Rol de las proteinas desacoplantes UCP1, UCP2 y UCP3 en el gasto energetico, diabetes tipo 2 y obesidad: Sinergismo con la tiroides / Role of uncoupling proteins UCP1, UCP2 and UCP3 in energy balance, type 2 diabetes and obesity: Synergism with the thyroid

La formación de tejido graso resulta del balance entre la ingestión y el consumo de energía, lo cual destaca la importancia del estudio de los factores que controlan el gasto energético. La hormona tiroidea es conocida desde hace tiempo como el principal regulador del metabolismo basal, a través de la estimulación del consumo de oxígeno en las células. El descubrimiento de la grasa parda y de la proteína desacoplante-1 (UCP1) demostró la importancia de este tejido para la regulación del consumo energético em mamíferos. La proteína desacoplante-2 (UCP2) se expresa en muchos tejidos y tendría una acción protectora de la función celular, al preservar el potencial de membrana afectado por el superóxido. La proteína desacoplante- 3 (UCP3) estaría vinculada a la producción de calor, facilitando la combustión de ácidos grasos en la cadena respiratoria mitocondrial, pero no parece participar en el control del gasto energético. El exceso de UCP3 em ratones transgénicos disminuyó la grasa corporal y aumentó la sensibilidad a la insulina seguido de hipoglucemia, sugiriendo así un futuro, hipotético uso de esta proteína en la diabetes 2 y en la obesidad. Los estudios que se realizan sobre estas proteínas y sobre hormonas del tejido adiposo blanco como la leptina, adiponectina, resistina, de péptidos hipotalámicos como neuropéptido Y, CRF, hormona alfa-melanocítica y péptidos regulados por cocaína y anfetamina (CART), muestran resultados promisorios para una futura aplicación en el control del gasto energético en humanos y con ello en la prevención o el tratamiento de la obesidad y la diabetes tipo 2.

Rol de las proteinas desacoplantes UCP1, UCP2 y UCP3 en el gasto energetico, diabetes tipo 2 y obesidad: Sinergismo con la tiroides / Role of uncoupling proteins UCP1, UCP2 and UCP3 in energy balance, type 2 diabetes and obesity: Synergism with the thyroid

La formación de tejido graso resulta del balance entre la ingestión y el consumo de energía, lo cual destaca la importancia del estudio de los factores que controlan el gasto energético. La hormona tiroidea es conocida desde hace tiempo como el principal regulador del metabolismo basal, a través de la estimulación del consumo de oxígeno en las células. El descubrimiento de la grasa parda y de la proteína desacoplante-1 (UCP1) demostró la importancia de este tejido para la regulación del consumo energético em mamíferos. La proteína desacoplante-2 (UCP2) se expresa en muchos tejidos y tendría una acción protectora de la función celular, al preservar el potencial de membrana afectado por el superóxido. La proteína desacoplante- 3 (UCP3) estaría vinculada a la producción de calor, facilitando la combustión de ácidos grasos en la cadena respiratoria mitocondrial, pero no parece participar en el control del gasto energético. El exceso de UCP3 em ratones transgénicos disminuyó la grasa corporal y aumentó la sensibilidad a la insulina seguido de hipoglucemia, sugiriendo así un futuro, hipotético uso de esta proteína en la diabetes 2 y en la obesidad. Los estudios que se realizan sobre estas proteínas y sobre hormonas del tejido adiposo blanco como la leptina, adiponectina, resistina, de péptidos hipotalámicos como neuropéptido Y, CRF, hormona alfa-melanocítica y péptidos regulados por cocaína y anfetamina (CART), muestran resultados promisorios para una futura aplicación en el control del gasto energético en humanos y con ello en la prevención o el tratamiento de la obesidad y la diabetes tipo 2. (AU)

Modulation of liver mitochondrial NOS is implicated in thyroid-dependent regulation of O(2) uptake.

