Prolactin inhibition at the end of lactation programs for a central hypothyroidism in adult rat

Malnutrition during lactation is associated with hypoprolactinemia and failure in milk production. Adult rats whose mothers were malnourished presented higher body weight and serum tri-iodothyronine (T(3)). Maternal hypoprolactinemia at the end of lactation caused higher body weight in adult life, suggesting an association between maternal prolactin (PRL) level and programming of the offspring's adult body weight. Here, we studied the consequences of the maternal PRL inhibition at the end of lactation by bromocriptine (BRO) injection, a dopaminergic agonist, upon serum TSH and thyroid hormones, thyroid iodide uptake, liver mitochondrial alpha-glycerophosphate dehydrogenase (mGPD), liver and pituitary de-iodinase activities (D1 and/or D2), and in vitro post-TRH TSH release in the adult offspring. Wistar lactating rats were divided into BRO - injected with 1 mg/twice a day, daily for the last 3 days of lactation, and C - control, saline-injected with the same frequency. At 180 days of age, the offspring were injected with (125)I i.p. and after 2 h, they were killed. Adult animals whose mothers were treated with BRO at the end of lactation presented lower serum TSH (-51%), T(3) (-23%), and thyroxine (-21%), lower thyroid (125)I uptake (-41%), liver mGPD (-55%), and pituitary D2 (-51%) activities, without changes in the in vitro post-TRH TSH release. We show that maternal PRL suppression at the end of lactation programs a hypometabolic state in adulthood, in part due to a thyroid hypofunction, caused by a central hypothyroidism, probably due to decreased TRH secretion. We suggest that PRL during lactation can regulate the hypothalamus-pituitary-thyroid axis and programs its function.

Maximum acute exercise tolerance in hyperthyroid and hypothyroid rats subjected to forced swimming

Thyroid dysfunction can compromise physical capacity. Here, we analyze the effects of hyperthyroidism and hypothyroidism on maximum swim time in rats subjected to acute forced swimming, as an indicator of anaerobic capacity. Animals were forced to swim against a load (5% of body weight) attached to the tail and were killed 48 hours after the last test. Hyperthyroid rats were treated with thyroxine (50 mug/100 g body weight, i. p. for 7 days). The hypothyroid group received 0.03% methimazole in the drinking water for 4 weeks. Thyroid state was confirmed by alterations in serum thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), and liver mitochondrial glycerol phosphate dehydrogenase (mGPD) activity. Hyperthyroid rats presented significantly lower visceral fat mass (VFM) and higher food intake (p<0.05) with unchanged body weight. Maximum swim time (MST), glycogen content (skeletal muscle and liver), and leptin levels were lower while corticosterone was higher (p<0.05). In hypothyroid rats body weight was lower (p<0.05), without changes in VFM. Tested at 7-day intervals, MST was lower for tests 2, 3, and 4 (p<0.05). Muscle glycogen was higher in extensor digitorum longus (EDL) and soleus (p<0.05), without changes in liver. Serum corticosterone was lower, while leptin was higher (p<0.05). These results suggest that in hyperthyroid and hypothyroid rats, thyroid hormones together with corticosterone and/or leptin may impair exercise capacity differently through its known effects on glycogen metabolism.

Thyroid function and body weight programming by neonatal hyperthyroidism in rats - the role of leptin and deiodinase activities

Several authors have shown that secondary hypothyroidism was programed by neonatal thyroxine (T4) treatment. However, the associated changes of body weight (BW) were less studied, especially those related to the body fat proportion. Here, we have evaluated the effect of neonatal thyroxine treatment on BW, fat proportion, serum leptin, and thyroid function of 60-day-old rats. Wistar rats were treated with thyroxine (50 microg/100 g BW, ip) (T) or saline (S), during the first 10 days of life. BW, nose-rump length (NRL), and food consumption were monitored for 60 days, when the animals were sacrificed. Thyroid function was evaluated by thyroid radioiodine uptake (RAIU), serum T3, T4, TSH, and liver mitochondrial alpha-glycerophosphate dehydrogenase (mGPD) and type 1 and 2 deiodinases (D1 and D2) activities, which are thyroid hormone-dependent enzymes. T animals showed lower food intake, BW and NRL, but higher total fat mass (+33%) and serum leptin (+46%). They also showed lower serum T3 (-23%), T4 (-32%), TSH (-36%), RAIU (-29%) and mGPD activity (-22%). Hypothalamic and pituitary D2 activities were higher (+24% and 1.4 fold, respectively), while brown adipose tissue (BAT) D2 and skeletal muscle D1 activities were lower (-30% and -62%, respectively). Thus, neonatal hyperthyroidism programs for a higher fat proportion and hyperleptinemia, which can explain the lower food intake. The TH-dependent enzymes activities changed accordingly, except for the decrease in BAT D2, which may be due the role played by the hyperleptinemia. Finally, the decrease in peripheral deiodination may contribute to a lower me-tabolic rate that may increase the adiposity.

