Thyroid hormones and renal transport: cellular and biochemical aspects

Subclinical Hypothyroidism in Advanced Chronic Kidney Disease Patients: Prevalence and Associated Factors

Introduction

Renal function and thyroid metabolism are tightly related. However, evidence about subclinical hypothyroidism prevalence in patients with chronic kidney disease and its related factors is scarce.

Objectives

Our aim is to analyze subclinical hypothyroidism prevalence and its related factors in patients with advanced chronic kidney disease. Materials and methods. Nondialysis-dependent patients with chronic kidney disease at stages 3 to 5 were included. Other inclusion criteria were age above 18 years and clinical stability. Patients with diagnosed thyroid illnesses were excluded. Subclinical hypothyroidism was defined as thyroid stimulating hormone (TSH) > 5.3 mU/L, with free thyroxine 4 (FT4) between 0.54 and 1.24 ng/dl. Filiation data, comorbidities, and routine blood and urine test results were registered.

Results

A total of 299 patients were included. Of them, 184 (61.5%) were men. The mean age was 71 ± 13 years old. The mean glomerular filtration rate (CKD-EPI) was 22 ± 9 ml/min/1.73 m². According to chronic kidney disease stages, global distribution of patients was as follows: Stage 3, 67 patients (22.4%); Stage 4, 155 patients (51.8%); and Stage 5, 77 patients (25.8%). We found subclinical hypothyroidism in 54 (18.1%) patients. According to chronic kidney disease stages, distribution of affected patients was as follows: Stage 3, 9 patients (13%); Stage 4, 25 patients (16.1%); and Stage 5, 20 patients (26%). Differences among stages were statistically significant. By univariate analysis, factors related with subclinical hypothyroidism were as follows: age RR 1.048 (95% CI 1.019–1.078; p=0.001), hypertension RR 2.705 (95% CI 1.026–7.130; p=0.04), glomerular filtration rate RR 0.962 (95% CI 0.929–0.996; p=0.03), and proteinuria higher than 1 gram/day RR 2.387 (95% CI 1.303–4.374; p=0.005). By multivariate analysis adjusted by age, hypertension, glomerular filtration rate, proteinuria, diabetes, and cardiovascular disease history, only age RR 1.016 (95% CI 1.009–1.028; p=0.04) and glomerular filtration rate RR 0.963 (95% CI 0.930–0.997; p=0.03) preserved their independent association with subclinical hypothyroidism.

Conclusions

Subclinical hypothyroidism prevalence in patients with chronic kidney disease is high and increases with renal disease severity. Factors independently related to subclinical hypothyroidism are age and glomerular filtration rate.

Treatment of hypothyroidism improves glomerular filtration rate (GFR) in geriatric patients

Background/aim

Renal function of patients with hypothyroidism increases after reaching euthyroid state. There is no data regarding geriatric age group. The aim of the study was determined to investigate whether renal function of geriatric patients with hypothyroidism increases after they become euthyroid.

Materials and methods

Patients who were sixty-five years or older were retrospectively screened in two centers. TSH, T3, T4, creatinine, and eGFR calculated by CKD-EPI formula were recorded under the presence of accompanying hypothyroidism. The same variables were recorded after the patients became euthyroid.

Results

285 patients were included in the study, the median age was 73(65–84), and 234 patients were female. Patients were examined in four groups according to TSH values. There were 160 (56.1%) patients with TSH 5–9.9 uIU/mL, 60(21.1%) patients with TSH between 10–19.9 uIU/mL, 41(14.4 %) patients with TSH between 20–49.9 uIU/mL and 24(8.4%) patients with TSH> 50uIU/mL. There was a significant and negative correlation between the initial TSH values and the first calculated eGFR values (p: 0.001; r: –0.191). The median eGFR of the patients in hypothyroid cases was 66.59 (14.62–116.07), while the median eGFR value of patients was 69.6 (12.91–109.31) in the euthyroid state. This value obtained after thyroid replacement was significantly improved when compared to the first eGFR (p: 0.001). In logistic regression analysis, pretreatment TSH value was found to independently affect eGFR (p: 0.009; Exb: 1.017).

Conclusion

It has been observed that hypothyroidism treatment increases eGFR in geriatric patients. Similar results were obtained after studies with younger patients in the literature. This study is a study in which only geriatric age group patients were examined. It should be kept in mind that hypothyroidism which is not corrected in geriatric patients may also contribute to a decrease in eGFR.

