Propylthiouracil-treated Rats Research Articles

Curcumin exerts protective effects on the thyroid gland in propylthiouracil-treated rats.

Among the plant ingredients, some compounds interfere with the functions of the thyroid gland. However, there is limited research on the effect of curcumin (CMN) on the functions of this gland. The aim of this study was to analyze the effect of CMN on morphology, histochemical reactivity of cytochrome c oxidase (CCO) and secretion functions of the thyroid gland under conditions of hypothyroidism induced by propylthiouracil (PTU). The rats were treated for 30 days by gavage with CMN (100 mg/kg b.w.) and/or PTU (1 mg/kg b.w.). Control rats received vehicle only. Histomorphometric tests were performed on the thyroid glands, cytochrome c oxidase activity was visualized using the histochemical method, and the levels of thyroid hormones were measured using the radioimmunoassay method. Rats receiving PTU showed compensatory changes in their thyroid glands, including a significant increase in thyroid epithelium height, a decrease in colloid volumen density, a decrease in the percentage of small follicles, an increase in medium-sized follicles compared to the control group, as well as a significant increase in CCO histochemical reactivity in the columnar epithelium and a decrease in FT4 serum level compared to the control group. The administration of CMN reversed these adverse changes caused by PTU. The PTU + CMN group exhibited a significant decrease in the height of the thyroid follicle epithelium compared to the PTU group. The percentage of small and medium-size follicles in the CMN + PTU group did not differ from the control group. Furthermore, CCO reactivity in the cubic epithelium and serum FT4 levels increased compared to the PTU group. Administration of CMN alone resulted in a significant increase in FT4 levels compared to the control group. The administration of CMN to rats with induced hypothyroidism resulted in a reduction of hyperplasia, hypertrophy, and increase in secretory activity of the thyroid gland. These findings suggest the protective effect of CMN against induced hypothyroidism.

Study of the Expression Transition of Cardiac Myosin Using Polarization-Dependent SHG Microscopy

Detection of the transition between the two myosin isoforms α- and β-myosin in living cardiomyocytes is essential for understanding cardiac physiology and pathology. In this study, the differences in symmetry of polarization spectra obtained from α- and β-myosin in various mammalian ventricles and propylthiouracil-treated rats are explored through polarization-dependent second harmonic generation microscopy. Here, we report for the, to our knowledge, first time that α- and β-myosin, as protein crystals, possess different symmetries: the former has C6 symmetry, and the latter has C3v. A single-sarcomere line scan further demonstrated that the differences in polarization-spectrum symmetry between α- and β-myosin came from their head regions: the head and neck domains of α- and β-myosin account for the differences in symmetry. In addition, the dynamic transition of the polarization spectrum from C6 to C3v line profile was observed in a cell culture in which norepinephrine induced an α- to β-myosin transition.

L71F mutation in rat cardiac troponin T augments crossbridge recruitment and detachment dynamics against α-myosin heavy chain, but not against β-myosin heavy chain.

The N-terminal extension of human cardiac troponin T (TnT), which modulates myofilament Ca2+ sensitivity, contains several hypertrophic cardiomyopathy (HCM)-causing mutations including S69F. However, the functional consequence of S69F mutation is unknown. The human analog of S69F in rat TnT is L71F (TnTL71F). Because the functional consequences due to structural changes in the N-terminal extension are influenced by the type of myosin heavy chain (MHC) isoform, we hypothesized that the TnTL71F-mediated effect would be differently modulated by α- and β-MHC isoforms. TnTL71F and wild-type rat TnT were reconstituted into de-membranated muscle fibers from normal (α-MHC) and propylthiouracil-treated rat hearts (β-MHC) to measure steady-state and dynamic contractile parameters. The magnitude of the TnTL71F-mediated attenuation of Ca2+-activated maximal tension was greater in α- than in β-MHC fibers. For example, TnTL71F attenuated maximal tension by 31% in α-MHC fibers but only by 10% in β-MHC fibers. Furthermore, TnTL71F reduced myofilament Ca2+ sensitivity by 0.11 pCa units in α-MHC fibers but only by 0.05 pCa units in β-MHC fibers. TnTL71F augmented rate constants of crossbridge recruitment and crossbridge detachment dynamics in α-MHC fibers but not in β-MHC fibers. Collectively, our data demonstrate that TnTL71F induces greater contractile deficits against α-MHC than against β-MHC background.