Neonatal programming of neuroimmunomodulation--role of adipocytokines and neuropeptides

Programming is an epigenetic phenomenon by which nutrition, environment and stress acting in a critical period earlier in life change the organism's development. This process was evolutionarily selected as an adaptive tool for the survival of organisms living in nutritionally deficient areas and submitted to stressful conditions. Thus, perinatal malnutrition turns on different genes that provide the organism with a thrifty phenotype. In conditions of abundant supply of nutrients, those programmed organisms can be at risk of developing metabolic diseases (obesity, dyslipidemia, diabetes and hypertension). How nutrition or neonatal stress can program the immune system is less well known. Here, we discuss some of the hormonal and metabolic changes that occur in mothers and neonates and how those factors can imprint hormonal or metabolic changes that program neuroimmunomodulatory effects. Some of these changes involve thyroid hormones, leptin, insulin, glucocorticoids and prolactin as potential imprinting factors. Most of them can be transferred through the milk and may change with malnutrition or stress. We discuss the programming effects of these hormones upon body weight, body composition, insulin action, thyroid, adrenal and immune and inflammatory responses, with special emphasis on leptin, a cytokine that seems to play a central role in these events.

Chronic leptin treatment inhibits liver mitochondrial alpha-glycerol-beta-phosphate dehydrogenase in euthyroid rats

Leptin modulates the hypothalamus-pituitary-thyroid axis and peripheral metabolism of thyroid hormones (THs). We have studied the effect of acute and chronic leptin treatment upon liver mitochondrial glycerol phosphate dehydrogenase activity (mGPD), whose expression and activity are TH dependent. We performed 2 experiments: 1) acute leptin treatment - LepA: adult rats received a single leptin injection (8 microg/100 g BW); 2) chronic leptin treatment - LepC: adult rats received leptin (8 microg/100 g BW) daily, for 6 days. In both experiments, control groups were saline-treated. All rats were sacrificed 2 hours after the last dose. Liver mGPD activity was determined by colorimetric method. Liver D1 activity was measured by the release of (125)I from (125)I-rT3. Serum hormones were measured by RIA. LepA rats showed higher serum thyroid stimulating hormone (TSH) (+ 64%, p<0.05), free T4 (+ 34%, p<0.05), free T3 (+ 64%, p<0.05), and liver D1 activity (+ 85%, p<0.05), but no change in mGPD activity. Since THs increase mGPD activity, the unchanged level in the acute experiment is suggestive of an inhibitory role of leptin. LepC rats presented lower mGPD activity (-1.7-fold, p<0.05) and higher liver D1 activity (+ 32%, p<0.05), but no alteration in serum TSH and free THs. Our results show that leptin downregulates mGPD activity, mainly when hyperleptinemia is chronic.