Relationships of Chronic Kidney Disease and Thyroid Dysfunction in Non-Dialysis Patients: A Pilot Study

<b><i>Context:</i></b> Patients with chronic kidney disease (CKD) usually manifest with disorder of thyroid hormone; however, the correlation is unknown. <b><i>Objective:</i></b> The study was designed to explore the relationships between CKD and thyroid dysfunction. <b><i>Design, Setting, and Participants:</i></b> A total number of 905 non-dialysis participants were collected at Nanjing First Hospital from August 2009 to October 2012 according to the case records system. Patients were grouped via the estimated glomerular filtration rate (eGFR) according to the KDIGO guideline. Levels of thyroid hormone and biomarkers in different CKD groups were compared by ANOVA. Prevalence of different thyroid diseases was calculated by χ² test. <b><i>Results:</i></b> We found that FT3 or T3 became more prevalent with increasing eGFR with the lowest level in CKD5 (<i>p</i> <i>&#x3c;</i> 0.01). No significant differences were found between groups in FT4, T4, or TSH (<i>p</i> &#x3e; 0.05). Frequency of euthyroid sick syndrome (ESS) in CKD groups was high, especially in CKD stage 5 (69.1%, <i>p</i> &#x3c; 0.01). eGFR had positive correlation with T3 and FT3 (<i>r</i> = 0.239, <i>p</i> = 0.0001; <i>r</i> = 0.292, <i>p</i> = 0.0001). ESS had correlations with prealbumin, β2-microglobin, eGFR, and C-reactive protein (<i>r</i> = 0.095, <i>p</i> = 0.004; <i>r</i> = –0.12, <i>p</i> = 0.001; <i>r</i> = 0.091,<i> p</i> = 0.007; <i>r</i> = –0.096, <i>p</i> = 0.008; <i>r</i> = 0.154, <i>p</i> = 0.001). After adjustment for prealbumin, uric acid, HbA1c, age, gender, eGFR, and β2-microglobin, binary regression revealed that hemoglobin, C-reactive protein, and albumin were independent influence factors of ESS (<i>p</i> = 0.016, <i>r</i> = 1.014; <i>p</i> = 0.023, <i>r</i> = 1.007; <i>p</i> = 0.029, <i>r</i> = 0.996). <b><i>Conclusion:</i></b> CKD patients have a high morbidity of ESS, mainly low T3 syndrome. Anemia, inflammation, and malnutrition may contribute to ESS in CKD.

Effects of hypothyroidism on serotonin 1A receptors in the rat brain

PURPOSE

We investigated the effects of hypothyroidism on serotonin 1A receptors in the rat brain in vivo.

METHODS

Five surgically thyroidectomized male Sprague-Dawley (SD) rats and five hypophysectomized SD rats were used as animal models of hypothyroidism; the same number of sham-operated SD rats served as age-matched controls. After hypothyroidism was confirmed by thyroid function tests, serotonin positron emission tomography (PET) was performed for 120 min. All PET data were spatially normalized to T2-weighted magnetic resonance imaging templates; then, time-activity curves of the hippocampus, septum, and cerebellum were extracted using predefined volume-of-interest templates. Non-displaceable binding values in the hippocampus and septum were calculated using a multilinear reference tissue model and parametric maps were constructed. Both volume-of-interest and voxel-based analyses showed higher brain uptake in the thyroidectomized and hypophysectomized rats compared to the respective sham-operated rats.

RESULTS

Time-activity curves showed that the brain uptake values for the thyroidectomized and hypophysectomized groups were 21-52% higher than were those in the respective control groups. In the thyroidectomized group, the binding potential values for the hippocampus and septum were 20-26% higher than were those in the sham-thyroidectomized group. In the hypophysectomized group, the binding value for the hippocampus was 23% higher than was that in the sham-hypophysectomized group, whereas the septal binding was not significantly different from that in the sham-hypophysectomized group. Parametric maps for the hypothyroidism also showed significantly higher binding values than did those for the controls.

CONCLUSION

Our results demonstrate that hypothyroidism elevates serotonin 1A receptor binding in the limbic system.

