Responses of mesenteric and renal blood flow dynamics to acute denervation in anesthetized rats

Abstract

Previous studies have shown that renal autoregulation dynamically stabilizes renal blood flow (RBF). The role of renal nerves, particularly of a baroreflex component, in dynamic regulation of RBF remains unclear. The relative roles of autoregulation and mesenteric nerves in dynamic regulation of blood flow in the superior mesenteric artery (MBF) are similarly unclear. In this study, transfer function analysis was used to identify autoregulatory and baroreflex components in the dynamic regulation of RBF and MBF in Wistar rats and young spontaneously hypertensive rats (SHR) anesthetized with isoflurane or halothane. Wistar rats showed effective dynamic autoregulation of both MBF and RBF, as did SHR. Autoregulation was faster in the kidney (0.22 ± 0.01 Hz) than in the gut (0.13 ± 0.01 Hz). In the mesenteric, but not the renal bed, the admittance phase was significantly negative between 0.25 and 0.7 Hz, and the negative phase was abrogated by mesenteric denervation, indicating the presence of an arterial baroreflex. The baroreflex was faster than autoregulation in either bed. The presence of sympathetic effects unrelated to blood pressure was inferred in both vascular beds and appeared to be stronger in the SHR than in the Wistar rats. It is concluded that a physiologically significant baroreflex operates on the mesenteric, but not the renal circulation and that blood flow in both beds is effectively stabilized by autoregulation.

Modulation of the myogenic mechanism: concordant effects of NO synthesis inhibition and O2− dismutation on renal autoregulation in the time and frequency domains

“…Exaggerated vasoconstriction by one of these agonists might explain the enhanced myogenic response during NOS inhibition. However, ANG II and catecholamines do not potentiate the myogenic response in the time domain (20,35) or the frequency domain (1,71,80) as markedly as that seen during NOS inhibition of NO production. On the other hand, O 2 Ϫ does enhance the myogenic response by an action independent of NO (50).…”

Blood pressure-renal blood flow relationships in conscious angiotensin II- and phenylephrine-infused rats

“…The reasons remain to be defined (45,54); however, vascular myogenic responses have been implicated in the generation and buffering of LF BP fluctuations (1,24,60,66). Of particular relevance, parallel differences between ANG II and PE were observed with respect to the fractional gain of the myogenic response in the renal transfer function data (see Table 2).…”

Dynamic characteristics and underlying mechanisms of renal blood flow autoregulation in the conscious dog

“…Teleologically, this could provide protection for the capillaries from rapid increases in pressure, which might be more important in the kidney than in skeletal muscle. The same consideration might apply to the mesenteric vasculature, where the myogenic response also seems to be faster than in muscular tissue (1). The fast response of the renal vessels does not seem to be an invariable feature, because other response times, more closely resembling the pattern in skeletal muscle arterioles, have also been observed in renal vessels (17,52).…”

“…Although these temporal differences have been experimentally investigated by studying the renal and the mesenteric circulation (1) and discussed in a recent review (20), a direct comparison with other vascular beds to our knowledge has never been done, except for a cursory notion in the original work of Bayliss (5) and a step function analysis in artificially perfused organs (31).…”