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L J W Jack
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S Kahl
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D L St Germain
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A V Capuco
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Abstract

Thyroxine 5′-deiodinase (5′D) catalyses deiodination of the prohormone thyroxine (T4) to the metabolically active hormone 3,5,3′-tri-iodothyronine (T3). Previously, it has been demonstrated that rat mammary gland expresses a 5′D with enzymatic properties equivalent to those of the type I enzyme (5′D-I) found in rat liver and kidney. Using complementary DNA (cDNA) for rat hepatic 5′D-I, we have examined expression of 5′D-I messenger RNA (mRNA) in liver, and mammary gland from virgin and lactating rats, and in seven other tissues from virgin rats. 5′D-I mRNA could not be detected in mammary gland either by Northern blotting or by the more sensitive technique of reverse transcribing mRNA and then amplifying the cDNA by polymerase chain reaction (RTPCR). Analysis of the seven tissues from virgin rats by RT-PCR showed 5′D-I amplicons in liver, kidney and thyroid. No amplicons were detected in adrenal gland, cardiac muscle, skeletal muscle or spleen. In addition, the effect of lactation intensity on circulating thyroid hormones, hepatic and mammary gland 5′D activity, and hepatic 5′D-I mRNA levels was examined. A strong inverse relationship was noted between increased lactation intensity (suckling burden) and circulating T4 and T3, hepatic 5′D-I activity and hepatic 5′D-I mRNA levels. Mammary gland 5′D activity was positively correlated to lactation intensity. The data presented strongly suggest that the 5′D activity expressed in lactating mammary gland is encoded by a mRNA different from the 5′D-I message found in rat liver, kidney and thyroid gland, and may help explain the differential regulation of 5′D-I activity in these organs during lactation. In addition, hepatic 5′D-I activity was found to be correlated with the concentration of 5′D-I mRNA, suggesting that regulation is pretranslational. Results are consistent with a previously suggested involvement of 5′D in establishing metabolic adaptations to support lactation.

Journal of Endocrinology (1994) 142, 205–215

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G Dai
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D Wang
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B Liu
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JW Kasik
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H Muller
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RA White
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GS Hummel
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MJ Soares
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The prolactin (PRL) family consists of a collection of genes expressed in the uterus, placenta and anterior pituitary. These cytokines/hormones participate in the control of maternal-fetal adaptations to pregnancy. In this report, we establish the presence of three new members of the PRL family. Novel expressed sequence tags (ESTs) with homology to PRL were isolated from embryonic and placental cDNA libraries. The cDNAs were sequenced and compared with those of other members of the PRL family. The three new cDNAs were assigned to the PRL family on the basis of sequence similarities and were referred to as PRL-like protein-J (PLP-J), PRL-like protein-K (PLP-K) and PRL-like protein-M (PLP-M). Both rat and mouse PLP-J cDNAs were identified. Rat PLP-J cDNA encodes for a predicted 211 amino acid protein containing a 29 amino acid signal peptide and two putative N-linked glycosylation sites, whereas the mouse PLP-J cDNA encodes for a 212 amino acid protein containing a 29 amino acid signal peptide with a single N-linked glycosylation site. Rat and mouse PLP-J proteins share approximately 79% and 70% nucleotide and amino acid sequence identity, respectively. A full-length rat PLP-K cDNA and a partial tentative mouse PLP-K cDNA were identified. The rat PLP-K cDNA encodes for a predicted 228 amino acid protein containing a 31 amino acid signal peptide and one putative N-linked glycosylation site; the mouse PLP-M cDNA encodes for a predicted 228 amino acid protein containing a 28 amino acid signal peptide and one putative N-linked glycosylation site. Genes for PLP-J, PLP-K and PLP-M are situated at the Prl family locus on mouse chromosome 13. PLP-J was exclusively expressed in decidual tissue from both the mouse and rat. PLP-K was expressed in trophoblast cells of the chorioallantoic placenta and showed an apparent species difference. In the mouse, virtually all trophoblast lineages expressed PLP-K, whereas in the rat, PLP-K expression was restricted to the labyrinthine trophoblast cells. Mouse PLP-M expression was restricted to the junctional zone of the chorioallantoic placenta. In summary, we have identified three new members of the rodent PRL gene family that are expressed in uterine and placental structures. Future experimentation is needed to determine the specific roles of each of these ligands in the biology of pregnancy.

