Iron deficiency transiently suppresses biliary neuronal nitric oxide synthase.

BACKGROUND: Iron deficiency results in altered gallbladder and sphincter of Oddi (SO) motility and cholesterol crystal formation. In addition, gallbladder neuronal nitric oxide synthase (nNOS) has been shown to be markedly reduced after 8 weeks on an iron-deficient diet. However, the effects of prolonged iron deficiency on gallbladder and SO nNOS as well as crystal formation have not been determined. Therefore, we tested the hypothesis that iron deficiency would downregulate both gallbladder and SO nNOS expression and that nNOS downregulation and cholesterol crystal formation would progress over time.

MATERIALS AND METHODS: Thirty-eight adult female prairie dogs were fed either an ironsupplemented (Fe+) (200 ppm) or an iron-deficient (Fe-) (8 ppm) diet for 8 weeks (Fe+ n = 9, Fe- n = 10) or 16 weeks (Fe+ n = 9, Fe- n = 10). Blood hemoglobin (HbG) was measured; gallbladder cholesterol crystals were counted; and cholesterol saturation indices (CSI) were calculated. Gallbladder and SO nNOS levels were measured by Western blot.

RESULTS: The Fe+ prairie dogs had significantly higher HbG than the Fe- animals (16.9 +/- 0.6 g/dl vs 15.2 +/- 0.5 g/dl, respectively, P < 0.05) after 8 weeks. This difference was even greater after 16 weeks (16.1 +/- 0.4 g/dl vs 14.0 +/- 0.5 g/dl, P < 0.01). At 8 weeks, more cholesterol crystals per 10 HPF were observed in the Fe- animals (0.4 +/- 0.3 vs 1.6 +/- 0.4 per 10 HPF, P < 0.05). This difference was even greater after 16 weeks (0.0 +/- 0.0 vs 52.6 +/- 25.3 per 10 HPF, P < 0.01). No difference in the CSI was observed in the four groups. Iron deficiency decreased the nNOS/beta-actin protein levels in the gallbladder and SO at 8 weeks (57.0 +/- 29.6 vs 7.4 +/- 2.6, gallbladder, P < 0.05) (98.4 +/- 39.7 vs 29.9 +/- 11.0, SO, P = 0.09), but these levels returned to baseline at 16 weeks.

CONCLUSIONS: We conclude that iron deficiency acutely suppresses gallbladder and SO nNOS, and that compensatory mechanisms return nNOS to baseline levels while cholesterol crystal formation increases over time.