Interplay between the effects of a Protein Kinase C phosphomimic (T204E) and a dilated cardiomyopathy mutation (K211Δ or R206W) in rat cardiac troponin T blunts the magnitude of muscle length-mediated crossbridge recruitment against the β-myosin heavy chain background

Failing hearts of dilated cardiomyopathy (DCM)-patients reveal systolic dysfunction and upregulation of several Protein Kinase C (PKC) isoforms. Recently, we demonstrated that the functional effects of T204E, a PKC phosphomimic of cardiac troponin T (TnT), were differently modulated by α- and β-myosin heavy chain (MHC) isoforms. Therefore, we hypothesized that the interplay between the effects of T204E and a DCM-linked mutation (K211Δ or R206W) in TnT wouldmodulate contractile parameters linked-to systolic function in an MHC-dependent manner. To test our hypothesis, five TnT variants (wildtype, K211Δ, K211Δ+T204E, R206W, and R206W+T204E) were generated and individually reconstituted into demembranated cardiac muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rats. Steady-state and mechano-dynamic measurements were performed on reconstituted fibers. Myofilament Ca(2+) sensitivity (pCa50) was decreased by both K211Δ and R206W to a greater extent in α-MHC fibers (~0.15pCa units) than in β-MHC fibers (~0.06pCa units). However, T204E exacerbated the attenuating influence of both mutants on pCa50 only in β-MHC fibers. Moreover, the magnitude of muscle length (ML)-mediated crossbridge (XB) recruitment was decreased by K211Δ+T204E (~47%), R206W (~34%), and R206W+T204E (~36%) only in β-MHC fibers. In relevance to human hearts, which predominantly express β-MHC, our data suggest that the interplay between the effects of DCM mutations, PKC phosphomimic in TnT, and β-MHC lead to systolic dysfunction by attenuating pCa50 and the magnitude of ML-mediated XB recruitment.

Rat cardiac troponin T mutation (F72L)-mediated impact on thin filament cooperativity is divergently modulated by α- and β-myosin heavy chain isoforms.

The primary causal link between disparate effects of human hypertrophic cardiomyopathy (HCM)-related mutations in troponin T (TnT) and α- and β-myosin heavy chain (MHC) isoforms on cardiac contractile phenotype remains poorly understood. Given the divergent impact of α- and β-MHC on the NH2-terminal extension (44-73 residues) of TnT, we tested if the effects of the HCM-linked mutation (TnTF70L) were differentially altered by α- and β-MHC. We hypothesized that the emergence of divergent thin filament cooperativity would lead to contrasting effects of TnTF70L on contractile function in the presence of α- and β-MHC. The rat TnT analog of the human F70L mutation (TnTF72L) or the wild-type rat TnT (TnTWT) was reconstituted into demembranated muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts to measure steady-state and dynamic contractile function. TnTF72L-mediated effects on tension, myofilament Ca(2+) sensitivity, myofilament cooperativity, rate constants of cross-bridge (XB) recruitment dynamics, and force redevelopment were divergently modulated by α- and β-MHC. TnTF72L increased the rate of XB distortion dynamics by 49% in α-MHC fibers but had no effect in β-MHC fibers; these observations suggest that TnTF72L augmented XB detachment kinetics in α-MHC, but not β-MHC, fibers. TnTF72L increased the negative impact of strained XBs on the force-bearing XBs by 39% in α-MHC fibers but had no effect in β-MHC fibers. Therefore, TnTF72L leads to contractile changes that are linked to dilated cardiomyopathy in the presence of α-MHC. On the other hand, TnTF72L leads to contractile changes that are linked to HCM in the presence of β-MHC.

Effects of pseudo-phosphorylated rat cardiac troponin T are differently modulated by α- and β-myosin heavy chain isoforms.

