Fatty acid composition and insulin-like activity of chicken cerebrospinal fluid

Investigations were made to characterize the fatty acid composition of normal and hypoglycemic plasma and cerebrospinal fluid (CSF) and to clarify whether or not insulin crosses the avian blood-brain barrier. Plasma and CSF fatty acids (total and free) were separated and quantitated from normal and hypoglycemic female adult Single Comb white leghorn chickens utilizing a gas chromatographic method. Insulin-induced hypoglycemia decreased plasma total and free fatty acids and CSF free fatty acids; CSF total fatty acids increased. The passage of [raised 14]C-inulin and the influence of 10 U/kg (beef) insulin on the transport of inulin into CSF was followed by collecting CSF from the cisterna magna of chickens. Maximum [raised 14]C-inulin activity was detected 80 minutes after injection. Insulin injected simultaneously with inulin appeared to hasten the CSF appearance of [raised 14]C-inulin, the maximum counts appearing 40 minutes later. Estimation of the existence of endogenous insulin levels (ILA) in avian CSF was accomplished by bioassay of fresh CSF employing the rat hemidiaphragm method. One tenth ml CSF was found to possess the same level of ILA as 0,2 U insulin. There was a failure to observe ILA levels in excess of those levels found in normal CSF in samples obtained at various times during the hypoglycemic period.