LIPID-STIMULATED SOMATOSTATIN SECRETION IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

Previous work has shown that somatostatins (SS) affect teleost lipid m etabolism indirectly by inhibition of insulin (INS) and directly by st imulation of hepatic lipolysis. In the present study, rainbow trout (O ncorhynchus mykiss) were used to characterize further the lipid-SS rel ationship by evaluating how lipid contributes to SS secretion both in vivo and in vitro. In vivo hyperlipidemia was induced for up to 3 h by short-term (2 min) infusion of a triacylglycerol (TG)-rich lipid emul sion (20% Intralipid(R)). Plasma total lipid concentration increased 1 18 and 155% over control levels 1 h and 3 h, respectively, after infus ion, much of this increase was due to elevated plasma fatty acids (FA) , which increased 39 and 520%, respectively, over the same time-frame. The hyperlipidemic pattern was attended by a significant increase in the plasma concentration of SS. The specific effects of fatty acids we re evaluated on isolated Brockmann bodies. Palmitic acid and oleic aci d stimulated SS release 378 and 82%, respectively, over baseline level s. These results indicate that lipids, and in particular fatty acids, modulate SS secretion in rainbow trout.