In utero glucocorticoid exposure reduces fetal skeletal muscle mass in rats independent of effects on maternal nutrition.

Maternal stress and undernutrition can occur together and expose the fetus to high glucocorticoid (GLC) levels during this vulnerable period. To determine the consequences of GLC exposure on fetal skeletal muscle independently of maternal food intake, groups of timed-pregnant Sprague-Dawley rats (n = 7/group) were studied: ad libitum food intake (control, CON); ad libitum food intake with 1 mg dexamethasone/l drinking water from embryonic day (ED)13 to ED21 (DEX); pair-fed (PF) to DEX from ED13 to ED21. On ED22, dams were injected with [(3)H]phenylalanine for measurements of fetal leg muscle and diaphragm fractional protein synthesis rates (FSR). Fetal muscles were analyzed for protein and RNA contents, [(3)H]phenylalanine incorporation, and MuRF1 and atrogin-1 (MAFbx) mRNA expression. Fetal liver tyrosine aminotransferase (TAT) expression was quantified to assess fetal exposure to GLCs. DEX treatment reduced maternal food intake by 13% (P < 0.001) and significantly reduced placental mass relative to CON and PF dams. Liver TAT expression was elevated only in DEX fetuses (P < 0.01). DEX muscle protein masses were 56% and 70% than those of CON (P < 0.01) and PF (P < 0.05) fetuses, respectively; PF muscles were 80% of CON (P < 0.01). Muscle FSR decreased by 35% in DEX fetuses (P < 0.001) but were not different between PF and CON. Only atrogin-1 expression was increased in DEX fetus muscles. We conclude that high maternal GLC levels and inadequate maternal food intake impair fetal skeletal muscle growth, most likely through different mechanisms. When combined, the effects of decreased maternal intake and maternal GLC intake on fetal muscle growth are additive.

Reduced hypothalamic neuropeptide Y expression in growth hormone- and prolactin-deficient Ames and Snell dwarf mice.

Neuropeptide Y (NPY)-producing neurons in the hypothalamic arcuate nucleus (ARC) have been implicated in GH feedback in several studies in rats. Ames (df/df) and Snell (dw/dw) dwarf mice carry mutations in transcription factors Prop-1 and Pit-1, respectively, that abrogate detectable expression of GH, prolactin, and TSH. The present study was undertaken to determine whether and to what extent hypothalamic NPY neurons are affected by the lifelong absence of pituitary hormone feedback in hypopituitary Ames and Snell dwarf mice. Total ARC NPY mRNA levels were quantified using in situ hybridization, and numbers of ARC NPY-producing cells were quantified using immunocytochemistry. For in situ hybridization, dwarf and normal coronal brain sections were hybridized with 35S-labeled riboprobe complementary to rat NPY cDNA, and then analyzed for total signal intensity from the entire ARC for each animal as well as for mRNA per neuron. NPY-containing perikarya in ARC were counted in sections of colchicine-treated (intracerebroventricular) dwarf and normal mice. Total ARC NPY mRNA was reduced in df/df mice to 33.6% (P < 0.01) of that in normal littermates, and reduced in dw/dw mice to 46.3% (P < 0.05) of normals, but there was no difference in expression per neuron as determined by reduced silver-grain counting. The decrement in dwarf mice of total ARC NPY mRNA without reduction in mRNA per cell suggested a reduction in NPY-containing neuron number, which was the case as shown by immunocytochemistry. NPY neuronal number in adult Ames dwarf mice (1048 +/- 104) was significantly (P < 0.01) reduced to 68% of that in DF/df littermates (1536 +/- 73), and significantly (P < 0.05) reduced in Snell dwarf mice to 63% of normals (1138 +/- 137 vs. 1726 +/- 205). This study represents the first enumeration of NPY-producing neurons in mouse hypothalamus and the first demonstration of lower NPY neuron number in a hypopituitary model. The reduction in total NPY mRNA was greater than that reported in studies of GH-deficient rats, suggesting that NPY expression may be affected by the lifelong absence of prolactin or TSH or both, as well as GH.