The fine structure of human digital arterio-venous anastomoses (Hoyer-Grosser's organs)

Abstract

Hoyer-Grosser's organs were studied in human digital biopsies. The fine structure of both the supplying arteries and collecting veins was found to be inconspicuous. Endothelial cells in the AV canals form a continuous layer. They are characterized by their rich content of specific organelles (Weibel-Palade bodies), especially in the venous segments. The epitheloid zone is composed of a variety of ramified smooth muscle cells (RSM). These appear either dense, when well provided with bundles of myofilaments, or clear, when including only a few myofilaments. The nuclei of dense RSM show condensed chromatin, while those of clear RSM are larger with loose chromatin texture. In addition, all transitional forms occur. Cell organelles are rarely seen within all types of RSM. The cytoplasmic processes reach other as well as endothelial cells. The preservation of our material did not allow observation of specialized membrane contacts in these zones. All RSM are invested with a regular basal lamina and well provided with surface vesicles. Profiles of free basal lamina material and faint collagen (argyrophil) fibers are seen in the wide intercellular spaces. RSM poor in myofilaments are interpreted to represent "epitheloid cells" of light microscopy. Their number constantly decreases from the arterial segment of the AV canal to the venous segment. Here the cytoplasmic processes of RSM become less pronounced and the wall of the anastomotic segment continuously changes to that of the collecting vein. Dense RSM rich in myofilaments are compared with pacemaker cells found inthe ureter. Both internal and external elastic membranes are absent in AV canals. A dense network of unmyelinated nerve fibers is found in the adventitial layer of the AV canal, especially in its arterial segment. The axons branch out from small dermal nerves which also contain two or three myelinated axons. The myelin sheaths terminate where the axons reach the adventitia of the AV canals. Axon varicosities filled with mitochondria are thought to be terminals of myelinated axons and are interpreted as receptory. Axon varicosities with synaptic-type vesicles are assumed to be terminals of sympathetic and para sympathetic fibers. All axon profiles are confined to the adventitial layer of the anastomotic segment.

Differential effects of surgical sympathetic block at the T2 and T4 level on vasoconstrictor function

“…Rewarming kinetics of the hands has been successfully used to assess the effects of surgical sympathetic block previously [19].We confirmed that the main effect of the ESB is observed in the fingertips, as would be expected according to the rich vasoconstrictory innervation of the arterio-venous shunts in the fingertips [6,12]. ESB at the level of T4 was by far less effective in suppressing vasoconstrictor outflow and also in reducing palmar sweating as compared to ESB at T2.…”

Skin sympathetic adrenergic innervation: An immunofluorescence confocal study

“…16 The abundance of D␤H-ir fibers around the canal suggests their function in blood flow regulation. 11 Our data show that AVAs also present VIP-ir fibers that could be sensitive 12 or more likely, parasympathetic 8 with a role in vasodilation. 17 The presence of myelinated fibers supplying AVAs suggests that their main afferences are fast conducting fibers, able to detect to rapidly changing hemodynamic conditions.…”

“…Their constituents include a small feeding artery, a small canal (Suquet-Hoyer canal) with a virtual space delimited by an endothelium and a very thick collagen wall and a draining vein. 11 We observed a heavy innervation surrounding the canal, whereas nerves were less abundant around the feeding artery and sparse around the draining vein ( Fig 1A). The PGP-ir fibers around the canal presented a wavy ribbon-like shape at high magnification.…”

Inhibition of nitric oxide biosynthesis and carotid arteriovenous anastomotic shunting in the pig

“…The carotid arteriovenous anastomoses have been localized, as demonstrated by simultaneous injections of radioactive microspheres of different sizes, particularly in the skin, ears and dura mater, but also in the eyes and tongue (Saxena & Verdouw, 1985;Den Boer et al, 1992). Although arteriovenous anastomoses are anatomically distinct from the rest of the microvasculature, light and electron microscopy studies have shown the presence of an endothelial layer in both human and rabbit peripheral arteriovenous anastomoses (Gorgas et al, 1977;Fujiwara & Iijima, 1990). The finding that L-arginine, the endogenous substrate for NO-synthase, partly reversed the L-NAME-induced reductions in the carotid arteriovenous anastomotic blood flow and conductance suggests that NO, released from the endothelium, may provide a vasodilator tone in these specialized vessels.…”