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Summary.

Rabbit blastocysts obtained 6 days after coitus were incubated individually or in groups for periods from 24 to 96 hr in a synthetic medium. Radioactive progesterone, pregnenolone, 17α-hydroxypregnenolone, androstenedione and sodium acetate were used as substrates in these incubations. The blastocysts could biosynthesize cholesterol and pregnenolone from acetate, and promote biotransformation of the various steroid substrates. Addition of interstitial cell stimulating hormone and adrenocorticotrophic hormone to the medium increased the rate of differentiation of the blastocysts during in-vitro growth.

Summary.

Plasma progesterone concentrations in rats were determined by a method employing gas-liquid chromatography with electron capture detection. Progesterone concentration was found to decrease before parturition and to increase again during lactation. A maximal post-partum concentration of this hormone was found during the 4th day of lactation. Removal of the litter or the placenta at delivery resulted in a decrease in the progesterone concentration at this time. Injection of large doses of prolactin in hypophysectomized female rats was associated with an increase in plasma progesterone concentration.

Summary.

Pregnant mare serum (pms) increased the secretion of testosterone and the incorporation of acetate-1-¹⁴C into testosterone-¹⁴C when administered intravenously to anaesthetized dogs, whether the pms was given as a single rapid injection or by continuous infusion during a period of 60 min. When pms was added to slices of rabbit testis in vitro, it increased both the incorporation of acetate-1-¹⁴C into testosterone¹⁴C and the synthesis of testosterone as shown by measurements of radioactivity and mass of testosterone-¹⁴C. It is therefore concluded that pms is capable of increasing the biosynthesis oftestosterone by testicular tissue and that the response of the testis to pms is qualitatively the same as that to interstitial cell-stimulating hormone.

Western forms of the spotted skunk, Spilogale putorius latifrons, breed in late September. The fertilized oocytes undergo cleavage and blastulation but further development is greatly retarded and implantation is deferred for 180 to 200 days. Nidation occurs in mid-April and parturition takes place in mid-May (Mead, 1968). The hormonal control of delayed implantation in this species and other members of the family Mustelidae has long been a perplexing problem. Numerous investigators have suggested that delayed implantation might be the result of inadequate progesterone secretion; however, all attempts to induce nidation by injections of progesterone, have, thus far, failed (Hansson, 1947; Hammond, 1951; Canivenc & Laffargue, 1958; Cochrane & Shackelford, 1962; Wright, 1963). It has been conjectured that the temporary inhibition of nidation results from

Summary.

Normal, male rabbits were either allowed to copulate with receptive females, or were injected with human chorionic gonadotrophin (hcg), or with adrenocorticotrophic hormone (acth). Copulation and hcg injection produced significant increases in plasma testosterone while acth administration failed to do so. Rabbits treated with either chloropromazine or fluoxymestrone before copulation did not increase plasma levels of testosterone following coitus.

Departments of Anatomy and Physiology, University of Southern California, School of Medicine, Los Angeles, California 90033, U.S.A., and Institute of Biophysics, University of Trondheim, Trondheim 7000, Norway

(Received 18th October 1974)

In an earlier study (Ahmad, Haltmeyer & Eik-Nes, 1973), we reported maintenance of spermatogenesis in tubules of hypophysectomized rats adjoining intratesticular implants of silastic capsules containing testosterone or dihydrotestosterone (DHT). It was suggested that the local differences in the testes of the rats receiving the two treatments might be attributed to the relative amounts of hormone escaping from the silastic capsules. It was calculated that only 8·3 μg DHT/day escaped from the capsule over the course of the experiment compared to 12·0 μg testosterone/day.

In order to compare the maintenance of spermatogenesis in DHT- and testosterone-treated rats with that in normal controls, experiments were undertaken in which larger quantities of hormones than those in the previous study were administered

Summary. The toxicity of different metals on isolated Sertoli cells grown in culture has been investigated. Methyl mercury (CH³HgCl) and mercury chloride (HgCl₂) were more toxic than cadmium (CdCl²) which was slightly more toxic than arsenic (As₂O₃). Isolated peritubular cells and Sertoli cells were equally sensitive to cadmium. Cadmium reduced the Sertoli cell survival over the concentration range of 1–10 μm. Freeze-etch electron microscopy of cadmium-exposed Sertoli cells revealed circular areas of average diameter 500 nm devoid of intramembrane particles in the nuclear membrane, and general signs of degeneration such as vesiculation of the plasma membrane and intramembrane particle aggregation. However, cadmium did not dissolve junctional complexes between Sertoli cells. Isolated Sertoli cells were protected against cadmium-induced damage when the cells were preincubated for 48 h with selenium, zinc or low doses of cadmium. Preincubation with cobalt, FSH, testosterone or oestradiol did not protect against cadmium-induced damage. Cadmium bound to metallothionein had no toxic effects on isolated Sertoli cells.