Chronic lability of the arterial blood pressure produced by electrolytic lesions of the nucleus tractus solitarii in the rat.

Abstract

SUMMARY. The purpose of this study was to assess the chronic effects of lesions of the nucleus tractus solitarii on the cardiovascular activity of rats. Arterial pressure and heart rate were recorded in conscious, unrestrained rats 7-216 days following placement of electrolytic lesions in the nucleus tractus solitarii. To assess the impact of environmental stimuli on the mean level and lability of the mean arterial pressure, cardiovascular activity was recorded under conditions of controlled and uncontrolled environmental stimulation. Nucleus tractus solitarii lesions abolished the reflex bradycardia to a phenylephrine-induced elevation in arterial pressure. A marked increase in the lability of the mean arterial pressure was produced with nucleus tractus solitarii lesions. The standard deviation of the mean arterial pressure, an index of lability, was 380% greater in rats with lesions than in control rats. The average mean arterial pressure, heart rate and heart rate variability were not significantly different between the lesion and control groups, regardless of the environmental conditions under which the measurements were made. Nucleus tractus solitarii lesions also greatly exaggerated the arterial pressure response to naturally occurring behaviors, such as eating and drinking. Vagal and /S-adrenergjc blockade with methyl atropine and propranolol did not alter the average level or lability of the mean arterial pressure, although heart rate responses were similar in both groups. a-Receptor blockade with prazosin significantly lowered the mean arterial pressure in both lesion and control rats, but the decrease in mean arterial pressure was significantly greater in rats with nucleus tractus solitarii lesions (42 ± 6 mm Hg, 38.5%) than in control rats (27 ± 4 mm Hg, 23.2%). Prazosin also reduced the lability of the mean arterial pressure to control levels in rats with lesions. Thus, the chronic effects of nucleus tractus solitarii lesions in rats are to abolish the cardiomotor component of the baroreflexes and to produce extreme lability of the arterial pressure without altering the average level of the mean arterial pressure. Exaggerated blood pressure responses are seen in association with various behaviors. These effects are mediated primarily by changes in sympathetic discharge to the vasculature and are independent of the ambient level of environmental stimuli. (Circ Res 54: 227-238, 1984)

Involvement of vasodilator mechanisms in arterial pressure lability after sino‐aortic baroreceptor denervation in rat.

“…However, in our study, ,-adrenoceptor blockade with propranolol did not stabilize arterial pressure and regional vascular conductances. Therefore, like other authors (Buchholz & Nathan, 1984;Alper et al 1987), we exclude a major contribution of a fl-adrenoceptor-mediated mechanism in the depressor component of arterial pressure lability in rats after disruption of the baroreceptor reflex loop. An alternative explanation would implicate spontaneous withdrawal of sympathetic vasomotor tone leading to vasodilatation.…”

“…This has been verified after: (i) surgical denervation of arterial baroreceptors (sinoaortic baroreceptor denervation, SAD) in several animal species including dogs (Cowley, Liard & Guyton, 1973), cats , lambs (Yardley et al 1983), rabbits (Saito, Terui, Numao & Kumada, 1986), rats (Alper, Jacob & Brody, 1987) and monkeys (Bishop, Shade, Haywood & Hamm, 1987); (ii) electrolytic lesions of the nucleus tractus solitarii in cats (Nathan & Reis, 1977) and rats (Buchholz & Nathan, 1984); and (iii) chemical destruction of postganglionic sympathetic nerve terminals in rats (Julien, Kandza, Barres, Lo, Cerutti & Sassard, 1990;Daffonchio et al 1991). Arterial pressure lability has also been reported in humans after mediastinal radiation and carotid bypass surgery (Aksamit, Floras, Victor & Aylward, 1987).…”

Comparison of 1-hour and 24-hour blood pressure recordings in central or peripheral baroreceptor-denervated rats.

“…23 Moreover, ambient environmental stimuli had no effect on the average level or lability of the MAP in rats, regardless of the presence or absence of functioning arterial baroreceptor reflexes. However, these determinations were based only on 1-hour continuous recordings of arterial pressure.…”

“…Bilateral electrolytic lesions were placed in the NTS at the level of the obex, as described in detail elsewhere. 23 Briefly stated, lesions were made by passing a direct anodal current (0.8 mA) through a Teflon-coated tungsten electrode (outside diameter, 0.18 mm; tip exposure, 0.2 mm) for 5 seconds. After placement of the lesions, a light plane of anesthesia was maintained for 8 to 10 hours after operation with supplemental doses of pentobarbital (16 mg/kg i.p.…”

Functional Arterial Baroreflex Attenuates the Effects of Antihypertensive Drugs in Conscious Rats

“…The baroreflex arc may be interrupted by sinoaortic denervation or completely lesion of the nucleus tractus solitarus (2,3). In these animals with baroreflex dysfunction, blood pressure variability (BPV) is dramatically high (4 -6).…”