Interplay between the protein kinase C (PKC)-mediated phosphorylation of troponin T (TnT)- and myosin heavy chain (MHC)-mediated effects on thin filaments takes on a new significance because: (1) there is significant interaction between the TnT- and MHC-mediated effects on cardiac thin filaments; (2) although the phosphorylation of TnT by PKC isoforms is common to both human and rodent hearts, human hearts predominantly express β-MHC while rodent hearts predominantly express α-MHC. Therefore, we tested how α- and β-MHC isoforms differently affected the functional effects of phosphorylated TnT. Contractile measurements were made on cardiac muscle fibers from normal rats (α-MHC) and propylthiouracil-treated rats (β-MHC), reconstituted with the recombinant phosphomimetic-TnT (T204E; threonine 204 replaced by glutamate). Ca2+ -activated maximal tension decreased differently in α-MHC + T204E (~68%) and β-MHC + T204E (~35%). However, myofilament Ca2+ sensitivity decreased similarly in α-MHC + T204E and β-MHC + T204E, demonstrating that a decrease in Ca2+ sensitivity alone cannot explain the greater attenuation of tension in α-MHC + T204E. Interestingly, dynamic contractile parameters (rates of tension redevelopment, crossbridge (XB) recruitment dynamics, XB distortion dynamics, and XB detachment kinetics) decreased only in α-MHC + T204E. Thus, the transition of thin filaments from the blocked- to closed-state was attenuated in α-MHC + T204E and β-MHC + T204E, but the closed- to open-state transition was attenuated only in α-MHC + T204E. Our study demonstrates that the effects of phosphorylated TnT and MHC isoforms interact to bring about different functional states of cardiac thin filaments.

Effects of Pseudophosphorylation of Rat Cardiac Troponin T Residue 204 are Differently Affected by α- and β-Myosin Heavy Chain Isoforms

We tested our hypothesis that α-myosin heavy chain (MHC) and β-MHC differently modulate the functional effects of protein kinase C (PKC)-mediated phosphorylation of rat cardiac troponin T (RcTnT). We generated a chimeric pseudophosphorylated RcTnT in which the threonine 204 was replaced by glutamic acid (cTnTT204E) to mimic the PKC-mediated phosphorylation effect. Recombinant proteins were reconstituted into detergent-skinned cardiac muscle fibers from normal rats expressing α-MHC or propylthiouracil-treated rats expressing β-MHC.

Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T

Divergent effects of α– and β–myosin heavy chain (MHC) isoforms on contractile behavior arise mainly because of their impact on thin filament cooperativity. The N terminus of cardiac troponin T (cTnT) also modulates thin filament cooperativity. Our hypothesis is that the impact of the N terminus of cTnT on thin filament activation is modulated by a shift from α- to β-MHC isoform. We engineered two recombinant proteins by deleting residues 1–43 and 44–73 in rat cTnT (RcTnT): RcTnT1–43Δ and RcTnT44–73Δ, respectively. Dynamic and steady-state contractile parameters were measured at sarcomere length of 2.3 µm after reconstituting proteins into detergent-skinned muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts. α-MHC attenuated Ca2+-activated maximal tension (∼46%) in RcTnT1–43Δ fibers. In contrast, β-MHC decreased tension only by 19% in RcTnT1–43Δ fibers. Both α- and β-MHC did not affect tension in RcTnT44–73Δ fibers. The instantaneous muscle fiber stiffness measurements corroborated the divergent impact of α- and β-MHC on tension in RcTnT1–43Δ fibers. pCa50 (-log of [Ca2+]free required for half-maximal activation) decreased significantly by 0.13 pCa units in α-MHC + RcTnT1–43Δ fibers but remained unaltered in β-MHC + RcTnT1–43Δ fibers, demonstrating that β-MHC counteracted the attenuating effect of RcTnT1–43Δ on myofilament Ca2+ sensitivity. β-MHC did not alter the sudden stretch–mediated recruitment of new cross-bridges (ER) in RcTnT1–43Δ fibers, but α-MHC attenuated ER by 36% in RcTnT1–43Δ fibers. The divergent impact of α- and β-MHC on how the N terminus of cTnT modulates contractile dynamics has implications for heart disease; alterations in cTnT and MHC are known to occur via changes in isoform expression or mutations.

Effects of the N-Terminus of Cardiac Troponin T on Contractile Activation Depend on the Type of Myosin Heavy Chain Isoform

