Effect of a short-term fast on hepatic microsomal glutathione-insulin transhydrogenase

The effect of nutritional state on the hepatic insulin degrading enzyme glutathione-insulin transhydrogenase (GIT) was assessed by comparing the distribution of GIT activity between its nonlatent and latent forms in fractionated liver microsomes from ad lib fed (n = 11) and overnight fasted (n = 11) rats. In fed state microsomes, treatment with the membrane disrupting agent phospholipase-A2 (PLA2) over a range of PLA2 concentrations (less than or equal to 2.0 micrograms/ml) caused biphasic release of GIT with a peak activity of 651 +/- 58 U/mg microsomal protein (n = 11) occurring at PLA2 = 1.0 microgram/ml. In total liver microsomes from fasted animals, GIT release in response to PLA2 was sigmoidal over the entire range of PLA2 concentrations, with a plateau of activities (450 U/mg microsomal protein) occurring at PLA2 greater than or equal to 0.75 microgram/ml. Peak activities (478 +/- 88 U/mg prot., n = 11, PLA2 = 1.0 microgram/ml) were 30% lower as compared to the fed state (p less than .05). In untreated (intact) microsomes from fed rat liver nonlatent activity was 126 +/- 8 U/mg protein, representing 19.9 +/- 1.2% of the total GIT activity. In contrast, nonlatent activity measurable in suspensions of intact microsomes from fasted rat liver (110 +/- 6 U/mg) expressed as a % of total activity was significantly increased (p less than .05) being 23.3 +/- 1.1%. Similar fasting-induced changes were also apparent in isolated smooth microsomes but not in rough membrane preparations.(ABSTRACT TRUNCATED AT 250 WORDS)