Acute effects of leptin on 5'-deiodinases are modulated by thyroid state of fed rats

Leptin has been shown to modulate deiodinase type 1 (D1) and type 2 (D2) enzymes responsible for thyroxine (T4) to triiodothyronine (T3) conversion. Previously, it was demonstrated that a single injection of leptin in euthyroid fed rats rapidly increased liver, pituitary, and thyroid D1 activity, and simultaneously decreased brown adipose tissue (BAT) and hypothalamic D2 activity. We have now examined D1 and D2 activities, two hours after a single subcutaneous injection of leptin (8 microg/100 g BW) into hypo- and hyperthyroid rats. In hypothyroid rats, leptin did not modify pituitary, liver and thyroid D1, and thyroid D2 activity, while pituitary D2 was decreased by 41% (p<0.05) and hypothalamic D2 showed a 1.5-fold increase. In hyperthyroid rats, thyroid and pituitary D1, and pituitary and hypothalamic D2 were not affected by leptin injection, while liver D1 showed a 42% decrease (p<0.05). BAT D2 was decreased by leptin injection both in hypo- and hyperthyroid states (42 and 48% reduction, p<0.001). Serum TH and TSH showed the expected variations of hypo- and hyperthyroid state, and leptin had no effect. Serum insulin was lower in hypothyroid than in hyperthyroid rats and remained unchanged after leptin. Therefore, acute effects of leptin on D1 and D2 activity, expect for BAT D2, were abolished or modified by altered thyroid state, in a tissue-specific manner, showing an IN VIVO interplay of thyroid hormones and leptin in deiodinase regulation.

Cold exposure restores the decrease in leptin receptors (OB-Rb) caused by neonatal leptin treatment in 30-day-old rats

We had previously shown that neonatal leptin treatment programs thyroid function in adulthood. As both thyroid hormones (TH) and leptin increased thermogenesis, it was interesting to evaluate the effect of cold exposure on the thyroid function of neonate rats treated with leptin. Pups were divided into two groups: Lep, injected with leptin (8 mug/100 g/BW, s.c.) for the first 10 days of lactation and control (C), injected with saline. When they were 30 days old, the groups were subdivided into two subgroups: LepC and CC, which were exposed to 8 degrees C for 12 h and compared with C and Lep groups, maintained at 25 +/- 1 degrees C. Serum leptin, TH, and TSH were measured by RIA. Type I liver deiodinase (D1) and mitochondrial alpha-glycerol-3-phosphate dehydrogenase (mGPD) activities were assayed by the release of (125)I from (125)I-reverse and colorimetric method respectively. Leptin receptor (OB-Rb) was evaluated by western blot. Lep group had hyperleptinemia (+22%) and lower free tri-iodothyronine (FT(3); -33%). Cold exposure increased TH both in LepC and CC groups compared with respective controls free thyroxine (FT(4):+63 and +39%; FT(3):+75 and +40%). Liver D1 activity was lower in Lep (-22%) and increased with cold exposure (LepC +51% and CC +22%). The mGPD activity was lower in Lep (-34%) and increased (fourfold) when this group is cold exposed. Hypothalamic and thyroidal OB-Rb receptors were lower in Lep group (-47 and -36% respectively) and they were restored to normal levels after cold exposure. Leptin-programmed rats had higher TH response after cold exposure. OB-Rb had a fast response to cold exposure normalizing the lower levels observed in the leptin-programmed animals and may contribute to the higher TH cold responses.

Maternal low-protein diet during lactation programmes body composition and glucose homeostasis in the adult rat offspring

Previously we have reported that maternal malnutrition during lactation programmes body weight and thyroid function in the adult offspring. In the present study we evaluated the effect of maternal protein restriction during lactation upon body composition and hormones related to glucose homeostasis in adult rats. During lactation, Wistar lactating rats and their pups were divided into two experimental groups: control (fed a normal diet; 23 % protein) and protein-restricted (PR; fed a diet containing 8 % protein). At weaning, offspring received a normal diet until they were 180 d old. Body weight (BW) and food intake were monitored. Serum, adrenal glands, visceral fat mass (VFM) and carcasses were collected. PR rats showed lower BW ( − 13 %;P < 0·05), VFM ( − 33 %;P < 0·05), total body fat ( − 33 %;P < 0·05), serum glucose ( − 7 %;P < 0·05), serum insulin ( − 26 %,P < 0·05), homeostasis model assessment index ( − 20 %), but higher total adrenal catecholamine content (+90 %;P < 0·05) and serum corticosterone concentration (+51 %;P < 0·05). No change was observed in food intake, protein mass or total body water. The lower BW of PR rats is due to a reduction of white fat tissue, probably caused by an increase in lipolysis or impairment of lipogenesis; both effects could be related to higher catecholaminergic status, as well as to hypoinsulinaemia. To conclude, changes in key hormones which control intermediary metabolism are programmed by maternal protein restriction during lactation, resulting in BW alterations in adult rats.

