TY - JOUR
T1 - Impairment of sympathetic baroreceptor reflexes in obese Zucker rats
AU - Schreihofer, Ann M.
AU - Mandel, Daniel A.
AU - Mobley, Susan C.
AU - Stepp, David W.
PY - 2007/10
Y1 - 2007/10
N2 - Adult obese Zucker rats (OZRs) have elevated sympathetic vasomotor tone and arterial pressure (AP) with blunted baroreflex-mediated changes in heart rate (HR) compared with adult lean Zucker rats (LZRs). The present study examined whether compromised cardiac baroreflexes are indicative of attenuated sympathetic responses. In addition, because juvenile OZRs have a normal mean AP, we determined whether baroreflexes are fully functional prior to hypertension. At 13 wk, adult OZRs had an elevated baseline mean AP compared with LZRs (137 ± 3 vs. 123 ± 5 mmHg, P < 0.05) under urethane anesthesia. Phenylephrine-induced increases in AP evoked smaller inhibitions of splanchnic sympathetic nerve activity (SNA) and HR in OZRs compared with LZRs. In addition, sympathoexcitatory responses to nitroprusside-induced hypotension were also blunted in OZRs. Sigmoid analysis revealed a decreased gain, a higher mean AP at the midpoint of the curve (AP50), and a reduced range of changes in SNA in OZRs. In contrast, at 7 wk of age, although juvenile OZRs weighed more than LZRs (313 ± 13 vs. 204 ± 4 g, P < 0.05), mean AP was comparable in both groups (122 ± 5 vs. 121 ± 4 mmHg, not significant). In these rats, rapid changes in AP evoked comparable changes in SNA and HR in OZRs and LZRs. Sigmoid analysis revealed that, although the gain of the reflex was blunted in OZRs (P < 0.05), the mean AP50 and range of changes in SNA were comparable in OZRs and LZRs. Together, these data indicate that in adult OZRs, sympathetic responses to acute changes in AP are smaller than those observed in adult LZRs and that impairment of baroreceptor reflexes in OZR is not limited to the regulation of HR but extends to sympathetic vasomotor control. In addition, most of these deficits in baroreflex control of SNA develop in adulthood long after the onset of obesity and when other deficits in cardiovascular regulation are present.
AB - Adult obese Zucker rats (OZRs) have elevated sympathetic vasomotor tone and arterial pressure (AP) with blunted baroreflex-mediated changes in heart rate (HR) compared with adult lean Zucker rats (LZRs). The present study examined whether compromised cardiac baroreflexes are indicative of attenuated sympathetic responses. In addition, because juvenile OZRs have a normal mean AP, we determined whether baroreflexes are fully functional prior to hypertension. At 13 wk, adult OZRs had an elevated baseline mean AP compared with LZRs (137 ± 3 vs. 123 ± 5 mmHg, P < 0.05) under urethane anesthesia. Phenylephrine-induced increases in AP evoked smaller inhibitions of splanchnic sympathetic nerve activity (SNA) and HR in OZRs compared with LZRs. In addition, sympathoexcitatory responses to nitroprusside-induced hypotension were also blunted in OZRs. Sigmoid analysis revealed a decreased gain, a higher mean AP at the midpoint of the curve (AP50), and a reduced range of changes in SNA in OZRs. In contrast, at 7 wk of age, although juvenile OZRs weighed more than LZRs (313 ± 13 vs. 204 ± 4 g, P < 0.05), mean AP was comparable in both groups (122 ± 5 vs. 121 ± 4 mmHg, not significant). In these rats, rapid changes in AP evoked comparable changes in SNA and HR in OZRs and LZRs. Sigmoid analysis revealed that, although the gain of the reflex was blunted in OZRs (P < 0.05), the mean AP50 and range of changes in SNA were comparable in OZRs and LZRs. Together, these data indicate that in adult OZRs, sympathetic responses to acute changes in AP are smaller than those observed in adult LZRs and that impairment of baroreceptor reflexes in OZR is not limited to the regulation of HR but extends to sympathetic vasomotor control. In addition, most of these deficits in baroreflex control of SNA develop in adulthood long after the onset of obesity and when other deficits in cardiovascular regulation are present.
KW - Heart rate
KW - Nitroprusside
KW - Phenylephrine
KW - Splanchnic
KW - Sympathetic
UR - http://www.scopus.com/inward/record.url?scp=35349001645&partnerID=8YFLogxK
U2 - 10.1152/ajpheart.01201.2006
DO - 10.1152/ajpheart.01201.2006
M3 - Article
C2 - 17704284
AN - SCOPUS:35349001645
SN - 0363-6135
VL - 293
SP - H2543-H2549
JO - American Journal of Physiology - Heart and Circulatory Physiology
JF - American Journal of Physiology - Heart and Circulatory Physiology
IS - 4
ER -