Changes in O(2) uptake at different thyroid status have been explained on the basis of the modulation of mitochondrial enzymes and membrane biophysical properties. Regarding the nitric oxide (NO) effects, we tested whether liver mitochondrial nitric oxide synthase (mtNOS) participates in the modulation of O(2) uptake in thyroid disorders. Wistar rats were inoculated with 400 microCi (131)I (hypothyroid group), 20 microg thyroxine (T(4))/100 g body wt administered daily for 2 wk (hyperthyroid group) or vehicle (control). Basal metabolic rate, mitochondrial function, and mtNOS activity were analyzed. Systemic and liver mitochondrial O(2) uptake and cytochrome oxidase activity were lower in hypothyroid rats with respect to controls; mitochondrial parameters were further decreased by L-arginine (-42 and -34%, P < 0.05), consistent with 5- to 10-fold increases in matrix NO concentration. Accordingly, mtNOS expression (75%) and activity (260%) were selectively increased in hypothyroidism and reverted by hormone replacement without changes in other nitric oxide isoforms. Moreover, mtNOS activity correlated with serum 3,5,3'-triiodothyronine (T(3)) and O(2) uptake. Increased mtNOS activity was also observed in skeletal muscle mitochondria from hypothyroid rats. Therefore, we suggest that modulation of mtNOS is a substantial part of thyroid effects on mitochondrial O(2) uptake.

[Thyroid hormones, obesity and brown adipose tissue thermogenesis]. / Hormonas tiroideas, obesidad y termogénesis en grasa parda.

Brown adipose tissue (BAT) is the main site for hormone-dependent (non-shivering) thermogenesis in response to cold in lower mammals. The hypothalamus controls the cold-induced BAT activation by stimulating the sympathetic nerves and the secretion of norepinephrine (NE) in BAT. Mediated by beta-3 noradrenergic receptor and in the presence of triiodothyronine (T3), NE promotes the synthesis of the uncoupling protein 1 (UCP1). UCP1 is a 32 kDa protein located in the inner membrane of BAT mitochondria, where it dissipates the proton gradient created by oxidations in the mitochondria. UCP1 functions as a proton translocator, substituting for another translocator, the ATP synthetase. The uncoupling of oxidations and phosphorylations and the inhibition of ATP synthesis lead to dissipation as heat of all energy produced in the respiratory chain. The supply of adequate amounts of T3 is ensured by the cold-induced enhancement of the enzyme 5'-deiodinase type II activity, which deiodinates thyroxine (T4) to T3. The absence of T3 blocks UCP1 synthesis, leading to hypothermia. BAT has a limited significance in humans, except in the newborn, where it serves for a rapid acclimation to ambient temperature. The study of BAT physiology will provide more insight into the mechanisms regulating energy balance and body weight in humans, thus contributing to prevent and treat human obesity.

Hormonas tiroideas, obesidad y termogénesis en grasa parda. / [Thyroid hormones, obesity and brown adipose tissue thermogenesis]

Brown adipose tissue (BAT) is the main site for hormone-dependent (non-shivering) thermogenesis in response to cold in lower mammals. The hypothalamus controls the cold-induced BAT activation by stimulating the sympathetic nerves and the secretion of norepinephrine (NE) in BAT. Mediated by beta-3 noradrenergic receptor and in the presence of triiodothyronine (T3), NE promotes the synthesis of the uncoupling protein 1 (UCP1). UCP1 is a 32 kDa protein located in the inner membrane of BAT mitochondria, where it dissipates the proton gradient created by oxidations in the mitochondria. UCP1 functions as a proton translocator, substituting for another translocator, the ATP synthetase. The uncoupling of oxidations and phosphorylations and the inhibition of ATP synthesis lead to dissipation as heat of all energy produced in the respiratory chain. The supply of adequate amounts of T3 is ensured by the cold-induced enhancement of the enzyme 5-deiodinase type II activity, which deiodinates thyroxine (T4) to T3. The absence of T3 blocks UCP1 synthesis, leading to hypothermia. BAT has a limited significance in humans, except in the newborn, where it serves for a rapid acclimation to ambient temperature. The study of BAT physiology will provide more insight into the mechanisms regulating energy balance and body weight in humans, thus contributing to prevent and treat human obesity.

