Acute in vivo stimulatory effects of human pituitary lipid-mobilizing factor on plasma levels of glucagon and insulin in rabbits.
The lipid-mobilizing factor LMF is prepared from deep-frozen human pituitary glands by alkaline extraction, followed by acetone precipitation at pH 4.8, Sephadex gel filtration and DEAE-cellulose chromatography. In addition to its adipokinetic effect in rabbits, LMF also increased the plasma levels of glucagon and insulin in rabbits in doses of 15 to 100 micrograms. The LMF-induced increases in the plasma levels of glucagon were most pronounced in fasted rabbits, whereas the increases in the plasma levels of insulin were most pronounced in fed rabbits. Glucose infusions decreased the LMF-induced hyperglucagonaemia and increased the LMF-induced hyperinsulinaemia. Somatostatin did not inhibit the LMF-induced hyperglucagonaemia with statistical significance, but inhibited the LMF-induced hyperinsulinaemia. The plasma levels of glucose were slightly decreased by 20 and 40 micrograms LMF in fasted rabbits and were unchanged in fed rabbits. In fasted rabbits, LMF had a toxic effect and 100 micrograms LMF killed one rabbits. Human growth hormone (hGH), prepared from the pituitary glands after removal of LMF, also increased the plasma levels of glucagon and insulin in rabbits. It is possible that the observed effects of LMF and hGH were due to the presence of some biologically active substances from the pituitary gland. These postulated substances could be involved in the pituitary control of the endocrine pancreas, and work is in progress to isolate them from the LMF preparation.