Ethanol increases and vitamin D metabolites decrease the production of cyclic AMP by canine renal cortical membranes.

Ethanol 0.16% increased cyclic AMP production by canine renal cortical membranes in the basal state and when challenged with different parathyroid hormone or fluoride concentrations. 1,25-dihydroxycholecalciferol (1,25(OH)2D3) 40 pM completely inhibited this effect of ethanol and reversed cyclic AMP production to the level observed in buffer alone. The same inhibitory effect was observed with 25OHD3 and with 24,25-dihydroxycholecalciferol (24,25(OH)2D3). The inhibitory effect was related to the vitamin D metabolites' concentration and was maximal for 160 pM; it was independent of their biological activity. This suggests that the effect is mediated through an interaction with the membrane lipids. The effect of vitamin D metabolites on cyclic AMP production was also observed in the presence of serum proteins and should be taken into account if unextracted plasma is assayed in the renal cortical membrane system for PTH bioactivity.