A CROSS-SECTIONAL AND SHORT-TERM LONGITUDINAL CHARACTERIZATION OF NIDDM IN PSAMMOMYS-OBESUS

The present study was undertaken to examine the cross-sectional and sh ort-term longitudinal changes in glucose and insulin concentrations as well as measure the enzymatic activity of PEPCK and glycogen synthase in our Psammomys obesus colony. In the cross-sectional study, blood s amples were taken from one group of animals at 19 weeks of age (n = 37 ) in the fed state and following a 4-h fast. In a separate group of 19 -week-old animals (n = 69), samples were taken 1 h following an OGTT ( 1 g/kg body weight) in Psammomys subjected to a 16-h fast. In the long itudinal study, blood samples were taken from one group of animals in the fed state at 7, 11, 15 and 19 weeks of age. All of the cross-secti onal data have described the classic inverted U-shaped curve (Starling 's curve of the pancreas) in the relationship between glucose and insu lin levels. This trend was also reflected by Psammomys subjected to th e OGTT; a mild impairment in glucose tolerance was associated with an increase in the insulin response and a further impairment in glucose t olerance was associated with a reduction in the insulin response. Simi lar results were obtained following a 4-h fast. The short-term longitu dinal glucose and insulin data revealed that of the 37 animals examine d over the 12-week period, 16 progressed along the inverted U-shaped c urve described by the cross-sectional data. Of the other animals, 8 re mained unchanged, 7 were unclassifiable and 6 hyperglycaemic Psammomys developed normoglycaemia at the expense of elevated insulin levels. P sammomys were divided into four separate groups based on their glucose and insulin levels in the fed state at age 19 weeks: group A were nor moglycaemic (4.5 +/- 0.2 mmol/l) and normoinsulinaemic (81 +/- 15 mU/l ); group B were normoglycaemic (5.3 +/- 0.3 mmol/l) and hyperinsulinae mic (267 +/- 19 mU/l); group C were hyperglycaemic (16.9 +/- 1.4 mmol/ l) and hyperinsulinaemic (356 +/- 29 mU/l); group D were hyperglycaemi c (20.4 +/- 1.4 mmol/l) and normoinsulinaemic (92 +/- 56 mU/l). Analys is of liver and soleus muscle tissue revealed that active glycogen syn thase activity was reduced in the hyperglycaemic Psammomys (C and D). Total glycogen synthase activity (in liver and muscle) and PEPCK activ ity (in liver) were not different between groups A-D. These findings a dd to those already published which suggest Psammomys is an ideal anim al model for the study of NIDDM.