Triiodothyronine regulates cell growth and survival in renal cell cancer

Triiodothyronine plays an important role in the regulation of kidney cell growth, differentiation and metabolism. Patients with renal cell cancer who develop hypothyreosis during tyrosine kinase inhibitor (TKI) treatment have statistically longer survival. In this study, we developed cell based model of triiodothyronine (T3) analysis in RCC and we show the different effects of T3 on renal cell cancer (RCC) cell growth response and expression of the thyroid hormone receptor in human renal cell cancer cell lines from primary and metastatic tumors along with human kidney cancer stem cells. Wild-type thyroid hormone receptor is ubiquitously expressed in human renal cancer cell lines, but normalized against healthy renal proximal tube cell expression its level is upregulated in Caki-2, RCC6, SKRC-42, SKRC-45 cell lines. On the contrary the mRNA level in the 769-P, ACHN, HKCSC, and HEK293 cells is significantly decreased. The TRβ protein was abundant in the cytoplasm of the 786-O, Caki-2, RCC6, and SKRC-45 cells and in the nucleus of SKRC-42, ACHN, 769-P and cancer stem cells. T3 has promoting effect on the cell proliferation of HKCSC, Caki-2, ASE, ACHN, SK-RC-42, SMKT-R2, Caki-1, 786-0, and SK-RC-45 cells. Tyrosine kinase inhibitor, sunitinib, directly inhibits proliferation of RCC cells, while thyroid hormone receptor antagonist 1-850 (CAS 251310‑57-3) has less significant inhibitory impact. T3 stimulation does not abrogate inhibitory effect of sunitinib. Renal cancer tumor cells hypostimulated with T3 may be more responsive to tyrosine kinase inhibition. Moreover, some tumors may be considered as T3-independent and present aggressive phenotype with thyroid hormone receptor activated independently from the ligand. On the contrary proliferation induced by deregulated VHL and or c-Met pathways may transgress normal T3 mediated regulation of the cell cycle.

Pleiotropic effects of thyroid hormones: learning from hypothyroidism

Hypothyroidism induces several metabolic changes that allow understanding some physiopathological mechanisms. Under experimental hypothyroid conditions in rats, heart and kidney are protected against oxidative damage induced by ischemia reperfusion. An increased resistance to opening of the permeability transition pore seems to be at the basis of such protection. Moreover, glomerular filtration rate of hypothyroid kidney is low as a result of adenosine receptors-induced renal vasoconstriction. The vascular tone of aorta is also regulated by adenosine in hypothyroid conditions. In other context, thyroid hormones regulate lipoprotein metabolism. High plasma level of LDL cholesterol is a common feature in hypothyroidism, due to a low expression of the hepatic LDL receptor. In contrast, HDL-cholesterol plasma levels are variable in hypothyroidism; several proteins involved in HDL metabolism and structure are expressed at lower levels in experimental hypothyroidism. Based on the positive influence of thyroid hormones on lipoprotein metabolism, thyromimetic drugs are promising for the treatment of dyslipidemias. In summary, hypothyroid status has been useful to understand molecular mechanisms involved in ischemia reperfusion, regulation of vascular function and intravascular metabolism of lipoproteins.

Biochemical markers of liver and kidney function are influenced by thyroid function-a case-controlled follow up study in Indian hypothyroid subjects

Thyroid hormones regulate the renal hemodynamics and basal metabolic rate of most cells. This hospital-based case-control study was done to evaluate the changes in biochemical markers of liver and kidney function in hypothyroid subjects before and after treatment. The study included 176 subjects randomly selected from Thyroid clinics. Serum T(3), T(4), TSH, Liver and Kidney Function tests were analysed using standard kits. Forty-six hypothyroid patients were re-evaluated 6 weeks after thyroxine substitution therapy. Hypothyroid subjects (n=80) showed significantly raised serum creatinine and uric acid levels as compared to euthyroid subjects (n=96). After 6 weeks of thyroxine replacement, serum creatinine and uric acid decreased significantly and were comparable to euthyroid group. A positive correlation of ALT, AST, uric acid, protein and albumin with TSH levels (p<0.05) and negative correlation of serum T(4) levels with ALT, AST, proteins (p<0.05) was observed in the hypothyroid group. Hypothyroidism results in reversible impairment of hepatorenal function.

