Plasma concentrations of oxytocin and vasopressin were measured in relationship to oxytocin cell firing during suckling in urethane-anaesthetized rats. Preliminary experiments showed that plasma concentrations of oxytocin and vasopressin, which were increased immediately after anaesthesia, reverted to basal concentrations 3 h later. Moreover, it was found that exogenous oxytocin had entirely disappeared 5 min after i.v. bolus injections of known doses of oxytocin. Suckling did not modify the basal plasma concentration of oxytocin (14.6 +/- 2.9 compared with 14.6 +/- 1.5 pmol/l before suckling) except during a brief period immediately after neurosecretory bursts on oxytocin cells (37.8 +/- 5.2 pmol/l; P less than 0.001, n = 11). The plasma concentration of oxytocin did not differ significantly from the basal concentration 1.5 min later. The plasma concentration of vasopressin never varied. After two neurosecretory bursts of similar amplitude (total number of spikes during the burst) recorded on the same oxytocin cell, the variations in plasma concentration of oxytocin were also similar. When, for a given cell, the amplitude of neurosecretory bursts increased or decreased, the amount of oxytocin released changed in the same way. These data demonstrate (1) that suckling induces pulsatile release of oxytocin without vasopressin, and (2) a direct relationship between the amounts of oxytocin released and the amplitude of oxytocin cell neurosecretory bursts which argue in favour of simultaneous increases or decreases in the neurosecretory burst amplitudes on all oxytocin cells.

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Haemostatic and lipid parameters were determined for groups of women treated for at least 3 years with different types of hormonal contraception (HO, and compared to data of matched control groups without contraception and with IUD. A group of women starting HC were examined before HC, and after I cycle, 3 cycles and 1 year of HC.Slight increases of factor VII and thrombotest were observed immediately with all HC. Cold activation of thrombotest was observed with much higher frequency and at higher levels in HC groups than in controls. Decrease of antithrombin III was most markedly observed with the immunological assay, and occurred progressively throughout the first year of treatment. Fibrinolytic activity was affected differently by progestagen which fnc eased euglobulin lysis time, and by combined HC which shortened it. Plasminogen activator values confirmed these results. Response to local anoxia was not significantly modified. Significant increases of total lipids and phospholipidsand a slight increase of chblesterol occurred progressively during the first year of HC.As these modifications are possibly involved in thrombotic accidents in predisposed or high-risk women, and are more likely to occur during the initial period of He, closer supervision remains advisable during this period.

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