| Co-Investigator(Kenkyū-buntansha) |
HIRAKAWA Haruhisa National Defense Medical College, Department of Physiology, Associate Professor, 医学部, 助教授 (10258626)
KUSAKABE Tatsumi Kokusihikann University, Department of Sport and Medicial Science, Professor, 体育学部, 教授 (80117663)
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| Research Abstract |
Systemic hypoxia has been shown to produce different cardiovascular responses depending on arterial tension of carbon dioxide through central and peripheral chemoreceptors. This study was undertaken to examine the molecular mechanism of increases in size and number of glomus cells and vasculature of the rat carotid body, which has been exposed chronically to 10% hypoxia with 3 different tension of carbon dioxide (Hypocapnic hypoxia : Hypo, Isocapnic hypoxia : Iso and Hypercapnic hypoxia : Hyper). The results were as follows : 1) the carotid body increased several folds in size, when the duration of hypoxia lasted from 2 up to 12 weeks, but there was no difference in size of the carotid body between 8 and 12 weeks of hypoxia. This result suggested that 8 weeks are necessary time period for adaptation of the carotid body to hypoxia. 2) the abundance of neuropeptide Y (NPY)-, vasoactive intestinal polypeptide (VIP)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreac
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tive nerve fibers was examined in rats chronically exposed to Hypo, Iso and Hyper, respectively. SP and CGRP decreased, but VP increased in all 3 of hypoxia. NPY did not change in Hypo and Iso, but increased in Hyper. When the abundance of neuropeptide-containing nerve fibers were examined in the carotid body exposed to Hypo for 2, 4, and 8 weeks, SP and CGRP increased transiently after 4 weeks and decreased after 8 weeks of Hypo. VIP increased in all periods of Hypo, and NPY was unchanged in the carotid bodies during Hypo. These results suggested that the neuropeptide-containing nerve fibers were involved in dilatation and/or contraction of blood vessels of the carotid body. 3)the carotid bodies without sinus nerve (sinus nerve denervation), the carotid body without both sinus nerve and sympathetic innervation, or the carotid body without both sinus nerve and sympatho-vagal innervation did not so increase in size in response to chronic Hypo as the intact one, but the carotid body without both sinus nerve and sympathetic innervation increased most in size among the three denervation groups. The result suggested that sinus nerve played a role in an incease in number and size of glomus cells and the vagus nerve did in control of the carotid body vasculature. 4) Hypercapnic normoxia (6% CO2) did neither produce an increase in size of the carotid body nor in number of glomus cells. Less
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