Acute and chronic leptin effect upon in vivo and in vitro rat thyroid iodide uptake

Leptin has stimulatory effects on the hypothalamic-pituitary-thyroid axis and on deiodinases activities. Here, we evaluated the effect of leptin injection upon in vivo and in vitro thyroid 125I uptake (RAIU). We designed two experiments: acute leptin (LepA) with a single dose of leptin (8 microg/100 g BW/sc), and chronic leptin (LepC), injected with the same dose of LepA, once a day, for 6 days. In parallel, control groups were saline-injected. For in vivo study, part of the animals were injected with 125I (3700 Bq) and killed after 15 or 120 min. In vivo thyroid RAIU was not changed in LepA animals. However, LepC animals showed higher in vivo thyroid RAIU (15 min:+130% and 120 min:+72%; p<0.05). For in vitro study, the other animals were killed and their thyroids were incubated with 125I. Thyroids explants from LepA and LepC groups presented lower thyroid 125I content (-32% and -29% p<0.05, respectively). The amount of our data suggest that, in vitro, leptin causes a direct inhibition of the rat thyroid RAIU, but in vivo, the effect of leptin was different according to the treatment period, which indicates that other indirect mechanisms are involved in the in vivo leptin chronic stimulation of the thyroid gland.

Maternal leptin treatment during lactation programs the thyroid function of adult rats

Recently, we showed that both maternal malnutrition during lactation and leptin treatment during the neonatal period program thyroid function. In this study we evaluate whether maternal leptin treatment during lactation programs thyroid function of the offspring in the adulthood. The dams were divided into 2 groups: Lep-daily sc single injected with 8 microg/100 g of body weight with recombinant rat leptin during the last 3 days of lactation and control group (C) that received the same volume of saline. The 180 day-old animals received a single i.p. injection of (125)I (2.22x10(4) Bq) and they were killed 2 h after the injection. Triiodothyronine (T3), thyroxine (T4), thyrotropin (TSH) and leptin concentrations were measured by radioimmunoassay. The milk of leptin-treated mothers on the last day of treatment had higher leptin (p<0.05) concentration. The pups of the leptin-treated mothers had at 21 days an unchanged T3, T4 and leptin serum concentrations with higher TSH (p<0.05). The offspring of Lep mothers had at 180 days a higher T3 (p<0.05) with normal thyroid (125)I uptake, T4 and TSH serum concentrations compared to the controls. So, the mother's hyperleptinaemia during lactation programs to a higher T3 serum concentration on the offspring, probably by a higher leptin transfer through the milk.

Neonatal leptin treatment programmes leptin hypothalamic resistance and intermediary metabolic parameters in adult rat

We previously showed that neonatal leptin treatment programmes higher body weight and food intake in adult rats. Here we investigate whether leptin treatment during lactation affects the anorectic effect of leptin on adult rats and their hypothalamic leptin receptors (OB-Rb) and whether those changes could have consequences on intermediary metabolism. When the offspring were born, pups were divided into two groups: the Lep group, injected daily with leptin (8μg/100g body weight, subcutaneously) for the first 10d of lactation, and the control group, injected daily with saline. After weaning (day 21), body weight and food intake were monitored until the rats were 150d old. Food intake was higher in the Lep group (approximately 14%,p<0·05) from day 133 onwards, and body weight was higher (approximately 10%,p<0·05) from day 69 onwards, compared with the control group. At 150d of age, the rats were tested for food intake in response to either leptin (05mg/kg body weight intraperitoneally; groups CL and LepL) or saline (groups CSal and LepSal). The CL group showed a decrease in food intake, but no response was observed in the LepL group, suggesting leptin resistance. The Lep group demonstrated a decrease in OB-Rb expression (−40%p<0·05), hyperleptinaemia (+78%,p<0·05), hyperinsulinaemia (+100%,p<0·02), hypertriacylglycerolaemia (+17%,p<0·05) and a higher protein content in the body (+16%,p<0·05) without changes in fat mass and glycaemia. We conclude that neonatal leptin treatment programmes both hyperleptinaemia and hyperinsulinaemia in adulthood, which leads to leptin resistance by reducing the expression of the hypothalamic leptin receptor.

