Fasting and refeeding modulate neutral amino acid transport activity in the basolateral membrane of the rat exocrine pancreatic epithelium: fasting-induced insulin insensitivity.

The effects of fasting and refeeding on amino acid transport in the perfused rat exocrine pancreas were investigated using a rapid dual tracer dilution technique. Unidirectional amino acid influx (15 s) was quantified (relative to the extracellular tracer D-mannitol) over a wide range of perfusate concentrations in pancreata isolated frm fed and 24 h, 48 h, and 72 h fasted and 72 h fasted and refed (24 h) animals. In fed animals transport of phenylalanine (1-24 mM) and L-serine (1-50 mM) was saturable and weighted non-linear regression analyses of the overall transport indicated an apparent Kt = 10 +/- 3 mM and Vmax = 7.0 +/- 1.0 mumol/min per g (n = 7) for phenylalanine and Kt = 16 +/- 3 mM and Vmax = 20.6 +/- 2.1 mumol/min per g (n = 5) for serine. Fasting animals for 24 h or 48 h did not change the kinetics of either phenylalanine or serine transport. After a 72 h fast the rate of phenylalanine transport (Vmax = 15.9 +/- 2.9 mumol/min per g, n = 5) was enhanced whereas the transport affinity (Kt = 11 +/- 3 mM) remained unaltered. L-Serine transport was essentially unaltered. When 72 h fasted animals were refed for 24 h the Vmax for phenylalanine transport was reduced to values observed in fed animals. In parallel experiments refeeding had no significant effect on serine transport. Perfusion of pancreata isolated from 72 h fasted animals with bovine insulin (1 mU/ml or 1 microU/ml) did not stimulate either phenylalanine or serine transport.(ABSTRACT TRUNCATED AT 250 WORDS)