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240 HEMODYNAMIC RESPONSES OF LAMBS AND ADULT SHEEP TO HEMORRHAGE

Hemorrhage stimulates the secretion or cateoholamines by newborns and adults. This study directly compares the response of newborn and adult sheep to hemorrhage after alpha-blockade. We chronically instrumented 11 newborn lambs, and 8 adult sheep for continuous measurement of blood pressure (BP), heart rate (HR), and thermodilution cardiac output (CO). After pretreatraent with prazosin (P), an alpha-1 blocker, or vehicle (V) in a randomized, crossover fashion, each animal was hemorrhaged 20% of its blood volume. Cardiac output was measured at baseline; 20 mins after drug administration; after hemorrhage; at 100 mins, after which the animal was retransfused; and at 150 mins. Stroke volume (SV) and total peripheral resistance (TPR) were calculated. The effects of treatment with P and V on the measurements are shown in the table. All deviations from baseline were significant (p<.05). There were greater decreases in BP, CO, SV and TPR in P-treated versus V-treated ewes (indicated by *, p<.05). This difference was not seen in the lambs. (NC denotes no change.)We conclude that catecholamines do not play a major part in the response to hemorrhage in the lamb. (Supported by NIH Grant HD 17644.)