Abstract 351: Temperature Dependency of Blood Pressure and Heart Rate in Norepinephrine-Deficient Mice
Dopamine beta-hydroxylase (Dbh) knockout mice lack the sympathetic neurotransmitter, norepinephrine, but have intact sympathetic neurons and adrenergic receptors. These mice offer an excellent model for assessing the role of the sympathetic nervous system in physiological and pathophysiological processes. Mouse blood pressure (BP) and heart rate (HR) increase as ambient temperature drops below the thermoneutral temperature (30° C), apparently due to sympathetic nervous system activation. The present study tested the hypothesis that BP and HR are not sensitive to changes in ambient temperature in Dbh knockout (KO) mice lacking sympathetic function. BP, HR and activity data were obtained at least one week after BP telemeters were implanted in the carotid artery. Eight Dbh wild type (WT) and 7 KO mice were initially maintained at 23° C, singly housed in temperature-controlled brooders with a 12-hour light-dark cycle. With 3° C temperature changes every 3-4 days, chambers were warmed to 32° C, followed by cooling back to 23° C. Twenty-four hour averaged BP and HR were significantly lower in KO than WT mice at all temperatures, although activity levels were no different. HR, averaged over 24hr, were significantly higher at 23° C after cooling from 32° C for both genotypes (mean±SD; KO: 376±24 to 462±53 beats/min, P=0.016; WT: 411±22 to 542±46 beats/min, P=0.008). In contrast, BP increased with the drop in temperature only in the WT mice (KO: 83±7 to 87±10 mmHg, P=0.109; WT: 94±9 to 107±9 mmHg, P=0.008), and BP differences between 32° and 23° C were greater in WT mice (delta BP23°-32° averaged 12.2±5.4 mmHg for WT and 4.2±5.0 mmHg for KO, P=0.011). Activity did not change as ambient temperature was lowered. These data indicate that effects of ambient temperature on HR occur independently of sympathetic activation, but our results confirm that an intact sympathetic nervous system is required for the pressor effect of a cooler environmental temperature.
- © 2012 by American Heart Association, Inc.