Adrenocorticotropin response to graded blood loss in the cat

To assess the early endocrine and physiological responses to rapid blood loss, adult cats anesthetized with chloralose-urethan sustained transient hemorrhage (H) of different magnitudes for a 3-min duration. The magnitude of H was expressed as a percentage of initial total blood volume after plasma volume determination by dye dilution or on a per unit body weight basis. Considerable variation in total blood volume was observed at all body weights (range, 44.5-80.2 mg/kg). Adrenocorticotropin (ACTH) in peripheral venous plasma was not significantly altered by 10% H but increased modestly after 20% H by 5 min (148 ± 67 pg/ml) and rose promptly after 30% H by 2 min (541 ± 155 pg/ml) with a peak at 5 min (579 ± 171 pg/ml). Total change in ACTH during the 15-min sampling period was proportional to the magnitude of H (r = 0.730, P < 0.001). Mean arterial pressure (MAP) decreased significantly to all magnitudes of H by 1 min with a graded recovery during the 3-min hypovolemic period that was well correlated (r = 0.602, P < 0.005) with the percentage of blood volume removed. Mean plasma glucose concentration was not significantly changed by 10 or 20% H but increased after 30% H by 5 min (46.2 ± 10.2 mg/dl). Total glucose change from prestimulus levels during the 15-min sampling period was correlated with the magnitude of H (r = 0.731, P < 0.001). Plasma norepinephrine increased equally after 20 or 30% H or 10 ml/kg H but was not significantly elevated after 10% H. No evidence for proportional change in norepinephrine against the magnitude of H was seen (r = 0.426, P > 0.05). These results indicate that increasing the magnitude of H as a percentage of measured initial blood volume 1) increased the rate and magnitude of the ACTH response, 2) increased the magnitude of the MAP and glucose responses, 3) increased the magnitude of the norepinephrine response in a nongraded manner, and 4) was a better indicator of the ACTH response than was the decrease in MAP. We conclude that the volume magnitude of H is a major determinant of the responses to transient H but that other factors such as rate and/or duration of H may also contribute to the diversity of response patterns.