Kidney growth in children with congenital hypothyroidism

The effect of hypothyroidism on kidney size has not been studied in children. The aim of this study was to examine the role of congenital hypothyroidism and levothyroxine (L-thyroxine) treatment on renal growth. Forty children with congenital hypothyroidism and 37 healthy controls were prospectively included. The mean age of patients was 8.2+/-4.7 years. Patients had lower height and weight standard deviation scores compared with controls. The mean L-thyroxine initial age and treatment duration were 37.0 and 60.5 months, respectively. In 62.5% of patients, L-thyroxine was initiated after 6 months of age, and 60.0% of patients had severe hypothyroidism. Patients had lower kidney length and total kidney volume compared with controls (P < 0.05). No significant differences were found in kidney volume/body weight and kidney volume/ body height ratios between patients and controls (P > 0.05). Multiple regression analysis showed significant relationship between relative kidney volume and average free thyroxine level (P < 0.05). No significant differences in kidney sizes were found between patients who had L-thyroxine initiated before and after 6 months of age or between mild/moderate and severe hypothyroidism at diagnosis (P > 0.05). In conclusion, normal renal growth can be accomplished with L-thyroxine replacement despite considerable delay in treatment initiation and/or severe hypothyroidism.

Thyroid hormones increase Na+–Pi co-transport activity in intestinal brush border membrane: Role of membrane lipid composition and fluidity

In the present study, we documented the promising role of thyroid hormones status in animals in modulation of Na+-Pi transport activity in intestinal brush border membrane vesicles (BBMV) which was accompanied with alterations in BBM lipid composition and fluidity. Augmentation of net Pi balance in hyperthyroid (Hyper-T) rats was fraternized with accretion of Pi transport across BBMV isolated from intestine of Hyper-T rats as compared to hypothyroid (Hypo-T) and euthyroid (Eu-T) rats while Na+-Pi transport across BBMV was decreased in Hypo-T rats relative to Eu-T rats. Increment in Na+-Pi transport in intestinal BBMV isolated from Hyper-T rats was manifested as an increase in the maximal velocity (Vmax) of Na+-Pi transport system. Furthermore, BBMV lipid composition profile in intestinal BBM from Hyper-T was altered to that of Hypo-T rats and Eu-T rats. The molar ratio of cholesterol/phospholipids was higher in intestinal BBM from Hypo-T rats. Fluorescence anistropy of diphenyl hexatriene (rDPH) and microviscosity were significantly decreased in the intestinal BBM of Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats which corroborated with the alteration in membrane fluidity in response to thyroid hormone status of animals. Therefore, thyroid hormone mediated change in membrane fluidity might play an important role in modulating Na+-Pi transport activity of intestinal BBM.

Hypothyroidism induces expression of the peptide transporter PEPT2

The kidney is a target organ for thyroid hormone action and a variety of renal transport processes are altered in response to impaired thyroid functions. To investigate the effect of thyroid hormone on the expression of the renal proximal tubular high-affinity-type H+-peptide cotransporter (PEPT2) in rats, hypothyroidism was induced in animals by administration of methimazole (0.05%) via drinking water. After 7 weeks of treatment, hypothyroidism was confirmed by determining serum free T3 and free T4 concentrations. Northern blotting was used to examine the expression of PEPT2 mRNA in kidney tissues from hypothyroid rats compared to control rats. Hypothyroidism resulted in an increased level of total renal PEPT2 mRNA (121.1±3.3% vs. control 100±2.8%; p=0.008). The mRNA results were confirmed by immuno-blotting, which demonstrated significantly increased protein levels (162% vs. control 100%; p<0.01). Immunohistochemistry also revealed increased PEPT2 protein levels in the proximal tubules of treated compared to non-treated rats. In summary, PEPT2 is the first proximal tubule transporter protein that shows increased expression in states of hypothyreosis. As PEPT2 reabsorbs filtered di- and tripeptides and peptide-like drugs, the present findings may have important implications in nutritional amino acid homeostasis and for drug dynamics in states of altered thyroid function.

