Responses of Sympatho-Adrenal Medullary System to Hypoxia and Hypercapnia in Anesthetized Artificially Ventilated Rats

Abstract

Since pioneering works by Cannon and Hoskins (1911) and Czubalski (1913), it has been well established both in humans and experimental animals that adrenaline concentration in systemic blood or urine is increased and also adrenaline contents in the adrenal medulla are decreased in response to hypoxia, hypercapnia, or asphyxia (Kellaway, 1919; Houssay and Molinelle, 1926; Tenny, 1956; Becker and Kreuzer, 1968; O’Brodovich et al., 1982; Rose et al., 1983). Despite a great deal of these research efforts over 8 decades, its neural mechanisms have remained unsolved. The present experiments were undertaken to assess the contributions of the carotid chemoreceptors and the adrenal sympathetic efferent nerve to the responses of the adrenal medullary catecholamine secretion during systemic hypoxia and hypercapnia. For this purpose, we measured the adrenal sympathetic efferent nerve activity and catecholamine secretion rates from the adrenal medulla in response to systemic hypoxia and hypercapnia in two groups of animals. In one group carotid chemoreceptors were intact, and in the other group carotid chemoreceptor afferents were severed bilaterally. Furthermore, catecholamine secretion rates in response to systemic hypoxia and hypercapnia were investigated in animals whose splanchnic nerves innervating the ipsilateral adrenal gland were severed.