DISAPPEARANCE IN PLASMA AND TISSUE UPTAKE OF RADIOACTIVITY AFTER AN INTRAVENOUS INJECTION OF [6,7-3H] NORETHYNODREL IN WOMEN

Abstract

ABSTRACT After an iv injection of [6,7-3H] norethynodrel to six women, the disappearance of radioactivity in plasma and the uptake in endometrium, myometrium and cervix at different times have been studied. The plasma disappearance curve due to norethynodrel and its metabolites showed an initial rapid disappearance with an average half-life of 76 min and a subsequent slower disappearance with a mean half-life of 45 h. The average volumes of distribution V1 and V̄ are about 17 and 119 litres respectively. The disappearance curve has been analysed on the basis of a biexponential curve representing a model consisting of two compartments. The second average half-life of 45 h is much longer than that of other hormones studied and it also explains the effectiveness of norethynodrel for 24 h or longer. Disappearance of radioactivity in the erythrocytes followed a similar pattern of disappearance of radioactivity in plasma, however, the levels were lower. The molar concentration of radioactivity was of the order of 14.5 × 10−9 m in the endometrium, 7.1 × 10−9 m in the myometrium and with the progress of time a higher uptake in the endometrium compared with the myometrium was found. Sub-cellular distribution showed 60–70% in the 105 000 g supernatant and 30% in the nuclear fraction of the endometrium. The significance of these results on the transport and action of norethynodrel is discussed.