Key result
ANP-knockout mice exhibited a significantly depressed tachycardic response to transient hypotension compared to wild-type controls, indicating reduced baroreceptor sensitivity.
Why the study?
Does ANP depletion alter baroreflex gain during transient hypotension or hypertension in mice?
Does ANP depletion alter baroreflex gain during transient hypotension or hypertension in mice?
ANP-knockout mice exhibit impaired baroreflex-mediated tachycardic responses to hypotension, likely due to an inability to further increase their already high basal sympathetic nervous activity.
We studied baroreflex gain in inactin-anesthetized mice that had been genetically modified to be depleted of atrial natriuretic peptide (ANP -/-). Wild-type mice (ANP +/+) served as controls. ANP -/- mice had a significantly higher basal arterial blood pressure (ABP) than ANP +/+ mice [112+/-7 vs. 80+/-5 mmHg (mean +/- SEM)]. Their basal heart rates were not different (491+/-13 vs. 446+/-19 bpm). A third group, composed of ANP +/+ mice only, was rendered acutely hypertensive by an intravenous infusion of arginine vasopressin acetate (0.3 pg bolus followed by 0.3 pg/h) so as to serve as a control for the elevated ABP in the ANP -/- mice. Transient changes in ABP were caused by bolus injections of oxymetazoline hydrochloride (1.5-3 ng) or sodium nitroprusside (20-100 ng). Baroreflex gain was calculated as the ratio of the peak heart rate change that followed the peak change in mean ABP resulting from injection of oxymetazoline or nitroprusside. There were no significant differences among the groups in their responses to transient hypertension. On the other hand, the ANP -/- mice showed a significantly depressed tachycardic response to transient hypotension when compared with the other two groups. We conclude that the ANP -/- mice are unable to increase efferent sympathetic nervous activity adequately above the high basal activity that is a feature of this animal model.
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Ackermann et al. (2001) studied ANP-knockout mice. ANP knockout (ANP -/-) vs. Wild-type mice (ANP +/+) and ANP +/+ mice rendered acutely hypertensive was evaluated on Baroreflex gain (ratio of peak heart rate change to peak change in mean ABP). ANP-knockout mice exhibited a significantly depressed tachycardic response to transient hypotension compared to wild-type controls, indicating reduced baroreceptor sensitivity.
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