ORIGINAL ARTICLE
Year : 2016 | Volume
: 13 | Issue : 2 | Page : 93--97
Orchidectomy reduces blood pressure, but testosterone increases it in intact and orchidectomized normotensive rats
Fati O Aliyu1, Abdullateef I Alagbonsi2, Ali AU Dikko3,
1 Department of Human Physiology, Faculty of Medicine, Ahmadu Bello University, Zaria, Kaduna State, Nigeria
2 Department of Standards and Quality Assurance, National Health Insurance, Scheme, North Central A Zonal Office, Kwara State Ministry of Health Premises, Fate; Department of Physiology, College of Health Sciences, University of Ilorin, Ilorin, Kwara State, Nigeria
3 Department of Physiology, Faculty of Medicine, Bayero University, Kano, Kano State, Nigeria
Correspondence Address:
Abdullateef I Alagbonsi
Department of Standards and Quality Assurance, National Health Insurance Scheme, North Central A Zonal Office, Kwara State Ministry of Health Premises, Fate, Ilorin, Kwara
Nigeria
Abstract
Background: The cardioprotective effect of estrogen has been well documented, and the effect of testosterone on blood pressure (BP) is controversial and remains inconclusive.
Aim: The present study is aimed at investigating the effect of testosterone on BP in normotensive rats.
Materials and Methods: In a blind study, 30 male albino rats (200-250 g) were divided into 5 oral treatment groups (n = 6 rats each) as follows: Groups I and II were intact rats that received 1 ml/kg normal saline (vehicle) and 25 mg/kg testosterone subcutaneously for 24 days. Group III was sham-operated and received normal saline for 24 days. Groups IV and V were bilaterally orchidectomized and received normal saline and 25 mg/kg testosterone subcutaneously for 24 days.
Results: The systolic BP (SBP), diastolic BP (DBP), pulse pressure (PP), and mean arterial pressure (MAP) of the sham-operated rats that received normal saline were not significantly different from the intact (control) rats that received normal saline (P > 0.05). Testosterone treatment in control rats caused a sustainably higher SBP (P < 0.001), DBP (P < 0.001), PP (P < 0.001), and MAP (P < 0.001) when compared to control that received normal saline. The SBP (P < 0.01), DBP (P < 0.001), MAP (P < 0.001), but not PP (P > 0.05) was significantly reduced in orchidectomized rats that received normal saline when compared to control. However, administration of testosterone in orchidectomized rats abolished orchidectomy-induced reduction in SBP, DBP, MAP, but not PP and further increased them above the control level (P < 0.05).
Conclusion: This study shows that testosterone is prohypertensive in normotensive rats.
How to cite this article:
Aliyu FO, Alagbonsi AI, Dikko AA. Orchidectomy reduces blood pressure, but testosterone increases it in intact and orchidectomized normotensive rats.Nig J Cardiol 2016;13:93-97
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How to cite this URL:
Aliyu FO, Alagbonsi AI, Dikko AA. Orchidectomy reduces blood pressure, but testosterone increases it in intact and orchidectomized normotensive rats. Nig J Cardiol [serial online] 2016 [cited 2023 May 30 ];13:93-97
Available from: https://www.nigjcardiol.org/text.asp?2016/13/2/93/187705 |
Full Text
INTRODUCTION
Generally, males are at greater risk for cardiovascular and renal diseases than their age-matched premenopausal females. This created an impression that gender influences blood pressure (BP) and sex hormones contribute to the pathophysiology of hypertension. [1] In humans, for instance, 24-h ambulatory BP is higher in men than in women of similar ages. [2],[3],[4],[5] In different hypertensive rat models, many investigators have found that males have higher BP than do females. [6],[7],[8],[9],[10],[11],[12],[13],[14] However, there was evidence of higher BP in postmenopausal women than their age-matched men. [2]
The factor(s) responsible and the mechanism(s) involved in the increased BP in male rats and perhaps in elderly female rats remain to be fully understood, but androgens have been implicated. [15] For instance, data from some studies clearly showed that BP is higher in boys than in girls during adolescence and puberty, when androgen levels are increasing. [16],[17] Similarly, castration at a young age (3-5 weeks) was reported to attenuate the development of hypertension in different hypertensive models. [7],[8],[10],[12],[14],[18],[19],[20],[21],[22] Furthermore, chronic blockade of androgen receptor with the antagonist flutamide attenuates BP in male spontaneously hypertensive rats (SHR) to the level found in female SHR. [23] Perhaps the observed gender differences and the increased incidence of cardiac events in women after menopause are not entirely due to the depletion of estrogen but are also related to significant amounts of circulating testosterone, because postmenopausal ovaries reportedly produce significant amounts of androgens in the form of testosterone and androstenedione. [24]
