The observation that sympathomimetic drugs or electrostimulation of the lumbar sympathetic trunks produces reticulocytosis has been reported by a number of authors in the literature. The mechanism underlying this phenomenon has been determined, although there is speculation that the result is caused by either activation of the reticuloendothelial system, vasoconstriction of the marrow blood vessels or stimulation of the suprarenal glands, spleen, or other erythropoetin-producing organs. The present study is a series of experiments to determine if the action of noradrenaline, in producing reticulocytosis, can be localized to the bone marrow. In addition, an attempt was made to identify the adrenoreceptor involved. Anaesthetized animals were given an infusion of noradrenaline into the marrow cavity of one femur. Reticulocytes were counted in peripheral blood smears before and after the infusion. Reticulocytes were also counted from the bone marrow of the injected femur and compared to reticulocyte numbers in the contralateral uninjected femur of the same animal and the femoral bone marrow of untreated control animals. The data from these experiments were compared to those obtained in experiments in which the lumbar sympathetic trunks were stimulated. One group of several animals was given propranolol prior to the infusion of noradrenaline or stimulation of the sympathetic trunks. The reticulocyte counts from these animals were compared to those from animals which did not receive the beta-adrenoreceptor blocker. All animals which received either an infusion of noradrenaline or stimulation of the lumbar sympathetic trunks demonstrated a pronounced reticulocytosis and a decrease of reticulocytes in the bone marrow. The beta-adrenoreceptor antagonist, (+/-)-propranolol, was effective in blocking these changes.(ABSTRACT TRUNCATED AT 250 WORDS)

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