Effects of thyroxine on rat brown fat and muscle thermogenesis in the cold.

We studied whether the activation of rat brown adipose tissue (BAT) by cold exposure or by the administration of beta-3-noradrenergic agonist CGP-12177 could be prevented by the inhibition of thyroxine (T4) to triiodothyronine (T3) conversion. Hypothyroid rats were treated with replacement doses of T4, T4 plus iopanoic acid (IA) or T3. Groups of rats were placed at 4 degrees C for 24 h or kept at room temperature. Cold exposure induced a significant increase in guanosine diphosphate (GDP) binding to BAT mitochondrial proteins in T4-treated rats, an effect not abolished by IA. No significant changes were seen in T3-treated rats. In rats maintained at room temperature and injected with CGP-12177, T4 induced a significant rise in GDP binding which was not blocked by IA. T3 also induced a significant increase in binding. The study of mitochondrial oxygen consumption in muscle from cold-exposed rats showed a marked decrease in consumption in T3-treated rats as compared to values in the warm. Normal oxygen consumption was restored with 2-fold doses of T3 replacement, whereas 5-fold doses increased consumption above normal. The data suggest that in states with low or absent T3, T4 can stimulate heat production and preserve normothermia.

[Zinc inhibits the in vitro conversion of thyroxine to triiodothyronine in brown adipose issue]. / El cinc inhibe la conversión de tiroxina en triiodotironina en grasa parda in vitro.

The effect of in vitro addition of zinc sulphate on T4 deiodination in brown adipose tissue (BAT) of rats exposed to 4 degrees C or 22 degrees C temperature during 24 h, was studied. Animals were killed by cervical dislocation and BAT was immediately removed and homogenized in sucrose buffer (320 mM) containing HEPES (10 mM) pH 7.4. The preparation was centrifuged at 4 degrees C during 10 min. Aliquots were separated adding 50, 100 microM, 1 o 5 mM zinc sulphate plus 0, 5, 10 or 25 mM dithiothreitol plus 1 microCi 125I-T4. The mixture was incubated at 37 degrees C during 60 min. Aliquots were applied to Whatman paper and chromatographed. BAT from control rats kept at 22 degrees C produced 79 +/- 30 pg T3/g protein/h. This value was significantly reduced in homogenates containing 1 or 5 mM zinc. In rats exposed to 4 degrees C, T3 production increased to 248 +/- 37 pg/mg protein/h. The addition of 100 microM, 1 or 5 mM zinc significantly decreased T3 production. The inhibitory action of zinc on BAT T4 deiodination may have a deleterious effect on BAT thermogenesis.

El cinc inhibe la conversión de tiroxina en triiodotironina en grasa parda in vitro. / [Zinc inhibits the in vitro conversion of thyroxine to triiodothyronine in brown adipose issue]

The effect of in vitro addition of zinc sulphate on T4 deiodination in brown adipose tissue (BAT) of rats exposed to 4 degrees C or 22 degrees C temperature during 24 h, was studied. Animals were killed by cervical dislocation and BAT was immediately removed and homogenized in sucrose buffer (320 mM) containing HEPES (10 mM) pH 7.4. The preparation was centrifuged at 4 degrees C during 10 min. Aliquots were separated adding 50, 100 microM, 1 o 5 mM zinc sulphate plus 0, 5, 10 or 25 mM dithiothreitol plus 1 microCi 125I-T4. The mixture was incubated at 37 degrees C during 60 min. Aliquots were applied to Whatman paper and chromatographed. BAT from control rats kept at 22 degrees C produced 79 +/- 30 pg T3/g protein/h. This value was significantly reduced in homogenates containing 1 or 5 mM zinc. In rats exposed to 4 degrees C, T3 production increased to 248 +/- 37 pg/mg protein/h. The addition of 100 microM, 1 or 5 mM zinc significantly decreased T3 production. The inhibitory action of zinc on BAT T4 deiodination may have a deleterious effect on BAT thermogenesis.

