Gail Dunphy

Spontaneously Hypertensive Rat Y Chromosome Increases Indexes of Sympathetic Nervous System Activity

Previous studies from our laboratory have demonstrated that the Y chromosome from the spontaneously hypertensive rat (SHR) is responsible for a significant portion of the elevated blood pressure and also produces an earlier pubertal rise in plasma testosterone. We performed the following studies to determine whether the SHR Y chromosome raises blood pressure by sympathetic nervous system responses as measured by adrenal chromogranin A and plasma and tissue catecholamines. Male SHR from the University of Akron colony were studied from 5 to 20 weeks of age. Blood pressure was measured by tail-cuff, tail artery cannulation, and aortic telemetry (Data Sciences); acute (air stress) and chronic (territorial colony) social stressors were compared; blood was collected for determination of plasma catecholamines; and adrenal glands were analyzed at 15 weeks for catecholamines. Rats with the SHR Y chromosome had higher blood pressure and plasma norepinephrine than those with the normotensive Wistar-Kyoto (WKY) Y chromosome. However, the SHR Y chromosome did not significantly change responsiveness to acute or chronic stressors. Phentolamine and clonidine prevented the stress responses. Adrenal chromogranin A levels were elevated 37% and 40% and adrenal norepinephrine content 29% and 100% at 4 and 10 weeks of age, respectively, in rats with an SHR Y chromosome compared with WKY. Chemical sympathectomy normalized blood pressure in all strains and significantly reduced norepinephrine (36% to 41%) in all strains except in WKY, which already had a normal blood pressure. In conclusion, the SHR Y chromosome appears to increase the chronic sympathetic nervous system. A potential mechanism could be a Y locus that influences chronic sympathetic nervous system activity, which may reinforce neurohumoral factors and structural components of the vessel wall, accelerating the development of hypertension.

An examination of Perceived Stress in family caregivers of older adults with heart failure

This investigation evaluates the moderating influence of social support on the negative effects of stress for family caregivers and validates the Perceived Stress Scale as a standard of measurement. Seventy-five family caregivers to older adults with heart failure were interviewed in their homes about perceived stress, depressive symptoms, and social support after hospital discharge. The Perceived Stress Scale demonstrated internal consistency. Social support did not moderate the effects of stress on depressive symptoms. Lack of a significant association between salivary cortisol and the Perceived Stress Scale did not support testing of construct validity. Stress levels, however, frequently vary due to caregiving demands and additional influencing factors.

The spontaneously hypertensive rat Y chromosome produces an early testosterone rise in normotensive rats.

Objective To investigate the relationship between testosterone and blood pressure during the rapid development phase of blood pressure rise in four strains of rats: Wistar–Kyoto (WKY) rats; spontaneously hypertensive rats (SHR); SHR/y, a substrain with an SHR Y chromosome and WKY rat autosomes and X chromosomes; and SHR/a, a substrain with SHR autosomes and X chromosomes and the WKY rat Y chromosome. Methods Blood pressure was measured every 2 weeks by the tail-cuff method, and was verified in selected rats at 23 weeks by aortic telemetry. Serum testosterone was measured, by radioimmunoassay, every 2 weeks from 5 to 23 weeks of age. Results During the rapid phase of blood pressure rise, between 5 and 9 weeks of age, there was a significantly larger rise in serum testosterone in SHR and SHR/y than in WKY rats and SHR/a groups. The hypertensive Y chromosome in the SHR and SHR/y accelerated peak testosterone approximately 4 weeks earlier, and blood pressure was increased in these two groups compared with the SHR/a and WKY rat groups, respectively. A gene on the SHR Y chromosome (Tty) affecting the timing of testosterone in development is proposed. At approximately 15 weeks of age testosterone levels decreased sharply towards prepubertal levels in WKY rats and at 23 weeks in SHR/y, whereas testosterone levels were maintained in SHR and SHR/a, which suggests an autosomal component. Conclusion The SHR Y chromosome may accelerate the start of puberty and a cascade of molecular and neuroendocrine events that raise blood pressure.

