The thyroid gland has one of the most important functions in the human body as it regulates most of the body’s physiological actions. It produces hormones (tetraiodo-L-thyronine (T4) and triiodo-L-thyronine (T3)) that are responsible for many actions including metabolism, development, protein synthesis, and the regulation of many other important hormones and enzymes [
Thyroid hormone disorders, whether hypofunction or hyperfunction, can have essential effects on the cardiovascular system [
Thyroid hormones have direct and indirect effects on the cardiovascular function, through effects on the heart and effects on the peripheral vasculature, respectively [
Hyperthyroidism leads to a hypermetabolic state that is characterized by increased resting energy expenditure, increased weight loss, decreased cholesterol levels, increased lipolysis, and gluconeogenesis [
Deficiency of thyroid hormone leads to a clinical state of hypothyroidism. The deficiency could be due to reduced production, deranged distribution, or lack of thyroid hormone effects. It is characterized by decreased metabolic rate and by a high serum thyroid-stimulating hormone [
Thyroid hormones have important effects at cardiac and vascular level. They directly affect heart rate control, myocardial excitability, inotropic status, systemic vascular resistance, and blood pressure. Furthermore, they can affect cardiovascular system activity by interacting with other factors (catecholamines, renin-angiotensin-aldosterone system) [
One of the most important mechanisms that regulate blood pressure, fluid volume, and sodium-potassium balance is the renin-angiotensin-aldosterone system (RAAS). That is why change in any molecules that compose RAAS contributes to developing arterial hypertension [
Renin and angiotensin-converting enzyme (ACE) are part of the renin-angiotensin-aldosterone system (RAAS) and are important regulators of blood pressure and salt-water homeostasis [
Aliskiren is a direct inhibitor of the enzyme renin and it is indicated for the treatment of essential hypertension. It can be used alone or in combination with other antihypertensive agents for the treatment of high blood pressure [
Angiotensin-converting enzyme inhibitors (ACEIs) are a group of drugs that are effective in controlling high blood pressure and their use in patients has been linked to reduced cardiovascular morbidity and mortality [
Fosinopril is an angiotensin-converting enzyme inhibitor that has great effect on reducing blood pressure [
Fosinopril is a prodrug, which is hydrolyzed to pharmacologically active metabolite, Fosinopril, in liver and gastrointestinal mucosa [
Both hypothyroidism and hyperthyroidism can cause renal and cardiovascular dysfunction [
This study was conducted to find out the various effects of angiotensin-converting enzyme inhibitors (ACE inhibitors) (Fosinopril) and direct renin inhibitors (Aliskiren) on the RAAS system in rats with thyroid disorders.
Laboratory male albino rats with body weight 200–320 grams were used in the present study. Rats were kept in cages in the animal house of College of Medicine (Hawler Medical University). They were housed under controlled conditions of illumination (12 h light/12 h darkness) and temperature 20°C–25°C, throughout the experimental period. They had free access to standard pellet diet fortified with vitamins and water.
Elabscience ELISA (Enzyme-Linked Immunosorbent Assay) rat kits were used for TSH, renin, angiotensin I, angiotensin II, and aldosterone analysis. Fosinopril sodium (Monopril) 20 mg manufactured by Deva was purchased from a licensed pharmacy in Istanbul, Turkey. Aliskiren (Rasilez) 150 mg manufactured by Novartis was purchased from Germany. Propylthiouracil (Prouracil) 50 mg manufactured by Iran Hormone was used for induction of hypothyroidism. Levothyroxine (Eltroxin) 100 mcg manufactured by aspen was used for hyperthyroid induction.
