N-acetyl-L-tyrosine as a tyrosine source in adult parenteral nutrition.

Background: N-acetyl-L-tyrosine (NAT) is commonly used in place of tyrosine in parenteral nutrition, but human studies carried out to date indicate considerable amounts of it are excreted unchanged in the urine. NAT retention has not been well studied in parenterally fed adults.

Methods: NAT retention was measured in 13 adults receiving continuous parenteral nutrition with Aminosyn II 15% (Abbott Laboratories, Abbott Park, IL).

Foveal contrast thresholds exhibit spatial-frequency- and polarity-specific contour interactions.

Traditionally, contour interaction has been investigated at the visual acuity limit using a Landolt C and flanking bars, performance being quantified in terms of a percent correct measure. More recently, it has been shown that the properties of the contour interaction are different when larger stimuli are used: Contour interaction is not polarity specific, and spatial frequency tuning for an unflanked C is broader. Here we quantify contour interaction for stimuli 5x larger than the resolution limit in terms of contrast thresholds.