Renal effects of continuous negative pressure breathing.
Continuous negative pressure breathing (CNPB) was utilized to simulate the thoracic vascular distension of zero G or Space, in 11 anesthetized rats. The animals underwent renal clearance and micropuncture renal nephron studies before, during, and after CNPB. Four rats were pretreated with a high salt diet and I-M desoxycorticosterone (DOCA) in excess. None of these rats diuresed with CNPB. In contrast, five of the seven remaining rats increased the fraction of the filtered sodium excreted (CNa/GFR, p less than 0.05) and their urinary flow rate (V, p less than 0.05). Potassium excretion increased (UK V, p less than 0.05). End proximal tubular fluid specimen's TF/P inulin ratios were unchanged. Whole kidney and single nephron glomerular filtration rates fell 10%. CNPB, a mechanism for atrial distension, appears to cause in the rat a decrease in distal tubular sodium and water reabsorption. Exogenous mineral-corticoid prevents the diuresis, saluresis, and kaluresis. In a separate group of five rats, the CNPB was prolonged or excessive (CNPB greater than 3.5 cm H2O negative pressure); in these, the diuresis ceased and/or antidiuresis occurred. This confirmed the adequacy of other nonatrial volume control mechanisms in regulating renal salt and water conservation in opposition to the studied atrial-renal (Henry-Gauer) reflex of thoracic vascular distension. It encourages us to suggest that the atrial distension reflex diuresis that occurs with shifts of blood to the thorax in assuming a weightless condition, if comparable to the thoracic vascular distension of this model, will not progressively impair the circulation or the mammal but will be minor and short-lived.
D000818:Animals; D001274:Atmospheric Pressure; D005919:Glomerular Filtration Rate; D007444:Inulin / Q000378:metabolism; D007668:Kidney / Q000502:physiology*; D007677:Kidney Function Tests; D008297:Male; D008657:Metabolic Clearance Rate; D011188:Potassium / Q000652:urine; D051381:Rats; D012119:Respiration; D012964:Sodium / Q000652:urine; D013026:Space Flight; D014893:Weightlessness
D007444:Inulin; D012964:Sodium; D011188:Potassium