Response of the Microcirculation in Rat Cremaster Muscle to Peripheral and Central Sympathetic Stimulation
Authors: Bernard P. Fleming, Kirk W. Barron, Timothy W. Howes, J. Kevin Smith
Journal: Circulation Research (1987)

Microvascular diameter and flow responses to peripheral and central sympathetic stimulation were measured in different segments of the arteriolar network in rat cremaster muscle.For peripheral stimulation, a bipolar electrode was placed on the internodal segment of the lumbar sympathetic chain between ganglia LI and L2.For central stimulation, a bipolar electrode was stereotaxically implanted in the posterior hypothalamus.Inside vessel diameter, red blood cell velocity, and volumetric flow rate were recorded in response to electrical stimulations of varying magnitude in four series-coupled segments of the arteriolar network: 1A, 2A, 3A, and 4A.Systemic arterial pressure was also monitored.The vasoconstriction and flow reduction produced by stimulation of the lumbar chain was graded with the frequency of stimulation over the range of 0.5-16.0Hz in all arteriolar segments.Examination of the relation between stimulation frequency and vasoconstrictor response measured as percent of control diameter indicated a sequence of responsiveness to peripheral stimulation where 4A = 3A>2A = 1 A. No changes in diameter were recorded in the venous microcirculation at any level of stimulation.Stimulation of the posterior hypothalamus with currents of 38-300 /u,A for 60 seconds produced graded vasoconstriction in only 3A and 4A vessels.Fluorescence histochemistry for biogenic amines was used to examine the distribution of innervation to the microvasculature.All segments of the arteriolar network from 1A to 4 A possessed an adrenergic inner vation; no vessels of the venous network were found to be innervated.The results indicate that the pattern of response of the arteriolar network in rat cremaster muscle to peripheral and central sympathetic stimulation is segmentally differentiated and consistent with the distribution of the vasomotor innervation.(Circulation Research 1987;61(suppl n):II-26-II-31)N eurogenic regulation of the peripheral circula- tion is accomplished in large part by controlled variations in sympathetic adrenergic discharge to the arteriolar resistance vessels of the microcirculatory network.To date, the majority of our knowledge of neural control mechanisms has been derived from hemodynamic studies on whole organs or on the responses of larger vessel segments studied in vitro. 1 " 3 Recently, there has been an increasing interest in using microcirculatory models and methodology in studies on neurogenic control of the microvasculature. 4-5 An often-described aspect of the response of the peripheral circulation to sympathetic neural stimuli is the apparent specialization of the response pattern in the various series-coupled segments of the precapillary resistance network. 5" 7 This differentiated pattern of response in the various segments of the arterial-arteriolar network implies a complex system of microcirculatory neural control that would have important physiologic implications.In direct studies on the microcirculation in skeletal