The Role of the Adrenal Medulla in Posthemorrhagic Pulmonary Hypertension

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Abstract
A marked increase in pulmonary vascular resistance (PVR) is known to develop in cats during hemorrhagic hypotension. The present investigation is an attempt to evaluate the role played by adrenal catecholamines in this posthemorrhagic PVR‐development. Anesthetized cats with open chests and on positive pressure ventilation were used. Six animals in which the adrenals had been acutely denervated were bled until the mean arterial pressure was 50 mm Hg. This level of hypotension was maintained for 3 h by further bleedings and/or small retransfusions. Cats similarly treated received catecholamines continuously infused (5 μg/kg/min) during the hemorrhagic period. Adrenaline alone, noradrenaline alone, or a 1:4 mixture of the two catecholamines were used. Comparisons were carried out between these animals and animals similarly bled but with intact adrenal innervation.In the cats with denervated adrenals the posthemorrhagic rise in PVR was low as compared with the high level seen in animals with intact adrenals. The gradual fall in the number of circulating thrombocytes was also significantly less in the denervated group than in the control group. Infusions of catecholamines to animals with denervated adrenals caused pulmonary hypertension in the hemorrhagic period. These findings indicate that catecholamines released from the adrenals play an important role in the development of the posthemorrhagic pulmonary hypertension previously described.