title: Osmolality, NaCl dietary intake, and regulation of ventilation by CO2.
abstract: The ventilatory response to CO2 (VR) was examined in six awake dogs during the 2nd week of sequential dietary periods of low NaCl (less than 5 meq NaCl/day), high NaCl (approximately 120 meq NaCl/day), and then repeated low NaCl. Water intake was maintained constant at 77 ml.kg-1.day-1. PCO2 of arterial blood (PaCO2) and the PaCO2 threshold of the VR increased between the high-NaCl and the second low-NaCl period; the PaCO2 threshold did not change between the first low-NaCl and the high-NaCl period. In contrast, arterial [H+] ([H+]a) threshold of the VR increased between the first low-NaCl period and the high-NaCl period, but did not change further in the second low-NaCl period. Variations in [H+]a threshold of the VR between dogs on high- and low-NaCl diets were correlated with plasma osmolality, and this accounted for a positive linear relation between [H+]a and plasma osmolality. During the high-NaCl period, the arterial strong ion difference [[SID]a = ([Na+] + [K+]) - ([lactate-] + [Cl-])] decreased, forcing [H+]a to increase. However, during high-NaCl diet, PaCO2 decreased relative to plasma osmolality, counterbalancing the decrease in [SID]a and maintaining the relation between [H+]a and plasma osmolality. The compensatory mechanism for the decrease in PaCO2 during high NaCl was a shift in the relation between PaCO2 threshold of the VR and plasma osmolality to a lower PaCO2 threshold. Chemoreceptor, osmoreceptor, and/or humoral mechanisms are potentially involved in these respiratory adaptations to alterations in electrolyte and water balance.
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000494:pharmacology*; D004285:Dogs; D008297:Male; D012119:Respiration / Q000187:drug effects*; D012965:Sodium Chloride / Q000008:administration & dosage*; D012982:Sodium, Dietary / Q000008:administration & dosage*; D014882:Water-Electrolyte Balance
chemical_list: D012982:Sodium, Dietary; D002245:Carbon Dioxide; D012965:Sodium Chloride