Effects of sympathetic stimulation and changes in arterial pressure on segmental resistance of cerebral vessels in rabbits and cats.

Summary:The effect of angiotensin converting enzyme inhibition with captopril (10 mg/kg i.v.) on CBF autoreg ulation was studied in 16 spontaneously hypertensive rats (8 control and 8 treated with captopril) sUbjected to acute cervical sympathectomy. CBF was measured repetitively by the intra-arterial I33Xe injection method, during the manipulation of MABP by norepinephrine or hemor rhagic hypotension. Prior to the administration of drugs, baseline MABP was 112 ± 10 mm Hg in the control group Although it was speculated that the effect of cap topril was caused by a reduction of the angiotensin II-induced tone in the larger cerebral arteries (Barry et aI., 1984), the mechanism for the observed effect of ACE inhibition on CBF autoregulation remains to be clarified. Since the renin-angiotensin system interacts with the sympathetic nervous system (Zimmerman, 1978), the effect might result from in hibition of cerebrovascular sympathetic tone, rather than direct inhibition of the angiotensin II induced tone in cerebral arteries. In that case, how-

Section: Discussionmentioning

confidence: 59%

Acute Sympathetic Denervation Does Not Eliminate the Effect of Angiotensin Converting Enzyme Inhibition on CBF Autoregulation in Spontaneously Hypertensive Rats

Waldemar

1990

“…, , 1982Sercombe et aI., 1979) and the Harper et al dual hypothesis (1972): Large pial arteries, supplied by a dense network of sympathoadrenergic fibers, con sistently constrict during the period of sympathetic stimulation. The smaller arteries downstream with fewer sympathetic nerves, likely to underlie the mechanism of myogenic propagation (Johansson and Ljung, 1968), are now under lower intravas cular pressure (Baumbach and Heistad, 1983). As the small arteries commence to redilate, CBF re turns to normal, and so does ICP as a consequence of increasing intravascular volume.…”

mentioning

confidence: 99%

Pial Vascular Behavior during Bilateral and Contralateral Cervical Sympathetic Stimulation

Auer

Ishiyama

1986

“…They obtained indirect evidence to suggest a dilation of the intraparenchymal vessels or a decrease in the intraparenchymal vas cular resistance. Baumbach and Heistad (1983) es timated the segmental cerebral vascular resistance during sympathetic nerve stimulation and reported that the vascular resistance increased in the large cerebral arteries but decreased in the small intra parenchymal vessels. They stressed the dilation of the intraparenchymal vessels but did not indicate an initial constriction of the intraparenchymal vessels as demonstrated in the present study.…”

Section: Discussionmentioning

confidence: 99%

Comparison between Pial and Intraparenchymal Vascular Responses to Cervical Sympathetic Stimulation in Cats. Part 1. Under Normal Resting Conditions

Gotoh

Fukuuchi

Amano

et al. 1986

Summary:To investigate the role of sympathetic regula tion in both resistance and capacitance vessels in cerebral circulation, the responses of pial and intraparenchymal vessels to sympathetic nerve stimulation were simulta neously examined in 14 cats by means of a newly devel oped video camera photoelectric system. The system consisted of a video camera system for measurement of pial vascular diameters and a photoelectric apparatus for estimating regional cerebral blood volume in the intrapa renchymal vessels. The ipsilateral superior cervical gan glion was electrically stimulated for 5 min. Initially. both the pial and intraparenchymal vessels constricted. TheIt is well documented that sympathetic nerves derived from the superior cervical ganglion con strict cerebral vessels down to the pial arterioles and venules (Auer et aI. , 1982) and exert a protec tive effect against breakthrough of autoregulation of CBF during acute hypertension (Bill and Linder, 1976). However, the role of the sympathetic nerves in the regulation of the resting CBF is still disputed Purves, 1978). This controversy seems to depend partly on the method ological limitations of measuring CBF and on the homeostatic mechanism of cerebral circulation. Harper et al. (1972) hypothesized that under most circumstances, sympathetic constriction of the ex traparenchymal and pial vessels might be com pen- 342large pial arteries (173 ± 25 f.Lm, mean ± SEM) remained constricted throughout the stimulation. whereas the in traparenchymal vessels began to dilate after the initial constriction and exceeded the control level at 175 ± 25 s despite continued stimulation. In conclusion. such sym pathetic nerve stimulation is considered to exert a con strictive effect on the intraparenchymal as well as the pial vessels at the early stage. The compensatory dilation of the intraparenchymal vessels was delayed 3 min after ini tiation of the stimulation. Key Words: Cerebral blood volume-Escape phenomenon-Pial vessel-Sympa thetic stimulation. sated for by a metabolic dilation of the intraparen chymal vessels and that CBF might be kept con stant. Recently, we developed a video camera photoelectric system that permits simultaneous and continuous measurement of pial vascular diameter and changes in regional cerebral blood volume (CBV). In the present study, to test Harper et al. 's hypothesis, we compared the responses of pial and intraparenchymal vessels to superior cervical gan glion stimulation by using this new method. MATERIALS AND METHODSExperiments were performed on 14 cats weighing from 2.3 to 3.4 kg, anesthetized by intraperitoneal injection of a-chloralose (50 mg/kg) and urethane (5 00 mg/kg). The bilateral femoral arteries and one femoral vein were can nulated for monitoring arterial blood pressure (BP). ana lyzing blood gases. and injection of drugs. The animals were subjected to tracheostomy and were ventilated with a respirator (Harvard 662) after immobilization with al curonium chloride (2 mg i.v.). The animal's head was fixed in a stereotactic head ho...