MDCK cells express serotonin-regulable 11beta-hydroxysteroiddehydrogenase type 2

Prior to this work, we found that adrenal as well as extra-adrenal factors activate the response of renal 11beta-hydroxysteroid dehydrogenase 2 to stressful situations. These results -showing ways through which the organism hinders the pathological occupation of mineralocorticoid receptors by glucocorticoids leading to sodium retention and hypertension- prompted the present study on the nature of the above-mentioned extra-adrenal factors. Serotonin was chosen because of its properties as a widely distributed neurohormone, known to interact with glucocorticoids at many sites, also exhibiting increased levels and effects under stressful situations. We studied serotonin effects on 11beta-hydroxysteroiddehydrogenase 2 activity in a cell line derived from distal nephronpolarized-epithelium, employing 3H-corticosterone as substrate. The end-product, 3H- 11 -dehydrocorticosterone was separated from the substrate by HPLC and quantified. Serotonin stimulated 1I beta-hydroxysteroiddehydrogenase 2 activity only at 2nM and 25pM, the magnitude of the responsedepending also on substrate concentration. The stimulation was blocked by thespecific inhibitors methiothepin and ketanserin. We postulate that the organism partially prevents renal mineralocorticoid receptor occupancy by glucocorticoids, circulating at enhanced levels under stressful situations, through serotonin-mediated catabolic regulation of the 11beta-hydroxysteroid dehydrogenase 2 activity. Given many, mostly positive, interactions between both hormones, this might eventually pave the way to studies on a new regulatory axis.

Regulation of nephron acidification by costicosteroids

The present paper reviews work from our laboratories evaluating the importance of adrenal cortical hormones in acidification by proximal and cortical distal tubules. Proximal acidification was determined by stationary microperfusion, and measurement of bicarbonate reabsorption using luminal pH determination was performed with H+ -ion-sensitive microelectrodes. Rats were adrenalectomized (ADX) 48 h before the experiments, and corticosteroids (aldosterone(A), corticosterone(B), and 18-OH corticosterone (18-OH-B)) were injected intramuscularly 100 and 40 min before the experiments. In ADX rats stationary pH increased significantly to 7.03 as compared to sham-operated rats (6.78). Bicarbonate reabsorption decreased from 2.65 + 0.18 in sham-operated rats to 0.50 + 0.07 mmol cm-2 S(-1) after ADX. The administration of the three hormones stimulated proximal tubule acidification, reaching, however, only 47.2 per cent of the sham values in aldosterone-treated rats. Distal nephron acidification was studied by measuring urine minus blood pCO2 differences (U-B pCO2) in bicarbonate-loaded rats treated as above. This pCO2 difference is used as a measure of the distal nephron ability to secrete H+ ions into an alkaline urine. U-B pCO2 decreased significantly from 39.9 + 1.26 to 11.9 + 1.99 mmHg in ADX rats. When corticosteroids were given to ADX rats before the experiment, U-B pCO2 increased significantly, but reached control levels only when aldosterone (two 3-mug doses per rat) plus corticosterone (220 mug) were given together. In order to control for the effect of aldosterone on distal transepithelial potential difference one group of rats was treated with amiloride, which blocks distal sodium channels. Amiloride-treated rats still showed a significant reduction in U-B pCO2 after ADX. Only corticosterone and 18-OH-B but not aldosterone increased U-B pCO2 back to the levels of sham-operated rats. These results show that corticosteroids stimulate renal tubule acidification both in proximal and distal nephrons and provide some clues about the mechanism of action of these steroids.

Appearance and persistence of 11 beta-hydroxypregna-1,4-diene-3,20-dione (delta HOP) effect [quot ]in vivo[quot ]

The effect [quot ]in vivo[quot ] of 11 beta-hydroxy-pregna-1,4-diene-3,20-dione (delta HOP) in acute and chronic treatment was studied in mice compared to those treated with dexamethasone and vehicle. In acute experiments an injection of 2 mg/100 g body weight of delta HOP had a maximal inhibitory effect in 3H-uridine incorporation by thymocytes 18 h after the injection, disappearing 36 h later, meanwhile no change was observed in plasma corticosterone levels at any time. The dose 0.033 mg/100 g body weight of dexamethasone produced a high inhibition 5 h after the injection, and a significant decrease in plasma corticosterone was produced at this time; the effect disappeared at 24 h. In the chronic treatment delta HOP produced the maximal inhibition 5 h after the treatment; this effect was maintained until 36 h and disappeared at 48 h without change in corticosterone levels. Meanwhile dexamethasone produced the same inhibition as delta HOP 5 h after the treatment; this effect disappeared after 18 h. In those animals plasma corticosterone decreased during longer time than in acute treatment, since it continued lower than normal at 18 h and it recovered at 24 h. After 5 h of a chronic treatment delta HOP did not change thymus and spleen weights, but they decreased with dexamethasone treatment. These results suggest that the [quot ]in vivo[quot ] actions of delta HOP is different from that of glucocorticoids.