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1,25-Dihydroxyvitamin D3 (1,25-(OH)2-D3) (0.1 pM to 2 nM) induces a concomitant very rapid (within 5 s) and transient release of inositol trisphosphate and diacylglycerol in enterocytes from 3-month-old rats. This high level is not maintained but declines to a lower level 60 s after stimulation. The stimulating effect is dose-dependent and biphasic with a maximum effect at 10 pM. 1,25-(OH)2-D3 induces a rapid (within 10 s) accumulation of inositol bisphosphate and its effect on inositol monophosphate is delayed (120 s). The primary action of 1,25-(OH)2-D3 is to initiate hydrolysis of phosphatidyl 4,5-bisphosphate to yield inositol trisphosphate and diacylglycerol. In contrast, 1,25-(OH)2-D3, for any of the concentrations and the incubation time periods tested, has no effect on inositol trisphosphate and diacylglycerol formation in enterocytes from 16-day-old rats at a time when specific binding sites for 1,25-(OH)2-D3 cannot be detected. In conclusion, the early (within 5-60 s) effects of 1,25-(OH)2-D3 on small intestinal epithelium may be mediated via the phosphoinositide transduction system and require the presence of functioning cell membrane-type receptors.
Lieberherr et al. (Fri,) studied this question.