Evidence suggesting that cadmium induces a non-thyroidal illness syndrome in the rat.

The effect of in vivo administration of cadmium chloride on the pituitary-thyroidal axis was assessed in 200 g body weight Wistar rats. A dose of 2.5 mg/kg body weight was injected i.v. 24 h before the experiments were initiated. Plasma thyroxine (T4) and tri-iodothyronine (T3) concentrations in cadmium-treated rats were significantly (P < 0.01) decreased, whereas plasma TSH failed to increase in response to low T4 and T3. However, the TSH response to TRH and the pituitary content of TSH in these rats were both normal. Cadmium induced a significant (P < 0.01) decrease in 4-h thyroidal 131I uptake and in thyroid/plasma radioactivity ratio. The in vitro conversion of T4 to T3 in the pituitary was significantly (P < 0.01) blocked by cadmium whereas there was no in vivo effect. Parameters of peripheral T4 kinetics in cadmium-treated rats, such as metabolic clearance rate (P < 0.01), fractional turnover rate (P < 0.01), absolute disposal rate (P < 0.05), urinary clearance (P < 0.05) and faecal clearance (P < 0.05), were all decreased by cadmium. The lack of response of TSH to low plasma T4 and T3 and the normal response to exogenous TRH in this and in other non-thyroidal illness syndromes produced by other pathologies suggest a decreased stimulation of pituitary thyrotrophs by endogenous TRH.

Relative roles of the thyroid hormones and noradrenaline on the thermogenic activity of brown adipose tissue in the rat.

We have assessed the relative contribution of the thyroid hormones and noradrenaline (NA) on the calorigenic function of brown adipose tissue (BAT) as indicated by GDP binding and O2 consumption of BAT mitochondria. Male Wistar rats of 200 g body weight were made hypothyroid with 131I. Groups of animals were injected s.c., in divided doses, daily for 10 days, with thyroxine (2 micrograms/100 g body weight) or tri-iodothyronine (T3; 0.3 microgram/100 g body weight). Animals were used 7 days after bilateral or unilateral sympathetic nerve excision of BAT (Sx). Sham-operated rats were used as controls. In normal rats kept at 22 degrees C, GDP binding reached 94 +/- 24 pmol/mg protein; untreated hypothyroid rats had normal binding values whereas the T3-treated group showed an increased binding. Sx induced a sharp fall in the three groups (P < 0.01). After 24-h exposure to 4 degrees C GDP binding increased in normal rats to about 410% (P < 0.01) whereas binding failed to increase in response to cold in the untreated hypothyroid and the T3-treated groups. Sx reduced GDP binding in the three groups significantly (P < 0.01). The consumption of O2 by BAT mitochondria showed similar variations in response to Sx and to cold exposure as did GDP binding. The data indicated that, at room temperature, BAT calorigenesis can function without the thyroid hormones, though not without the catecholamines. The findings in rats exposed to cold showed that the lack of NA was significantly more effective than the lack of thyroid hormones in preventing the BAT hyperactive response. This does not negate an active role for T3 in BAT calorigenesis.

Changes induced by zinc on thyroxine deiodination by rat liver in vivo and in vitro.

