Responses of vasopressin and enkephalins to hemorrhage in adrenalectomized dogs.

To study responses of methionine enkephalin-like substance (MELS) and vasopressin (AVP) to hemorrhage, plasma MELS, AVP, and catecholamine levels and mean arterial blood pressure (MAP) and central venous pressure (CVP) were investigated in intact and adrenalectomized dogs (n = 34) under pentobarbital anesthesia. Plasma MELS increased significantly following a hemorrhage-induced rise in plasma epinephrine in intact dogs (n = 6). Plasma AVP rose concomitantly with a fall in CVP before MAP fell, but the subsequent fall in MAP was accompanied by a further elevation in plasma AVP concentration. In nonhemorrhaged control dogs (n = 6) these parameters did not change during the experiment. In adrenalectomized dogs (n = 6) the hemorrhage-induced increase in plasma MELS and AVP was significantly attenuated despite similar decreases in MAP as in intact dogs. In sham-operated dogs (n = 10) changes in these parameters were similar to those in intact dogs. The differences between plasma MELS in the superior vena cava and thoracic aorta did not change during hemorrhage in intact dogs (n = 6), but the differences in plasma AVP rose significantly, indicating a release of the hormone from the head. These results indicate that MELS release elicited by hemorrhage may largely arise from the adrenal gland and not the brain. Adrenalectomy attenuated AVP response to hemorrhagic hypotension.