Forty-two rats were used in this current study. The rats were divided into three groups. The first group of 6 rats served as a control. The second group was of 18 hypothyroid rats, which were subdivided into three subgroups (each subgroup consisted of 6 rats). The first subgroup served as positive control. The second and third subgroups received a daily dose (10 mg/kg) of Fosinopril and Aliskiren, respectively [
The third group involved 18 hyperthyroid rats, which were divided into three subgroups (each of 6 rats). Again the first subgroup served as positive control. The second and third subgroups received a daily dose (10 mg/kg) of Fosinopril and Aliskiren, respectively [
Blood pressure, heart rate, body weight, and 24-hour urine volume were recorded on the first day of the study and were repeated on the
The hyperthyroid groups were given (0.0012% w/v) L-Thyroxine in drinking water for 40 days [
On the
This study was approved by the Ethical Committee of College of Medicine, Hawler Medical University, in the meeting coded 6, paper code 3 dated
Data was analyzed statistically using the Statistical Package for the Social Sciences (SPSS) Version 20.0 for Windows. All the data was expressed as mean ± SD and SE. Comparisons between groups were done using Duncan test and student t-test. P value of 0.05 or less was considered statistically significant
Induction of hyperthyroidism in rats by using daily L-Thyroxine significantly (P <0.05) increased the level of T4 when compared to normal rats, while the change in T3 level, although higher than normal, was statistically nonsignificant.
TSH on the other hand showed a significant drop in its level compared to the control rats (Table
Mean and SE (standard error) of serum levels of T3 (tri-iodothyronine), T4 (thyroxine), and TSH (thyroid stimulating hormone) in normal, hyperthyroid, and hypothyroid rats.
Normal Control | Hyperthyroid | Hypothyroid | |
---|---|---|---|
T3 nmol/L | 1.73±0.04 | 2.33±0.29 | 1.03±0.08 |
| |||
T4 | 78.88±16 | 295.62±16.15 | 17.52±4.37 |
| |||
TSH ng/L | 6.08±0.89 | 1.21±0.25 | 19.55±4.26 |
Daily PTU administration for induction of hypothyroidism significantly (P <0.05) lowered levels of both T3 and T4 while TSH level was profoundly higher than the level in normal rats (Table
Hyperthyroid rats showed a nonsignificant increase of renin level. Although this parameter was increased in both Fosinopril and Aliskiren groups, the changes were nonsignificant when compared to the hyperthyroid group (Table
Effects of hyperthyroidism, Aliskiren, and Fosinopril on serum levels of renin, angiotensin I & II, and aldosterone.
Data | Control | Hyperthyroid | Aliskiren | Fosinopril |
---|---|---|---|---|
Renin | 274.57±24 | 372.42±42 | 531.44±129 | 462.05±52 |
pg/mL | a | ab | b | ab |
| ||||
Angiotensin I | 216.22±5 | 244.90±9 | 207.92±4 | 187.86±5 |
pg/mL | b | a | b | c |
| ||||
Angiotensin II | 143.25±9 | 166.24±4 | 119.16±20 | 114.08±4 |
pg/mL | ab | b | a | a |
| ||||
Aldosterone | 353.86±36 | 363.10±27 | 273.32±16 | 245.00±16 |
pg/mL | a | a | b | b |
Different letters indicate significance differences at P<0.05.
On the other hand, angiotensin I was significantly increased in hyperthyroid group compared to the control group. Both Aliskiren and Fosinopril caused a significant decrease (P <0.05) (Table
The effect of hyperthyroidism on angiotensin II was a nonsignificant increase, while Aliskiren and Fosinopril caused significant lowering when compared to the hyperthyroid group (Table
Aldosterone was slightly and nonsignificantly increased in hyperthyroid group while both Aliskiren and Fosinopril caused a significant reduction in the serum level of aldosterone in hyperthyroid rats (Table
Although hypothyroidism markedly lowered serum renin, the change was nonsignificant while it was significantly increased (P <0.05) in Fosinopril and Aliskiren groups when compared to the hypothyroid group and normal rats (Table
Effects of hypothyroidism, Aliskiren, and Fosinopril on serum levels of renin, angiotensin I & II, and aldosterone.