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Fung M-L
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SY Lam
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X Dong
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Y Chen
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PS Leung
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In the present study, the effects of postnatal hypoxemia on the AT1 angiotensin receptor-mediated activities in the rat carotid body were studied. Angiotensin II (Ang II) concentration-dependently increased the chemoreceptor afferent activity in the isolated carotid body. Single- or pauci-fiber recording of the sinus nerve revealed that the afferent response to Ang II was enhanced in the postnatally hypoxic carotid body. To determine whether the increased sensitivity to Ang II is mediated by changes in the functional expression of Ang II receptors in the carotid body chemoreceptors, cytosolic calcium ([Ca2+]i) was measured by spectrofluorimetry in fura-2 acetoxymethyl ester-loaded type I cells dissociated from carotid bodies. Ang II (25-100 nM) concentration-dependently increased [Ca2+]i in the type I cells. The proportion of clusters of type I cells responsive to Ang II was higher in the postnatally hypoxic group than in the normoxic control (89 vs 66%). In addition, the peak [Ca2+]i response to Ang II was enhanced 2- to 3-fold in the postnatally hypoxic group. The [Ca2+]i response to Ang II was abolished by pretreatment with losartan (1 microM), an AT1 receptor antagonist, but not by PD-123177 (1 microM), an AT(2) antagonist. Double-labeling immunohistochemistry confirmed that an enhanced immunoreactivity for AT1 receptor was co-localized to the lobules of type I cells in the hypoxic group. In addition, RT-PCR analysis of subtypes of AT1 receptors showed an up-regulation of AT1a but a down-regulation of AT1b receptors, indicating a differential regulation of the expression of AT1 receptor subtypes by postnatal hypoxia in the carotid body. These data suggest that postnatal hypoxemia is associated with an increased sensitivity of peripheral chemoreceptors in response to Ang II and an up-regulation of AT1a receptor-mediated [Ca2+]i activity of the chemoreceptors. This modulation may be important for adaptation of carotid body functions in the hypoxic ventilatory response and in electrolyte and water homeostasis during perinatal and postnatal hypoxia.

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C. E. Grosvenor
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F. Mena
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Lactating rats were fed at a level equivalent to 75% of the daily food consumed by controls, which had food available ad libitum, from days 4–14 or from days 4–12 post partum. The underfed mothers lost about 10% of their initial weight whereas control mothers gained weight slightly during this time. The litters (six pups) of underfed mothers gained 20% less weight than those of controls but remained healthy. The milk obtained by the pups from six glands (the remaining six glands had been ligated on day 3) during a timed suckling, plus that subsequently obtained after oxytocin injections to the mother, totalled 7·4± 0·80 g in underfed and 15± 0·62 g in control mothers on day 14, and 6 ± 0·41 g in underfed compared with 8 ±0·50 g in control mothers on day 12. The pups of underfed mothers obtained a significantly greater percentage of the total milk after 10 (30 v. 6%), 15 (84 v. 32%) and 45 (100 v. 57%) min of suckling than did those of control mothers. In two trials for the milk ejection test, the litters of control and underfed mothers were exchanged. The pups of control mothers suckled by underfed mothers in both trials obtained a significantly greater percentage of the total milk (64%) in 15 min than did the pups of underfed mothers suckled by control mothers (25%).

Oxytocin-induced intramammary pressure (IMP) responses recorded under urethane anaesthesia achieved a greater amplitude in underfed than in control mothers in response to each dose (0·4, 0·8 and 1·6 mu.) of oxytocin administered intravenously. The average slope of the dose–response curve was 1·25 cm H2O/0·1 mu. oxytocin compared with 0·75cm H2O/0·1 mu. for fed mothers. The amplitude of the IMP in response to a 1·6 mu. dose of oxytocin also was greater in underfed mothers over a range of volumes of milk added incrementally to empty glands. The difference was most striking at low volumes of milk (0·2–0·6 ml) within the gland. The data from these experiments suggest the more rapid transfer of milk from mother to pups in underfed rats is due at least in part to adaptations within the mammary gland, possibly involving reductions in the sympathetic-mediated tone of mammary ducts.

