Biological action of the lipotrophic peptides A and B from pig pituitary glands.

In vitro lipolysis was stimulated by porcine pituitary peptides A and B in the rabbit, rat, mouse, and guinea pig. The minimal effective doses were calculated from log dose response curves for free fatty acids and free glycerol liberation. The rabbit was most sensitive responding to 0.008 mug/ml (1.4 pM/ml) peptide A and 0.06 mug/ml (5.3 pM/ml) peptide B respectively. Minipig adipose tissue showed no reaction up to a peptide concentration of 100 mug/ml. After intravenous injection of either peptide at the concentration of 50 mug/kg, FFA and free glycerol increased rapidly in the rabbit with maximal concentrations at 30 min, returning to near normal concentrations after 240 min. Blood glucose concentrations increased continuously in spite of hyperinsulinaemia with a peak concentration at 60 min and complete normalisation after 2 h. Hypertriglyceridaemia and hypocalcaemia were observed in both lipotrophin and control groups. Furthermore, the saline injected rabbits also displayed a slight increase of glucose, FFA, and free glycerol plasma concentrations towards the end of the experiments, suggesting stress stimulated lipolysis. The insulinotrophic effect of both peptides was verified by the fact that injection of lipid emulsion plus heparin led to a comparable increase in FFA and glucose, but to no change in insulin concentrations.