Possible effect of the water-salt metabolism on the action of dopamine on the kidney
Agnoli, G.C.; Caggiari, M.; Cariani, A.; Montini, T.
Bollettino Della Societa Italiana di Cardiologia 21(7): 1149-1186
1976
ISSN/ISBN: 0037-878X PMID: 1031273 Document Number: 97149
The renal effects of dopamine (3,4-dihydroxyphenylethylamine) infused i.v. in a subpressor dose (0.1 .mu.g/kg per min) were investigated in 2 patients with spontaneous polyuria (caused in the one by hypothalamic-hypophyseal diabetes insipidus and in the other by psychogenic polydipsia) infused with moderately hypertonic gluco-saline solution, and in 3 healthy subjects infused with isotonic glucose solution. In each patient the effects of dopamine were studied in 2 conditions: salt depletion (pre-treatment with diuretics) and in salt loading (pretreatment with minerals corticoids). The glomerular filtration rate was measured by sodium thiosulfate clearance or by endogenous creatinine clearance; effective renal plasma flow was measured by P.A.H. [p-aminohippuric acid] clearance. Osmolar clearance and tubular reabsorption of Na and K were determined by traditional methods; in a state of constant hypotonic polyuria its was possible to calculate the isosmotic (proximal) and anisosmotic (distal) Na reabsorption in % of the respective Na loads. In conditions of salt depletion, dopamine evoked a blunted or short lived hyperemic response or a sustained ischemic response. The percentage of total reabsorbed Na did not vary and its isomotic component varied by a small amount of the control. The distal Na load and the fraction of such a load reabsorbed in the absence of water from the distal tubules did not change during the salt depletion study and the diuresis did not change. With salt retention, dopamine determined an increase in the renal blood flow and in the initial stages, an increase in the filtration rate. Na reabsorption was depressed at various levels of the nephron: the fraction of filtered Na reabsorbed isosmotically and the fraction of the distal Na load reabsorbed anisosmotically from the distal segments were reduced. By this mechanism, dopamine apparently promotes a distinct increase in diuresis and natriuresis. It is possible that the dopamines hyperemic, natriuretic and diuretic properties depend on the baseline salt and water metabolism.