A variety of hormones have been implicated in the process of liver regeneration. Despite the demonstration of specific estrogen receptors (ER) in mammalian liver and the identification of responses to estrogen which occur in liver, there has been little or no investigation of the relation of that hormone or its receptor to liver regeneration or liver growth. This report provides information which indicates: (a) the effect of 17 beta-estradiol on the mass of both intact and regenerating rat liver; (b) the percentage of hepatocytes in neonatal and adult normal intact livers which contain ER, i.e., the estrogen receptor index (ERI); (c) changes in ERI and in nuclear ER occurring in that cell population following partial hepatectomy (PH) and/or 17 beta-estradiol administration; and (d) the temporal relation of the changes in ER with those related to DNA synthesis and liver regeneration and to liver growth. Approximately 55 to 60% of parenchymal cells from intact livers in adult rats were found to contain ER which was entirely located in the cytoplasm. No nuclear ER was evident in such cells. By 1 hr, and subsequently following 17 beta-estradiol administration to such animals, there resulted a depletion in the number of ER-containing cells and the identification of nuclear ER. These changes were followed by the onset of increased DNA synthesis and an increase in liver weight (p less than 0.001). Subsequent to 70% PH, a similar series of events occurred in liver remnants. Not only was there a decrease in the ERI from 60% at the time of PH to 40% 3 hr later and 30% after 72 hr, there was a decrease in cytosol ER as well. Accompanying the decrease was an increase in the number of cells with nuclear ER. By 24 hr post-PH, 29% of the cells with ER displayed that receptor in their nuclei. At that time, DNA synthesis was at its peak, and liver regeneration was taking place. When 17 beta-estradiol was administered at the time of PH, there was a more rapid onset of translocation of ER to the nuclei of parenchymal cells. At PH, when 17 beta-estradiol was given, no cells displayed nuclear ER. One hr later, 18% of cells with ER had nuclear ER, in contrast to the finding that only 3% of cells had nuclear ER 1 hr post-PH when 17 beta-estradiol was not administered. Regeneration was greater (59 versus 73%; p = 0.003) when animals received 17 beta-estradiol prior to PH.(ABSTRACT TRUNCATED AT 400 WORDS)

/pdf/relation-of-estrogen-and-its-receptor-to-rat-liver-growth-530xteknod.pdf

Relation of Estrogen and Its Receptor to Rat Liver Growth and Regeneration

The ontogeny of GH and PRL synthesis and the inducibility of PRL gene expression by estrogens during postnatal development in mice were studied. Synthetic rates were assessed by one- and two-dimensional gel electrophoresis and by immunoprecipitation of solubilized proteins from intact glands and monolayer cultures of pituitary cells labeled with [35S]methionine and [3H]leucine. We found that GH synthesis turns on dramatically between 16 and 17 days of gestation, comprising 15–20% of the total pituitary protein synthesis at birth. PRL synthesis was not detectable throughout gestation or in 1- to 4-day-old mice, and was barely detectable in 8-day-old mice. It was clearly demonstrable by 12 days of age and increased sharply thereafter, reaching 8–9% of the total protein synthesis by day 20 in both sexes. However, transplantation of pituitaries from newborns under the renal capsule of adult female hosts resulted in substantial PRL synthesis by the ectopic glands before the endogenous timetable. For studies of...

Ontogeny of Growth Hormone and Prolactin Gene Expression in Mice

The endocrine control of reproduction and molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. I. Annual changes in plasma levels of gonadal steroids and LH.

Thyroid hormones are of considerable importance for vertebrate reproductive function and during development. To further assess the role of these compounds in this capacity, we examined the expression pattern of the type 2 iodothyronine deiodinase (D2), which converts T(4) to the more active hormone T(3), in the rat uterus in both the nonpregnant and the pregnant state. D2 activity was identified as the predominant, if not only, 5'-deiodinase in the nonpregnant rat uterus. The expression of D2 messenger RNA was located by in situ hybridization to the endometrial stromal cells, where the signal was particularly enriched in the region adjacent to the epithelial cells of the uterine lumen. During pregnancy, D2 activity increased, peaking on day 17 of gestation (embryonic day 17). At that time, uterine D2 activity exceeded that in the placenta, as well as that in the fetal tissues. In the earlier stages of pregnancy before placental formation (e.g. embryonic days 10-11), D2 messenger RNA in the rat uterus was located outside the decidual tissue, which was observed, as in previous studies, to highly express the inactivating type 3 deiodinase. In summary, the rat uterus, particularly during pregnancy, seems to be a site of active thyroid hormone metabolism, presumably designed to maintain the optimal thyroid hormone environment for both the fetus and the maternal uterine tissue.

/pdf/the-type-2-iodothyronine-deiodinase-is-expressed-in-the-rat-2lalrxsneg.pdf

The Type 2 Iodothyronine Deiodinase Is Expressed in the Rat Uterus and Induced During Pregnancy

Proteolysis by the 26S proteasome is an important regulatory mechanism that governs the protein stability of several steroid/nuclear receptors and that has been implicated in the control of receptor transcriptional activation function. Herein, we report that thyroid hormone can prevent estrogen-induced proteolysis of estrogen receptor-α (ERα) protein in lactotrope cells of the pituitary. The stabilization of ERα protein by thyroid hormone represents a selective blockade against estradiol-stimulated degradation, because thyroid hormone (but not glucocorticoid) can protect estrogen-activated ERα. Moreover, thyroid hormone treatment does not interfere with signal-induced proteolysis of a separate proteasome target, IκBα or ERα proteolysis induced by ICI182780. Using thyroid hormone as a tool to inhibit ERα proteolysis, we examined the effect of loss of this regulatory function on estrogen-induced transcriptional responses. Consistent with earlier reports, estrogen activation of an idealized estrogen response...

/pdf/thyroid-hormone-is-an-inhibitor-of-estrogen-induced-21t2s5fjgh.pdf

Thyroid Hormone Is an Inhibitor of Estrogen-Induced Degradation of Estrogen Receptor-α Protein: Estrogen-Dependent Proteolysis Is Not Essential for Receptor Transactivation Function in the Pituitary

I. Assenmacher

Papers

Postnatal development of estradiol receptor in female and male rats

Effects of thyroid hormones on the ontogeny of oestradiol-binding sites in the rat