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
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Cortisol
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τ3-MSH
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Sheep