Neonatal hyperleptinaemia programmes adrenal medullary function in adult rats: effects on cardiovascular parameters

Epidemiological studies have shown a strong correlation between stressful events (nutritional, hormonal or environmental) in early life and development of adult diseases such as obesity, diabetes and cardiovascular failure. It is known that gestation and lactation are crucial periods for healthy growth in mammals and that the sympathoadrenal system is markedly influenced by environmental conditions during these periods. We previously demonstrated that neonatal hyperleptinaemia in rats programmes higher body weight, higher food intake and hypothalamic leptin resistance in adulthood. Using this model of programming, we investigated adrenal medullary function and effects on cardiovascular parameters in male rats in adulthood. Leptin treatment during the first 10 days of lactation (8 microg 100 g(-1) day(-1), s.c.) resulted in lower body weight (6.5%, P < 0.05), hyperleptinaemia (10-fold, P < 0.05) and higher catecholamine content in adrenal glands (18.5%, P < 0.05) on the last day of treatment. In adulthood (150 days), the rats presented higher body weight (5%, P < 0.05), adrenal catecholamine content (3-fold, P < 0.05), tyrosine hydroxylase expression (35%, P < 0.05) and basal and caffeine-stimulated catecholamine release (53% and 100%, respectively, P < 0.05). Systolic blood pressure and heart rate were also higher in adult rats (7% and 6%, respectively, P < 0.05). Our results show that hyperleptinaemia in early life increases adrenal medullary function in adulthood and that this may alter cardiovascular parameters. Thus, we suggest that imprinting factors which increase leptin and catecholamine levels during the neonatal period could be involved in development of adult chronic diseases.

Temporal evaluation of the thyroid function of rats programmed by leptin treatment on the neonatal period

Hormones and malnutrition can imprint several changes in the beginning of life that programs homeostatic changes in the adulthood. We analyzed the thyroid function in 21, 30, 60 and 150 days old animals that were injected with leptin on the first 10 days of life, to determine whether this corresponds to a critical period for the establishment of the hormonal imprinting in the programming of the thyroid function. Pups were divided, within 24 hours of birth, into two groups: Lep group, which was injected once daily with 8 microg/100 g B.W. of recombinant mouse leptin for the first 10 days of lactation, and C-control group that received the same volume of saline. Lep group had higher leptin concentration at days 30 (+6 x , p<0.001) and 150 (+108%, p<0.05) than the controls. These animals had lower serum TT4 (-13%; p<0.05) and TT3 (-17.3%; p<0.002) at 30 days and higher serum TT4 and FT4 concentrations at 150 days (+17.5% and +10%, p<0.05 %, respectively, p<0.05) with lower serum TSH concentrations at 60 (-38.5%, p<0.05) and 150 days (-46%, p<0.05). These animals had also lower hepatic mitochondrial alpha-glycerol-3-phosphate dehydrogenase (mGPDH) activity at 21 (-22.5%; p<0.05), 30 (-50.4%; p<0.05) and 150 days (-40%; p<0.05) than the controls. These data show that the leptin injection in the beginning of lactation cause a hypothyroidism on the offspring as soon as 30 days of age and this alteration may be the imprinted factor for the programming of a higher thyroid function at the adulthood.

Leptin acute modulation of the 5'-deiodinase activities in hypothalamus, pituitary and brown adipose tissue of fed rats

