1. Employing a precise and sensitive double-isotope derivative technique plasma noradrenaline and plasma adrenaline were measured in sixteen normal subjects, in eight patients with myxoedema and in ten patients with thyrotoxicosis. Venous blood was obtained while the subjects rested in the supine position. 2. In the normal subjects plasma noradrenaline averaged 0·22±SD 0·09 ng/ml and plasma adrenaline 0·05±SD 0·05 ng/ml. Plasma noradrenaline rose with increasing age. 3. In patients with myxoedema, plasma noradrenaline was increased approximately threefold. The difference between the normal subjects and the hypothyroid patients was more pronounced in the older age-groups. 4. Despite their elevated pulse rate patients with thyrotoxicosis showed significantly decreased plasma noradrenaline concentrations compared to the normal subjects. 5. In the hypothyroid and hyperthyroid subjects plasma adrenaline concentrations were not different from the values obtained in the normal subjects. 6. It is suggested that sympathetic nervous activity is decreased in thyrotoxicosis as a compensatory phenomenon to the direct effect of thyroid hormones on the cardiovascular system.

1. Plasma catecholamines, plasma renin activity, plasma aldosterone and haematocrit were measured in four subjects with physiologically complete cervical spinal cord transections, before, during and after head-up tilt to 45 degrees for 30 min. Plasma catecholamines were measured in five normal male volunteers in the supine position and after head-up tilt to 45 degrees for 10 min. 2. After 10 min of head-up tilt, the plasma noradrenaline rose 14% in the tetraplegic patients and 115% in the control subjects. These findings indicate a failure of sympathetic activity in response to head-up tilt in the tetraplegic patients, probably caused by interruption of pathways by which the brain normally controls sympathetic outflow. 3. In the tetraplegic patients the resting plasma renin activities were above normal, and rose more quickly and greater on head-up tilt than in published studies of normal subjects. It is likely that the renal baroreceptors are important in the control of renin release. 4. In the tetraplegic patients, there was a late rise in plasma aldosterone which was probably due to the elevation in plasma renin activity.

The hormonal responses to breast-feeding were studied during the first 3 post-partum weeks in ten women smoking more than fifteen cigarettes/day and in a control group. Basal PRL levels were significantly lower in smokers compared with non-smokers, but suckling induced acute increments in serum PRL and oxytocin-linked neurophysin, which were not influenced by smoking. The lactational pattern was normal, but smokers weaned their babies significantly earlier compared with non-smokers. Heavy cigarette smoking women have lower basal PRL levels and this may shorten the period of lactation.

No abstract