Experimental hypothyroidism modifies specific binding of A1 and A2A analogues to adenosine receptors in the rat kidney

1 Binding kinetic studies with the adenosine analogues [3H]CPA (0.250-50 nm) and [3H]CGS21680 (0.1-100 nm) were performed in renal tissue from control (NL) and thyroidectomised (HTX) rats. We propose that the low renal adenosine content reported in hypothyroid rats may induce changes in the density and/or affinity of adenosine receptor, distributed in the cortex (C), outer medulla (OM), and inner medulla (IM) of the kidney. 2 [3H]CPA and [3H]CGS21680 binding saturation isotherms were fitted by nonlinear regression analysis and evaluated by Furchgott's method. These results revealed high (KH) and low (KL) affinity (KD) sites for both compounds. As expected, a heterogeneous pattern was observed for Bmax and KD values. 3 Bound [3H]CPA and [3H]CGS21680 were displaced by increasing concentrations of nonlabelled DPCPX and NECA, respectively, indicating the presence of A1 and A2A adenosine receptors distributed in the renal segments studied. 4 The relative intrinsic efficacy (epsilon) for [3H]CPA and [3H]CGS21680 showed extreme values (far from 1.0), 0.5 in IM NL and 2.70 in IM HTX for [3H]CGS21680. 5 Our results indicate that A2A adenosine receptor is predominant in IM from HTX, but A1 receptors are expressed preferentially in C in NL. 6 We conclude that the changes observed in number, affinity, and epsilon for the A2A receptor in IM from HTX might be responsible from alterations in medullary function, that is, incapacity for urine concentration as observed in the hypothyroid kidney.

Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats

Hypothyroidism is associated with significant abnormalities in the renal handling of salt and water. To address the involvement of tubular transport proteins in these abnormalities, rats were rendered pharmacologically hypothyroid and the abundance of major tubular transport proteins was assessed by immunoblot and immunohistochemistry. Hypothyroidism resulted in a marked reduction in kidney size and creatinine clearance along with decreased or unchanged total kidney abundance of the transport proteins. Whereas the proximal tubular type 3 Na/H exchanger (NHE3) and type 2 Na-phosphate cotransporter (NaPi2) stood out by their disproportionately reduced abundance, the bumetanide-sensitive type 2 Na-K-2Cl cotransporter (NKCC2) and aquaporin-2 (AQP2) were unaltered in their total kidney abundance despite a markedly lower kidney mass. The latter proteins in fact showed enhanced immunostaining. Decreased NHE3 and NaPi2 expression was most likely due to a combination of triiodo-l-thyronine (T(3)) deficiency along with a reduced glomerular filtration rate. The increased abundance of NKCC2 and AQP2 may have been caused by an increased action of vasopressin since urinary excretion of this hormone was elevated. On the other hand, the thiazide-sensitive Na-Cl cotransporter; the alpha-, beta-, and gamma-subunits of the amiloride-sensitive epithelial Na channel; and the alpha(1)-subunit of Na-K-ATPase showed a moderate decrease in total kidney abundance that was largely proportional to the smaller kidney mass. Although the observed expression of transporters was associated with a balanced renal sodium handling, altered transporter abundance may become functionally relevant if the hypothyroid kidney is challenged by an additional destabilization of the milieu interieur that has previously been shown to result in an inadequate natriuresis and clinical symptoms.

Molecular basis of renal handling of calcium in response to thyroid hormone status of rat

We investigated the effect of thyroid hormone status on renal handing of Ca2+. Further, like kinetics of Ca2+ transport across brush-border membrane (BBM) and basolateral membrane (BLM) of renal epithelial cells was carried out. FE(Ca) was decreased in hyperthyroid (Hyper-T) rats and increased in hypothyroid (Hypo-T) rats as compared to euthyroid (Eu-T) rats. Ca2+ uptake into renal brush-border membrane vesicles (BBMV) was increased in Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats. K(m) was lower in Hyper-T rats and higher in Hypo-T rats as compared to Eu-T rats whereas, V(max) remained unaltered. The transition temperature for calcium uptake varied inversely with the thyroid hormone status. Renal BBM of Hyper-T rats showed decreased anisotropy and polarisation of DPH as compared to EU-T rats whereas these values were increased in Hypo-T rats. Thus, the altered BBM fluidity appears to modulate Ca2+ transport across BBM. Na+/Ca2+ exchange activity of renal cells was increased in Hyper-T and decreased in Hypo-T rats as compared to Eu-T rats. V(max) for Na+/Ca2+ exchange was increased in Hyper-T rats and deceased in Hypo-T rats as compared to Eu-T rats, whereas, [Na+](0.5) was similar in all three groups. The c-AMP levels of renal cortex of Hyper-T rats was increased and that of Hypo-T rats decreased as compared to Eu-T rats. Thus, thyroid hormones increased Ca2+ reabsorption in the kidney of rat. Thyroid hormone-mediated modulation of BBM fluidity appears to stimulate Ca2+ uptake into renal BBMV. Thyroid hormones possibly activated the Na+/Ca2+ exchanger through cAMP-dependent pathway.

