Comparative response of blood cortisol levels to two different doses of intravenous acth (tetracosactrin) in overweight cats

Abstract

Fifteen middle-aged to older, overweight cats were investigated to rule out hyperadrenocorticism as a cause of their weight problem, using two different protocols for the adrenocorticotrophic hormone (ACTH) stimulation test. The cats received intravenous synthetic ACTH (tetracosactrin) at a dose of 125 µg initially and then, between 2 and 3 weeks later, a second test was performed using a dose of 250 µg intravenously. The peak of the mean serum cortisol concentrations taken at all time points, occurred at 60 minutes following the 125 µg dose and at 120 minutes following the 250 µg dose. There was no statistically significant difference between the cortisol peaks attained using either dose of tetracosactrin. There was, however, a significantly higher serum cortisol concentration attained after the higher dose at the 180 minutes time point, indicating a more prolonged response, when compared with the lower dose. The mean basal cortisol concentration was 203 nmol/l (range 81 – 354 nmol/l). The cats were followed up for one year after the initial investigations. Urine obtained one year later in the cats’ home environment, showed a mean urinary cortisol/creatinine ratio (UCCR) of 3.3 x 10 -6 (range 0.85 - 8.67 x 10 -6). A mean weight loss of 6 per cent was achieved over the period of the study. The weight loss, lack of development of clinical signs and the normal UCCR’s confirm that none of these cats had gone on to develop hyperadrenocorticism.