Leptin and thyroid hormones (TH) have the ability to increase energy expenditure. Biological effects of TH are dependent on thyroxine (T4) to triiodothyronine (T3) conversion by deiodinase type 1 (D1) and type 2 (D2). Leptin has been shown to stimulate the hypothalamus-pituitary-thyroid axis and, also, to modulate 5'-deiodinases in different tissues, depending on energetic status of animals. Here, we examined the acute effects of leptin on hypothalamic, pituitary and BAT D2 and pituitary D1 activities. Male fed rats received a single subcutaneous injection of saline or leptin (8 microg/100 g BW) and sacrificed 2 hours later. Leptin promoted an important decrease in hypothalamic D2 (55% reduction, p <0.001) with no changes in pituitary D2, in concomitance with a 2-fold rise in serum TSH, suggesting that leptin acted at hypothalamus in order to stimulate TRH-TSH axis. In addition, BAT D2 was decreased by 25% (p<0.05). In contrast, pituitary D1 showed a 2-fold increase (p<0.001), indicating that, as demonstrated before for liver and thyroid D1, the pituitary enzyme is also acutely up-regulated by leptin. Serum concentrations of insulin and TH of leptin-injected animals remained unchanged. Regulation of 5'-deiodinases directing the local T3 production, is a mechanism by which leptin may alter hypothalamic, pituitary and BAT functions.

Leptin and prolactin, but not corticosterone, modulate body weight and thyroid function in protein-malnourished lactating rats

To understand the role of hormonal changes in the lower food ingestion and body weight in protein-restricted lactating rats as well as the higher serum T (3), higher deiodination, iodide and T (3) milk transfer, we measured maternal serum prolactin, leptin, TSH and corticosterone, which are hormones that could influence those parameters. After birth, dams were separated into: control-fed with a 23 % protein diet (n = 12) and PR (protein-restricted)-fed with an 8 % protein diet (n = 12). At the 4 (th) and 21 (st) day of lactation, half of the animals in each group were sacrificed. PR dams presented hyperleptinemia (day 4: + 20 %; day 21: + 19 %; p < 0.05) and hypoprolactinemia (day 4: - 85 %; day 21: - 92 %; p < 0.05), which could help explain the lower food consumption and body weight in lactating PR rats since leptin is anorexigenic and prolactin is orexigenic. Also, this hyperleptinemia could contribute for the increase in serum T (3) of PR dams, since leptin stimulates T (3) production, especially acting on deiodinases. Serum corticosterone was not different between PR and C groups, and TSH was lower only at the end of lactation. Thus, we suggest that both leptin and prolactin could play an important role in the body weight and thyroid hormone changes observed in protein-malnourished lactating rats.

Prolactin inhibition in lactating rats changes leptin transfer through the milk

Malnutrition during lactation reduces milk production and changes pup's leptin serum levels. To test prolactin role in this nutritional state, we evaluated whether prolactin suppression during lactation changes serum leptin in dams, its transfer through the milk, and pup's serum leptin. Lactating rats were treated with bromocryptine (1 mg/twice a day, s.c.) or saline three days before sacrifice (days 2-4 or days 19-21). Food intake and body weight were measured until sacrifice (4th and 21st day). Serum prolactin and leptin were determined by radioimmunoassay. Bromocryptine injected dams had lower serum prolactin and milk production as expected. The mothers presented lower food ingestion (day 21: -25%), lower body weight (day 4: -12%; day 21: -10%), higher serum leptin (day 4: +68%), lower milk leptin on the 4th day (11 times) and higher (8 times) on the 21st day. The offspring of bromocryptine-treated mothers presented lower body weight in both periods of lactation and lower serum leptin on the 4th day (-40%) and higher on the 21st day (+37%) of lactation. We suggest that prolactin, through its effect on leptin secretion into the milk, may play an important role in signalizing maternal nutritional status to the pups.

Effects of maternal leptin treatment during lactation on the body weight and leptin resistance of adult offspring

We investigate whether leptin treatment to lactating rats affects food intake, body weight and leptin serum concentration and its anorectic effect on their adult offspring. Lactating rats were divided into 2 groups: Lep-single injected with recombinant rat leptin (8 microg/100 g of body weight, daily for the last 3 consecutive days of lactation) and control group (C) that received the same volume of saline. After weaning all pups had free access to the control diet, their body weight and food intake were monitored at each 4 days until 180 days of age, when they were tested for its food intake and response to either leptin (0.5 mg/kg body wt, ip) or saline vehicle. The offspring of the leptin-treated dams gained more weight and had higher food intake from day 37 onward (p<0.05), higher amount of retroperitoneal white adipose tissue (RPWAT) (37%, p<0.05) and higher leptin serum concentration (40%, p<0.05) at 180 days of age compared to control group. The food intake at 2, 4, 6 and 24 h was unaffected after acute injection of leptin in these animals, suggesting resistance to the anorectic effect of leptin. The maternal leptin treatment during lactation makes their adult offspring more susceptible to overweight with resistance to the anorectic effect of leptin.

