Chronic angiotensin-II treatment potentiates HR slowing in Sprague–Dawley rat during acute behavioral stress

Abstract

This study examined the effect of two-weeks infusion of angiotensin-II (Ang-II; 175 ng/kg/min) via minipump in rats (n=7) upon the mean arterial blood pressure (mBP) and heart rate (HR) response to an acute stress as compared to rats infused with saline (n=7). The acute stress was produced by a classical aversive conditioning paradigm: a 15 sec. tone (CS+) followed by a half second tail shock. Baseline mBP in Ang-II infused rats (167.7 ± 21.3 mm Hg; mean ± SD) significantly exceeded that of controls (127.6 ± 13.5 mm Hg). Conversely, baseline HR in the Ang-II infused rats (348 ± 33) was significantly lower than controls (384 ± 19 bpm). The magnitude of the mBP increase during CS+ did not differ between groups, but the HR slowing during CS+ in the Ang-II infused rats (−13.2 ± 8.9 bpm) was significantly greater than that seen in controls (−4.2 ± 5.5 bpm). This augmented bradycardia may be inferentially attributed to an accentuated increase in cardiac parasympathetic activity during CS+ in the Ang-II infused rats. The mBP increased above baseline immediately post-shock delivery in controls, but fell in the Ang-II infused rats, perhaps because of a ‘ceiling effect’ in total vascular resistance. This classical conditioning model of ‘acute stress’ differs from most stress paradigms in rats in yielding a HR slowing concomitant with a pressor response, and this slowing is potentiated by Ang-II.

Effects of perinatal oxycodone exposure on the cardiovascular response to acute stress in male rats at weaning and in young adulthood

“…We reported beat-by-beat mBP via telemetry averaged over 24 h in rats ~60–90 days of age while in their home cages to be ~98 mm Hg, and that mBP gradually declined thereafter as the animals matured (Anigbogu et al, 2012). By comparison, we reported (Hoyt et al, 2013) a mBP of 127.6 ± 13.5 (SD) mm Hg via catheter in behaviorally conditioned adult rats during the 15 s baseline (i.e., as in the present study), which is clearly higher than our value from the 24 h telemetry. The present pups were not subject to the sock restraint or periodic handling between measurements at PD 40 and at PD 75, so the unexpectedly high mBP perhaps is attributable to the relatively unaccustomed restraint on PD 75.…”

Maternal separation diminishes α-adrenergic receptor density and function in renal vasculature from male Wistar-Kyoto rats

“…The neural control of the cardiovascular system is accomplished through the autonomic nervous system. Particularly, the sympathetic nervous system (SNS) branch plays an important role in the acute regulation of blood pressure (17,23,38,66). However, when chronically stimulated, it compromises the cardiovascular function by eliciting end-organ damage (50,53).…”