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Glycyl-L-glutamine antagonizes alpha-MSH-elicited thermogenesis
1Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City 64108.
Abstract:
The objective of this study was to determine whether glycyl-L-glutamine [beta-endorphin(30-31)] modulates the thermoregulatory actions of alpha-MSH. Microinjection of alpha-MSH (0.06 nmol) into PGE2-responsive thermogenic sites in the medial preoptic area of rats generated a hyperthermic response, inducing a 0.85 +/- 0.19 degrees C rise in colonic temperature (Tc) within 45 min. Coadministration of glycyl-L-glutamine (3.0 nmol) completely blocked the response, maintaining Tc at baseline levels. This was not attributable to glycyl-L-glutamine hydrolysis because coadministration of glycine and glutamine had no effect on alpha-MSH-induced thermogenesis. Glycyl-L-glutamine, injected alone, was similarly without effect. These data indicate that glycyl-L-glutamine inhibits alpha-MSH-induced thermogenesis but is devoid of thermoregulatory activity itself.
Insights
Glycyl-L-glutamine, a beta-endorphin fragment, was found to inhibit alpha-melanocyte-stimulating hormone (alpha-MSH)-induced hyperthermia in rats. This peptide fragment does not affect thermoregulation on its own.
Area of Science:
- Neuroendocrinology
- Physiology
- Thermoregulation
Background:
- Alpha-melanocyte-stimulating hormone (alpha-MSH) is known to induce hyperthermia.
- The medial preoptic area of the hypothalamus is a key site for thermoregulation.
- The role of specific endorphin fragments in modulating thermoregulatory responses is not fully understood.
Purpose of the Study:
- To investigate the effect of glycyl-L-glutamine [beta-endorphin(30-31)] on alpha-MSH-induced thermogenesis.
- To determine if glycyl-L-glutamine possesses intrinsic thermoregulatory activity.
Main Methods:
- Microinjection of alpha-MSH and/or glycyl-L-glutamine into the medial preoptic area of rats.
- Measurement of colonic temperature (Tc) changes over time.
- Control experiments using glycine and glutamine to assess hydrolysis.
Main Results:
- Microinjection of alpha-MSH (0.06 nmol) caused a significant rise in colonic temperature (0.85 +/- 0.19 degrees C).
- Coadministration of glycyl-L-glutamine (3.0 nmol) completely blocked the hyperthermic effect of alpha-MSH.
- Glycyl-L-glutamine alone, or its constituent amino acids (glycine and glutamine), did not alter baseline temperature.
Conclusions:
- Glycyl-L-glutamine acts as an inhibitor of alpha-MSH-induced thermogenesis.
- Glycyl-L-glutamine does not possess independent thermoregulatory properties.
- These findings suggest a specific modulatory role for this beta-endorphin fragment in central thermoregulation.