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

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Abstract
Isolated dog veins were used to examine whether correlations exist between the regional differences in sensitivity to drugs and their embryogenesis; 12 different veins were dissected. Data obtained previously for the inferior vena cava were included. Spiral strips were prepared and the contractile responses to cumulative application of norepinephrine (NE), 5-hydroxytryptamine (5-HT), histamine (Hist) and acetylcholine (ACh) were recorded isometrically. For each drug a histogram was drawn by stacking the overlapping ranges (mean .+-. SE) of the pD2 value for each vein. The histogram indicated the number of veins which could share the same pD2 value. Veins of the body wall had high sensitivity to NE (pD2 > 6.40) and 5-HT (pD2 > 6.60) and veins of the intestinal system, except for the splenic vein, were not so sensitive to NE and 5-HT, but exhibited high sensitivity to Hist (pD2 > 4.60). The middle segment of inferior vena cava responded similarly to portal and mesenteric veins. The responses of splenic vein to the agents used were different from those of portal and mesenteric veins. Possible correlations between the responsiveness of venous smooth muscles and embryogenesis of the venous system were suggested.