Renal handling of amino acids in 5/6-nephrectomized rats: stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

In anaesthetized adult female rats, the renal amino acid handling was measured six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indicate an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FEAA) of most endogenous amino acids measured were significantly enhanced. After bolus injection of leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/ 100 g b.wt.), dissolved in 2 ml normal saline per 100 g b.wt., the FEAA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more pronounced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FEAA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20 micrograms/100 g b.wt.) or dexamethasone (60 micrograms/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: the increase in FEAA after amino acid load was significantly lower compared to non-pretreated animals. This stimulation could be shown for the bolus amino acids and the endogenous amino acids and was more distinct in 5/6NX rats than in controls with two intact kidneys.

Prevalence and severity of hyponatremia and hypercreatininemia in short-term uncomplicated hypothyroidism

Hypothyroidism is widely accepted as a cause of hyponatremia and hypercreatininemia. However, the prevalence and severity of hyponatremia and hypercreatininemia in hypothyroid patients without comorbid conditions have not been well documented. We retrospectively studied serum sodium and creatinine levels in thyroid-ablated patients with differentiated thyroid cancer off (no.=128) and on (no.=60) thyroid hormone therapy. In the hypothyroid state, mean(+/-SD) TSH, sodium, and creatinine levels were 130.3+/-104.8 mU/l, 139.3+/-2.7 mEq/l, and 89.4+/-20 mmol/l respectively. Twenty-four patients (18.8%) had creatinine levels above the age- and sex-adjusted normal range, whereas only five patients (3.9%) had sodium levels below 135 mEq/l. No patient had a sodium level less than 130 mEq/l. Compared to their euthyroid values, mean sodium and creatinine levels of the hypothyroid patients changed by -1.18 mEq/l (p=0.003) and 17.2 mmol/l (p<0.0001), respectively. There was significant correlation of TSH levels in the hypothyroid state with the changes from the euthyroid state to the hypothyroid state in creatinine levels (r=0.29, p=0.02) but not with the corresponding changes in sodium levels (r=0.06, p=0.6). In thirty-seven patients studied in two hypothyroid episodes, there was a significant correlation between a) TSH levels in hypothyroid state 1 and hypothyroid state 2 (r=0.56, p=0.0003), and b) the change in creatinine levels from the euthyroid state to hypothyroid state 1 and the corresponding change from the euthyroid state to hypothyroid state 2 (r=0.48, p=0.003). There was no significant correlation between the change in sodium levels from the euthyroid state to hypothyroid state 1 and the corresponding change from the euthyroid state to hypothyroid state 2 (r=0.32, p=0.05). We conclude that hyponatremia is very uncommon, whereas mild to moderate elevation in serum creatinine level is not uncommon in patients with short-term uncomplicated hypothyroidism.

Changes of renal taurine transport after treatment with triiodothyronine or dexamethasone in amino acid loaded rats

In adult female anaesthetized rats, the influence of triiodothyronine or dexamethasone on renal amino acid (AA) handling was investigated in taurine (45 mg/100 g b.wt.) loaded animals. Bolus injections of taurine were followed by temporary increase in fractional excretion (FE(AA)) of taurine as well of the endogenous amino acids which were not administered. Under taurine load conditions, triiodothyronine treatment (20 microg/100 g b.wt. for 3 days, i.p. once daily) was followed by a slight stimulation of the renal taurine reabsorption: the increase in FE(taurine) after taurine load was lower than in untreated rats. Dexamethasone (60 microg/100 g b.wt. for 3 days, i.p. once daily) was without significant effect on FE(taurine) in taurine loaded rats. In non taurine loaded rats there was no hormone influence at all. Similarities and differences between the effects of bolus injections of taurine, glutamine, and leucine on the FE(AA) of these three amino acids were compared in detail to further clarify the reason for the increased amino acid reabsorption capacity after pretreatment with triiodothyronine or dexamethasone.

