RESPONSES OF IMMUNOREACTIVE ACTH AND BIOACTIVE ACTH TO LARGE HEMORRHAGE AND RESUSCITATION IN CONSCIOUS DOGS

We studied the effect of fluid resuscitation on immunoreactive adrenoc orticotropic hormone (irACTH) and bioactive ACTH (bioACTH) after hemor rhage in conscious dogs. Animals (n = 7) were bled 30% (similar to 25 ml/kg) over 3 min and 30 min later were either resuscitated [43.3 ml/k g 0.9% NaCl (1.8 times hemorrhage volume) over 10 min] or not. Blood w as reinfused after 210 min. Animals had both treatments (>4 days apart ). irACTH, bioACTH, cortisol, angiotensin II, and aldosterone increase d rapidly after hemorrhage. Resuscitation increased blood volume and c ardiac output to resting values, but arterial hypotension persisted. b ioACTH and irACTH decreased 40-90 min after hemorrhage in both groups, but each decreased more rapidly after resuscitation. The elimination half-life of bioACTH was shorter than that of irACTH, but neither was affected by resuscitation. The ratio of bioACTH to irACTH followed the same pattern with or without resuscitation. Angiotensin II and aldost erone remained increased without resuscitation but decreased promptly after resuscitation. In conclusion, 1) saline infusion at 1.8 x hemorr hage volume provides effective cardiovascular resuscitation, with reso lution of hormonal responses to hemorrhage; 2) although ACTH responses resolved with or without resuscitation, resuscitation produced more r apid resolution without changing the parameters of ACTH elimination; 3 ) the dynamics of the resolution of the ACTH response to hemorrhage ar e similar whether induced by stimulus removal or feedback inhibition.