SUMMARY In the uterus of pregnant mice an increase in uptake of tritiated uridine occurs between days 2 and 3 of pregnancy, followed by a further increase from day 4 onwards. Uridine uptake changes in the same manner in pseudopregnant mice up to day 4, but thereafter declines to a minimum at day 6. The non-pregnant horn of the unilaterally pregnant mouse shows the same changes as the uterus of the pseudopregnant mouse. The results suggest that implantation occurs during a period of declining ovarian stimulation of the uterus and that the increased uptake of uridine in pregnant mice is stimulated locally by implantation.
Miller, Owen & Emmens (1968) described the changes in uridine incorporation into uterine and vaginal RNA during early pregnancy and pseudopregnancy in the mouse and discussed their significance. A large increase in uridine incorporation occurred in the uteri in both conditions between 10.30 hr. on day 2 and 10.30 hr. on day 3, with a further increase from day 4 onwards only in the uteri of pregnant mice. The former increase is in both cases believed to reflect increasing ovarian oestrogen secretion, a conclusion supported by the studies of Finn & Martin (1967), Martin & Finn (1968) and Galassi (1968). In view of the widely held belief in a discrete surge of ovarian oestrogen on day 4 of pregnancy in the rat (Tic, Marcus & Shelesnyak, 1967) it was considered desirable to study the corresponding changes in this species.Randomly bred female rats of the Wistar strain, weighing 200\p=n-\280 g., were used. Three to four weeks before the experiment, the left Fallopian tube was interrupted by electrocautery via incisions in the dorso-lateral abdominal wall. Rats were mated over¬ night, and the following morning those with vaginal smears showing spermatozoa were removed and called day 1 pregnant. Changes in the non-pregnant horn were considered to simulate those which occur in the uteri of pseudopregnant rats.Vaginal smears were taken on the morning of the day of uridine injection, and rats not showing a leucocytic smear were rejected. At 09.30 hr. or 21.30 hr. the rats received 50 pc uridine ([5-3H]uridine, sp.act. 20-5 mc/mg., Radiochemical Centre, Amersham) in 0-5 ml. of 0-9 % NaCl solution through a lateral tail vein. They were killed by cervical dislocation 1 hr. after uridine administration, and the organs immediately dissected; uridine incorporation into RNA was estimated as previously described (Miller & Emmens 1967). Results were expressed as mean organ weight in mg./animal and mean disintegrations/min./animal due to the uptake of uridine into organ RNA (d.p.m.). Data were transformed to log10 for analysis. Fig. 1 shows the changes in mean organ weight and uridine uptake into RNA over the first 6 days of pregnancy in the fertile and sterile uterine horns, vagina, cervix and right ovary. Vaginal and cervical weights fell during the first 2 days and were fairly constant from day 3 onwards. Changes in vaginal and cervical uptake were similar and significant differences were few. The changes in fertile and sterile uterine horns were similar up to day 5, after which wet weight and uridine uptake declined in the sterile horn. The difference in both wet weight and uridine uptake between the two horns became highly significant (P < 0-001) at 10.30 hr. on day 6. The mean weight of each uterine horn declined from 10.30 hr. on day 1 to a minimum on day 3 and then increased, so that the sterile horn reached a maximum weight between
SUMMARY Cortisol and cortisone were identified and their levels determined in sea raven plasma by a double isotope derivative assay involving acetylation with [1-3H]acetic anhydride, purification by thin-layer and paper chromatography, followed by recrystallization to constant 3H: 14C ratios. The mean level of cortisol in four plasma samples was 7·2±1·0 μg/100 ml (range 4·0–9·2) and the mean level for cortisone in three samples was 1·1 ± 0·2 μg/100 ml (range 0·7–1·5). Metabolic clearance rates (MCR) were determined for both corticosteroids by the method of continuous infusion over an 8-h period. The mean MCR for cortisol in five fish was 126 ± 17 ml/kg/h, and for cortisone 449 ± 48 ml/kg/h in six fish. The mean percentage conversion of [1,2-3H]cortisol to cortisone was 9·4 ± 2·9%. There was no evidence of any significant conversion of cortisone to cortisol.
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