Data | Control | Hypothyroid | Aliskiren | Fosinopril |
---|---|---|---|---|
Renin | 274.58±24 | 191.30±19 | 779.28±126 | 462.05±52 |
pg/mL | a | a | b | b |
| ||||
Angiotensin I | 216.23±5 | 181.012±12 | 182.01±5 | 187.86±5 |
pg/mL | a | b | b | b |
| ||||
Angiotensin II | 143.25±9 | 109.16±9 | 124.23±6 | 134.86±15 |
pg/mL | a | a | a | a |
| ||||
Aldosterone | 353.86±6 | 396.16±49 | 264.40±15 | 306.88±43 |
pg/mL | a | a | a | a |
Different letters indicate significance differences at P<0.05.
Compared to the control group, hypothyroid induced a significant reduction of serum angiotensin I, but the change was nonsignificant in Fosinopril and Aliskiren groups when compared to the hypothyroid group (Table
Table
Hypothyroidism nonsignificantly increased the level of aldosterone while this parameter was markedly but statistically nonsignificantly reduced in Fosinopril and Aliskiren groups when compared to the hypothyroid group (Table
Following induction of hyperthyroidism in the rats, systolic BP was significantly increased (P <0.05). There was a significant reduction in Aliskiren group while the reduction was nonsignificant by Fosinopril compared to the hyperthyroid group (Table
The relation between blood pressure (BP) and heart rate in control, hyperthyroid, Aliskiren, and Fosinopril groups.
Control | Hyperthyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Systolic BP | 119.38±2 | 147.77±3 | 121.72±3 | 136.14±4 |
mmHg | a | b | a | b |
| ||||
Diastolic BP | 88.57±1 | 107.33±4 | 88.65±3 | 98.78±2 |
mmHg | a | b | a | ab |
| ||||
Mean BP | 98.46±1 | 120.83±4 | 99.50±3 | 111.00±2 |
mmHg | a | b | a | ab |
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Heart rate | 382.53±7 | 425.26±19 | 414.23±16 | 390.64±11 |
Beat/Minute | a | a | a | a |
Different letters indicate significance differences at P<0.05.
Compared to normal rats, the hyperthyroid rats showed a significant rise in Diastolic BP. When hyperthyroid rats were treated with Aliskiren, there was a significant reduction of this parameter but the change by Fosinopril was nonsignificant (Table
In Table
The changes in heart rate were negligible in all groups (Table
Hypothyroid induction by PTU resulted in a nonsignificant reduction of systolic, diastolic, and mean BP. The same results were observed in Aliskiren and Fosinopril treated groups (Table
The relation between blood pressure (BP) and heart rate in control, hypothyroid, Aliskiren, and Fosinopril groups.
Control | Hypothyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Systolic BP | 119.38±2 | 107.07±4 | 107.58±2 | 105.83±5 |
mmHg | a | a | a | a |
| ||||
Diastolic BP | 88.57±1 | 80.83±4 | 81.85±3 | 79.81±4 |
mmHg | a | a | a | a |
| ||||
Mean BP | 98.46±1 | 89.35±4 | 90.17±3 | 88.33±5 |
mmHg | a | a | a | a |
| ||||
Heart rate | 382.53±7 | 301.93±3 | 312.10±4 | 298.63±2 |
Beat/Minute | a | b | b | b |
Different letters indicate significance differences at P<0.05.
While heart rate was significantly reduced in the hypothyroid group, it was nonsignificantly reduced in Aliskiren and Fosinopril groups compared to the hypothyroid group (Table
This table shows the results of blood urea, serum creatinine, and liver function enzymes in normal, hyperthyroid, and hyperthyroid groups treated with Aliskiren and Fosinopril. Urea was significantly reduced in the hyperthyroid rats. Both Aliskiren and Fosinopril were able to reduce urea levels too, but the reduction was nonsignificant (Table
Blood biochemistry tests in control, hyperthyroid, Aliskiren, and Fosinopril groups.
