title: Thyroid hormone regulation of rat hepatocyte proliferation and polyploidization.
abstract: The liver of adult mammals contains various classes of polyploid hepatocytes produced by a process that is partially regulated by hormones. However, it is not well understood how the hormones affect the rate of hepatocyte proliferation under physiological conditions. Here we have studied the specific roles of 3,5,3'-triiodothyronine (T3), growth hormone (GH), and sex steroids on the percentage of diploid nuclei in S phase and on the population of liver tetraploid (4C) cell nuclei in several rat model systems. Gonadal steroids had no effect on the S phase but account for gender differences in the 4C nuclei. Hypophysectomy in adult male rats produced a moderate decrease in 4C nuclei that was reversed by treatment with 25 micrograms T3. kg-1. day-1, whereas treatment with 200 micrograms human recombinant GH (hGH). kg-1. day-1 was ineffective. Rats made hypothyroid by methimazole treatment of dams and pups until death showed a low S phase and only 5% of 4C nuclei at 70 days of age. T3 significantly increased the S phase 24 h after administration and restored the adult normal level of 4C nuclei after 10 days of treatment. hGH did not affect the 4C nuclei or the S phase in the hypothyroid rats. These results suggest that the processes of hepatocyte proliferation and polyploidization of the rat liver are under endocrine control, with thyroid hormones playing the essential regulatory role.
authors.affiliation: Laboratorio de Fisiología, Departamento de Endocrinología Celular y Molecular y, Universidad de Las Palmas de Gran Canaria, E-35080, Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Torres
authors.forename: B P
authors.initials: BP
authors.lastname: Díaz
authors.forename: J J
authors.initials: JJ
authors.lastname: Cabrera
authors.forename: J C
authors.initials: JC
authors.lastname: Díaz-Chico
authors.forename: B N
authors.initials: BN
authors.lastname: Díaz-Chico
authors.forename: A
authors.initials: A
authors.lastname: López-Guerra
mesh_terms: D000375:Aging / Q000502:physiology; D000818:Animals; D001707:Biopsy, Needle; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000502:physiology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000166:cytology* / Q000187:drug effects*; D008297:Male; D011123:Polyploidy; D051381:Rats; D017208:Rats, Wistar; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D012727:Sex Characteristics; D013739:Testosterone / Q000494:pharmacology; D013963:Thyroid Hormones / Q000502:physiology; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D013739:Testosterone; D004958:Estradiol; D013006:Growth Hormone