SHR Y chromosome enhances the nocturnal blood pressure in socially interacting rats

The SHR Y chromosome increases cardiovascular, endocrine, and behavioral responses to stress compared to the WKY Y chromosome

The SHR Y chromosome has loci which are involved with behavioral, endocrine and brain phenotypes and respond to acute stress to a different degree than that of the WKY Y chromosome. The objectives were to determine if WKY males with an SHR Y chromosome (SHR/y) when compared to males with a WKY Y chromosome would have: 1. a greater increase in systolic and diastolic blood pressures (BP), heart rate (HR), and locomotor activity when placed in an open field environment and during an acute stress procedure; 2. enhanced stress hormone responses; 3. greater voluntary running; and 4. increased brain Sry expression. The SHR/y strain showed a significant rise in BP (32%) and HR (10%) during the open field test and exhibited higher BP (46% change) during air jet stress. SHR/y had higher locomotor activity and less immobility and had increased stress induced plasma norepinephrine and adrenocorticotrophic hormone and 3-4× more voluntary running compared to WKY. Differential Sry expression between WKY and SHR/y in amygdala and hippocampus was altered at rest and during acute stress more than that of WKY. Evidence suggests that this animal model allows novel functions of Y chromosome loci to be revealed. In conclusion, a transcription factor on the SHR Y chromosome, Sry, may be responsible for the cardiovascular, endocrine and behavioral phenotype differences between SHR/y and WKY males.

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.

Longitudinal studies on the effect of hypertension on circadian hemodynamic and autonomic rhythms in telemetered rats

This study dealt with the long-term effects of hypertension on circadian rhythms of hemodynamic and cardiovascular autonomic functions in radiotelemetered rats. Blood pressure (BP), heart rate (HR), spontaneous locomotor activity, and respiration.were monitored in spontaneously hypertensive rats (SHRs), a model of human hypertension, from 14 to 27 weeks of age and in Wistar-Kyoto rats (WKY) as controls. Cardiovascular autonomic changes were determined by time-domain analysis of the variability of BP (standard deviation of mean arterial pressure, SDMAP) and HR (standard deviation of R-R intervals, SDRR, and the root mean square of successive differences in R-R intervals, rMSSD). Compared with WKY rats, the 24-hr MAP and SDMAP were higher at week 14 in SHRs and showed stepwise increases over the study duration, suggesting progressive increases in vasomotor sympathetic activity in hypertensive rats. Also, higher SDRR, rMSSD, and activity and lower HR and respiration were demonstrated in SHRs. Normal circadian rhythms (higher dark-time values) of MAP, HR, SDMAP, and SDRR were evident in WKY rats at week 20 and continued thereafter. Compared with WKY rats, the circadian BP and HR patterns were abolished and inverted, respectively, in SHRs. Lower dark-time, compared with light-time, SDMAP values were observed in SHRs that were associated with temporal increases in HR variability indices. These findings demonstrate that hypertension elicits significant alterations in circadian autonomic and hemodynamic profiles. Further, the steady increases in BP, average level and oscillations, in SHRs may explain the reported progressive age-related vascular and cardiac hypertrophy in these rats.

Regulation of tyrosine hydroxylase gene transcription by Sry

Testes determining factor Sry is encoded by the Sry locus on the Y chromosome and may be involved in the regulation of blood pressure. Here we tested the hypothesis that Sry regulates transcription of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines. Sry was found to be expressed in catecholaminergic regions, in male but not female rats. Co-transfection of PC12 cells with expression vector for Sry and the reporter construct [p5'TH(-773/+27)/Luc], containing 773 of the proximal nucleotides of the TH promoter directing luciferase reporter activity, led to elevation of reporter activity. The reporter activity of a shorter construct [p5'TH(-272/+27)/Luc] lacking putative Sry sites also responded to Sry. However, mutation of the AP1 site in the TH promoter greatly reduced induction by Sry, indicating that the regulation is primarily at this motif. The remaining, significantly increased expression with the mutated TH promoter construct may reflect Sry function at other sites in addition to the AP1 motif. These results reveal that Sry can regulate TH transcription and suggest that this may be one of the mechanisms of Sry mediated regulation of catecholamine biosynthesis in catecholaminergic neurons in males.

Sodium-induced rise in blood pressure is suppressed by androgen receptor blockade

Our objective was to test the hypothesis that 1) a high Na (HNa, 3%) diet would increase blood pressure (BP) in male Wistar-Kyoto (WKY) and spontaneously hypertensive Y chromosome (SHR/y) rat strains in a territorial colony; 2) sympathetic nervous system (SNS) blockade using clonidine would lower BP on a HNa diet; and 3) prepubertal androgen receptor blockade with flutamide would lower BP on a HNa diet. A 2 x 4 factorial design used rat strains (WKY, SHR/y) and treatment [0.3% normal Na (NNa), 3% HNa, HNa/clonidine, and HNa/flutamide]. BP increased in both strains on the HNa diet (P < 0.0001). There was no significant decrease in BP in either strain with clonidine treatment. Androgen receptor blockade with flutamide significantly decreased BP in both strains (P < 0.0001) and normalized BP in the SHR/y colony. Neither heart rate nor activity could explain these BP differences. In conclusion, a Na sensitivity was observed in both strains, which was reduced to normotensive values by androgen blockade but not by SNS blockade.