Dose-dependence of the effects of corticosterone and the non-glucocorticoid, 18-hydroxycorticosterone, on the brush-border Na+/K+ exchanger.
Up to now, only glucocorticoids were thought to act on the renal proximal Na+/H+ exchanger. Using fluorimetric techniques we studied the kinetics of Na+/H+ exchange in brush border vesicles from ADX rats treated with increasing doses of corticosterone (B) and 18-hydroxycorticosterone (18OHB). Significant linear correlations were obtained when the Vmax of each treatment were plotted against log doses. 18OHB exhibits a slightly higher sensitivity than B and log-dose responses were steeper for 18OHB than for B treated rats. Differences between both treatments were highly significant at the 4.8 microg/100 g level, corresponding to the physiological blood level of 18OHB. Physiological doses of both steroids elicited equal Na+/H+ exchange-responses. 18OHB is not a glucocorticoid since even 88 microg/100 g did not promote hepatic glycogen deposition while the same dose of B increases glycogen deposits 3.5-fold. These results demonstrate the importance of the Na+/H+ exchanger as a mediator between corticoid action and H+ transport and that of the non-glucocorticoid 18OHB in this process.
Igarreta
P
P
Lab. de Esteroides, FCEN UBA, Cdad. Universitaria Pab.2, Buenos Aires, Argentina.
Lantos
C P
CP
Calvo
J C
JC
Paladini
A A
AA
Damasco
M C
MC
D015069:18-Hydroxycorticosterone / Q000494:pharmacology*; D000315:Adrenalectomy; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D003345:Corticosterone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006003:Glycogen / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D028021:Sodium-Potassium-Chloride Symporters; D015069:18-Hydroxycorticosterone; D006003:Glycogen; D003345:Corticosterone