The Effect of Repetitive Haemorrhage on Plasma Cortisol, Beta-Endorphin and N-Terminal Pro-Opiomelanocortin in Conscious Sheep

Summary

We measured the effect of repeated haemorrhagic stress, performed on four consecutive days in conscious adult sheep, on the plasma concentrations of cortisol and ACTH-related peptides to determine whether the pituitary-adrenal response was altered by stress repetition. Peptides from the C-terminus of the ACTH pro-hormone were measured by β-endorphin RIA. Glycopeptides derived from the N-terminus of the ACTH pro-hormone were measured by τ₃-MSH RIA. The immunoreactive τ₃-MSH in sheep plasma was found to have an apparent molecular weight of approximately 10,000 by gel chromatography through Sephadex G-75, which is similar to the size of the major circulating form of pro-τ-MSH found in human and rat plasma. Daily haemorrhage consistently elevated plasma concentrations of cortisol and pro-τ-MSH. There was no significant difference in the daily responses of either cortisol or pro-τ-MSH when considered individually. However, there was a significant change over the four days in the relationship between the cortisol and pro-τ-MSH responses, as judged by analysis of variance of the difference in daily z-scores of cortisol and pro-τ-MSH. This trend indicated a relative increase in the secretion of pro-τ-MSH from the pituitary compared to the cortisol response, and suggested that repeated exposure to stressful stimuli may alter the pituitary-adrenal-axis.

Key-Words

Haemorrhage - Cortisol - τ₃-MSH - Sheep