Testosterone increased blood pressure and decreased renal tyrosine hydroxylase activity in SHR/y and Wistar-Kyoto rats

Testosterone modulates vasodilation in mesenteric arteries of hypertensive rats

AIMS

To evaluate the effects of testosterone on endothelium-dependent vasodilation and oxidative stress in mesenteric resistance arteries.

MAIN METHODS

Spontaneously hypertensive rats (SHR), aged 8 to 10 weeks, were divided into four groups: intact (SHAM), intact treated with testosterone (TTO; 3 mg/kg/day) via subcutaneous route (s.c.), intact treated with testosterone and anastrozole [aromatase enzyme inhibitor (TTO + ANA; 0.1 mg/kg/day, s.c.)] and intact treated with testosterone and finasteride [5 α-reductase enzyme inhibitor (TTO + FIN; 5 mg/kg/day, s.c.)] for four weeks. Concentration-response curves to acetylcholine (ACh, 0.1 nmol/L - 10 μmol/L) were obtained in mesenteric resistance arteries previously contracted with phenylephrine (PE, 3 μmol/L), before and after the use of selective inhibitors. Reactive oxygen species (ROS) levels were assessed in the vessels and the endothelium analyzed by scanning electron microscopy.

KEY FINDINGS

TTO group showed a lower participation of nitric oxide (NO), increased oxidative stress, and participation of prostanoids and endothelium-dependent hyperpolarization (EDH), possibly to maintain the vasodilator response. Lower participation of NO and prostanoids, combined to an increased participation of EDH, were observed in the TTO + ANA group, in addition to higher levels of ROS and altered endothelial morphology. The vasodilation to ACh was impaired in TTO + FIN, along increased participation of NO, reduction of prostanoids, and greater EDH-dependent vasodilation.

SIGNIFICANCE

Testosterone contributes to endothelial vasodilation by enhancing EDH through an increased participation of epoxyeicosatrienoic acids. While the decrease in NO appears to involve the participation of dihydrotestosterone, 17 β-estradiol seems to stimulate the action of the NO pathway and prostanoids.

Analysis of salivary flow rate, biochemical composition, and redox status in orchiectomized spontaneously hypertensive rats

OBJECTIVE

This study aimed to analyze the salivary flow rate, biochemical composition, and redox status in orchiectomized spontaneously hypertensive rats (SHR) compared to normotensive Wistar rats.

DESIGN

Thirty-two young adult male SHR and Wistar (3-months-old) rats were randomly distributed into four groups; either castrated bilaterally (ORX) or underwent fictitious surgery (SHAM) as Wistar-SHAM, Wistar-ORX, SHR-SHAM, and SHR-ORX. Two months beyond castration, pilocarpine-induced salivary secretion was collected from 5-month-old rats to analyze salivary flow rate, pH, buffer capacity, total protein, amylase, calcium, phosphate, sodium, potassium, chloride, thiobarbituric acid reactive substances (TBARs), carbonyl protein, nitrite, and total antioxidant capacity.

RESULTS

The salivary flow rate was higher in the Wistar-ORX compared to the Wistar-SHAM group, while remaining similar between the SHR-SHAM and SHR-ORX groups. ORX did not affect pH and salivary buffer capacity in both strains. However, salivary total protein and amylase were significantly reduced in the Wistar-ORX and SHR-ORX compared to the respective SHAM groups. In both ORX groups, salivary total antioxidant capacity and carbonylated protein were increased, while lipid oxidative damage (TBARs) and nitrite concentration were higher only in the Wistar-ORX than in the Wistar-SHAM group. In the Wistar-ORX and SHR-ORX, the salivary calcium, phosphate, and chloride were increased while no change was detected in the SHAM groups. Only salivary buffering capacity, calcium, and chloride in the SHR-ORX adjusted to values similar to Wistar-SHAM group.

CONCLUSION

Hypertensive phenotype mitigated the orchiectomy-induced salivary dysfunction, since the disturbances were restricted to alterations in the salivary biochemical composition and redox state.