Control | Hyperthyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Urea | 58.22±7 | 40.20±1 | 33.40±1 | 33.00±1 |
mg/dl | a | b | b | b |
| ||||
Creatinine | 0.451±0.04 | 0.452±0.009 | 0.446±0.01 | 0.446±0.01 |
mg/dl | a | a | a | a |
| ||||
AST | 125.65±34 | 134.40±8 | 146.80±18 | 104.20±7 |
unit/L | a | a | a | a |
| ||||
ALT | 45.32±6 | 51.20±4 | 49.20±5 | 43.60±2 |
unit/L | a | a | a | a |
| ||||
ALP | 228.09±88 | 256.40±41 | 190.80±27 | 174.80±16 |
unit/L | a | a | a | a |
Different letters indicate significance differences at P<0.05.
Abbreviations. AST: aspartate aminotransferase, ALT: alanine aminotransferase, ALP: alkaline phosphatase.
Neither hyperthyroidism nor treatment with Aliskiren and Fosinopril had any effect on serum creatinine (Table
The rise in AST level in hyperthyroid and Aliskiren groups was nonsignificant. Although the Fosinopril group shows a marked decrease in AST, the change was nonsignificant (Table
The changes that were observed in ALT and ALP levels were nonsignificant in all groups (Table
No significant changes were observed in blood urea, serum creatinine, and liver function tests of all groups (Table
Blood biochemistry tests in control, hypothyroid, Aliskiren, and Fosinopril groups.
Control | Hypothyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Urea | 58.22±7 | 49.72±3 | 34.60±5 | 68.80±27 |
mg/dl | a | a | a | a |
| ||||
Creatinine | 0.45±0.04 | 0.69±0.05 | 0.48±0.04 | 0.65±0.14 |
mg/dl | a | a | a | a |
| ||||
AST | 125.65±34 | 147.00±22 | 126.60±13 | 129.60±8 |
unit/L | a | a | a | a |
| ||||
ALT | 45.32±6 | 41.83±7 | 59.20±4 | 52.80±4 |
unit/L | a | a | a | a |
| ||||
ALP | 228.09±88 | 262.95±73 | 197.60±18 | 257.60±34 |
unit/L | a | a | a | a |
Different letters indicate significance differences at P<0.05.
Abbreviations. AST: aspartate aminotransferase, ALT: alanine aminotransferase, ALP: alkaline phosphatase.
Although Aliskiren was able to cause twofold increase in the rate of urine flow in hyperthyroid rats, it was nonsignificant. It was noticed that Fosinopril has a greater effect in increasing urine flow rate, as Fosinopril has caused significant threefold increase (P <0.05) in urine flow when compared to the hyperthyroid group (Table
Urine flow, Na+ excretion rate, and K+ excretion rate in hyperthyroidism, Aliskiren, and Fosinopril.
Control | Hyperthyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Urine flow | 1.35±0.24 | 1.24±0.31 | 2.49±0.52 | 3.40±0.6 |
ml/hr | a | a | ab | b |
| ||||
Na+ excretion rate | 44.81±9 | 52.42±16 | 138.75±26 | 175.23±40 |
mmol/hr | a | a | b | b |
| ||||
K+ excretion rate | .032±0.006 | .01±0.001 | .08±0.03 | .09±0.02 |
mmol/hr | ab | a | bc | c |
Different letters indicate significance differences at P<0.05.
Abbreviations. Na: sodium, K: potassium.
While there was a nonsignificant change in the sodium excretion rate of the hyperthyroid group, the rise of this parameter in the Aliskiren and Fosinopril treated groups was significant (Table
Hyperthyroidism nonsignificantly reduced potassium excretion rate. However it was significantly increased (P <0.05) by daily administration of Aliskiren and Fosinopril to the hyperthyroid rats (Table
The reduction in urine flow is negligible in the hypothyroid group as well as the Fosinopril treated group. While in Aliskiren treated group urine flow was increased, this was nonsignificant when compared to the hypothyroid group (Table
Urine flow, Na+ excretion rate, and K+ excretion rate in hypothyroidism, Aliskiren, and Fosinopril.