The hepato-renal syndrome: renal amino acid transport in bile duct ligated rats (DL)--influence of treatment with triiodothyronine or dexamethasone on renal amino acid handling in amino acid loaded rats

The influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in anaesthetized, bile duct-ligated (DL) adult female rats. 3 days after DL, glomerular filtration rate (GFR) was unchanged whereas urine flow was decreased. Plasma concentrations of 5 out of 16 amino acids were significantly enhanced after DL. On the other hand, the fractional excretion (FE) of 11 out of 16 amino acids was significantly reduced as a sign of improved reabsorption capacity. Bolus injections of leucine (20 mg/100 g b.wt.), glutamine (45 mg/100 g b.wt.), or taurine (45 mg/100 g b.wt.) were followed by a temporary increase in the FE of the administered amino acids as well of the endogenous amino acids which were not administered. This phenomenon was more pronounced in DL than in control rats. Under load conditions, dexamethasone (60 microg/100 g b.wt.) or triiodothyronine (20 microg/100 g b.wt.) treatment for 3 days, i.p. once daily, was followed by a stimulation of renal amino acid reabsorption in DL rats. The increase in fractional amino acid excretion after amino acid load was significantly lower than in untreated rats. This effect was also more pronounced in DL rats.

Influence of sex differences on the renal secretion of organic anions

The kidney's responsiveness to male sexual hormones has been often neglected. Renal secretion of organic anions is higher in male than in female individuals; as a consequence, most of the xenobiotics that are excreted from the organism through this pathway are eliminated more rapidly by males than by female animals. To gain further insight into this issue, we studied in vitro and in vivo characteristics of the transport of p-aminohippurate (PAH), a suitable marker for this system, in male and female rats, under different hormonal conditions. Kinetics of PAH showed a shorter elimination half-time in male than in female rats (t(1/2el): male = 16.2 +/- 2.1 min, female = 25.7 +/- 4.5 min, P < 0.05). Castration of male rats increased t(1/2el) to a value similar to that of female rats (t(1/2el): orchiectomized rat = 28.1 +/- 7.1 min). Testosterone treatment of female rats increased the elimination rate to a value similar to that of male rats. In vitro PAH uptake by renal cortical slices from intact male rats was higher than that by slices from orchiectomized rats. Kinetic analyses of PAH uptake suggest that the difference was caused by a lower number of transporting molecules in orchiectomized than in intact animals, whereas the transporting capacity for each carrier was similar in male and in orchiectomized rats. Our results suggest that testosterone increases the number of functional carriers for PAH in the kidney.

Maturation of rat renal phosphate transport: effect of triiodothyronine

1. Prevention of weaning prevents the increase in the carrier affinity for Na(+)-cotransported phosphate (Pi) and the normal elevation of plasma 3,5,3'-triiodothyronine (T3) which occur between postnatal days 14 and 21. 2. This study examines the possible role of T3 in the control of the maturation process of Pi transport. Clearance experiments and brush-border membrane studies were performed on 14-day-old rats given T3. 3. The fractional excretion of Pi of T3-treated rats was 33% lower compared with controls (P < 0.01). After Pi perfusion, it remained at a lower level, and the amount of Pi reabsorbed per minute, corrected for the glomerular filtration rate (RPi/GFR), was higher. 4. The membrane vesicles from 14-day-old rats given T3 showed a 30% increase in carrier affinity for Na(+)-cotransported Pi. In addition to this maturational effect of T3, a 46% increase in Vmax was also observed. 5. The amount of immunoreactive Pi transporter, detected using anti-(NaPi-2) antiserum, was increased in T3-treated rats. 6. Glucose transport, another Na(+)-dependent transport system, was not altered by T3. 7. It is concluded that exogenous T3 given before the third postnatal week specifically induced precocious maturation of renal Pi transport in 14-day-old rats, suggesting that thyroid hormone is normally involved in this maturation.

