beta-endorphin and Starvation

beta-Endorphin stimulates glycerol release from adipose tissue in vitro in the rabbit. Thirty different amino acid sequences of this peptide were tested for lipolytic activity. Four turned out to be active: porcine and human beta-endorphin-(1-31), human beta-endorphin-(6-31), and human beta-endorphin-(1-5)-(16-31). Structure-activity investigations showed that for the lipolytic action of beta-endorphin the C-terminal part [longer than beta-endorphin-(27-31)] is relatively important. Of special importance seems to be the C-terminal amino acid residue, because none of the sequences lacking the last two amino acid residues was lipolytically active. Furthermore, a different lipolytic response to beta-endorphin was obtained in starved, ad libitum-fed, and starved-refed animals, showing that the regulation of the lipolytic potency is not only mediated by peptide concentrations in the medium.

Topics: Adipose Tissue; Animals; beta-Endorphin; Endorphins; Female; Food; Glycerol; Lipolysis; Peptide Fragments; Rabbits; Starvation; Structure-Activity Relationship

The effects of beta-endorphin (beta-Ep) on plasma glucose levels in rats and on glucose metabolism in isolated rat liver cells were examined. Intravenous injection of beta-Ep (5 micrograms/100 g BW) into ether-anaesthetized rats resulted in prompt and sustained hyperglycaemia with increases in the plasma glucagon and somatostatin levels and decrease in the plasma insulin level. When liver cells isolated from fed rats were incubated in the presence of beta-Ep at concentrations of 6 X 10(-8) M to 6 X 10(-7) M, glucose release into the medium increased within 15 min in a dose-related manner. Time course experiments showed that beta-Ep increased the level of cyclic AMP within 3 min. Significant increase in gluconeogenesis in liver cells isolated from fasted rats was also observed on addition of 10(-7) M beta-Ep in the presence of 10 mM L-lactate. These results suggest that the hyperglycaemia induced by beta-Ep may be caused, at least in part, by the effects of beta-Ep on releases of pancreatic hormones and glucose production in liver cells.

Topics: Animals; beta-Endorphin; Blood Glucose; Cyclic AMP; Dose-Response Relationship, Drug; Endorphins; Glucagon; Gluconeogenesis; Glucose; In Vitro Techniques; Insulin; Liver; Male; Rats; Rats, Inbred Strains; Somatostatin; Starvation

To study the effect of starvation on hypothalamic beta-endorphin and somatostatin (SRIF) concentrations in relation to starvation induced anestrus, groups of 8 rats were fed 50% of their normal daily chow consumption. Rats were sacrificed after 4, 8, 12, and 16 days during diestrus or anestrus. beta-endorphin concentrations decreased in the preoptic suprachiasmatic area (0.52 +/- 0.13 vs 0.21 +/- 0.05 ng/mg tissue wet weight) and increased in the posterior hypothalamus (0.31 +/- 0.06 vs 0.57 +/- 0.11 ng/mg) after 4 days of starvation. No significant change occurred in the arcuate nucleus or in the median eminence. On day 8 and 12 of starvation, beta-endorphin was unaltered in all areas compared to controls. Vaginal smears showed constant diestrus in a significant number of rats (5 out of 8) after 12 days. beta-endorphin concentrations in the arcuate nuclei of these rats were significantly reduced on day 16 (1.00 +/- 0.33 vs 0.30 +/- 0.11 ng/mg). The SRIF levels changed only in the median eminence with increased concentrations on day 12 (45.2 +/- 8.4 vs 79.5 +/- 14.8 ng/mg). At this time serum levels of luteinizing hormone (LH), prolactin (PRL), and growth hormone (GH) were significantly reduced. The results indicate that changes in hypothalamic beta-endorphin accompany the events leading to starvation induced anestrus.

Topics: Anestrus; Animals; Arcuate Nucleus of Hypothalamus; beta-Endorphin; Diestrus; Endorphins; Female; Hypothalamus; Hypothalamus, Anterior; Hypothalamus, Posterior; Median Eminence; Pregnancy; Rats; Rats, Inbred Strains; Somatostatin; Starvation