[Effect of beta-lipoprotein derivatives on the drinking and feeding behavior of rats].

The effects of some previously unexplored beta-lipotropin derivatives (fragments of beta-MSH 4-7 and 5-8 corresponding to fragments of beta-lipotropin 40-43, 41-44; an enkephalin analog--an enkephalin-like tetrapeptide Tyr-D-Ala-Gly-Phen-NH2) on drinking and food behavior of rats were studied and compared. beta-MSH 5-8 was found to possess a remarkable dipsogenic action but to produce no effect on food intake in rats. At the same time a structurally related analog beta-MSH 4-7 and enkephalin-like tetrapeptide did not alter drinking behavior of animals, exerting, however, a substantial satiating action on hungry rats and initiating food behaviour in fed animals. The effects of the peptides on drinking and food behavior appeared long-term, persisting for 14-16 days and even up to 4-4.5 months upon administration of the enkephalin-like tetrapeptide. The data obtained suggest that the structural similarity of peptides does not always determine the common characteristics of their physiological effects which depend to a considerable degree on the initial food motivation.