Effects of angiotensins on day-night fluctuations and stress-induced changes in blood pressure

Abstract

In this study we evaluated by telemetry the effects of ANG II and ANG-(1-7) infusion on the circadian rhythms of blood pressure (BP) and heart rate (HR) and on the cardiovascular adjustment resulting from restraint stress in rats. ANG II or ANG-(1-7) or vehicle were infused subcutaneously for 7 days. Restraint stress was carried out before, during, and after infusion at 7-day intervals. Parallel with an increase in MAP, ANG II infusion produced an inversion of MAP circadian rhythm with a significant MAP acrophase inversion. It also produced bradycardia during the first 3 days of infusion. Thereafter, HR progressively increased, reaching values similar to or above those of the control period at the end of the infusion period. HR circadian variation was not changed by ANG II infusion. Strikingly, ANG II significantly attenuated the increase in MAP induced by restraint stress without altering the HR response. ANG-(1-7) infusion produced a slight but significant decrease in MAP restricted to the daytime period. No significant changes in the MAP acrophase were observed. In addition, ANG-(1-7) infusion produced a small but significant sustained bradycardia. ANG-(1-7) did not change cardiovascular responses to restraint stress. These data indicate that ANG II can influence the activity of brain areas involved in the determination of stress-induced or circadian-dependent variations of blood pressure without changing HR fluctuations. A significant modulatory influence of ANG-(1-7) on basal MAP and HR is also suggested.

Systemic and regional hemodynamic effects of angiotensin-(1–7) in rats

“…The opposite changes in TPR and CO could explain the absence of substantial changes in blood pressure during ANG-(1-7) administration described previously (2,4,60). The increased CO could be explained by an increase in venous return, which in turn can be consequence of the reduced TPR resulting from the vasodilatation in several territories, including mesenteric, cerebral, renal, and cutaneous vascular beds.…”

“…The blood vessels are an important site for the opposing actions of ANG II and ANG- (1)(2)(3)(4)(5)(6)(7). Vascular responses to ANG-(1-7) significantly differ from those induced by ANG II.…”

“…One important question that arises from these observations is how this peptide contributes to the regulation of both regional and systemic hemodynamics in vivo. From the contrast between the vasodilatory effects of ANG-(1-7) and its negligible effects on blood pressure (2,4,60), we hypothesized that this peptide could influence blood flow distribution and present opposite effects on cardiac output (CO) and total peripheral resistance (TPR). To test this hypothesis, we determined the effects of ANG-(1-7) and of its selective antagonist A-779 on regional blood flow distribution in rats.…”

Effects of Angiotensin Type 2 Receptor Overexpression in the Rostral Ventrolateral Medulla on Blood Pressure and Urine Excretion in Normal Rats

“…25 On the other hand, systemic Ang II infusion also reversed the blood pressure circadian rhythm. 26,27 Interestingly, the circadian expression pattern of AT 1 R mRNA expression in the suprachiasmatic nuclei of the anterior hypothalamus in rats has been reported recently. 28 In addition, in a recent report from our laboratory, central AT 1 R expression exhibited a circadian rhythm in the central nervous system that was lost in mice after the induction of chronic heart failure.…”

Effects of Urocortin, Corticotropin-Releasing Factor (CRF) Receptor Agonist, and Astressin, CRF Receptor Antagonist, on the Sleep-Wake Pattern: Analysis by Radiotelemetry in Conscious Rats

“…Transmitter volumes are also variable, ranging from 1.75 to 33 ml. By using these telemetry systems, many researchers reported body temperature, 1) motor activity, 2) biopotentials [electroencephalogram (EEG), electrocardiogram, and electromyogram (EMG)], 3) and other physiological and behavioral variables in conscious and freely-moving animals throughout the circadian cycle (e.g., blood pressure 4) ). In 1990, Livezey and Sparber 5) reported an implantable radiotelemetry system to measure EEG in rats.…”