T4 is bound to transthyretin (TTR; 75%) and albumin (Alb; 25%) in rat serum and only to TTR in cerebrospinal fluid (CSF). In addition to the liver, TTR is synthesized in large amounts in the choroid plexus and then secreted into the CSF, suggesting that serum T4 could be transported to the CSF and brain via the choroid plexus. We determined whether serum T4 bound to TTR is transported into the choroid plexus and CSF. N-Bromoacetyl-L-[125I]T4, a derivative of T4 that binds covalently to TTR, was used as the affinity label for the T4-binding site on TTR. Rats were injected with [125I]T4, acetyl-[125I]T4 covalently bound to human TTR ([125I]T4Ac.human hTTR), or acetyl-[125I]T4 covalently bound to human Alb ([125I]T4Ac.hAlb). The quantities of [125I]T4Ac.hTTR and [125I]T4Ac.hAlb present in the choroid plexus, CSF, and brain 90 min later were barely detectable. In contrast, [125I]T4 injected as the unbound form accumulated in the choroid plexus and CSF to levels 6-11 times higher than with [125I]T4Ac.hTTR (P less than 0.005). We then used a synthetic flavonoid (EMD) that competitively inhibits binding of T4 to serum TTR and transiently increases serum free T4 to determine the role of choroid plexus TTR and CSF TTR in the transport of T4 from serum to brain. Rats were given 110 microCi [125I]T4 15 min after the injection of vehicle, a low (0.3 mumol/100 g BW) or high dose of EMD (2.0 mumol/100 g BW). Rats were killed 60 min later. In serum, the percentage of [125I]T4 bound to TTR decreased and free T4 increased similarly in the low and high dose EMD-treated rats. In contrast, the percentage of [125I]T4 bound to TTR in choroid plexus and, subsequently, CSF was significantly decreased in rats given the high dose of EMD, but was not affected by the low dose of EMD, suggesting that in high doses, EMD crossed from serum to choroid plexus and CSF and occupied TTR-binding sites for T4. There was a significant decrease (P less than 0.05) in the percentage of injected [125I]T4 in the high dose vs. the low dose EMD-treated rats in total choroid plexus (61%), 1 ml CSF (94%), and 1 g cerebral cortex (46%) and cerebellum (46%).(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoreactive PRL which is not of pituitary origin, has been identified in many regions of the rat brain. We have previously demonstrated that estradiol increases hypothalamic immunoreactive PRL content in hypophysectomized female rats. To determine if estradiol stimulates PRL synthesis, we examined the effect of estradiol on the in vivo production of PRL, and on the expression of PRL messenger RNA (mRNA) in the hypothalamus, pons, and cerebral cortex. To examine the effect of estradiol on the in vivo production of PRL, [35S] methionine was injected into the lateral ventricle and its incorporation into immunoprecipitable PRL was determined by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In estradiol, but not vehicle-treated hypophysectomized rats, a 24,000 M(r) immunoprecipitable PRL protein was detected in the hypothalamus and pons-medulla, 2 and 4 h after methionine administration. No immunoprecipitable PRL proteins were detected in the amygdala, hippocampus, cortex, or serum at either time point. In addition, in the hypothalamus, but not the pons-medulla, a second PRL band was detected with an apparent mol wt of 16,000K. To determine if estradiol increased the expression of PRL mRNA, copy DNA was obtained by reverse transcription of poly(A+) mRNA prepared from intact and vehicle or estradiol-treated hypophysectomized rats and analyzed by polymerase chain reaction amplification. In tissues from hypophysectomized rats, there was little, or no, detectable levels of PRL mRNA. In contrast, in estradiol-treated hypophysectomized rats PRL mRNA was easily detected in the hypothalamus and pons-medulla by polymerase chain reaction amplification. These data suggest that estradiol increases the PRL content in the hypothalamus and pons-medulla by increasing PRL gene expression, in a manner similar to that reported in the pituitary.

ABSTRACT. In adult male rats, selenium deficiency results in a near complete loss in the selenoprotein 5'-deiodinase in the liver, resulting in decreased peripheral deiodination of thyroxine (T4) and increased serum T 4 concentrations. Serum 3,5,3'-triiodothyronine concentrations are normal or slightly decreased, and serum 3,3',Sftriiodothyronine concentrations are normal or slightly increased in selenium-deficient rats. W e now report the effects of selenium deficiency on maternal and fetal thyroid hormone economy and on placental 5-deiodinase activity in the rat. Weanling female rats were fed either a seleniumdeficient or selenium-supplemented diet for 4 wk before mating and then throughout gestation. Rats were killed a t 21 d of gestation. Selenium deficiency was confirmed by a 9 5 and 94% decrease in glutathione peroxidase and a 8 4 and 56% decrease in liver type I outer ring 5' deiodinase activity in the mother and the fetus, respectively. In contrast to the increase in circulating T 4 observed in seleniumdeficient male and nonpregnant female adult rats, serum T 4 was not affected by selenium deficiency in pregnant rats, but there was a 3-fold increase in serum 3,3',5'-triiodothyronine concentrations associated with a 70% decrease in maternal brain type I1 outer ring 5' deiodinase activity. Maternal serum 3,5,3'-triiodothyronine concentrations were decreased by 21%. Placental 5-deiodinase activity was unaffected by selenium deficiency. In the fetus, serum T4, 3,3',5'-triiodothyronine, and T S H concentrations were not affected by selenium deficiency. These data suggest that placental 5-deiodinase is not a selenoenzyme and that the failure of selenium deficiency to increase serum T 4 concentrations in the mother a s well a s the minor role played by liver type I outer ring 5' deiodinase in the fetus results in the protection of fetal thyroid hormone economy against the potentially deleterious effects of selenium deficiency.

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Prolactin (PRL) has been reported to activate cellular proliferation in nonreproductive tissue, such as liver, spleen, and thymus. Recently, we have extended the possible role of PRL as a mammalian mitogen by demonstrating a mitogenic effect of PRL in cultured astrocytes. Although the cellular mechanisms by which PRL regulates cell growth are not fully understood, protein kinase C (PKC) has been implicated as one of the transmembrane signaling systems involved in the regulation of PRL-induced cell proliferation in Nb2 lymphoma cells and liver. In the present studies, we examined the possible role of PKC in PRL-induced proliferation of cultured astrocytes. Incubation of cultured astrocytes with 1 nM PRL resulted in a rapid translocation of PKC from the cytosol to the membrane, with maximal PKC activity in the membrane occurring 30 min after exposure to PRL. Translocation of PKC activity occurred over a physiological range of PRL, with maximal PKC activation occurring at 1 nM. At concentrations greater than 10 nM PRL, there was a decrease in the amount of PKC activity associated with the membrane fraction compared with that of cells stimulated with 1 nM PRL. Incubation of astrocytes with PRL in the presence of the PKC inhibitors staurosporine, 1-(-5-isoquinolinesulfonyl)-2-methylpiperazine, or polymyxin B blocked the PRL-induced increase in cell number with IC50 values of approximately 2 nM, 10 microM, and 6 microM, respectively. PKC is the only known cellular receptor for 12-O-tetradecanoylphorbol 13-acetate (TPA), which stimulates the translocation of PKC from the cytosol to the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)