Growth hormone-enhanced acid production and glutamate and glutamine utilization in LLC-PK-F+ cells

Growth hormone (GH), recombinant human (rh) GH, effects on transepithelial proton gradient, acid production, and glutamine (Gln) and glutamate (Glu-) utilization were studied in LLC-PK-F+ cells. Monolayers were incubated in Dulbecco's modified Eagle's media containing either 2 mM Gln or Glu- and 5 mM glucose plus 10% fetal bovine serum for 4 h, after which samples were taken for metabolite and acid-base parameter measurements. Monolayers grown on porous supports in Glu- media responded to 32 nM rhGH by decreasing Glu- net uptake 29% (470 +/- 135 to 336 +/- 98 nmol/4 h, P < 0.05), reflecting elimination of basolateral uptake (189 +/- 80 to 2 +/- 35 nmol/4 h, P < 0.05) as ammonium production decreased. In 2 mM Gln, rhGH decreased Gln net uptake 84% (1,096 +/- 215 to 155 +/- 150 nmol/4 h, P < 0.05), with basolateral uptake reversing to release; Glu- formation increased as ammonium production decreased. Monolayers grown on porous supports required rhGH to generate a transepithelial proton gradient within 4 h (0.01 +/- 0.05 control vs. 0.27 +/- 0.11 U for rhGH, P < 0.05); in addition, rhGH increased acid production (16.7 +/- 2.0 to 21.5 +/- 0.6 mumol x 4 h-1 x mg protein-1, P < 0.05). Adding insulin-like growth factor I (IGF-I) to the basolateral media decreased pH and enhanced Glu- and Gln uptake from that compartment.(ABSTRACT TRUNCATED AT 250 WORDS)