Phosphorylcholine and phosphorylethanolamine in human and rhesus monkey lenses

Phosphorylcholine (P-choline) and phosphorylethanolamine (P-ethanolamine) are important precursors of phospholipids. The metabolism and concentration of P-choline has been shown to change in animal models of cataract, especially in oxidatively or osmotically stressed rat lenses. The concentrations of P-choline and P-ethanolamine were determined in monkey lenses and in normal and cataractous human lenses, and the rate of synthesis of P-choline was determined in human and monkey lenses. The concentration of P-choline in 53 clear human lenses was 0·94 mm (±0·31 s.d.), and was relatively unaffected by age, eye bank storage, or freezing. There was a 70% decrease in P-choline in brown cataracts but no significant change from normal in nonbrown cataracts. The concentration of P-ethanolamine in human lenses was 0·45 mm (±0·26 s.d.), and it appeared to decrease during frozen storage of lenses and in cataracts. The concentrations of P-choline and P-ethanolamine in 12 rhesus monkey lenses were 1·51 mm (±0·27 s.d) and 0·75 mm (±0·14 s.d.), respectively. The rate of synthesis of P-choline in monkey lenses incubated with [³H] choline was 8 nmol hr^-1 g^-1 wet weight in 1 mm choline. Adult human lenses incubated in 1 mm choline synthesized P-choline at a rate of 23 nmol hr^-1 g^-1 (±6 s.d.). This limited capacity for P-choline synthesis in primate lenses may contribute to the lower P-choline concentration relative to rat lenses, which contain 11 mm P-choline and can synthesize P-choline at an apparent maximum rate of 130 nmol hr^-1 g^-1.