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.