Leptin treatment during lactation increases transfer of iodine through the milk

We have previously shown that protein restriction during lactation is associated with changes in iodine secretion into the milk and that a pup's serum leptin concentration was increased at the end of lactation. So, here we evaluate whether leptin treatment during lactation affects iodine transfer through the milk to the pups. Lactating rats were divided into two groups: the leptin (Lep) group, single injected with recombinant rat leptin (8 microg/100g of body weight, daily for 3 consecutive days), and the control (C) group that received the same volume of saline. We studied iodine transfer to the pups through the milk on Days 4, 12 and 21 of lactation. In those days, the dams were separated from their pups for 4 h. Then, the mothers received an injection of 131I (2.22x10(4) Bq ip) and the pups were allowed to nurse for 2 h. The animals were sacrificed 2 h later. Leptin, total serum T3 and total serum T4 concentrations were higher (P<.05) in pups of Lep mothers only on Day 4, suggesting a higher transfer of leptin through the milk at this period, probably with a direct stimulatory effect on thyroid hormone secretion. In other periods, however, even without a detectable increase in a pup's serum leptin concentration, maternal leptin administration increased the pup's thyroid iodine uptake (Day 12, 39%; Day 21, 34%), probably caused by a higher transfer of iodine through the milk, since they had a higher gastric content of 131I on Days 12 (31%) and 21 (128%).

Absence of anorectic effect to acute peripheral leptin treatment in adult rats whose mothers were malnourished during lactation

Diets with restricted energy or protein during lactation programs body weight in the adult offspring. We have investigated the hypothesis that protein or energy-restricted diets during lactation alter the feeding response to peripheral leptin treatment of the adult offspring. Five Wistar rats were randomly assigned to one of the following groups on the day that the offspring were born: C, control diet with 23% protein; PR, protein restricted diet with 8% protein; and ER, energy-restricted, receiving the control diet in restricted quantities, which were calculated according to the mean ingestion of the PR group. After weaning (day 21), two animals from each litter (10 pups in each group) were randomly selected and placed together in the cage with free access to water and standard diet until 150 days of age, when they were tested for its response to either leptin (0.5 mg/kg body wt ip) for groups Clep, PRlep and ERlep or saline vehicle for groups Csal, PRsal and ERsal on food intake. In the control groups, food intake was reduced two hours (36%), four hours (41%) and six hours (25%) after leptin treatment. In contrast, no response was observed to leptin treatment in the PRlep and ERlep groups, suggesting leptin resistance. We demonstrated the development of resistance to the anorectic leptin effect and its program in a critical life period associated to nutritional and hormonal factors.

Increased 5'-iodothyronine deiodinase activity is a maternal adaptive mechanism in response to protein restriction during lactation

We have shown that protein restriction during lactation is associated with higher levels of serum and milk tri-iodothyronine (T(3)) with lower serum thyroxine (T(4)), suggesting an increased T(4) to T(3) conversion. To investigate this hypothesis, the activity of type 1 (D1) and/or type 2 (D2) iodothyronine deiodinases was evaluated on days 4, 12 and 21 of lactation in several tIssues of dams fed an 8% protein-restricted (PR) diet and controls fed a 23% protein diet. Serum TSH, T(3) and T(4) were measured by radioimmunoassay. Deiodinase activity was determined by the release of (125)I from (125)I-reverse T(3), under specific conditions for D1 or D2. PR dams had a transitory reduction in liver D1 activity (P<0.05) on day 12, and a small increase in thyroid D1 on day 12 followed by a small decrease on day 21. However, thyroid D2 activity was higher than controls (P<0.05) during the whole of the lactation period. Mammary gland D1 and D2 activities were lower on day 4 of lactation in PR dams (P<0.05), and D2 was higher on day 21 (P<0.05). Potentially, a lower conversion of T(3) to di-iodothyronine in the mammary glands of PR dams at the beginning of lactation may serve to provide more T(3) through the milk. Brown adipose tIssue (BAT) D2 activity was higher (P<0.05) in PR dams during all periods of lactation. PR dams showed higher skeletal muscle D1 activity only at the end of lactation, but no changes in D2 activity. Higher pituitary D1 and D2 activities in the PR group (P<0.05) at the end of lactation could have contributed to the lower serum TSH. These data suggest that the higher thyroid and BAT D2 activity during the whole of lactation and skeletal muscle D1 activity at the end of lactation may contribute to the higher serum T(3) in PR dams.

