Treatment of pregnant mice ovaricctomized on day 3 (23.00-2330 h) with progesterone (1 mg/day/mouse, from day 4 through 11 post coitum (p.c.)) and oestrogen (single injection of 0.05 \g=a\g on day 8 p. c.) induced implantation in all the animals. Implantation was inhibited in animals following three subcutaneous injections of indomethacin given on the morning and afternoon of day 8 and the morning of day 9 p. c. A single injection of histamine on day 8 p. c. partially compensated the effect of indomethacin. A complete reversal of the antifertility effect of indomethacin was achieved following intraperitoneal administration of histamine (2 \g=a\g at noon of day 8 p. c.) and PGF2\g=a\(20 \g=m\g on the morning and afternoon of day 8 p. c.). This study suggests that in the mouse uterus indomethacin impairs the physiological changes which are required for the decidual cell formation and implantation. It is likely that an injection of oestradiol in the progesterone treated ovariectomized mice triggers the release of PGF2\g=a\ and histamine and that these compounds are involved in the chain of events leading to implantation of the blastocysts.During the past few years, a considerable amount of evidence has suggested that prostaglandins are involved in various reproductive processes, including implantation. A sequence of hormonal changes occurs during normal implan¬ tation and any alteration of these events prevents implantation (Psychoyos
The concentrations of blood serum steroids from 12 to 450 days old male rats were determined by radioimmunoassay. Testosterone (T) was low (270 pg to less than 1 ng/ml) until day 42; adult levels (3--4 ng/ml) were attained by day 62 and declined tradually with advanced age. 5 alpha-dihydrotestosterone (5 alpha-DHT) did not change markedly (90--160 pg/ml) from prepubertal to advanced age. Except for a small peak on day 22, androstenedione (delta 4 A) levels ranged between 400-500 pg/ml in the adult but declined in older males. Progesterone (delta 4 P) rose steadily to a mean of 5.46 ng/ml at 52 days of age and dropped thereafter. High levels of estrone (268 +/- 38 pg/ml) and estradiol-17 beta (2.76 +/- 0.28 ng/ml) in 12 days old males are in contrast to the low estrogens (20-35 pg/ml) in adult animals. Both T/5 alpha-DHT and total T/estrogen ratios were low before puberty, increased in adults and decreased towards old age. The interplay between gonadotropin and prolactin, which exhibited reciprocal changes in the regulation of steroid production by the gonads with age, are discussed.
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