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François van Herp
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Nick H M van Bakel
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Anton J M Coenen
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Kjell Sergeant Department of Molecular Animal Physiology, Department of Environment and Agrobiotechnologies, Laboratory of Protein Biochemistry and Biomolecular Engineering, Faculty of Science, Donders Center for Neuroscience, Nijmegen Center for Molecular Life Sciences (NCMLS), Radboud University, Geert Grooteplein Zuid 28, 6525 GA Nijmegen, The Netherlands

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Bart Devreese Department of Molecular Animal Physiology, Department of Environment and Agrobiotechnologies, Laboratory of Protein Biochemistry and Biomolecular Engineering, Faculty of Science, Donders Center for Neuroscience, Nijmegen Center for Molecular Life Sciences (NCMLS), Radboud University, Geert Grooteplein Zuid 28, 6525 GA Nijmegen, The Netherlands

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Gerard J M Martens
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inactive and activated neuroendocrine cells. The model concerns a well-characterized physiological neuroendocrine reflex, namely skin color change as a result of adaptation to a changed background condition. By placing the animal on a black background, the

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Ian M Bird Perinatal Research Laboratories, Department of Obstetrics and Gynecology, University of Wisconsin–Madison, 7E Meriter Hospital/Park, 202 South Park Street, Madison, Wisconsin 53715, USA

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different physiologic states (see review by Boeldt et al . (2011) in this issue). Thus physiologic changes in eNOS activation may also be critically regulated at the level of sustained phase Ca 2 + signaling adaptation. Such adaptation occurs through

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David A Baltzegar Department of Biological Sciences, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695-7617, USA

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Benjamin J Reading Department of Biological Sciences, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695-7617, USA

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Jonathon D Douros Department of Biological Sciences, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695-7617, USA

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Russell J Borski Department of Biological Sciences, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695-7617, USA

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for meeting the energy requirements of acute salinity adaptation ( Bashamohideen & Parvatheswararao 1972 , Chang et al . 2007 ). The full complement of hormones regulating energy mobilization and expenditure in fishes is unclear, but it may differ to

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Sergio Di Meo Dipartimento di Biologia, Università di Napoli ‘Federico II’, Napoli, Italy

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Susanna Iossa Dipartimento di Biologia, Università di Napoli ‘Federico II’, Napoli, Italy

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Paola Venditti Dipartimento di Biologia, Università di Napoli ‘Federico II’, Napoli, Italy

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able to induce major adaptations in skeletal muscle, which are dependent on the nature of the adaptive stimulus. Heavy resistance exercise, also referred to as strength training, typically consists of a small number of contractions (often fewer than

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Urszula T Iwaniec Skeletal Biology Laboratory, School of Biological and Population Health Sciences, Oregon State University, Corvallis, Oregon, USA
Center for Healthy Aging Research, Oregon State University, Corvallis, Oregon, USA

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Russell T Turner Skeletal Biology Laboratory, School of Biological and Population Health Sciences, Oregon State University, Corvallis, Oregon, USA
Center for Healthy Aging Research, Oregon State University, Corvallis, Oregon, USA

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(2012) and Shapses and Sukumar (2012) . Mechanical loading and skeletal adaptation: mechanostat theory The skeleton serves multiple mechanical functions: (1) application of mechanical forces (e.g., jaws and fingers); (2) resisting mechanical

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Jay W Porter Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA

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Joe L Rowles III Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA
Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA

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Justin A Fletcher Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA
Research Service-Harry S Truman Memorial VA Hospital, Columbia, Missouri, USA
University of Texas Southwestern Medical Center, Dallas, Texas, USA

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Terese M Zidon Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA

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Nathan C Winn Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA

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Leighton T McCabe Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA

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Young-Min Park Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA
University of Colorado Denver – Anschutz Medical Campus, Denver, Colorado, USA

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James W Perfield II Lilly Research Laboratories, Indianapolis, Indiana, USA

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John P Thyfault Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, USA
Kansas City VA Medical Center, Kansas City, Missouri, USA

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R Scott Rector Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA
Research Service-Harry S Truman Memorial VA Hospital, Columbia, Missouri, USA

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Jaume Padilla Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA
Department of Child Health, University of Missouri, Columbia, Missouri, USA
Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA

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Victoria J Vieira-Potter Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, USA

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adaptations are not completely understood. Fibroblast growth factor 21 (FGF21), a pleotropic endocrine hormone produced by several tissues, plays an important role in systemic glucose and lipid metabolism ( Kharitonenkov et al . 2005 , Zhang et al . 2008

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