We have previously shown that two specific regions (residues 1-43 and residues 44-73) in rat cardiac troponin T (RcTnT) have divergent effects on contractile function against an α-myosin heavy chain (α-MHC) background (Mamidi et al., Abstract: Biophys J, vol.100, Issue 3, p586a, 2010). Because the effects of Tn isoforms are modulated by an interplay with MHC, we hypothesized that the divergent effects of residues 1-43 and residues 44-73 in cTnT would be further modulated by a shift in MHC isoform to β-MHC. This has a direct bearing on understanding the effects of alterations in cTnT and MHC isoforms not only in health but also in disease. We generated two recombinant mutants (RcTnT1-43 and RcTnT44-73) by deleting residues 1-43 and 44-73 in RcTnT, respectively. We studied contractile function by reconstituting RcTnT1-43 and RcTnT44-73 recombinant proteins into detergent-skinned papillary muscle fibers from normal rat hearts (α-MHC) and propylthiouracil-treated rat hearts (β-MHC). Our data shows that functional alterations induced by RcTnT1-43 and RcTnT44-73 were different in α-MHC vs. β-MHC fibers. For example, RcTnT1-43 decreased both Ca2+-activated maximal tension (by ∼46%) and myofilament Ca2+-sensitivity (by 0.09 pCa units) in α-MHC fibers. However, RcTnT1-43 modestly decreased maximal tension (by ∼18%), with no effect on Ca2+-sensitivity in β-MHC fibers. Thus, the desensitizing effect of RcTnT1-43 was attenuated by β-MHC. Ca2+-activated maximal tension data were supported by myofiber dynamic stiffness measurements. Another major finding is that RcTnT44-73 abolished the sarcomere length-dependent increase in Ca2+-sensitivity in β-MHC, but not in α-MHC fibers. Thus, our data demonstrates that the functional outcome of the N-terminus of cTnT is modulated by the type of MHC isoform present.

Experimental Hypothyroidism Delays Field Excitatory Post‐Synaptic Potentials and Disrupts Hippocampal Long‐term Potentiation in the Dentate Gyrus of Hippocampal Formation and Y‐Maze Performance in Adult Rats

Manipulations of thyroid hormones have been shown to influence learning and memory. Although a large body of literature is available on the effect of thyroid hormone deficiency on learning and memory functions during the developmental stage, electrophysiological and behavioural findings, particularly on propylthiouracil administration to adult normothyroid animals, are not satisfactory. The experiments in the present study were carried out on 12 adult male Wistar rats aged 6-7 months. Hypothyroidism was induced by administering 6-n-propyl-2-thiouracil in their drinking water for 21 days at a concentration of 0.05%. The spatial learning performance of hypothyroid and control rats was studied on a Y-maze. The rats were then placed in a stereotaxic frame under urethane anaesthesia. A bipolar tungsten electrode was used to stimulate the medial perforant path. A glass micropipette was inserted into the granule cell layer of the ipsilateral dentate gyrus to record field excitatory post-synaptic potentials. After a 15-min baseline recording of field potentials, long-term potentiation was induced by four sets of tetanic trains. The propylthiouracil-treated rats showed a significantly attenuated input-output (I/O) relationship when population spike (PS) amplitudes and field excitatory post-synaptic potentials (fEPSP) were compared. fEPSP and PS latencies were found to be longer in the hypothyroid group than in the control group. The PS amplitude and fEPSP slope potentiations in the hypothyroid rats were not statistically different from those in the control rats, except for the field EPSP slope measured in the post-tetanic and maintenance phases. The hypothyroid rats also showed lower thyroxine levels and poor performance in the spatial memory task. The present study provides in vivo evidence for the action of propylthiouracil leading to impaired synaptic plasticity, which might explain deficit in spatial memory tasks in adult hypothyroid rats.

Critical role of cyclin D3 in TSH-dependent growth of thyrocytes and in hyperproliferative diseases of the thyroid gland.

We report that cyclin D3 is rate limiting for G1 progression in thyroid follicular cells and that its constitutive upregulation by chronic stimulation of the TSH/cAMP pathway plays a role in human and experimental hyperproliferative diseases of the thyroid gland. These conclusions are supported by in vitro and in vivo studies. In rat thyrocytes (PC Cl 3 cells), cyclin D3 expression is enhanced in response to activation of the TSH/cAMP pathway. Interference with the expression of G1 cyclins (in particular cyclin D3) by the antisense methodology strongly reduced TSH-dependent proliferation of PC Cl 3 cells, indicating that proper progression through G1 requires cyclin D3. Accordingly, PC Cl 3 cells engineered to overexpress cyclin D3 (PC-D3 cells) show enhanced growth rate and elude hormone-dependence and contact inhibition. Using an animal experimental model of thyroid stimulation, we demonstrate that cyclin D3 is a key mediator of TSH-dependent proliferation of thyroid follicular cells also in vivo. Cyclin D3 protein levels were higher in the thyrocytes from glands of propylthiouracil-treated rats compared with control animals. The increase in cyclin D3 expression occurred after the propylthiouracil-induced increase in TSH levels and preceded the burst of cell proliferation. Finally, we found that cyclin D3 protein is expressed in a fraction of human goiters but it is strongly overexpressed in most follicular adenomas.