Long-term treatment with testosterone alters ovary innervation in adult pigs

BACKGROUND

Intraovarian distribution and density of nerve fibres immunoreactive (IR) to protein gene product 9.5 (PGP 9.5) and containing dopamine-β-hydroxylase (DβH), neuropeptide Y (NPY), somatostatin (SOM), galanin (GAL) were determined.

METHODS

From day 4 of the first oestrous cycle to day 20 of the second studied cycle, experimental gilts (n = 3) were injected with testosterone (T), while control gilts (n = 3) received corn oil.

RESULTS

After T administration the numbers of fibres IR to PGP 9.5 and fibres IR to DβH, NPY and SOM were decreased. Fewer PGP 9.5- and DβH-IR terminals were observed within the ground plexus and around arteries and medullar veins, and medium tertiary follicles, and DβH-IR terminals in the vicinity of small tertiary follicles. T decreased the density of NPY-IR fibres in the medullar part of the ground plexus, and SOM-IR in the cortical part of the ground plexus.

CONCLUSIONS

The obtained data show that long-term T treatment of gilts decreases the total number of intraovarian fibres, including sympathetic ones. These results suggest that elevated T levels that occur during pathological states may affect the innervation pattern of ovaries, and their function(s).

Influence of gender and estrous cycle on plasma and renal catecholamine levels in rats

Several studies have demonstrated that gonadal hormones show significant effects on the brain and signaling pathways of effector organs/cells that respond to neurotransmitters. Since little information is available concerning the impact of male and female gonadal hormones on the renal and peripheral sympathetic system, the objective of this study was to further assess whether and how the renal content and plasma concentration of catecholamines are influenced by gender and the estrous cycle in rats. To achieve this, males Wistar rats were divided into 4 groups: (i) sham (i.e., control), (ii) gonadectomized, (iii) gonadectomized and nandrolone decanoate replacement at physiological levels or (iv) gonadectomized and nandrolone decanoate replacement at high levels. Female Wistar rats were divided into 6 groups: (i) ovariectomized (OVX), (ii) estrogen replacement at physiological levels and (iii) estrogen replacement at at high levels, (iv) progesterone replacement at physiological levels and (v) progesterone replacement at at high levels, and (vi) sham. The sham group was subdivided into four subgroups: (i) proestrus, (ii) estrus, (iii) metaestrus, and (iv) diestrus. Ten days after surgery, the animals were sacrificed and their plasma and renal catecholamine levels measured for intergroup comparisons. Gonadectomy led to an increase in the plasma catecholamine concentration in females, as well as in the renal catecholamine content of both male and female rats. Gonadectomized males also showed a lower level of plasma catecholamine than the controls. The urinary flow, and the fractional excretion of sodium and chloride were significantly increased in gonadectomized males and in the OVX group when compared with their respective sham groups.

Alterations in vasomotor systems and mechanics of resistance-sized mesenteric arteries from SHR and WKY male rats following in vivo testosterone manipulation

Background

Testosterone (T) and the sympathetic nervous system each contribute to the pathology of hypertension. Altered blood vessel reactivity is also associated with the pathology of high blood pressure. The purpose of this study was to examine the effects of T manipulation in the regulation of resistance-sized blood vessel reactivity.

Methods

Adult spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) male rats at 8 weeks of age were used. The rats were divided into groups consisting of gonadally intact controls (CONT), castrate with sham implant (CAST) and castrate with T implant (CAST + T) (n = 6 to 12 per group). Following a short-term period of T treatment (approximately 4 weeks), plasma norepinephrine (NE) and plasma T were assessed by performing high-performance liquid chromatography and RIA, respectively. Resistance-sized mesenteric artery reactivity was assessed on a pressurized arteriograph for myogenic reactivity (MYO), phenylephrine (PE) responsiveness and passive structural mechanics.

Results

SHR and WKY males exhibited similar physiological trends in T manipulation, with castration significantly lowering plasma T and NE and T replacement significantly increasing plasma T and NE. T manipulation in general resulted in significant alterations in MYO of second-order mesenteric arteries, with T replacement decreasing MYO in SHR (P < 0.05) compared to CONT, T replacement increasing MYO, and CAST decreasing MYO in WKY rats (P < 0.001) compared to CONT rats. Additionally, PE-induced constriction was significantly altered in both strains following T treatment, with the effective concentration of PE to constrict the vessel to 50% of the total diameter significantly increased in the CAST + T SHR compared to CONT (P < 0.05). Comparisons of passive structural mechanics between SHR and WKY treatment groups indicated in SHR a significantly increased wall-to-lumen ratio and decreased circumferential wall stress compared to WKY treatment groups.

