Low PO₂ Dependency of Neutral Endopeptidase and Acetylcholinesterase Activities of the Rat Carotid Body

Abstract

Multiple neurochemicals contribute to the chemosensory response of the carotid body to hypoxia. In addition to biogenic amines, the mammalian carotid body contains several neuropeptides which include enkephalins (Enk), and substance P (SP) (Fidone & Gonzalez, 1986; Prabhakar et al., 1989). Several studies have demonstrated that hypoxia influences catecholamine metabolism in the carotid body by affecting their synthesis, re-uptake or degradation pathways (Fidone & Gonzalez, 1986; Wang et al., 1990). Few studies have addressed the effects of hypoxia on the neuropeptides in the carotid body (Prabhakar et al., 1989; Hansen et al., 1986). One hour of sustained, moderate hypoxia increased SP (Prabhakar et al., 1989) in the cat carotid body whereas intermittent hypoxia decreased the tissue content of SP and Enk in the rabbit carotid body (Hansen et al., 1986). After two weeks of hypoxic exposure, SP-like immunoreactivity of the type I cells significantly decreased in the cat carotid body (Wang et al., 1990). These results suggest that the effects of hypoxia on neuropeptides are complex and may arise either from enhanced in vivo peptide synthesis or decreased degradation.