Control | Hypothyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Urine flow | 1.35±0.24 | 1.24±0.28 | 2.07±0.44 | .95±0.2 |
ml/hr | ab | ab | b | a |
| ||||
Na+ excretion rate | 44.81±9 | 70.59±17 | 104.52±24 | 54.53±12 |
mmol/hr | a | ab | b | ab |
| ||||
K+ excretion rate | .03±0.006 | .08±0.03 | .04±0.007 | .02±0.002 |
mmol/hr | ab | b | ab | a |
Different letters indicate significance differences at P<0.05.
Abbreviations. Na: sodium, K: potassium.
Table
Both hypothyroidism and Aliskiren treated groups showed a nonsignificant rise in rate of potassium excretion, while Fosinopril on the other hand caused a significant reduction in the rate when compared to the hypothyroid group (Table
In Table
Levels of serum Na+ and K+ in hyperthyroid, hypothyroid, Aliskiren, and Fosinopril groups.
Control | Hyperthyroid | Aliskiren | Fosinopril | |
---|---|---|---|---|
Serum Na+ | 143.90±0.7 | 144.30±0.5 | 144.10±0.4 | 142.44±0.4 |
mmol/L | ab | b | b | a |
| ||||
Serum K+ | 4.72±0.4 | 5.17±0.2 | 5.49±0.5 | 4.79±0.07 |
mmol/L | a | a | a | a |
| ||||
Control | Hypothyroid | Aliskiren | Fosinopril | |
| ||||
Serum Na+ | 143.90±0.7 | 143.75±1 | 147.48±1 | 144.20±1 |
mmol/L | a | ab | b | ab |
| ||||
Serum K+ | 4.72±0.4 | 4.04±0.1 | 4.53±0.1 | 4.83±0.1 |
mmol/L | a | a | a | a |
Different letters indicate significance differences at P<0.05.
Abbreviations. Na: sodium, K: potassium.
Although Aliskiren and Fosinopril treated groups showed an increase in serum sodium levels of hypothyroid rats, the changes were within the normal range and were regarded as nonsignificant (Table
On the other hand, no significant changes were seen in the serum potassium level of all groups (Table
In Table
Mean and SE (standard error) of weights of rats (in grams). Hyperthyroid, hypothyroid, and after treatment with Aliskiren and Fosinopril.
Hyperthyroid | After treatment | P value | |
---|---|---|---|
Aliskiren group | 284± 14.00 | 272± 4.63 | Ns |
(Weight in grams) | |||
| |||
Fosinopril group | 293± 10.90 | 280 ±2.73 | Ns |
(Weight in grams) | |||
| |||
Hypothyroid | After treatment | ||
| |||
Aliskiren group | 284± 7.00 | 272 ±4.00 | Ns |
(Weight in grams) | |||
| |||
Fosinopril group | 293± 6.04 | 290±7.90 | Ns |
(Weight in grams) |
NS: nonsignificant.
The results obtained from this study revealed that induction of hyperthyroidism with the daily use of L-Thyroxine significantly increased the level of T4 and lowered TSH level significantly when they were compared to the normal rats. Thyroxine is a synthetic T4 and is identical to the natural hormone in its action; as a result, there will be a rise in levels of T3 and T4 and a drop in TSH level due to hypothalamic pituitary feedback mechanism. On the other hand, hypothyroid induction by daily PTU resulted in a significant drop in levels of circulating T3 and T4 with a significant rise in TSH level compared to the euthyroid rats. PTU acts by inhibiting the iodination of tyrosyl residues in thyroglobulin along with inhibition of peripheral conversion of T4 to T3. Through the negative feedback mechanism, levels of TSH will be increased [
It is well known that thyroid hormones regulate BP by increasing the response of cardiovascular system to the action of the sympathetic nervous system or/and by directly activating the RAAS [
In this study we have observed that hyperthyroidism has caused an upsurge in the levels of serum renin, angiotensin II, and aldosterone, but the changes were of no significance when they were compared to the normal rats. On the other hand, angiotensin I raise was of statistical significance in the hyperthyroid induced rats. These results are in accordance with that of Ramos et al. (2006) [
In the hyperthyroid rats, systolic, diastolic, and mean blood pressure were obviously increased and these changes are the consequences of sympathetic overactivity, which is characteristic of hyperthyroidism just as has been observed by Chen et al. (2010) [
The results obtained from this study show that hyperthyroidism reduced levels of blood urea. Urine flow in the hyperthyroid rats was slightly decreased but their medication with Aliskiren and Fosinopril caused two- and three-fold increase in the rate, respectively. Along with the urine flow, Na+ and K+ excretion rates were markedly increased, which is consistent with the work of Nussberger et al. (2002) [
In the current study the results show, except for serum sodium in Fosinopril treated group, that Fosinopril decreases the formation of angiotensin II and consequently aldosterone release. Aldosterone is known for its salt and water retaining properties. As Fosinopril decreases serum sodium levels, it is preferable for patients with salt sensitive hypertension. The effects of hypothyroidism on body functions are usually opposite to the effects of hyperthyroidism. As was concluded by Kumar et al. (2013) [
In hypothyroidism there was significant lowering in angiotensin I.
