The metabolic conversion of 1, 2, or 4 mM galactose to glucose was studied in isolated livers of suckling rats. Whereas galactose uptake during perfusion with 1 and 2 mM galactose was linear throughout the 90-min experiment, uptake was delayed for 35 min when 4 mM galactose was perfused. Studies with radioactive galactose revealed a parallel disappearance of galactose and the appearance of [14C]glucose; about 80% of the galactose taken up was converted to glucose. Galactose perfusion appeared to reduce the basal amount of glucose derived from substrates other than galactose. The specific activities in the galactose-perfused livers of the three major galactose metabolizing enzymes, galactokinase, galactose-1-phosphate uridylyltransferase, and uridine diphosphogalactose-4-epimerase, revealed that the transferase was significantly lower, whereas that of galactokinase and epimerase were significantly higher than in livers perfused without galactose. No meaningful changes were observed in the levels of either phosphorylated or uridylated hexoses in these studies.
The l i v e r i s both t h e p r i n c i p a l organ f o r g a l a c t o s e d i sp o s i t i o n and a l s o a t a r g e t of g a l a c t o s e induced t o x i c i t y . I n t h e t r a n s f e r a s e d e f i c i e n t galactosemic i n d i v i d u a l t h e neonat a l p e r i o d i s t h e most s i g n i f i c a n t and hazardous. For t h e s e reasons we have undertaken s t u d i e s of g a l a c t o s e metabolism and i t s consequences i n t h e i s o l a t e d perfused l i v e r of t h eweanling r a t s . I n a closed r e c i r c u l a t i n g system using t h e Mortimore p e r f u s i o n apparatus 18-21 day o l d r a t puppies were perfused with no s u b s t r a t e , 10 mM glucose and g a l a c t o s e a t 1, 2, 4 , 10, 20, 40 and 60 mM. Glucose production peaks a t 2 mM g a l a c t o s e . Galactose uptake i s s a t u r a t e d by t h e 10 mM l e v e l of g a l a c t o s e . ATP decreases with c i r c u l a t i n g g a l a c t o s e > 4 mM. The l e v e l s of t h e L e l o i r pathway enzymes remain cons t a n t w i t h time and s u b s t r a t e l e v e l f o r a t l e a s t 135 minutes of perfusion. UDPG/UDPgal, G-1-PIG-6-P and l a c t a t e f p y r u v a t e r a t i o s remain unchanged a t varying l e v e l s of galactose. No g a l a c t i t o l o r g a l a c t o n a t e was produced by t h e s e l i v e r s a t any l e v e l of g a l a c t o s e . This system provides an e x c e l l e n t p h y s i o l o g i c a l model f o r t h e i n v e s t i g a t i o n of t h e r e g u l a t i o n and c o n t r o l of g a l a c t o s e metabolism.EFFECT OF GESTATIONAL AGE ON THE UTILIZATION OF INTRAVENOUS AMINO ACIDS I N THE FIRST WEEK OF LIFE. M.H. Bryan, G.H. Anderson, R.N. Roy, K.N. Jeejeebhoy. The Research I n s t . of The Hosp.f o r Sick Children, Depts. of P e d i a t r i c s , N u t r i t i o n , Medicine; Univ. of Toronto, Toronto, Canada. ( I n t r . by P.R. Swyer)The use of intravenous a l i m e n t a t i o n i n newborn i n f a n t s has increased where o r a l n u t r i t i o n i s inadequate. This study rep o r t s t h e response of 28 newborns ( g e s t . 28-40 wks) t o a t o t a l p a r e n t e r a l i n f u s i o n of 3.0g L amino acid/kg/day i n d e x t r o s e during t h e f i r s t 7 days. The i n f u s a t e contained no t y r o s i n e o r c y s t i n e . N r e t e n t i o n r o s e with maturity from 28-30 wks and remained constant from 31-40 wks. N l o s s e s were a s urea and not a s a amino N , suggesting t h a t even <31 wk newborns hgve t h e c a p a c i t y t o u t i l i z e amino a c i d s f o r gluconeogenesis. Blood amino a c i d l e v e l s were s i m i l a r on days 1 and 6. Phenylalanine l e v e l s were normal and t y r o s i n e l e v e l s r o s e i n d i c a t i n g convers i o n a t a l l g e s t a t i o n a l ages. Cystine l e v e l s were n e g l i g i b l e , methionine l e v e l s high and taurinelmethionine r a t i o s low sugg e s t i n g t h a t c y s t i n e i s an e s s e n t i a l amino a c i d i n <31 wk inf a n t s . These f i n d i n g s r e v e r s e w i t...
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