Thyroid hormone upregulates gene expression, synthesis and release of pro-epidermal growth factor in adult rat kidney

Attempts were made to elucidate whether thyroid hormone upregulates renal pro-epidermal growth factor (pro-EGF) gene expression, biosynthesis and release in adult rats which were rendered hypothyroid. Predominantly pro-EGF was detected in renal cortex, whereas pro-EGF and its degraded species were found in urine. We demonstrated that T3 increased pro-EGF levels in renal cortex to 2.2 +/- 0.17, 2.37 +/- 0.19, 2.73 +/- 0.25, and 3.10 +/- 0.45 fold within day 1, 2, 4 and 8, respectively following treatment. Immunoreactive EGF, assessed by immunohistochemical methods, was confined in the distal convoluted tubule and thick ascending limb of Henle. T3 markedly enhanced the density of irEGF in these nephrons. T3 augmented the concentration of urinary irEGF to 2.1, 2.2, 2.8 and 3.6 fold within day 1, 2, 4 and 8 and the abundance of urine pro-EGF to 2.53 +/- 1.39, 3.8 +/- 0.70, 3.59 +/- 1.48 fold within day 1, 2, 4, respectively. Moreover, we employed reverse transcriptase/polymerase chain reaction method to analyze relative abundance of pro-EGF mRNA in kidneys of various thyroid states and found T3 markedly increased pro-EGF mRNA levels after treatment of 1, 2 and 4 days. These results indicated that thyroid hormone augmented the gene expression, biosynthesis and excretion of pro-EGF in adult rat kidney.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Effects of triiodothyronine and dexamethasone on plasma and tissue angiotensin converting enzyme in the rat

In order to identify tissue specific regulation of angiotensin converting enzyme (ACE), the effects of dexamethasone (0.04 mg sc per day for 7 days) and triiodothyronine (T3) (0.5 mg/kg sc per day for 10 days) on ACE activity were investigated in different tissues in male Wistar rats. ACE activity was measured by fluorimetry in the plasma, heart, lung and kidney. In the kidney, ACE activity was measured in the medulla, cortex and brush border of proximal tubular cells and 3H-ramiprilat binding was used to characterise the changes in brush border ACE activity. Dexamethasone elicited a significant increase in lung ACE activity and a significant decrease in plasma ACE activity, but did not alter enzyme activity in the other tissues studied. T3 produced a significant decrease in lung ACE activity and an increase in ACE activity in the plasma and heart. In the kidney, ACE activity was not modified in the medulla whereas in the cortex and brush border ACE activity was doubled. This increase in ACE activity corresponded to a similar increase in the maximum number of binding sites of 3H-ramiprilat, suggesting that the increase in activity corresponded to an increase in the ACE level. The increased heart and kidney ACE activity in response to T3 may contribute to the cardiovascular effects of thyroid hormones through increased local angiotensin II generation. These results show that under dexamethasone or T3, ACE activity can vary from one tissue to another, suggesting that the ACE regulatory mechanism acts differently in each tissue.

Tissue-specific regulation of the expression of rat kallikrein gene family members by thyroid hormone

We have altered the thyroid hormonal status of both male and female rats and examined the expression of six functional members of the rat kallikrein gene family (PS, S1, S2, S3, K1 and P1) in the submandibular gland (SMG), kidney, prostate, testis and anterior pituitary gland (AP) of these animals. On Northern-blot analysis with gene-specific oligonucleotide probes, the steady-state mRNA levels of S1, S2, S3, K1 and P1 were all dramatically altered in the SMG of male and female rats treated with propylthiouracil (PTU; 100 mg/litre of drinking water) or thyroxine (T4; 10 micrograms/100 mg body wt.) for 3 weeks. The SMG mRNA levels of these five genes were all lowered (30-90%) in hypothyroid (PTU-treated) male and female rats and elevated (1.4-4-fold, male; 1.5-11-fold, female) in the hyperthyroid (T4-treated) and PTU/T4-treated animals. In contrast, PS (true kallikrein) mRNA levels in the male or female SMG or kidney were essentially unchanged. K1 mRNA levels in the kidney were considerably less responsive to thyroid status than those in the SMG. Changes in S3 and P1 mRNA levels in the prostate were also variable, but essentially unaffected by these treatments. AP PS mRNA levels were also unaffected by changes in thyroid-hormonal status, as were levels of a novel P1-like mRNA in the testis. In summary, these studies demonstrate that the same kallikrein gene family member(s) may be differentially regulated by thyroid hormones in the rat SMG, kidney, prostate and pituitary, and thus further extend the concept of tissue-specific expression and hormonal regulation of the kallikrein gene family in the rat.