Conclusions

These data suggest that T and NE are involved in a complex interaction with both myogenic reactivity and structural alterations of resistance-sized blood vessels and that these factors likely contribute to the development and maintenance of hypertension.

Colony social stress differentially alters blood pressure and resistance-sized mesenteric artery reactivity in SHR/y and WKY male rats

Increased sympathetic nervous system (SNS) activity, testosterone, and spontaneously hypertensive rat Y chromosome (SHR Yc) play a role in a genetic model of hypertension. Male rats with the SHR Yc and Wistar-Kyoto (WKY) autosomes (denoted SHR/y) exhibit these characteristics when compared to rats with the WKY Yc and WKY autosomes (denoted WKY). We hypothesized that chronic social stress will increase blood pressure and SNS activity more in SHR/y males compared to WKY males, resulting in increased myogenic reactivity along with decreased vasoconstriction of small mesenteric arteries. SHR/y and WKY males were housed in strain- specific colonies (10 males with 10 females) or as controls (10 males). Systolic blood pressure (SBP) and blood samples were collected prior to termination. Second-order mesenteric arteries were studied using a pressure arteriograph in which myogenic reactivity and phenylephrine (PE) responsiveness were measured. SHR/y colony SBP, and circulating norepinephrine and testosterone concentrations were elevated compared to control and WKY colony males (p < 0.05). Mesenteric artery myogenic reactivity was increased in SHR/y colony males (p < 0.001). Mesenteric arteries from SHR/y colony males exhibited a significant decrease in PE-induced constriction. Colony social stress elevated both SNS activity and testosterone level which may be responsible for the increased mesenteric artery myogenic reactivity, and SBP as noted in SHR/y males.

The amelioration of olfactory acuity upon sexual maturation might affect food preferences

Upon sexual maturation, olfactory acuity in women ameliorates and starts oscillating across the cycle. During ovulation, mean olfactory threshold is 30 times lower than during bleeding. Interestingly, menstruated women undergo maleodorant trimethylaminuria. We argued that olfactory amelioration during ovulation might concur to a mating strategy, whereas olfactory impairment during bleeding might protect women against self-refusal. Testosterone and its 17β-estradiol derivative might be responsible for the synchronization of these menstrual events. Furthermore, we posed the question whether olfactory detection amelioration upon sexual maturation might provoke a change in food preferences, for instance a reduction in fish consumption. A preliminary survey in Italy provided encouraging results: 15-44 year-old women have lower fish consumption than 3-14 year-old girls. Surprisingly, men exhibited the same behaviour, so new olfactory tests as well as testosterone measurements are under way.

Sry delivery to the adrenal medulla increases blood pressure and adrenal medullary tyrosine hydroxylase of normotensive WKY rats

Background

Our laboratory has shown that a locus on the SHR Y chromosome increases blood pressure (BP) in the SHR rat and in WKY rats that had the SHR Y chromosome locus crossed into their genome (SHR/y rat). A potential candidate for this Y chromosome hypertension locus is Sry, a gene that encodes a transcription factor that is responsible for testes development and the Sry protein may affect other target genes.

Methods

The following study examined if exogenous Sry would elevate adrenal Th, adrenal catecholamines, plasma catecholamines and blood pressure. We delivered 10 μg of either the expression construct, Sry1/pcDNA 3.1, or control vector into the adrenal medulla of WKY rats by electroporation. Blood pressure was measured by the tail cuff technique and Th and catecholamines by HPLC with electrochemical detection.

Results

In the animals receiving Sry there were significant increases after 3 weeks in resting plasma NE (57%) and adrenal Th content (49%) compared to vector controls. BP was 30 mmHg higher in Sry injected animals (160 mmHg, p < .05) compared to vector controls (130 mmHg) after 2–3 weeks. Histological analysis showed that the electroporation procedure did not produce morphological damage.

