Differences in the Response of Three Embryologically Distinct Segments of the Isolated Canine Posterior Vena cava to Vasoactive Substances

Abstract

The canine posterior vena cava was excised and divided into three embryologically distinct segments: segment A (supradiaphragm), segment B-C (intra-hepatic and that between liver and renal veins), and segment D (infrarenal). Circular and longitudinal strips were cut from each segment, suspended in Krebs bicarbonate solution and isometric tensions were recorded. The responses to six vasoactive agents, as well as transmural neural stimulation were studied. Maximum tension and ED₅₀ were obtained for norepinephrine, epinephrine, acetylcholine, bradykinin, histamine and 5-hydroxytryptamine (5-HT). The responses were not only quantitatively, but qualitatively different among the three segments. Bradykinin constricted the strip:; in A and B-C but not in D. 5-HT (<10^–5 m) caused a dose-dependent contraction in A and D through its direct stimulating action, while in C, a contractile response appeared only after administration of a higher dose of 5-HT. This was due to an indirect sympathomimetic action of the agent. Segment B-C, which histologically contained massive longitudinal muscle bundles in the outer layer of the wall, exhibited spontaneous, rhythmic contractions. The existence of a cholinergic excitatory innervation, in addition to adrenergic, was demonstrated in C by transmural neural stimulation.

Possible embryogenetical differences of the dog venous system in sensitivity to vasoactive substances.

“…The second contraction induced by 5-hydroxytryptamine is due to its action on the sympathetic nerves (2). In the present study, remarkable second contractions were observed in the cephalic, portal, mesenteric and lateral saphenous veins and segment B-C of the inferior vena cava.…”

“…In addition to the findings in the twelve veins, the analyses included the data of three segments of the inferior vena cava which were obtained in the previous study (2). The three segments were segment A (supradiaphragm), segment B-C (intrahepatic and that between the liver and renal veins) and segment D (infrarenal).…”

“…Their pD2 values were obtained under comparable experimental conditions and by the same method except that they were not estimated graphically, but computed following a mathematic procedure. The results were schematically shown in the previous paper (2), but the numerical data were not presented.…”

A Regional Difference in Endothelium-Dependent Relaxation Responses to Acetylcholine in the Canine Venous System

“…However, there are only a few reports de scribing the endothelium-dependent re sponses of veins (3,4). In previous papers, we repeatedly indicated that the canine venous system consists of veins characteristically different in pharmacological responses (5)(6)(7)(8)(9). Therefore, in the present study, distribution of endothelium-dependent relaxation re sponses in the venous system was inves tigated by using 15 canine veins selected systematically (5,6).…”

Distribution of cholinesterase in canine venous system.

“…These three veins are embryologically related to the digestive tube, being characterized by the presence of massive longitudinal muscles, spontaneous rhythmic contractile activity, as well as cholinergic excitatory innervation (1 4). Some evidences of the innervation ob tained by in vitro and in vivo experiments were reported (3,(5)(6)(7). Additional findings were reported by Uematsu et al (8).…”