Fig. 6.

Luminal and plasma levels of levodopa are compromised by higher abundance of tyrosine decarboxylase gene in the small intestine of rats. Scatter plot of tdc gene abundance measured by qPCR in jejunal content of wild-type Groningen rats (n = 18) orally supplied with levodopa/carbidopa mixture (4:1) versus a the dopamine: levodopa/carbidopa levels in the jejunal content, the levodopa/carbidopa levels in the jejunal content, b or the levodopa/carbidopa levels in the plasma, fitted with a linear regression model. Intake of levodopa/carbidopa was corrected by using carbidopa as an internal standard. Pearson’s r correlation was used to determine significant correlations between tdc abundance and jejunal dopamine levels (r = 0.78, R² = 0.61, P value = 0.0001), jejunal levodopa/carbidopa levels (r = −0.68, R² = 0.46  P value = 0.021), or plasma levodopa/carbidopa levels (r = −0.57, R² = 0.33, P value = 0.017). No levodopa/carbidopa, dopamine, or DOPAC were detected in the control group (n = 5). c Significant difference in plasma levels of levodopa/carbidopa orally supplied to rats after treatment with EFS^WT (n = 10) or EFS^ΔTDC (n = 10). Significance was tested using parametric unpaired T-test (**p < 0.01)