CORTICOSTEROID INVOLVEMENT IN THE CHANGES IN NORADRENERGIC RESPONSIVENESS OF TISSUES FROM RATS MADE HYPERTENSIVE BY SHORT‐TERM ISOLATION

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Abstract
1 The responses to noradrenaline and to noradrenergic nerve stimulation of spontaneously beating right atria, electrically driven left atria and vasa deferentia taken from rats made hypertensive by short-term isolation have been compared with the responses of tissues from normotensive, group-housed animals. 2 Adrenocortical activity of isolated animals was assessed by plasma corticosterone determinations and measurement of adrenal weights. 3 The hearts of the isolated animals were weighed and the myocardial contents of water, sodium, potassium and calcium were measured. 4 Spontaneously beating right atria from isolated animals showed a lower resting rate, no difference in the response to nerve stimulation but a greater sensitivity to noradrenaline compared to atria from group-housed animals. 5 Vasa deferentia from isolated animals showed a decreased maximal response to noradrenaline, but no change in noradrenaline sensitivity or in the response to transmural stimulation. 6 There were indications of hyperactivity of the adrenals throughout a 5 week period of isolation, manifest as elevated plasma corticosteroid levels and increased adrenal weights. 7 Myocardial levels of sodium and calcium were elevated at the same time as the tissue level of potassium was reduced, but heart weights did not significantly change. 8 It is possible that adrenal steroid action caused the changes in tissue ionic balance. These ionic disturbances may have been responsible for some of the changes in tissue sensitivity found in the isolated hypertensive animals.