Maternal prolactin inhibition during lactation is associated to renal dysfunction in their adult rat offspring.

The renal function of rats whose mothers had hypoprolactinemia at the end of lactation was evaluated during development. Lactating Wistar rats were treated with bromocriptine (BRO, 1 mg twice a day, s.c.) or saline on days 19, 20, and 21 of lactation, and their male offspring were followed from weaning until 180 days old. 1 rat from each of the 12 litters/group was evaluated at 2 time points (90 and 180 days). Body and kidney weights, sodium, potassium, and creatinine were measured. Values were considered significant when p<0.05. Adult BRO-treated offspring presented higher body weight (+10%), lower relative renal weight at 90 and 180 days (-9.2% and -15.7%, respectively), glomerulosclerosis, and peritubular fibrosis. At 90 and 180 days, creatinine clearance was lower (-32% and -30%, respectively), whereas serum potassium was higher (+19% and +29%, respectively), but there were no changes in serum sodium. At 180 days, higher proteinuria (+36%) and serum creatinine levels (+20%) were detected. Our data suggest that prolactin inhibition during late lactation programs renal function damage in adult offspring that develops gradually, first affecting the creatinine clearance and potassium serum levels with further development of hyperproteinuria and higher serum creatinine, without affecting sodium. Thus, precocious weaning programs some components of the metabolic syndrome, which can be a risk factor for further development of kidney disease.

Prolactin inhibition at mid-lactation influences adiposity and thyroid function in adult rats.

Maternal hypoprolactinemia at the end of lactation (a precocious weaning model) increases milk leptin transfer and results in overweight, leptin resistance, and secondary hypothyroidism at adulthood. We studied the effects of prolactin (PRL) inhibition during mid-lactation (a partial malnutrition model) on milk leptin transfer, leptinemia, body composition, and thyroid function. Lactating rats were treated with bromocryptine (BRO, 1 mg/twice daily) or saline on days 7, 8, and 9 of lactation. Offspring were sacrificed 10, 21, and 90 days after birth. After treatment, BRO-treated dams showed hypoprolactinemia and hyperleptinemia, and produced less milk with lower levels of lactose and higher milk triglycerides. Milk leptin levels were lower at weaning. Offspring of BRO-treated dams had lower body weight and length as well as less visceral fat during lactation and adulthood. Total fat was also lower at weaning and adult life, whereas total protein was higher at 90 days-old. BRO offspring presented lower serum T4 and TSH at 10 days-old and weaning, respectively. When adults, these rats exhibited hypoleptinemia, lower levels of thyroid hormones, and higher TSH. Early inhibition of PRL therefore leads to offspring malnutrition and affects subsequent growth. Also, inhibition of PRL during lactation predisposes offspring to hypothyroidism; however, when the inhibition occurs during late lactation, the hypothyroidism is secondary, whereas when it is restricted to mid-lactation, the thyroid hypofunction is primary. The programming effect of milk suppression thus depends on the developmental stage of offspring.

Neonatal low-protein diet changes deiodinase activities and pituitary TSH response to TRH in adult rats.

Protein malnutrition during neonatal programs for a lower body weight and hyperthyroidism in the adult offspring were analyzed. Liver deiodinase is increased in such animals, contributing to the high serum triiodothyronine (T3) levels. The level of deiodinase activities in other tissues is unknown. We analyzed the effect of maternal protein restriction during lactation on thyroid, skeletal muscle, and pituitary deiodinase activities in the adult offspring. For pituitary evaluation, we studied the in vitro, thyrotropin-releasing hormone (TRH)-stimulated thyroid-stimulating hormone (TSH) secretion. Lactating Wistar rats and their pups were divided into a control (C) group, fed a normal diet (23% protein), and a protein-restricted (PR) group, fed a diet containing 8% protein. At weaning, pups in both groups were fed a normal diet until 180 days old. The pituitary gland was incubated before and after TRH stimulation, and released TSH was measured by radioimmunoassay. Deiodinase activities (D1 and D2) were determined by release of (125)I from [(125)I]reverse triiodothyronine (rT3). Maternal protein malnutrition during lactation programs the adult offspring for lower muscle D2 (-43%, P<0.05) and higher muscle D1 (+83%, P<0.05) activities without changes in thyroidal deiodinase activities, higher pituitary D2 activity (1.5 times, P<0.05), and lower TSH response to in vitro TRH (-56%, P<0.05). The evaluations showed that the lower in vivo TSH detected in adult PR hyperthyroid offspring, programmed by neonatal undernutrition, may be caused by an increment of pituitary deiodination. As described for liver, higher skeletal muscle D1 activity suggests a hyperthyroid status. Our data broaden the knowledge about the adaptive changes to malnutrition during lactation and reinforce the concept of neonatal programming of the thyroid function.

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 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.

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.

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 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.