Food-restricted and dehydrated-induced anorexic rats present differential TRH expression in anterior and caudal PVN. Role of type 2 deiodinase and pyroglutamyl aminopeptidase II.

TRH synthesized in hypothalamic paraventricular nucleus (PVN) regulates thyroid axis function and is also implicated in anorexigenic effects. Under energy deficit, animals present decreased PVN TRH expression and release, low TSH levels, and increased appetite. Dehydration-induced anorexia (DIA) model allows insight into underlying mechanisms of feeding regulation. Animals drinking a 2.5% NaCl solution for 7 d present body weight reduction; despite their negative energy balance, they avoid food and have increased PVN TRH expression and TSH serum levels. These findings support an inhibiting role of PVN TRH in feeding control. We compared TRH expression by in situ hybridization in PVN subdivisions of 7-d dehydrated male rats to those of a pair-fed group (forced food-restricted) with similar metabolic changes than DIA, but motivated to eat, and to controls. We measured peripheral deiodinase activities, and expression and activity of medial basal hypothalamic type 2 deiodinase and pyroglutamyl-aminopeptidase II, to understand their regulating role in PVN TRH changes between food restriction and anorexia. TRH mRNA levels increased in anterior (aPVN) and medial-caudal subdivisions in DIA rats, whereas it decreased in medial PVN in both experimental groups. We confirmed the nonhypophysiotropic nature of aPVN TRHergic cells by injecting ip fluorogold tracer. Findings support a subspecialization of TRHergic hypophysiotrophic cells that responded differently between anorexic and food-restricted animals; also, that aPVN TRH participates in food intake regulation. Increased type 2 deiodinase activity seemed responsible for low medial PVN TRH synthesis, whereas increased medial basal hypothalamic pyroglutamyl-aminopeptidase II activity in DIA rats might counteract their high TRH release.

Uptake and antiproliferative effect of molecular iodine in the MCF-7 breast cancer cell line.

This study analyzes the uptake and antiproliferative effect of two different chemical forms of iodine, iodide (I-) and molecular iodine (I2), in MCF-7 cells, which are inducible for the Na+/I- symporter (NIS) and positive for pendrin (PDS). The mouse fibroblast cell line NIH3T3 was used as control. Our results show that in MCF-7 cells, I- uptake is sustained and dependent on NIS, whereas I2 uptake is transient with a maximal peak at 10 min and a final retention of 10% of total uptake. In contrast, no I- was taken up by NIH3T3 cells, and although I2 was captured with the same time pattern as in MCF-7 cells, its uptake was significantly lower, and it was not retained within the cell. The uptake of I2 is independent of NIS, PDS, Na+, and energy, but it is saturable and dependent on protein synthesis, suggesting a facilitated diffusion system. Radioiodine was incorporated into protein and lipid fractions only with I2 treatment. The administration of non-radiolabeled I2 and 6-iodo-5-hydroxy-8,11,14-eicosatrienoic acid (6-iodolactone, an iodinated arachidonic acid), but not KI, significantly inhibited proliferation of MCF-7 cells. Proliferation of NIH3T3 cells was not inhibited by 20 microM I2. In conclusion, these results demonstrate that I2 uptake does not depend on NIS or PDS; they suggest that in mammary cancer cells, I2 is taken up by a facilitated diffusion system and then covalently bound to lipids or proteins that, in turn, inhibit proliferation.

Has the mammary gland a protective mechanism against overexposure to triiodothyronine during the peripartum period? The prolactin pulse down-regulates mammary type I deiodinase responsiveness to norepinephrine.

Peripartum is a crucial period for mammary gland final differentiation and the onset of lactation. Although the 'trigger' for lactogenesis depends on several hormones, a key factor is the peripartum prolactin (PRL) pulse whose deletion results in a failure to initiate milk production. Other hormones having a critical role during this period but exerting a contrary effect are the thyronines. A transitory hypothyroidism occurs at peripartum in serum and several other extrathyroidal tissues, whereas the induction of hyperthyroidism during late pregnancy is associated with the absence of lactation after delivery. We analyzed the mammary gland during pregnancy and lactation for: (a) the type and amount of thyroid receptors (TRs), (b) the local triiodothyronine (T3) generation catalyzed by type I deiodinase (Dio1), (c) the Dio1 response to norepinephrine (NE) and (d) the effect on Dio1 and TRs of blocking the PRL pulse at peripartum. Our data showed that during pregnancy the mammary gland contains Dio1 in low amounts associated with the highest expression of TRalpha1; whereas during lactation the gland shows high levels of both Dio1 and TRalpha1. However, at peripartum, both TRs and Dio1 decrease, and Dio1 becomes refractory to NE. This refractoriness disappears when the PRL pulse is blocked by the dopamine agonist bromocriptine. This blockade is also accompanied by a significant decrease in cyclin D1 expression. Our data suggested that the peripartum PRL pulse is part of a protective mechanism against precocious differentiation and/or premature involution of the alveolar epithelium due to T3 overexposure.