The effects of in vivo administration or in vitro addition of zinc on 5'-deiodination of thyroxine (T4) and the concentration of nonprotein sulfhydryl groups (NPSH) in rat liver were studied in 200-240 g body weight male Wistar rats. Twelve rats were injected i.p. with zinc sulphate 2 mg/kg body weight 24 h before the experiments were started. Animals were killed by cervical dislocation and the liver was immediately removed and homogenized. Dithiothreitol (DTT) (0, 2.5, 5 or 10 mM, final concentration) and 1 microCi 125I-T4 were added to homogenates. For the in vitro studies, animals were killed by cervical dislocation and the liver removed and added zinc or cadmium (2.5 or 5 mM) plus DTT and labelled T4. Homogenates were incubated for 90 min at 37 degrees C and thereafter chromatographed in Whatman 1 paper. Zinc-injected rats had a significant (P < 0.01) decrease in T4 deiodination and in the generation of iodine (P < 0.02) and T3 (P < 0.05). In the in vitro studies, both zinc and cadmium reduced (P < 0.02) the deiodination of T4, and the generation of iodine (P < 0.02) for zinc and P < 0.05 for cadmium) as well as the generation of T3 (p < 0.05). The NPSH in zinc-injected rats were within normal levels. Serum T4 and T3 in zinc-treated rats were normal, whereas in cadmium-treated rats were both significantly decreased (P < 0.01 for T4 and P < 0.02 for T3). The data indicate that zinc blocks the activity of liver 5'-deiodinase through a mechanism probably related to its binding to the sulfhydryl groups of the enzyme.

Changes induced by zinc on thyroxine deiodination by rat liver in vivo and in vitro

Se estudió el efecto de la administración in vivo o del agregado in vitro de zinc sobre la deiodinación 5'de la tiroxina (T4) por el hígado de rata y sobre la concentración hepática de grupos sulfhidrilos libres (NPSH). Se usaron ratas Wistar macho de 200-240g de peso corporal. A un grupo de 12 ratas se les inyectó i.p. sulfato de zinc 2mg/Kg de peso, 24h antes de iniciar el estudio. Se sacrificaron los animales por dislocación cervical y el hígado fue inmediatamente homogeneizado. Se agregó a los homogenatos dithithreitol (DTT) (0,2.5,5 o 10mM concentración final) y 1µCi de 125I-T4. Para los estudios in vitro en animales sin tratar, se agregó al homogenato de hígado sulfato de zinc o cloruro de cadmio (2.5 o 5mM) más DTT y T4 marcada. Todos los homogenatos fueron incubados durante 90 min a 37ºC y luego cromatografiados en papel Whatman 1. Las ratas inyectadas con zinc tuvieron una disminución significativa (p<0.01) de la deiodinación de T4, de la producción de 125 iodo (P<0.02) y de triiodotironina (T3) (P<0.05). En los estudios in vitro, el agregado de zinc o cadmio disminuyó significativamente la degradación de T4 (P<0.02) y la producción de iodo (P<0.02 para el zinc y P<0.05 para el cadmio) y de T3 (P<0.05). La concentración hepática de NPSH en los animales inyectados con zinc fue normal. La concentración sérica de T4 y T3 en los animales inyectados con zinc fue normal pero en los inyectados con cadmio se redujo significativamente (P<0.01 para T4 y P<0.02 para T3). Los resultados indican que el zinc inhibe la actividad de la 5'-deioidnasa hepática, por um mecanismo probablemente relacionado con la unión del metal a los grupos sulfhidrilos de la enzima

Changes induced by zinc on thyroxine deiodination by rat liver in vivo and in vitro.

