EFFECT OF DIETARY LIPIDS AND ENDOCRINE CHANGES ON POLYUNSATURATED FATTY-ACIDS IN PHOSPHOLIPIDS OF PANCREAS AND BROWN ADIPOSE-TISSUE OF OBESE AND LEAN RATS

Obese (fa/fa) rats fed on control diet have lower proportions of linol eic acid (18:2n-6) and/or arachidonic acid (20:4n6) in IBAT and pancre as phospholipids compared with lean (Fa/-) rats. Lower stearic acid (1 8:0) to oleic acid (18:1n-9) mean ratios in fa/fa compared with Fa/- s uggest enhanced Delta 9-desaturase activity in the former. 18:2/20:4 m ean ratios in pancreas, but not IBAT, are indicative of a reduced Delt a 6-desaturase activity in fa/fa rats. Absolute amounts of phospholipi ds (mg/unit tissue wt) were 2-fold greater in IBAT of fa/fa compared w ith Fa/- rats, irrespective of their diet. This was reflected in great er absolute amounts of 18:2n-6 and 20:4n-6 only in HSO and HTO fa/fa g roups, but not in the control group. Adrenalectomy (Adx) or T-3 treatm ent also modified phospholipid fatty acid composition of IBAT and panc reas phospholipids in animals fed on the control diet with fa/fa rats more sensitive to endocrine induced changes. In fa/fa rats T-3 treatme nt increased docosahexaenoic acid (22:6n1-3) in IBAT of both phenotype s compared with the control, but this effect was evident only in fa/fa and not Fa/- pancreas. T-3 treatment also increased docosapentaenoic acid (22:5n-3) in IBAT from, both phenotypes, but no 22:5n-3 was evide nt in the pancreatic tissue of these animals. ADX also increased 22:6n -3 in the IBAT of fa/fa (Fa/- values were less than 1%) but not in the pancreas of fa/fa or Fa/-. ADX modified the relative proportions of 1 8:0 to 18:1 and 18:2 to 20:4 in IBAT and pancreas of fa/fa in a way th at indicated decreased Delta 9-desaturase and Increased Delta 6-desatu rase activities; these effects tended toward normal again in pancreas of fa/fa rats on corticosterone replacement (CST).