Neonatal hyperthyroidism alters hepatic epidermal growth factor receptor ontogeny in mice

Perinatal deiodinase 2 expression in hepatocytes defines epigenetic susceptibility to liver steatosis and obesity

Thyroid hormone binds to nuclear receptors and regulates gene transcription. Here we report that in mice, at around the first day of life, there is a transient surge in hepatocyte type 2 deiodinase (D2) that activates the prohormone thyroxine to the active hormone triiodothyronine, modifying the expression of ∼165 genes involved in broad aspects of hepatocyte function, including lipid metabolism. Hepatocyte-specific D2 inactivation (ALB-D2KO) is followed by a delay in neonatal expression of key lipid-related genes and a persistent reduction in peroxisome proliferator-activated receptor-γ expression. Notably, the absence of a neonatal D2 peak significantly modifies the baseline and long-term hepatic transcriptional response to a high-fat diet (HFD). Overall, changes in the expression of approximately 400 genes represent the HFD response in control animals toward the synthesis of fatty acids and triglycerides, whereas in ALB-D2KO animals, the response is limited to a very different set of only approximately 200 genes associated with reverse cholesterol transport and lipase activity. A whole genome methylation profile coupled to multiple analytical platforms indicate that 10-20% of these differences can be related to the presence of differentially methylated local regions mapped to sites of active/suppressed chromatin, thus qualifying as epigenetic modifications occurring as a result of neonatal D2 inactivation. The resulting phenotype of the adult ALB-D2KO mouse is dramatic, with greatly reduced susceptibility to diet-induced steatosis, hypertriglyceridemia, and obesity.

Diurnal dynamics of cell proliferation in rat liver during early postnatal ontogeny and effect of epidermal growth factor on hepatocyte proliferative activity

Circadian rhythms of DNA synthesis, mitotic activity, and duration of mitosis in rat liver were studied on postnatal days 3, 7, and 12. Some age-related peculiarities of these rhythms were revealed. Epidermal growth factor was found to play an important role in the formation of cell proliferation rhythm during the early postnatal ontogeny and in the regulation of the pool of proliferating hepatocytes.

Time Course of Cell Proliferation in Rat Liver in the Early Postnatal Ontogeny and Role of Epidermal Growth Factor in Organization of Proliferative Regimen

Circadian rhythm of DNA synthesis, mitotic activity, and duration of mitosis in rat liver were studied on days 3, 7, and 12 of life. Age-associated differences in the rhythmic parameters of these characteristics were detected. Epidermal growth factor plays an important role in the formation of cell proliferation rhythm in the early postnatal ontogeny and in the formation of proliferative hepatocyte pool.

Developmental effects of phenytoin may differ depending on sex of offspring

Phenytoin (sodium salt), a developmental neurotoxicant, was administered orally by gavage (50-150 mg/kg) to pregnant rats on days 7-18 of gestation. Various developmental and behavioral indices were evaluated. Results indicated that phenytoin produced decreases in maternal and pup body weight gains, pup hindbrain, and F1 adult forebrain, whole brain, and cerebellar weights. Behavioral/developmental effects included performance deficits in a modified Morris water maze assay, in air righting and auditory startle responses, and increases in locomotor activity, accelerated eye opening, incisor eruption, negative geotaxis, and olfactory orientation. Female offspring appeared to be more severely affected when measuring incisor eruption, negative geotaxis, air righting, reactivity, and locomotor and maze activity. Males appeared to be more affected when measuring eye opening, olfactory orientation, and decreases in startle response. This study suggests that prenatal phenytoin exposure may result in developmental changes and behavioral deficits that may differ depending on the sex of the offspring.

Endocrine regulation of craniofacial growth

This paper presents an updated review of the role of endocrine factors in craniofacial and dental development. Some unpublished results of the author's own studies are presented. Longitudinal growth studies have shown the similarity of facial and somatic growth rates, whereas dental development has been found to be independent. The increased therapeutic use of the growth hormone (GH) has focused attention on the dental and craniofacial effects of GH. Whereas delayed and advanced cranial base and facial growth is obvious in conditions with either lack or excess of GH, the effect of GH on the dentition is less clear. Thyroid hormones seem to be necessary for the eruptive movement of teeth. Sex steroids clearly have an effect on facial and cranial base growth and are also odontogenic, but the effects have not been much studied. The growth-inhibiting effect of corticosteroids is explained partly by the reduced response of cartilage cells to insulin-like growth factor-1. Experimentally, the effect is also seen in the condylar cartilage, but clinical studies have not been published. In tooth eruption an accelerating effect has been noted in experimental animals. The role of androgenic hormones in mandibular growth stimulation is discussed.

Diethylnitrosamine-induced increase in γ-glutamyltranspeptidase in rat liver: Its association with thyroid hormone deficiency and its reversal by tri-iodothyronine

1. The nodular phase of hepatic premalignancy was induced in male Fischer 344 rats by the administration of diethylnitrosamine, 200 mg/kg i.p., followed by promotion utilizing the Solt-Farber promoting regime. 2. Relative to the situation in normal non-treated control rats: the activity of gamma-glutamyltranspeptidase was found to be increased 9.42-fold in homogenate and 7.33-fold in plasma membrane fractions prepared from the livers of saline-injected control rats; and 81.37-fold in homogenates and 91.92-fold in plasma membranes prepared from the livers of diethylnitrosamine-injected rats; plasma levels of total T3 and total T4 were found to be decreased 42.06 and 47.45% in saline-injected control rats and 88.7 and 83.2% in diethylnitrosamine-injected rats, respectively. 3. An early pre-nodular phase of hepatic premalignancy was produced in young immature and mature adult male Fischer 344 rats by the administration of diethylnitrosamine, 75 mg/kg, without subsequent application of the promotion regime. 4. Relative to the situation in control rats: the activity of gamma-glutamyltranspeptidase was found to be increased in liver homogenates prepared from diethylnitrosamine-treated rats, 1.62-fold in young immature rats 1.20-fold in mature adult rats; plasma levels of total T3 were found to be reduced in diethylnitrosamine-treated rats, 28% in young immature rats 9% in mature adult rats. 5. Treatment of diethylnitrosamine-injected young immature male Fischer 344 rats at the prenodular phase of hepatic premalignancy with tri-iodothyronine at 0.005 micrograms/kg s.c. daily for 7 days reversed the diethylnitrosamine-induced increase in liver homogenate gamma-glutamyltranspeptidase activity and the decrease in plasma total T3, restoring these parameters to normal levels.(ABSTRACT TRUNCATED AT 250 WORDS)