Cold-induced increment in rat adrenal gland type II deiodinase is corticosterone dependent.

In this study we analyzed whether corticosterone synthesis is involved in the regulation of adrenal gland type II deiodinase (AG-D2) activity during acute cold exposure. Two well-known inhibitors of steroidogenesis, aminoglutethimide (AGT) and metyrapone (MTP), were administered to male Wistar rats maintained either at room temperature or acutely exposed to cold (1 h at 4 degrees C). AG-D2 activity was measured by the radioiodide release method, and corticosterone circulating levels were measured by competitive protein binding assay. Results show that resting corticosterone levels and AG-D2 activity were lower in both AGT- and MTP-treated rats. Furthermore, the phasic increase normally exhibited by AG-D2 activity in response to acute cold stress was blunted in AGT- and MTP-treated animals. Therefore, we conclude that corticosterone synthesis is necessary in preserving the physiologic response of AG-D2 activity to cold exposure.

Polidipsia-hiponatremia intermitente-psicosis. A propósito de un caso tratado con clozapina / Polydipsia-intermittent hyponatremia-psychosis. A case treated with clozapine

La polidipsia primaria aparece en un 6-17 por ciento de los pacientes psiquiátricos crónicos, y el trastorno esquizofrénico es el diagnóstico del 80 por ciento de ellos. Algunos casos, como el que describimos a continuación, pueden desarrollar como complicación una hiponatremia, que puede provocar, a su vez, un grave compromiso del funcionamiento neuropsicológico. Exponemos un caso en el que el tratamiento con clozapina produjo una mejoría notable de estos síntomas (AU)

Neuroendocrine regulation of adrenal gland and hypothalamus 5'deiodinase activity. II. Effects of splanchnicotomy and hypophysectomy.

This study analyzes the role of the autonomic nervous system, the pituitary gland, ACTH, dexamethasone (DEX), and thyroid hormones in the regulation of 5'deiodinase (5'D) in the hypothalamus (HP) and adrenal gland (AG) of the rat. 5'D activity was analyzed in rats under basal conditions (22 C) and during cold exposure (4 C, during 15, 30, 60, and 120 min). Several experimental groups were formed: intact animals (INT), unilateral (left) splanchnicotomized, sham splanchnicotomized, hypophysectomized (HPX), and sham hypophysectomized. Results in the hypothalamus were: 1) independent of the experimental group, the HP 5'D activity increased during the first 15-30 min of cold exposure; however, this increase was greater in operated animals than in INT rats; and 2) basal 5'D activity was increased in HPX rats and was also regulated by thyroid hormones. Results in the adrenal gland were: 1) INT rats exhibited a biphasic pattern of 5'D activation during cold stress (30 and 60 min of exposure); 2) the splanchnic nerve exerted a tonic-stimulatory effect on basal AG 5'D activity; 3) the denervated gland preserved its ability to respond to cold; 4) in INT animals DEX but not ACTH had a stimulatory effect on basal activity; 5) the high 5'D activity post-HPX was reverted to basal values by T4 and DEX administration; 6) SHAM-HPX also was followed by a large increase in basal 5'D activity, and 7) this hyperresponse was abolished by acute ACTH and DEX administration. In conclusion, our results demonstrate that the mechanisms that participate in the regulation and activation of 5'D in the adrenal gland and the hypothalamus are of a neuroendocrine nature. Also, in both organs, but mainly in the HP, 5'D activity is T4-dependent. In addition to the tonic-stimulatory influence conveyed by the splanchnic nerve, AG 5'D activity is influenced by thyroid hormones, glucocorticoids, and probably extrapituitary factors whose nature is unknown yet.

Adrenal gland 5'deiodinase activity (AG-5'd). Kinetic characterization and fractional turnover rate (FTr).