However, there are other suggestions that female sex hormones may actually protect against a salt-induced increase in BP, possibly by augmenting the renal excretion of sodium. [25] Thus, when Dahl salt-sensitive (DS) rats receive a high-sodium diet, female rats become less hypertensive than male rats. [26] In this animal model, gonadectomy results in an accelerated development of salt-sensitive hypertension in females. The increase in salt sensitivity observed after ovariectomy is actually associated with a blunted pressure-natriuresis relationship. Interestingly, reversal of the diet to a low salt intake reverses the hypertension in intact male and female DS rats, but this was not the case in ovariectomized female DS rats, suggesting that female sex hormones act to suppress sodium-dependent as well as sodium-independent increases in BP. [27] A greater rise in BP also occurred in spontaneously hypertensive female rats after ovariectomy. [28],[29]
Testosterone replacement therapy is now being prescribed more often for aging men, the same population in which BP and prostate cancer incidence increases. The hypothesis that high levels of circulating androgens are a risk factor for prostate cancer is supported by the dramatic regression of the cancer after castration. [30] Over recent decades, testosterone has been increasingly abused for muscle buildings and enhancement of physical performance, [31] and the side effects on the cardiovascular system may include elevated BP [32] and harmful cholesterol levels leading to increased risk of cardiovascular diseases and coronary artery diseases.
The cardioprotective effect of estrogen has been extensively demonstrated. However, the hypothesis that androgens may contribute to cardiovascular risk is still debated. While some studies show that testosterone can attenuate BP through relaxation of the vascular smooth muscle, [33] other studies demonstrate its prohypertensive effect by the constriction of vascular smooth muscle. [34] Since majority of previous studies have established the prohypertensive effect of testosterone in hypertensive models, the present study is aimed at investigating the effect of testosterone on BP in normotensive rats.
MATERIALS AND METHODS
Animals
Thirty male albino rats (200-250 g) were housed at room temperature with free access to food and water ad libitum and were maintained on a 12-h light/dark cycle, with the lights on from 7:00 am "Principles of laboratory animal care (NIH publication No. 85-23, revised 1985)" were followed. All experiments have been examined and approved by our Institutional Ethics Committee.
Experimental protocol
After 2 weeks acclimatization to their new environment with standard laboratory diet and water given ad libitum, the 30 animals were randomly divided in a blinded fashion into 5 oral treatment groups as follows:
Group I served as control and received 1 ml/kg normal saline (vehicle) for 24 daysGroup II received 25 mg/kg testosterone subcutaneously for 24 daysGroup III was sham-operated and received normal saline for 24 daysGroup IV was orchidectomized and received normal saline for 24 daysGroup V was orchidectomized and received 25 mg/kg testosterone subcutaneously for 24 days.Surgical procedures
Each rat was anesthetized using chloroform, it was then placed on a dissecting board, and a pair of scissors was used to make a skin incision on the two scrotums. Bilateral orchidectomy was induced by removal of the two testes from the scrotums. Then chromic catgut suture was used to suture the incision, followed by a subcutaneous injection of 0.5 ml ampicillin to prevent infection. [26]
The procedure for sham operation was similar except that the testes were not removed from the scrotum.
Measurement of blood pressure
BP was measured by tail-cuff method of Buñag and Butterfield [35] as modified by Byrom and Wilson [36] using a noninvasive Ugo Basile, series 5b500 BP recorder. Each rat was placed in the restrainer and kept in a scanner for 30 min to warm the animal prior to obtaining pressure measurement. A cuff was placed on the base of the tail to occlude the blood flow. A transducer was placed close to the cuff which measured the systolic BP (SBP), diastolic BP (DBP), pulse pressure (PP), and mean arterial pressure (MAP). Upon deflation, the noninvasive BP sensor was used to monitor the BP, and an average of four readings was taken for each rat so as to ensure accuracy.
Statistical analyses
Data were analyzed with one-way ANOVA using GraphPad Prism (Version 5.0.3.0), followed by a post hoc Tukey test for multiple comparisons. Data were presented as the mean ± standard error of the mean. P ≤ 0.05 were considered statistically significant.
