Spontaneously hypertensive rats exhibited higher MAP variability and reduced HR variability compared to Wistar-Kyoto rats, with an increased dependence on the sympathetic nervous system with age.
The relative influences of sympathetic and parasympathetic neural modulation on mean arterial pressure (MAP) and heart rate (HR), and their respective variabilities, were studied in young spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). An on-line computerized system was used for continuous intra-arterial measurements of MAP and HR in unrestrained rats. In addition, the autonomic nervous control of MAP and HR was studied in ageing SHR and WKY. Both WKY and SHR showed diurnal rhythms with regard to MAP and HR. The MAP variability was higher in SHR than in WKY during both daytime (inactive) and night-time (active), and did not change in response to either beta 1-adrenoceptor- or cholinergic blockade. Structural vascular changes, with a resultant increase in reactivity, may explain the elevated MAP variability in SHR. HR variability was clearly reduced in SHR; this was not influenced by vagal blockade, whereas HR variability was significantly reduced in WKY. This pattern is suggested to be due to a reduced tonic vagal discharge in SHR, as part of a persistent, mild defence reaction. The initial reduction in vagal activity will in turn eliminate vagally mediated tachycardias. Furthermore, administration beta 1-blockade to SHR of different ages caused a greater fall in MAP and HR than in WKY, indicating an increased dependence upon the sympathetic nervous system in SHR with age.
Friberg et al. (Sun,) conducted a other in Hypertension. beta 1-adrenoceptor and cholinergic blockade vs. Wistar-Kyoto rats (WKY) was evaluated on Mean arterial pressure (MAP) and heart rate (HR) variability. Spontaneously hypertensive rats exhibited higher MAP variability and reduced HR variability compared to Wistar-Kyoto rats, with an increased dependence on the sympathetic nervous system with age.