Thyroid hormone enhances aggrecanase-2/ADAM-TS5 expression and proteoglycan degradation in growth plate cartilage.

Effects of thyroid hormone on proteoglycan degradation in various regions of cartilage were investigated. In propylthiouracil-treated rats with hypothyroidism, proteoglycan degradation in epiphyseal cartilage during endochondral ossification was markedly suppressed. However, injections of T(4) reversed this effect of propylthiouracil on proteoglycan degradation. In pig growth plate explants, T(3) also induced breakdown of proteoglycan. T(3) increased the release of aggrecan monomer and core protein from the explants into the medium. Accordingly, the level of aggrecan monomer remaining in the tissue decreased after T(3) treatment, and the monomer lost hyaluronic acid-binding capacity, suggesting that the cleavage site is in the interglobular domain. The aggrecan fragment released from the T(3)-exposed explants underwent cleavage at Glu(373)-Ala(374), the major aggrecanase-cleavage site. The stimulation of proteoglycan degradation by T(3) was less prominent in resting cartilage explants than in growth plate explants and was barely detectable in articular cartilage explants. Using rabbit growth plate chondrocyte cultures, we explored proteases that may be involved in T(3)-induced aggrecan degradation and found that T(3) enhanced the expression of aggrecanase-2/ADAM-TS5 (a disintegrin and a metalloproteinase domain with thrombospondin type I domains) mRNA, whereas we could not detect any enhancement of stromelysin, gelatinase, or collagenase activities or any aggrecanase-1/ADAM-TS4 mRNA expression. We also found that the aggrecanse-2 mRNA level, but not aggrecanase-1, increased at the hypertrophic stage during endochondral ossification. These findings suggest that aggrecanse-2/ADAM-TS5 is involved in aggrecan breakdown during endochondral ossification, and that thyroid hormone stimulates the aggrecan breakdown partly via the enhancement of aggrecanase-2/ADAM-TS5.

Acute inhibitory effect of excess iodide on ornithine decarboxylase in the thyroid of propylthiouracil-treated rats.

Polyamines such as putrescine, spermidine and spermine have been thought to play an important role in thyroid growth induced by goitrogens. Reduced biosynthesis of these polyamines might play a role in the antigoitrogenic effects of excess iodide. This study was designed to examine the effect of potassium iodide (KI) on ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Thyroidal ODC activity, protein content and mRNA were increased in rats made hypothyroid by 10 days of propylthiouracil treatment. The increase in ODC activity was suppressed after subcutaneous injection of KI (13mg/kg body weight); the apparent half-life of ODC activity after the treatment was estimated to be 19 min and the maximum suppression (90%) was seen 60 min after the treatment. On the other hand, administration of iodine-containing compounds including L-thyroxine, L-di-iodotyrosine,amiodarone, iopanoic acid and erythrosine showed no significant effect on ODC activity. The inhibitory effect of excess iodide was not reversed by pretreatment with dibutyryl cAMP and theophylline. The amount of immunoreactive ODC protein was reduced by iodide treatment (40%). However, the decrease was not as great as the decrease in ODC activity (90%). No significant change in thyroidal ODC mRNA content was seen 1 and 3 h following KI treatment. These results suggest that excess iodide reduces ODC activity in the rat thyroid gland by a post-transcriptional mechanism.

Effects of hypothydroidism on the gene expression of progesterone receptors in the neonatal rat brain

The effects of neonatal hypothyroidism on the gene expression of progesterone receptors (PRs) in the 8-day-old female rat brain were examined. The levels of PR (‘A’+‘B’)-, PR (‘B’)-, estrogen receptor (ER)- and β-actin mRNAs in the cerebral cortex and hypothalamus-preoptic area of propylthiouracil-treated rats (PTU group) or untreated rats (control group) were analyzed using a quantitative reverse transcription-polymerase chain reaction-Southern blotting assay. When the levels of PR mRNAs were calibrated by respective levels of β-actin mRNA, the levels of PR (‘A’ + ‘B’)- and PR (‘B’) mRNAs in the cerebral cortex of the PTU group were markedly less than those in the control group with no significant changes in the levels of PR messages in the hypothalamus-preoptic area of both groups. No significant difference in the calibrated levels of ER mRNA between both groups was found in these tissues. These results on the PR-, and ER mRNAs were essentially similar to those on the levels of PR- and ER proteins previously reported suggesting that thyroid hormones affect the transcriptional machinery of PR in the developing brain, in a region-specific manner.

