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The protein (αP), prepared by delipidation of canine serum α1-lipoprotein (αLP), when labeled with I131 and injected into dogs, was metabolized at the same rate as native αLP, labeled in the protein moiety with I131. When αP-I131 was added to serum or injected into dogs, the radioactivity promptly appeared only in the αLP fraction, indicating a preferential interaction of the labeled protein with its own lipoprotein class. The nature of this interaction was not established. Mixing of αP-I131 with the low density lipoprotein class (βLP), in absence of serum, yielded two radioactive fractions, floating at d 1.063 and d 1.21. These two fractions had electrophoretic mobility similar to radioiodinated native °LP and αLP. In the absence of serum, αP-I131 reacted also with chylomicrons from serum or chyle. When the radioactive chylomicrons thus formed were injected into dogs, their disappearance from circulation paralleled that of an injected Lipomul (artificial triglyceride emulsion)-αLP-I131 complex. In both instances the disappearance of triglycerides was accompanied by appearance of radioactivity in the αLP fraction of plasma. When Lipomul was given intravenously to dogs injected with αLP-I131, it combined with a small amount of this labeled lipoprotein. The possible participation of αLP in the metabolism of triglycerides is briefly discussed.

The effect of the central nervous system on regulation of serum lipid, glucose, and protein levels under basal conditions and after excitement, or cold exposure, was studied in 11 normal dogs and in 4 of the 11 after spinal cord transection at level C-6.Serum total cholesterol, “Β-” (−S 20–40), and “high-density α-” (−S 1–5) lipoprotein concentrations determined weekly for 5 months in two normal dogs varied little; −S 5–10 and −S 10–20 lipoproteins were less stable. For 1–3 weeks after cord transection, serum cholesterol and α-lipoprotein concentrations decreased along with weight loss. After weight stabilization they returned to near control levels and remained there.Levels of plasma free fatty acids (FFA) were low and of glucose were normal for several weeks after cord section; after several months the levels of FFA were consistently high and glucose became progressively lower than normal.Short periods of excitement caused increased plasma FFA and glucose levels in normal dogs, but only slightly increased FFA in spinal cord-transected animals. Two hours of cold exposure caused the same response in normal dogs as did excitement; in cord-transected dogs both plasma FFA and plasma glucose decreased.