RESULTS
The SBP, DBP, PP, and MAP of the sham-operated rats that received normal saline were not significantly different from the control rats that received normal saline (P > 0.05). Testosterone treatment in control rats caused a sustainably higher SBP (P < 0.001), DBP (P < 0.001), PP (P < 0.001), and MAP (P < 0.001) when compared to control that received normal saline. The SBP (P < 0.01), DBP (P < 0.001), MAP (P < 0.001), but not PP (P > 0.05) were significantly reduced in orchidectomized rats that received normal saline when compared to control. However, administration of testosterone in orchidectomized rats abolished orchidectomy-induced reduction in SBP, DBP, MAP, but not PP and further increased them above the control level (P < 0.05) [Figure 1] [Figure 2] [Figure 3] [Figure 4].{Figure 1}{Figure 2}{Figure 3}{Figure 4}
DISCUSSION
Gonadal hormones have been suggested to be responsible for the difference in BP found in males and females. However, previous studies on the effects of androgens and estrogens on BP are contradictory and remain inconclusive. [33],[34] The effect of testosterone on BP in normotensive rats was investigated in this study.
In the present study, supplementation of normotensive rats with testosterone persistently caused an increase in BP of rats and consequently elicit hypertension (BP >140/90 mmHg). Previously, low prevalence of coronary disease among men with hypotestosteronemia plus hyperestrogenemia [37] and increased risk of coronary artery disease and myocardial infarction in women suffering from chronic anovulation and exhibiting hypertestosteronemia have been documented. On the contrary, lower or unchanged circulating testosterone in hypertensive men [38],[39],[40] and in men with coronary artery disease [37] or myocardial infarction [41] has also been reported. These studies suggest that decreased, rather than increased, androgen levels are associated with hypertension, myocardial infarction, and coronary artery disease. However, the cardioprotective property of testosterone speculated by these aforementioned studies have been criticized by other authors who attributed the low testosterone level in cardiovascular diseases to stress, since reduced testosterone level has been shown to be a consequence of stress elicited by myocardial infarction, surgery, head trauma, burns, hypoxia, sleep deprivation, and psychological stressors. [41] The present study, taken together with these previous reports, support the contention that testosterone is a prohypertensive hormone and contribute to the higher BP generally observed in men when compared to women of similar age.
Having observed the prohypertensive effect of testosterone supplement in normotensive rats, we went further to investigate if testosterone deficiency will sustainably reduce BP in normotensive rats. It was observed that orchidectomy-induced testosterone deficiency caused a persistent decrease in BP in normotensive rats and consequently elicit hypotension (BP <90/60 mmHg). This finding is similar to the previous observation that orchidectomy at a young age (3-5 weeks) attenuated the development of hypertension in spontaneously hypertensive and DS rats. [7],[10],[12],[19],[42],[43]
In order to conclusively demonstrate the unique contribution of testosterone to the development of high BP, we investigated whether testosterone replacement in orchidectomized rats can potently reverse the BP to the level similar to the control. In the present study, supplementation of orchidectomized rats with testosterone not only completely abolished the orchidectomy-induced hypotension, but elevated it slightly above the control level. This observation is similar to the previous study where testosterone replacement in orchidectomized rats increased BP to levels similar to those in intact rats. [7],[42]
Some previous studies have suggested mechanisms by which testosterone could elevate BP and damage blood vessels. For instance, testosterone was reported to increase circulating level of homocysteine, which induces endothelial damage, thus leading to the development of atherosclerosis, and may adversely influence renal function by damaging glomerular endothelial cells. [44] In addition, testosterone increases endothelin-1 levels in subjects undergoing a sex change, suggesting a way through which it may cause BP elevation. [44],[45] Moreover, elevated catecholamine levels in SHR are associated with high BP, [46],[47] whereas castration reduces it to those observed in normotensive control rats, [47] suggesting that testosterone can also induce catecholamine synthesis. [47] This observation could be mediated by the stimulation of tyrosine hydroxylase which is the rate-limiting enzyme for catecholamine synthesis. [46],[47] Moreover, testosterone also stimulates angiotensin expression [48] and increases circulating levels of angiotensin-converting enzyme, thereby causing hypertension. [49]
CONCLUSION
The present study provides convincing evidence for the prohypertensive effect of testosterone in normotensive rats.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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