Preparation of Radio-Element by Means of an Electric Field I WISH to correct slightly my recent letter in NATURE 1 on this subject. The number of neutrons emitted by a radium plus beryllium neutron source has been accurately measured (C. J. Bakker 2 and other observers) and found to be (2•1 ± 0•2) X 10'

The effects of restraint stress and opiates on prolactin secretion in male rats have been measured. Both induced a short-lived increase in prolactinaemia. Experimental evidence indicates that both opioids and restraint stress bring about their actions by the activation of opioid receptors. When restraint stress was followed by administration of the specific kappa-agonist bremazocine, a second prolactin peak was observed. In contrast, morphine (predominantly a mu-agonist) lost its prolactin-stimulating capacity when given after a period of restraint stress. This indicates cross-tolerance between restraint stress and morphine. Tolerance was overcome when the dose of morphine was doubled, and an increase in prolactin secretion could again be obtained. The cross-tolerance phenomenon argues that a common opioid receptor is involved in morphine- and restraint stress-stimulated prolactin release. In another set of experiments, in which morphine administration replaced restraint stress as a means of inducing tolerance, a second rise in prolactinaemia was seen only with bremazocine and not with a further administration of morphine. This suggests a morphine (mu) receptor-specific development of tolerance. Two consecutive administrations of bremazocine also produced tolerance, in this case for the kappa-receptor. This illustrates the rapid and receptor-specific development of tolerance for the prolactin-releasing capacity of opioid compounds.

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In order to determine the incidence of pre-operative and postoperative deep venous thrombosis (DVT) in patients not receiving prophylactic anticoagulant therapy, bilateral phlebography was performed in a prospective study pre-operatively and on the 9th postoperative day, in 51 consecutive patients submitted for major abdominal surgery. The presence of a DVT before surgery was demonstrated in 15.7 per cent of the patients. This high frequency confirms objectively the rationale of starting prophylactic anticoagulant therapy before the surgical procedure. Thrombi were demonstrated postoperatively by phlebography in 54.9 per cent of the patients. Thus the true incidence of DVT induced by surgery was 39.2 per cent taking into account the 15.7 per cent pre-operative DVT rate.