Comparison of the effects of adrenocorticotropic hormone fragment 4-10 (ACTH(4-10)) and [D-Phe 7 ]ACTH(4–10) on the compensation of spontaneous nystagmus in guinea pig

Following unilateral labyrinthectomy (UL), spontaneous nystagmus (SN) was measured in guinea pigs which received i.m. injections of 100 or 400 µg/kg ACTH(4-10) or 800 µg/kg [D-Phe⁷]ACTH(4–10), every 4 h for 48 h post-UL. The results were compared to those from a previous study, conducted under identical conditions, in which guinea pigs received similar injections of 200 µg/kg ACTH(4–10) or 0.1 ml/kg saline. ACTH(4–10) significantly accelerated the rate of compensation of SN at 100, 200, and 400 µg/kg doses, although the average effects were larger for the 200 µg/kg condition. [D-Phe⁷]ACTH(4–10) significantly increased the frequency of SN following UL compared to saline-treated animals; however, it also accelerated the rate of SN compensation. These results indicate that the acceleration of SN compensation in guinea pig by ACTH(4–10) follows an inverted U-shaped dose-response curve and that [D-Phe⁷]ACTH(4–10) increases the frequency of SN.