The effects of in vivo administration or in vitro addition of zinc on 5-deiodination of thyroxine (T4) and the concentration of nonprotein sulfhydryl groups (NPSH) in rat liver were studied in 200-240 g body weight male Wistar rats. Twelve rats were injected i.p. with zinc sulphate 2 mg/kg body weight 24 h before the experiments were started. Animals were killed by cervical dislocation and the liver was immediately removed and homogenized. Dithiothreitol (DTT) (0, 2.5, 5 or 10 mM, final concentration) and 1 microCi 125I-T4 were added to homogenates. For the in vitro studies, animals were killed by cervical dislocation and the liver removed and added zinc or cadmium (2.5 or 5 mM) plus DTT and labelled T4. Homogenates were incubated for 90 min at 37 degrees C and thereafter chromatographed in Whatman 1 paper. Zinc-injected rats had a significant (P < 0.01) decrease in T4 deiodination and in the generation of iodine (P < 0.02) and T3 (P < 0.05). In the in vitro studies, both zinc and cadmium reduced (P < 0.02) the deiodination of T4, and the generation of iodine (P < 0.02) for zinc and P < 0.05 for cadmium) as well as the generation of T3 (p < 0.05). The NPSH in zinc-injected rats were within normal levels. Serum T4 and T3 in zinc-treated rats were normal, whereas in cadmium-treated rats were both significantly decreased (P < 0.01 for T4 and P < 0.02 for T3). The data indicate that zinc blocks the activity of liver 5-deiodinase through a mechanism probably related to its binding to the sulfhydryl groups of the enzyme.

Changes induced by zinc on thyroxine deiodination by rat liver in vivo and in vitro

Se estudió el efecto de la administración in vivo o del agregado in vitro de zinc sobre la deiodinación 5de la tiroxina (T4) por el hígado de rata y sobre la concentración hepática de grupos sulfhidrilos libres (NPSH). Se usaron ratas Wistar macho de 200-240g de peso corporal. A un grupo de 12 ratas se les inyectó i.p. sulfato de zinc 2mg/Kg de peso, 24h antes de iniciar el estudio. Se sacrificaron los animales por dislocación cervical y el hígado fue inmediatamente homogeneizado. Se agregó a los homogenatos dithithreitol (DTT) (0,2.5,5 o 10mM concentración final) y 1ACi de 125I-T4. Para los estudios in vitro en animales sin tratar, se agregó al homogenato de hígado sulfato de zinc o cloruro de cadmio (2.5 o 5mM) más DTT y T4 marcada. Todos los homogenatos fueron incubados durante 90 min a 37ºC y luego cromatografiados en papel Whatman 1. Las ratas inyectadas con zinc tuvieron una disminución significativa (p<0.01) de la deiodinación de T4, de la producción de 125 iodo (P<0.02) y de triiodotironina (T3) (P<0.05). En los estudios in vitro, el agregado de zinc o cadmio disminuyó significativamente la degradación de T4 (P<0.02) y la producción de iodo (P<0.02 para el zinc y P<0.05 para el cadmio) y de T3 (P<0.05). La concentración hepática de NPSH en los animales inyectados con zinc fue normal. La concentración sérica de T4 y T3 en los animales inyectados con zinc fue normal pero en los inyectados con cadmio se redujo significativamente (P<0.01 para T4 y P<0.02 para T3). Los resultados indican que el zinc inhibe la actividad de la 5-deioidnasa hepática, por um mecanismo probablemente relacionado con la unión del metal a los grupos sulfhidrilos de la enzima (AU)

Multicompartmental analysis of triiodothyronine kinetics in hypothyroid patients treated orally or intravenously with triiodothyronine.

Kinetic studies were performed with i.v. 125I T3 in four athyreotic women on two occasions each, once while they were taking oral T3 (30 micrograms T3 every 12 h) and again while on i.v. T3 replacement (same dosage schedule). The kinetic data were analyzed by a 7-compartment model, representing the plasma volume, the fast and slow peripheral exchange compartments, the iodide pool (as a delay compartment prior to appearance in the urine), the intestine (as a delay compartment before appearance in the feces), and the urine and feces. Modeling was done by the SAAM methodology. All data sets, and also the mean data treated as though they were data from a single subject, were fitted for the two limit solutions in which all metabolism was assumed to be in one or the other of the exchange compartments. The mean data set was also fitted to a solution in which limits were imposed on the excretion parameters and the partition of metabolism between the 2 peripheral exchange compartments was estimated. We found that steady-state parameters for removal of T3 from the circulation (the MCRs and DRs) were increased during the i.v. T3 replacement period compared with the oral replacement period, especially in the fast exchange compartment. Measured serum stable T3 levels (RIA) were lower in the i.v. than in the oral study, both at 8 and at 12 h after the most recent T3 dose. These values corresponded to similar differences in the circulating T3 levels projected from the model, although the T3 values projected from the model were greater than the measured T3 levels for unknown reasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes induced by cadmium administration on thyroxine deiodination and sulfhydryl groups in rat liver.