Effect of serum thyrotropin levels on the concentration of messenger RNA for thyroid peroxidase in the rat.

The effect of serum TSH on rat thyroid peroxidase mRNA levels was studied in order to investigate the regulation of thyroid peroxidase gene expression in vivo. A nearly full-length rat thyroid peroxidase cDNA clone was isolated from a bacteriophage cDNA library synthesized using poly A+ RNA isolated from the thyroids of propylthiouracil-treated rats. cDNA probes derived from this clone were used to study rat thyroid peroxidase mRNA levels in response to the level of serum TSH. Two major rat thyroid peroxidase mRNA bands were detected on Northern blots of total cellular RNA (at 3.2 kb and at 3.7 kb). Injection of thyroxine, which lowered the levels of serum TSH, also lowered the steady-state levels of both rat thyroid peroxidase mRNAs, whereas treatment with methimazole, which increased serum TSH, increased both rat thyroid peroxidase mRNA levels. In hypophysectomized rats 10 days postoperative, very low levels of thyroid peroxidase mRNA were observed. Injection of bovine TSH (1 IU/day) increased rat thyroid peroxidase mRNA expression, preferentially in the 3.2 kb band. These results clearly demonstrate that TSH regulates rat thyroid peroxidase mRNA levels in vivo.

Studies on the thyroid stimulating hormone-activated Na +K +-ATPase and iodide transporter in cultured rat thyroid cells and the effects of drugs

Exposure of rat thyroid FRTL-5 cells to high concentrations of thyroid stimulating hormone (TSH) for 24 hr in vitro activated 125iodide but not ouabain-sensitive 86Rb transport in the cells, whereas after 27 hr and above there were significant increases in the activity of both transporters. This was similar to results obtained in propylthiouracil-treated rats in vivo where, unlike the early reported increases in iodide transport, activation of thyroidal Na +K +-ATPase activity in thyroid membranes occurred around 24–48 hr following rises in serum TSH. These data confirm the presence of a Na +K +-ATPase in cultured rat FRTL-5 thyroid cells, which is activated several hours later than iodide accumulation by TSH stimulation. This pump is sensitive to the cardiac glycoside ouabain as well as other agents affecting intracellular Na + ion concentrations such as monensin and amiloride.

Regulation of liver angiotensinogen mRNA by glucocorticoids and thyroxine

This study examines the immediate and longer-term changes in angiotensinogen mRNA and in plasma angiotensinogen which follow the withdrawal and replacement of glucocorticoids or thyroxine. RNA from rat liver was analysed by Northern blot and dot-blot hybridization with a 40-mer oligodeoxynucleotide probe specific for angiotensinogen mRNA. Adrenalectomy decreased plasma angiotensinogen and angiotensinogen mRNA to 55 and 50% of control values respectively over a period of 16 days. Similar decreases were obtained after propylthiouracil (1 mg/kg for 16 days) treatment, except when injected simultaneously with T 3 (3 μg/kg/day). Over the same period plasma renin activity increased in adrenalectomized rats from 4.1 ± 0.8 to 7.0 ± 1.5 pmol angiotensin I (AI)/ml/h, and decreased in propylthiouracil-treated rats from 3.8 ± 0.4 to 1.6 ± 0.4 pmol AI/ml/h. Approximate half-times of 2–3 days were calculated for both plasma angiotensinogen and angiotensinogen mRNA post-adrenalectomy or after propylthiouracil treatment. Dexamethasone (400 μg/kg i.m.) given to intact rats rapidly increased angiotensinogen mRNA to a maximum of 250% of control by 8 h and with a half-maximal response of 2.8 h. Plasma angiotensinogen responded similarly, apart from an initial delay of 2 h. Treatment with different doses of propylthiouracil and dexamethasone showed that responses were dose-related. We conclude that changes in plasma angiotensinogen and angiotensinogen mRNA are closely correlated, and that under various physiological circumstances angiotensinogen mRNA has a rapid rate of accumulation but a slow rate of decay.

