Multi‐ and single‐fibre mesenteric and renal sympathetic responses to chemical stimulation of intestinal receptors in cats.

Abstract

SUMMARY1. In cats anaesthetized with a-chloralose and artificially respired, stimulation of intestinal receptors with bradykinin caused greater reflex excitation of mesenteric than of renal efferent multifibre nerve activity and significant pressor responses.2. Activity of all nerve bundles used in this study was inhibited by stimulation of pressoreceptors. Increases in systemic arterial pressure caused inhibition of activity of renal nerves which was significantly greater than that of mesenteric nerves.3. Spinal transection caused significant decreases in tonic renal nerve activity without altering the ongoing discharge rate of mesenteric nerves. Stimulation of intestinal receptors in spinal cats still caused significant increases in discharge of mesenteric and renal nerves, indicating that this reflex contains a spinal component.4. Recordings of activity of individual fibres within mesenteric (21) and renal (23) nerves provided information regarding the basis for the multifibre responses to stimulation of intestinal receptors. The same proportion of fibres from both nerves was excited, but the increase in activity of mesenteric fibres was significantly greater than that of renal fibres.5. Mesenteric fibres could be classified into two groups, based on their sensitivity to pressoreceptor influences. Fibres that exhibited pressoreceptor-independent discharge had the greatest responses to stimulation of intestinal receptors.6. Following spinal transection the majority of mesenteric fibres continued to fire, whereas most renal fibres became quiescent.7. The non-uniform pattern of neuronal excitation to chemical stimulation of intestinal receptors was manifest after spinal transection, demonstrating that exclusively spinal pathways can mediate this differential response pattern.8. These results support the hypothesis that viscero-sympathetic reflexes may be organized to cause preferential excitation of neural activity directed to the organ from which the reflex originates.

Predominant postglomerular vascular resistance response to reflex renal sympathetic nerve activation during ANG II clamp in rabbits

“…Such subpopulations of nerves have been demonstrated previously in the gut (13) and eye (3), although such a possibility in the kidney has received little attention until the last decade (8,9,11,15,39,40). It has generally been accepted that the stimulation of the renal nerves produces frequency-dependent decreases in renal function (see Ref.…”

“…On this basis, we hypothesized that different patterns of sympathetic outflow to the kidney may evoke selective changes in segmental renal vascular resistances. This concept of functionally specific populations of renal sympathetic nerves has also been addressed by other investigators (8,9,11,15,39,40).…”

The discharge behaviour of single vasoconstrictor motoneurones in human muscle nerves.

“…This conclusion could not have been reached in microneurographic recordings of multiunit sympathetic bursts, which have been the standard approach to recording from postganglionic sympathetic fibres in human peripheral nerves. The maximum number observed within a burst was seven, which is also what Hallin & Torebjork (1974) (0 5-3 Hz;Jainig, 1985), as well as from renal, splenic and mesenteric nerves in the cat (0-03-6-4 Hz, median 0 9 Hz; Meckler & Weaver, 1988;Stein & Weaver, 1988). It should be noted, however, that our subjects had low levels of spontaneous multiunit activity (range 9-17 bursts min-').…”

“…In the present material short interspike intervals, with instantaneous frequencies greater than 50 Hz, were produced by nine units, but only 2-4% of all intervals were so short. Single vasoconstrictor motoneurones in the renal, splenic and mesenteric nerves of the cat also generate high instantaneous firing rates, up to 59 Hz, and the frequency distribution is similarly broad (Meckler & Weaver, 1988;Stein & Weaver, 1988). Such erratic instantaneous frequencies may be physiologically appropriate; electrical stimulation of sympathetic nerves has shown that irregular interstimulus intervals are more effective than regular stimuli for contracting arterioles in the muscle vascular bed of the cat, the optimal pattern being a 32 Hz stimulus applied at 4 s intervals (Andersson, 1983).…”

Postprandial hypotension. Pathophysiological mechanisms and clinical implications in different disorders.

“…These include factors described in the dopamine /3-hydroxylase-deficient patients, since tetraplegics also have the ability to activate vagal efferent pathways and may release peptides and other vasoconstrictor active substances from sympathetic nerve endings. Studies in intact and spinalized animals suggest that viscerosympathetic reflexes may be organized so as to preferentially activate the nerves to the organ from which the reflex originates 34 ; whether this occurs in the tetraplegic patients on intestinal stimulation is but speculative at this stage.…”