The effects of cadmium on 5'-deiodination of thyroxine (T4) by rat liver and on the hepatic concentration of non-protein sulfhydryl groups (NPSH) were studied in Wistar rats of 200-250 g body weight. A group of ten rats was injected with cadmium chloride (300 micrograms/100 g body weight i.p.) daily for 4 days. Another group of six rats received, in addition, dithiothreitol (DTT; 1 mg/100 g body weight i.p.) daily for the same period. A group of eight normal untreated rats served as control. T4 deiodination was also determined in aliquots of liver from untreated rats, with cadmium (2 or 5 mmol/l) and with or without DTT (0, 2.5, 5 or 10 mmol/l) plus 1 microCi 125I-labelled T4. Hepatic NPSH were measured by a colorimetric method employing dithioldinitrobenzoic acid. Homogenates were incubated for 90 min at 37 degrees C and chromatographed in a tertiary amyl alcohol:hexane:ammonia (2 mol/l) (10:1:12) system. Cadmium-injected rats showed a significant (P < 0.01) decrease in T4 deiodination and in the generation of 125I (P < 0.01) and tri-iodothyronine (T3) (P < 0.02). NPSH were also decreased (P < 0.02). Administration of DTT restored T4 deiodination and NPSH to normal. In-vitro addition of cadmium or DTT to normal rat liver homogenates induced similar effects on the degradation of T4. Serum concentrations of T4 (P < 0.01) and T3 (P < 0.01) declined significantly in cadmium-injected rats, whereas DTT administration failed to normalize serum hormone levels. The data suggest that cadmium may have decreased 5'-deiodinating activity through binding to sulfhydryl groups of 5'-deiodinase as it does in other enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidermal growth factor stimulates thyrotropin secretion in the rat.

The present work studied the effects of epidermal growth factor (EGF) on the release of thyrotropin (TSH) and prolactin (PRL) from perifused pituitary glands of 200-gram male Wistar rats. Each pituitary gland, cut into halves, was placed in a chamber of a perifusion system connected to a peristaltic pump which conveyed the perifusion medium (Medium 199, pH 7.3, Gibco, USA) from a reservoir to a chamber at a flow rate of 100 microliters/min. Each tightly closed chamber contained one pituitary gland and 600 microliters medium and it was placed in a water bath at 37 degrees C throughout the experiment. One milliliter samples of effluent were collected every 10 min for 60 min to obtain baseline values of TSH and PRL. Thereafter, TSH-releasing hormone (TRH) 10(-8) M or EGF (10(-11), 10(-10), 10(-9) or 10(-8) M) were added to individual chambers and the 10-min sampling of effluent continued for 60 min. EGF 10(-11) M elicited no TSH response, but 10(-10) and 10(-9) M doses induced significant increases in TSH secretion (p < 0.01) with a peak at 10 min after addition of EGF. In another experiment, EGF 10(-8) M or TRH 10(-8) M significantly elevated TSH secretion (p < 0.01). However, TRH, but not EGF, stimulated PRL secretion (p < 0.01). In the in vivo studies, the intravenous administration of EGF 10(-5) M or TRH 10(-5) M both induced significant elevation of TSH release at 10 min after the injection (p < 0.02 for EGF and p < 0.01 for TRH).(ABSTRACT TRUNCATED AT 250 WORDS)