We determined the kinetic parameters as well as the fractional turnover rate (FTr) and half-life (t(1/2)) of rat adrenal gland 5'deiodinase activity (AG-5'D). Adrenal glands from male euthyroid or surgically thyroidectomized (Tx) Wistar rats were homogenized (HEPES, 10MM: ; pH 7.5; sucrose, 0.25M: ; EDTA 1MM: ) and centrifuged at 10,000g for 15 min at 4°C. The resulting crude microsomal supernatants were used for ail measurements of 5'D activity. Using rT(3) (2-500NM: ) the true Km and the Vmax values were of 20.2NM: and 289 fmol of I(-) release/mg protein/h. With T(4) as substrate these values were 5.8NM: and 622 fmol/h/mg protein. Protein inhibitor (cycloheximide 6 mg/100 g wt) administration allowed to determine an FTr of 0.68 h(-1) and a t(1/2) of 1.01 h. Results demonstrate that the greatest 5'D activity in the rat adrenal gland corresponds to isotype II, because the reaction is GTG and PTU-resistant (70-80%), accepts T(4) as a far better substrate than rT(3) (17-fold) and the former thyronine has a 50-90% inhibitory concentration in the 4-100NM: range. Furthermore, rats thyroidectomized for 5 and 15 days showed a conspicuous increase in cerebral cortex and adrenal 5'D-II activity. These characteristics as well as the rapid FTr and short †(1/2) are shared by type II 5'D present in rat pineal, pituitary and brain.

Neuroendocrine regulation of adrenal 5'-monodeiodination during acute cold exposure in the rat. I. Effects of hypophysectomy.

Circulating levels of T4, T3, corticosterone, noradrenaline, and adrenaline, as well as 5'-monodeiodinase activity (5'-MA) were measured in control and hypophysectomized rats acutely exposed to cold environment (15-120 min, 4 C). In addition to the well known activation of the sympathoadrenomedullary system and the hypothalamic-pituitary-adrenal and-thyroid axes, cold exposure was followed by a rapid and sustained increase of 5'-MA in the hypothalamus, and a byphasic course of activation in the adrenal gland in control rats. The adrenal rapid activation (30 min) corresponded to the medulla and the slower activation (120 min) to the cortex. Both, the basal adrenal 5'-MA and the response to cold in adrenal and hypothalamus were 2-fold higher in hypophysectomized rats compared to control. The time course of enzyme activation in these structures suggests that: 1) organ-specific increases in 5'-MA may be associated to a simultaneous rise in their metabolic and/or functional activity, 2) the triggering mechanisms involves an immediate sympathetic signal activating the hypothalamic-adrenal medulla response and a pituitary signal eliciting a slower adrenocortical response, and 3) the compensatory sympathetic hyperactivity after panhypopituitarism contribute to enhance both the adrenal enzyme basal activity and the hypothalamic and adrenal hyperresponse to cold stress.

Vestibular site of action of hypothyroidism in the pigmented rat.

The vestibular cell type affected by congenital hypothyroidism (CH) was investigated by measuring the activity of glutamate decarboxylase (GAD) and choline acetyltransferase (ChAT), synthesizing enzymes of putative afferent (GABA) and efferent (acetylcholine, ACh) neurotransmitters and thus, respectively, hair cell I and II (HC-I, HC-II), and efferent terminal (ET) marker enzymes, in vestibular homogenates of control, congenitally hypothyroid rats (CHR) and in thyroxine-replaced CHR (CHR-T4) whose postnatal age ranged from 20 to 60 days old. In the vestibule, CH-II and its efferent cholinergic contacting bouton mature prior to thyroid function whereas HC-I-differentiation and its efferent synapse arrival are the latest events in vestibular maturation. Therefore, a differential effect of CH upon GAD and ChAT in CHR could be anticipated. In control rats as in CHR the magnitude of GAD was the same with time starting on the 20th day. In CHR, ChAT gradually diminished beginning on day 28 to become 45% decreased with respect to control on the 60th postnatal day. Prevention of ChAT decrease in CHR by early administration of thyroxine (T4), a striking diminution of T4 and triiodothyronine (T3) in CHR serum and a normal level of these hormones found in CHR-T4 corroborated thyroid involvement. These results confirm the preference of hypothyroidism to affect cholinergic cell types (or compartments) of late maturation (HC-I-containing ET and hence 45% ChAT decrease) leaving HC-I, HC-II and HC-II-connecting ET untouched, supported by a 55% remanent ChAT and a constant GAD activity regardless of time and treatment.