Arterial baroreceptor reflex control of sympathetic nerve activity in the spontaneously hypertensive rat.

Abstract

SUMMARY The combined and individual carotid sinus and aortic baroreceptor control of sympathetic nerve activity (SNA) and mean arterial pressure (MAP) were studied by direct measurement In groups of spontaneously hypertensive rats (SHR) and normotensive Kyoto Wistar rats (WKY) of 5 to 40 weeks of age. The SHR showed a significantly greater SNA and resultant MAP increase as a function of age compared to that of the WKY rats. Both SHR and WKY rats showed a significant rise in SNA and MAP with ablation of all four major baroreceptors. The proportionate change of SNA and MAP after ablation was greater in the younger SHR than In the younger WKY groups and the change in these decreased as a function of age in the SHR. The reflex inhibition of SNA via baroreceptor stimulation also decreased as a function of age in the SHR, due to a 43% loss of aortic inhibitory function; no significant loss of carotid sinus function was found in either the SHR or WKY. The decrement in aortic function occurred after the rapid phase of blood pressure development; therefore baroreceptor dysfunction cannot be the cause of the high SNA and MAP observed in young SHR. An upward resetting of central sympathetic centers was evaluated via the baroreceptor deafferentatlon; and, it appears that the hyperactive sympathetic nervous system and resultant hypertension in the SHR is due to central resetting of sympathetic centers rather than baroreceptor dysfunction. T HE sympathetic nervous system has been shown to be hyperactive in the spontaneously hypertensive rat (SHR), and to be a significant factor in the development and maintenance of high blood pressure in this genetic model of hypertension. 16 The factors responsible for the elevated sympathetic nerve activity (SNA) in the SHR are unknown. Historically, it was hypothesized that in experimental renal hypertension a loss of carotid sinus and aortic reflex inhibitory control of SNA resulted in an increase in SNA which in turn produced the hypertensive condition. However, in such studies, the arterial baroreceptors have been shown to adapt or reset during hypertension, such that they have an increased stimulus pressure threshold, a normal firing frequency, and an extended operational range."

Avaliação da função barorreflexa em ratos jovens espontaneamente hipertensos

“…According to Ito et al 22 , although the inhibition of endogenous rho-kinase in the medulla oblongata augments the baroreflex control of heart rate in WKY and SHR, it improves the impaired baroreflex function in SHR. Earlier studies that described a significant difference in blood pressure between WKY and SHR at 3 weeks of age 23 or at birth 24 were based on the assessment of a few animals. However, the age at which the baroreflex function starts to decrease in SHR has yet to be demonstrated.…”

Sympathetic Regulation of the Renal Functions in Rats Reciprocally Congenic for Chromosome 1 Blood Pressure Quantitative Trait Locus

“…A number of studies have suggested the important role of the SNS in the spontaneously hypertensive rat (SHR) and the stroke-prone SHR (SHRSP); SHR have been shown to exhibit elevated efferent renal sympathetic nerve activity (RSNA) before hypertension is established (3). In addition, the renal norepinephrine (NE) content has been reported to be 2 times and 1.5 times greater in newborn (4) and adult SHR (5), respectively, when compared with age-and sex-matched Wistar-Kyoto rats (WKY).…”

Antihypertensive effect of vasopressin withdrawal in young and adult spontaneously hypertensive rats.

“…6 In rats, the baroreceptor reflex control of heart rate may be enhanced by AVP through V 2 receptors, 22 whereas the pressor activity of AVP may be buffered through a nonbaroreceptor reflex withdrawal of sympathetic tone. 23 Interestingly, sympathetic hyperactivity 24 and impairment of baroreceptor reflex function 25 are found in SHR. Unlike the normotensive dog 26 and rat 27 , in which baroreceptor reflex function improves with age, SHR has an age-dependent impairment of baroreceptor reflex function.…”