Thyroid and pituitary thyroxine-5'-deiodinase activity and thyrotrophin secretion in lithium-treated rats

Some authors have reported increased serum thyrotrophin (TSH) in animals chronically treated with lithium, suggesting that lithium might decrease pituitary thyroxine (T(4))-5'-deiodinase activity. On the other hand, the effect of lithium treatment on thyroidal T(4)-5'-deiodinase activity is also unknown. The present study was undertaken to evaluate the effects of lithium treatment on pituitary and thyroid T(4)-5'-deiodinase activity. Serum and pituitary TSH levels and thyroidal and pituitary T(4)-5'-deiodinase activities were determined in 3-month-old isogenic male Dutch-Miranda rats treated with lithium for 8 weeks. Chronic lithium treatment produced a slight increase in pituitary TSH content, but no change in serum TSH, and a significant increase in the thyroidal T(4)-5'-deiodinase activity. However, the pituitary T(4)-5'-deiodinase activity was unaffected by lithium administration. As far as we know, the present data show for the first time that chronic lithium treatment can increase the thyroxine to tri-iodothyronine conversion in the murine thyroid gland, be it directly or indirectly.

Inhibition of thyroid type 1 deiodinase activity by flavonoids

Some dietary flavonoids inhibit thyroperoxidase and hepatic deiodinase activity, indicating that these compounds could be classified as anti-thyroid agents. In this study, we evaluated the in vitro effect of various flavonoids on thyroid type 1 iodothyronine deiodinase activity (D1). D1 activity was measured in murine thyroid microsome fractions by the release of 125I from 125I-reverse T3. D1 activity was significantly inhibited by all the flavonoids tested; however, the inhibitory potencies on thyroid D1 activity differed greatly among them. A 50% inhibition of D1 activity (IC(50)) was obtained at 11 microM baicalein, 13 microM quercetin, 17 microM catechin, 55 microM morin, 68 microM rutin, 70 microM fisetin, 72 microM kaempferol and 77 microM biochanin A. Our data reinforce the concept that dietary flavonoids might behave as antithyroid agents, and possibly their chronic consumption could alter thyroid function.

Effect of medroxyprogesterone acetate on thyrotropin secretion in adult and old female rats

Steroid hormones have been implicated in the modulation of TSH secretion; however, there are few and controversial data regarding the effect of progesterone (Pg) on TSH secretion. Medroxyprogesterone acetate (MPA) is a synthetic alpha-hydroxyprogesterone analog that has been extensively employed in therapeutics for its Pg-like actions, but that also has some glucocorticoid and androgen activity. Both hormones have been shown to interfere with TSH secretion. The objective of the present study was to investigate the effects of MPA or Pg administration to ovariectomized (OVX) rats on in vivo and in vitro TSH release and pituitary TSH content. The treatment of adult OVX rats with MPA (0. 25 mg/100 g body weight, sc, daily for 9 days) induced a significant (P<0.05) increase in the pituitary TSH content, which was not observed when the same treatment was used with a 10 times higher MPA dose or with Pg doses similar to those of MPA. Serum TSH was similar for all groups. MPA administered to OVX rats at the lower dose also had a stimulatory effect on the in vitro basal and TRH-induced TSH release. The in vitro basal and TRH-stimulated TSH release was not significantly affected by Pg treatment. Conversely, MPA had no effect on old OVX rats. However, in these old rats, ovariectomy alone significantly reduced (P<0.05) basal and TRH-stimulated TSH release in vitro, as well as pituitary TSH content. The results suggest that in adult, but not in old OVX rats, MPA but not Pg has a stimulatory effect on TSH stores and on the response to TRH in vitro.