Conclusion

These results provide continued support that Sry is a candidate gene for hypertension. Also, these results are consistent with a role for Sry in increasing BP by directly or indirectly activating sympathetic nervous system activity.

Regulation of the transcriptional activity of the tyrosine hydroxylase gene by androgen receptor

Dopamine and the sex hormone testosterone are important factors regulating male sexual behavior. To investigate the possibility that these two factors are functionally interrelated, we investigated the potential role of the androgen receptor (AR) on transcriptional activity of the tyrosine hydroxylase (TH) gene that encodes the rate-limiting enzyme of the dopamine biosynthesis pathway. In this study, using transient co-transfection assays in TH-positive SK-N-BE(2)C and MN9D cells, we show that AR prominently transactivates TH promoter function in a ligand-dependent manner. Deletional and site-directed mutational analyses have mapped a putative androgen response element (ARE) in a region from -1562 to -1328 base pairs in the upstream TH promoter. We also found that DJ-1, one of recently identified genes whose mutations cause Parkinson's disease, down-regulated AR-dependent TH activation by approximately 50% in SK-N-BE(2)C cells. Based on these data, we propose that AR activates TH gene expression and that DJ-1 may modulate AR activity as a transcriptional co-repressor.

Renal denervation abolishes hypertension in low-birth-weight offspring from pregnant rats with reduced uterine perfusion

Low birth weight is a risk factor for the subsequent development of hypertension in humans. We previously reported that reduced uterine perfusion in the pregnant rat results in growth-restricted offspring predisposed to the development of hypertension. The purpose of this study was to determine whether the sympathetic nervous system plays a role in mediating hypertension in this model of low birth weight. Weight at birth was significantly decreased in male growth-restricted offspring (5.9+/-0.1 grams) as compared with male control offspring (6.5+/-0.2 grams; P<0.05). At 10 weeks of age, growth-restricted offspring and control offspring were randomly assigned to either an intact group (sham-denervated) or a group subjected to bilateral renal denervation. For sham-denervated offspring, mean arterial pressure was significantly elevated in growth-restricted offspring (145+/-4 mm Hg; n=7) as compared with control offspring (134+/-3 mm Hg; P<0.05; n=9) at 12 weeks of age. Bilateral renal denervation resulted in a marked reduction in arterial pressure in growth-restricted offspring (125+/-3 mm Hg; P<0.01; difference of 20 mm Hg versus sham growth-restricted; n=8) but no significant decrease in control offspring (127+/-3 mm Hg; difference of 7 mm Hg versus sham control; n=9). Adequacy of renal denervation was verified by >90% reduction in renal norepinephrine content. Therefore, these findings indicate the renal nerves play an important role in mediating hypertension in adult growth-restricted offspring.

Association of the Human Y Chromosome with Cholesterol Levels in the General Population

Objective— Males are at higher risk of cardiovascular diseases than females. The aim of the study was to test whether the potential of the Y chromosome to affect cardiovascular risk could be attributed to its influence on lipids.

Methods and Results— 1288 Polish men (1157 subjects from young healthy cohort and 131 individuals from middle-aged hypertensive population) were phenotyped for determinants of cardiovascular risk including BMI, blood pressures, lipids, and testosterone. Each subject was genotyped for the Hin dIII(+/−) polymorphism within the nonrecombining region of the Y chromosome. Men with the Hin dIII(−) variant exhibited significantly higher total cholesterol (TC) and low-density lipoprotein cholesterol (LDL) levels than subjects with the Hin dIII(+) genotype in both populations. The differences between the genotypes were 0.15 mmol/L ( P =0.0107) and 0.45 mmol/L ( P =0.0377) in TC and 0.15 mmol/L ( P =0.0059) and 0.41 mmol/L ( P =0.0432) in LDL among young apparently healthy men and middle-aged hypertensive men, respectively. The Hin dIII(+) was associated with a significant increase in blood pressure of the middle-aged men. Testosterone serum concentrations correlated positively with HDL-cholesterol levels, and this association was independent of the Y chromosome.

Conclusions— The results indicate that a locus/loci on the Y chromosome may influence LDL levels, independent of testosterone levels.