Glycyl- l-glutamine antagonizes α-MSH-elicited thermogenesis

The objective of this study was to determine whether glycyl- l-glutamine [β-endorphin(30–31)] modulates the thermoregulatory actions of α-MSH. Microinjection of α-MSH (0.06 nmol) into PGE 2-responsive thermogenic sites in the medial preoptic area of rats generated a hyperthermic response, inducing a 0.85 ± 0.19° C rise in colonic temperature ( T c ) within 45 min. Coadministration of glycyl- l-glutamine (3.0 nmol) completely blocked the response, maintaining T c at baseline levels. This was not attributable to glycyl- l-glutamine hydrolysis because coadministration of glycine and glutamine had no effect on α-MSH-induced thermogenesis. Glycyl- l-glutamine, injected alone, was similarly without effect. These data indicate that glycyl- l-glutamine inhibits α-MSH-induced thermogenesis but is devoid of thermoregulatory activity itself.