Induction of hypothyroidism by the use of daily PTU lowered systolic, diastolic, and mean BP nonsignificantly when compared to the euthyroid rats and such a result is expected, as there will be a decrease in sympathetic activity in hypothyroidism. This lowering in BP is in contrast to other studies which refer to long term hypothyroidism resulting in an increase in BP mainly diastolic and this is due to development of atherosclerosis, but this study showed a decrease in blood pressure which could be related to the duration of the study which lasted for only 40 days. Administration of Aliskiren and Fosinopril to the hypothyroid rats did not have a significant effect on the above parameters. While the changes in BP were minimal, the effect of hypothyroidism on heart rate was a marked drop in the rate compared to the normal rats, as hypothyroidism is characterized by decreased sympathetic activity and dominance of vagal stimulation with its accompanying bradycardia.
The result obtained from this study on effect of hypothyroidism on the level of serum creatinine was a marked but nonsignificant rise when compared to the normal rats and this is in accordance with the results of Kaur et al. ( 2015) [
Potassium excretion rate in hypothyroid rats treated with Fosinopril showed significant lowering when compared to the hypothyroid rats, as Fosinopril, like other renin-angiotensin inhibitors, decreases the action of aldosterone. Aldosterone is a well-known enhancer of renal potassium excretion. Therefore its inhibition results in decreased renal excretion of potassium.
Induction of hypothyroidism and treatment of the hypothyroid rats with Aliskiren and Fosinopril showed no significant changes in the levels of serum sodium and potassium when compared to the hypothyroid group. Physiologically, serum sodium concentration is maintained constant due to effect of different factors like kidney function, sympathetic nervous activity, and hormones (e.g., natriuretic peptides) [
Aliskiren and Fosinopril in hyperthyroid rats decreased serum angiotensin I, angiotensin II, and aldosterone. Blockade of renin and inhibition of angiotensin-converting enzyme both resulted in a rebound increase in level of renin in hypothyroid rats.
Aliskiren is better at controlling blood pressure in hyperthyroid rats.
Urine flow, sodium excretion, and potassium excretion rates were improved by the use of Aliskiren and Fosinopril in hyperthyroid rats, but in hypothyroid rats Fosinopril has decreased potassium excretion rate.
Fosinopril decreased serum Na+ in hyperthyroid rats.
Blood pressure
Renin-angiotensin-aldosterone system
Propylthiouracil
Aspartate aminotransferase
Alanine transaminase
Alkaline phosphatase.
The data that support the findings of this study are included in the article and are available from the corresponding author.
Limitations of the Study. Lack of prior studies on the same topic was one of the major limitations of this study that lead to taking too many parameters in such a sample size. As this study is part of a Ph.D. study, there was limitation on the time dedicated to the research. We have come to find out that it would have been better for the study if it included normal rats, but because of time and funding limitations we were not able to perform this part of the study.
Both authors declare that there are no conflicts of interest.
The final manuscript was reviewed and approved by both authors.