Review of The Y Chromosome, Sry and Hypertension

The following review examines the role of the SHR Y chromosome and specifically the Sry gene complex in hypertension and potential mechanisms that involve the sympathetic nervous system and renin-angiotensin system. There are consistent gender differences in hypertension, with a greater proportion of males affected than females in most mammalian populations. Our earlier studies demonstrated that a portion of the gender differences in blood pressure (BP) in the SHR rat mapped to the SHR Y chromosome. In rats, males with the SHR Y chromosome have higher BP than females, or males with a different Y chromosome. Consistent with these results, several human population studies have confirmed a Y chromosome effect on BP. Our more recent studies focus on a transcription factor, Sry, as the locus involved in not only BP modulation but effects on other phenotypes. The Sry locus is an evolutionarily conserved locus on the mammalian Y chromosome responsible for testis determination and is a transcription factor. The Sry locus contains a highly conserved High Mobility Group (HMG) box region responsible for DNA binding. Mutations in the HMG box result in sex reversal. We have found multiple functional copies of Sry in SHR and WKY male rats. There is abundant evidence that testes determination may not be Srys only function as it is expressed in the brain, kidney and adrenal gland of adult males. These findings have potential implications for gender physiology research which involves, the sympathetic nervous system, renin-angiotensin system, androgen receptor regulation and prostate physiology.

Delivery of sry1, but not sry2, to the kidney increases blood pressure and sns indices in normotensive wky rats

BackgroundOur laboratory has shown that a locus on the SHR Y chromosome increases blood pressure (BP) in the SHR rat and in WKY rats with the SHR Y chromosome (SHR/y rat). A candidate for this Y chromosome hypertension locus is Sry, a gene that encodes a transcription factor responsible for testes determination. The SHR Y chromosome has six divergent Sry loci. The following study examined if exogenous Sry1 or Sry2 delivered to the kidney would elevate renal tyrosine hydroxylase, renal catecholamines, plasma catecholamines and telemetered BP over a 28 day period. We delivered 50 μg of either the expression construct Sry1/pcDNA 3.1, Sry2/pcDNA 3.1, or control vector into the medulla of the left kidney of normotensive WKY rats by electroporation. Weekly air stress was performed to determine BP responsiveness. Separate groups of animals were tested for renal function and plasma hormone patterns and pharmacological intervention using alpha adrenergic receptor blockade. Pre-surgery baseline and weekly blood samples were taken from Sry1 electroporated and control vector males for plasma renin, aldosterone, and corticosterone. BP was measured by telemetry and tyrosine hydroxylase and catecholamines by HPLC with electrochemical detection.ResultsIn the animals receiving the Sry1 plasmid there were significant increases after 21 days in resting plasma norepinephrine (NE, 27%) and renal tyrosine hydroxylase content (41%, p < .05) compared to controls. BP was higher in animals electroporated with Sry1 (143 mmHg, p < .05) compared to controls (125 mmHg) between 2–4 weeks. Also the pressor response to air stress was significantly elevated in males electroporated with Sry1 (41 mmHg) compared to controls (28 mmHg, p < .001). Sry2 did not elevate BP or SNS indices and further tests were not done. The hormone profiles for plasma renin, aldosterone, and corticosterone between electroporated Sry1 and control vector males showed no significant differences over the 28 day period. Alpha adrenergic receptor blockade prevented the air stress pressor response in both strains. Urinary dopamine significantly increased after 7 days post Sry electroporation.ConclusionThese results are consistent with a role for Sry1 in increasing BP by directly or indirectly activating renal sympathetic nervous system activity.

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

BackgroundOur 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.MethodsThe 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.ResultsIn 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.ConclusionThese 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.

Social stress increases blood pressure and cardiovascular pathology in a normotensive rat model.

Territorial stress (TS) elevates blood pressure (BP) in several mammalian species. However, cardiovascular pathology following chronic stress has not been consistently shown in a non‐genetic hypertension model. Therefore, the hypothesis tested was that social stress would directly increase: BP, collagen deposition in coronary and mesenteric arteries, and myocardial fibrosis. Wistar–Kyoto (WKY) male rats, four weeks of age, were divided into one of three groups: controls (n = 9), territorial stress (TS, n = 12), and social isolation followed by territorial stress (SITS, n = 11). Blood pressure was measured biweekly, and blood samples biweekly for serum testosterone, corticosterone, epinephrine and norepinephrine. Blood pressure significantly increased in the TS (130 mmHg, p < 0.05) and SITS (150 mmHg, p < 0.05) groups, compared to controls (120 mmHg, ANOVA, F = 6.7, p < 0.001). Coronary collagen was increased 47% in the TS group and 90% in the SITS group compared to controls ( p < 0.05). The coronary wall/lumen ratio increased significantly (45%, p < 0.05) in the SITS group compared to the controls. Myocardial fibrosis was increased 27% in the TS group and 74% in the SITS group compared to controls ( p < 0.05). In conclusion, stress treatments increased BP and cardiac pathology in a normotensive rat strain.

