ADRENALINE AND REGULATION OF THE PLASMA POTASSIUM CONCENTRATION IN FETAL AND NEWBORN LAMBS

In young growing sheep (ca 6 months of age), adrenaline (0.25 nmol . m in(-1). kg(-1) intravenously for one hr, then 2.5 nmol . min(-1). kg(- 1) for a second hr) decreased plasma K+ concentration by 0.89 +/- 0.10 9 mmol/l (n = 4). In chronically cannulated late-gestation foetuses, h owever, adrenaline (ca 2.5 then 5.0 nmol . min(-1). kg(-1) each for on e hr) decreased plasma K+ by only 0.26 +/- 0.056 mmol/l (n 12), despit e metabolic and cardiovascular changes of comparable magnitude to thos e in postnatal sheep, In newborn lambs (<1 day of age), adrenaline (ca 1.25, then 6.0 nmol . min(-1). kg(-1) each for an hr) failed to decre ase plasma K+ significantly. In contrast, at 6 days of age, the decrea se in plasma K+ (0.71 +/- 0.095 mmol/l, n = 5) during adrenaline infus ion was similar to that in older sheep. The changes in plasma K+ obser ved during adrenaline infusion into foetuses and growing sheep were to tally abolished and those in lactate greatly attenuated after prolonge d (6-8 days) infusion of a beta(2)-selective adrenergic-receptor agoni st, ritodrine, Because insulin decreases plasma K+ in the foetus, thes e results imply a difference in developmental programming of the hypok alaemic action of catecholamines and insulin.