Plasma atriopeptin concentrations in hyperthyroidism, euthyroidism, and hypothyroidism: studies in man and rat.

Atriopeptin (AP) is a polypeptide produced by atrial myocytes that is capable of inducing diuresis, natriuresis, and vasodilatation. Because thyroid dysfunction is known to be associated with alterations in both renal function and vasomotor control, we investigate the possible effects of varying thyroid function on AP in humans and rats. Plasma AP concentrations were determined in hyperthyroid and hypothyroid patients and normal subjects. Plasma AP was also measured in some patients after the iv infusion of 1 L 150 mmol/L NaCl and after treatment of hyperthyroidism or hypothyroidism. Plasma and atrial AP concentrations were measured in hyperthyroid, euthyroid, and hypothyroid rats. Plasma AP concentrations did not differ in the hyperthyroid (n = 22), euthyroid (n = 45), and hypothyroid (n = 16) subjects [47.1 +/- 18.2 (mean +/- SD), 45.1 +/- 28.9, and 42.4 +/- 20.0 pg/mL, respectively]. After NaCl infusion, mean plasma AP concentrations did not increase significantly in any of the three groups. Treatment of hyperthyroidism and hypothyroidism did not result in a significant change in plasma AP levels. In contrast, plasma AP concentrations were significantly higher in T4-treated (hyperthyroid) rats than in either euthyroid or propylthiouracil-treated (hypothyroid) rats [621 +/- 17 vs. 266 +/- 41 (P less than 0.01) and 210 +/- 28 pg/mL (P less than 0.001), respectively], whereas atrial AP contents were similar in the three groups of rats. We conclude that hyperthyroidism and hypothyroidism in man are not associated with significantly altered plasma AP concentrations. The higher plasma AP levels in T4-treated rats may reflect the relatively shorter duration or greater severity of thyroid dysfunction or thyroid hormone-induced myocardial hypertrophy in the animals.

The perchlorate discharge test for examining thyroid function in rats

A perchlorate discharge test was developed for rats to detect changes in the thyroidal iodide accumulation and organification mechanisms. Rats were pretreated with compounds that alter thyroid function by different mechanisms: SK&F 93479 (an H 2-antagonist that enhances pituitary thyroid stimulating hormone drive by increasing thyroid hormone clearance) and propylthiouracil (an inhibitor of iodide organification). Six hours following administration of 125I, either potassium perchlorate (10 mg/kg × 2.5 min) or saline was given i.p. Perchlorate significantly reduced the thyroid: blood 125I ratio in propylthiouracil-treated rats but had no effect in those pretreated with SK&F 93479, indicating an iodide organification block in the former. At the same time thyroidal radioiodide accumulation in SK&F 93479-treated rats (no perchlorate) was enhanced, whereas that in propylthiouracil-treated animals (no perchlorate) was depressed.

Response of the hypothalamo-neurohypophyseal axis (AVP system) and the kidney to salt load in young propylthiouracil-treated rats.

The development of the ability of the kidney to concentrate urine was studied in normal and propylthiouracil-treated rats by measuring urinary sodium concentration and osmolarity at different ages. It was shown that the normal animals, but not the PTU-treated ones were able to concentrate urine at 35 days of age. The response of the hypothalamo-neurohypophyseal axis (AVP system) and that of the kidney were investigated in the two categories of animals at 35 days of age by measuring concomitantly the AVP content of the hypothalamus and neurohypophysis, the AVP plasma concentration and the natremia and plasma osmolarity at various intervals after intraperitoneal injection of a 5% NaCl solution. In normal, as well as in PTU-treated rats, salt load did not lead to significant modifications of the hypothalamic AVP content. In comparison with normal rats, the neurohypophysis of the PTU-treated ones released AVP more slowly, but with a similar amplitude. In normal rats, the plasma AVP concentration was already maximal 30 min after salt load and then decreased and returned to the normal value at 2 hrs; at the same time, the natremia and plasma osmolarity also recovered their normal value. In contrast, the plasma AVP concentration as well as the natremia remained high 1 h 30 after salt load in PTU-treated rats. It is concluded that PTU-treated young rat is unable to compensate the salt load in normal delays. Beside the slowing in AVP release by neurohypophysis and decreased AVP plasma level, the responsiveness of the kidney seems to be altered.