Testosterone Effects on Renal Norepinephrine Content and Release in Rats With Different Y Chromosomes

The Y chromosome in spontaneously hypertensive rats (SHR) and stroke-prone rats has been shown to contain a locus that contributes to the hypertensive effect; both the sympathetic nervous system and testosterone may be involved. The objective of this study was to look at the effects of testosterone on renal norepinephrine (NE) release and content in the isolated perfused kidney in different Y chromosome backgrounds. The study involved male SHR, Wistar-Kyoto rats (WKY), and 2 consomic strains with different Y chromosomes (n=5 to 8 per group). Adult animals were castrated, and implants containing testosterone propionate were placed at the base of the neck. Blood testosterone levels were measured by radioimmunoassay 2 weeks after castration. The left kidney was isolated and perfused with oxygenated Krebs solution at a constant flow and temperature with KCl and electrical stimulation of the renal nerves. Perfusate was collected and analyzed for NE by high-performance liquid chromatography. Lactate dehydrogenase analyses were performed as a marker for potential tissue damage. Renal perfusate and renal tissue NE levels were significantly elevated by testosterone. The average NE increase with a single testosterone implant was 13.2 ng/mL, and for a double testosterone implant it was 29.8 ng/mL. The Y chromosome from the SHR produced a significant increase in renal NE release compared with the WKY Y chromosome. Significance was shown between all groups: 1 versus 2 implants, P=0.0067; 1 versus sham implants, P=0.015; 2 versus sham implants, P<0.001. In conclusion, testosterone caused an enhanced renal NE release that was strain-specific, with the Y chromosome raising renal NE content and release.

Maintenance of left ventricular function (90%) after twenty-four-hour heart preservation with deferoxamine

During 24-h in vitro heart preservation and reperfusion, irreversible tissue damage occurs caused by reactive oxygen intermediates, such as superoxide radicals, singlet oxygen, hydrogen peroxide, hydroperoxyl, hydroxyl radicals, as well as the peroxynitrite radical. Reduction of the related oxidative damage of reperfused ischemic tissue by free radical scavengers and metal chelators is of primary importance in maintaining heart function. We assessed whether deferoxamine (DFR) added to a cardioplegia solution decreased free radical formation during 24-h cold (5 degrees C) heart preservation and normothermic reperfusion (37 degrees C) in the Langendorff isolated perfused rat heart. The deferoxamine treated hearts were significantly (p less than .001) better preserved than the control hearts after 24 h of preservation with regard to recovery of left ventricular diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), creatine kinase release, and lipid peroxidation. DFR preserved cell membrane integrity and maintained 93% of left ventricular contractility. The evidence suggests that DFR reduces lipid peroxidation damage by reducing free radical formation and thereby maintaining normal coronary perfusion flow and myocardial function.

CO2 asphyxia increases plasma norepinephrine in rats via sympathetic nerves

The objective of this study was to determine whether the plasma norepinephrine (NE) increase in rats exposed to CO2 asphyxia was due to adrenal gland release or sympathetic nerve ending (SNS) release. Plasma NE was measured by high-performance liquid chromatography in hypertensive and normotensive rats using the following protocol: control session, CO2 exposure, N2 exposure, reserpine + CO2, and adrenalectomy + CO2. Four strains of male and female rats were used: spontaneously hypertensive rats, Wistar-Kyoto rats, and two congenic strains with different Y chromosomes. The same rats were used throughout the experiment ( n = 80). Blood pressure measured by aortic telemetry increased ∼50-60 mmHg in response to CO2 in all strains. CO2 increased NE 6-10× in all strains and both genders. N2 produced a significant increase in NE (73% of CO2 response). Reserpine significantly decreased (67%) plasma NE after CO2. Adrenalectomy did not significantly reduce the NE response to CO2. In conclusion, the increase in plasma NE after CO2 was associated with SNS release and not adrenal medullary release, was mainly due to hypoxia, and was not a specific response to CO2.The objective of this study was to determine whether the plasma norepinephrine (NE) increase in rats exposed to CO2 asphyxia was due to adrenal gland release or sympathetic nerve ending (SNS) release. Plasma NE was measured by high-performance liquid chromatography in hypertensive and normotensive rats using the following protocol: control session, CO2 exposure, N2 exposure, reserpine + CO2, and adrenalectomy + CO2. Four strains of male and female rats were used: spontaneously hypertensive rats, Wistar-Kyoto rats, and two congenic strains with different Y chromosomes. The same rats were used throughout the experiment (n = 80). Blood pressure measured by aortic telemetry increased approximately 50-60 mmHg in response to CO2 in all strains. CO2 increased NE 6-10x in all strains and both genders. N2 produced a significant increase in NE (73% of CO2 response). Reserpine significantly decreased (67%) plasma NE after CO2. Adrenalectomy did not significantly reduce the NE response to CO2. In conclusion, the increase in plasma NE after CO2 was associated with SNS release and not adrenal medullary release, was mainly due to hypoxia, and was not a specific response to CO2.