Catecholamine secretion by the adrenal medulla of the foetal and new-born foal

1. The content and output of adrenaline and noradrenaline from the equine adrenal medulla has been investigated under different conditions in foetuses, foals and adult mares.2. In the foetus only small amounts of both amines were secreted in response to stimulation of the peripheral ends of the splanchnic nerves to the gland; during anoxia the adrenal discharge was far greater and was independent of any nervous mechanism.3. Whereas in the ruminant a direct adrenal response to low P(O2) is confined to the noradrenaline cells during foetal life only, the adrenal medulla of the foetal foal secreted both adrenaline and noradrenaline during asphyxia, and the direct response persisted for some days after birth. Noradrenaline was the amine predominantly released during asphyxia in the foetus.4. Catecholamine output from the equine adrenal medulla changed with age, in that there was a gradual increase in both the absolute and relative amount of adrenaline released, irrespective of the stimulus applied, although at any given stage of development a higher proportion of adrenaline was secreted in response to stimulation of the splanchnic nerves than during anoxia.5. The relative proportions of the two amines in the effluent blood bore little resemblance to those found in the glands, removed after prolonged asphyxia, in either foetuses or foals. Preliminary observations have indicated that more noradrenaline is present in the glands when the foetus remains relatively undisturbed within the uterus.6. The possible significance of the larger adrenal response to asphyxia in the foetal foal in comparison with other species is discussed in relation to the development of the innervation and the growth of the adrenal cortex.