles of the lactogens and GH in the control of perinatal and postnatal growth, fat deposition, insulin production, and insulin action, we generated a novel mouse model that combines resistance to all lactogenic hormones with a severe deficiency of pituitary GH. The model was created by breeding PRL receptor (PRLR)-deficient (knockout) males with GH-deficient (little) females. In contrast to mice with isolated GH or PRLR deficiencies, double-mutant (lactogen-resistant and GH-deficient) mice on d 7 of life had growth failure and hypoglycemia. These findings suggest that lactogens and GH act in concert to facilitate weight gain and glucose homeostasis during the perinatal period. Plasma insulin and IGF-I and IGF-II concentrations were decreased in both GH-deficient and double-mutant neonates but were normal in PRLR-deficient mice. Body weights of the double mutants were reduced markedly during the first 3–4 months of age, and adults had striking reductions in femur length, plasma IGF-I and IGF binding protein-3 concentrations, and femoral bone mineral density. By age 6–12 months, however, the double-mutant mice developed obesity, hyperleptinemia, fasting hyperglycemia, relative hypoinsulinemia, insulin resistance, and glucose intolerance; males were affected to a greater degree than females. The combination of perinatal growth failure and late-onset obesity and insulin resistance suggests that the lactogen-resistant/GH-deficient mouse may serve as a model for the development of the metabolic syndrome.

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