Cutaneous myiasis in sheep arising from the activity of Lucilia cuprina larvae can result in significant physiological changes in susceptible animals. The stress imposed on the pituitary-adrenal axis of the sheep in response to myiasis and acute restraint is the subject of this investigation. Merino wethers were exposed to handling restraint, and blood sampling, during examination for blowfly strike; where necessary, they were treated for cutaneous myiasis. Significant changes in the plasma concentrations of immunoreactive J3-endorphin (J3-EP), ACTH and cortisol were found in sheep with extensive myiasis, as compared with unstruck sheep or those with only localized myiasis. In five susceptible sheep with extensive cutaneous myiasis, mean plasma levels of J3-EP, ACTH and cortisol were 307 ± 71 pg ml-1, 953 ± 58 pg ml-1 and 232 ± 46 nmoll-1 respectively, compared with 818 ± 89 pg ml-1, 641 ± 41 pg ml-1 and 107 ± 17 nmol I-I in six unstruck sheep handled similarly. Whereas significant increases in plasma ACTH and cortisol can result from pituitary-adrenal responses to acute emotional or surgical stress, and are usually accompanied by a concomitant release of J3-EP from the pituitary, the present findings indicate a marked reduction in J3-EP levels and a significant increase in ACTH and cortisol in sheep following blowfly strike and acute handling restraint. This result suggests that cutaneous myiasis in susceptible sheep can alter the pituitaryadrenal response to acute restraint stress, and this could occur either by an alteration of precursor processing in the pituitary or by the selective release of ACTH.

Though minor sequence differences between-species have been reported for adrenocorticotrophin, ACTH(1-39), the steroidogenic moiety ACTH(1-24) has appeared invariant in mammals. We here report the isolation, purification and amino acid sequencing of guinea-pig (GP) ACTH in which Pro24 is replaced by Ala24, and the demonstration that GP-ACTH stimulates aldosterone production to maximal levels well above those seen with human ACTH(1-39) or Synacthen, ACTH(1-24) amide, the synthetic ACTH fragment widely used for diagnostic and therapeutic purposes.