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Biomedical subjects

B Breton

Publications and source records attributed to B Breton.

At least 73 records · Page 4Linked to original sources
PubMed1981

Changes in plasma gonadotropin after ovariectomy and estradiol supplementation at different stages at the end of the reproductive cycle in the rainbow trout (Salmo gairdneri R.).

To determine the effect of gonadal feedback on plasma GTH level, female rainbow trout were ovariectomized at three stages at the end of the reproductive cycle: at the end of vitellogenesis, during germinal vesicle migration and during the post-ovulatory period. A group of controls and one of castrates in each experiment were given an injection of physiological salt solution, and a third group of castrates was supplemented with estradiol-17 beta (E2) twice a week (200 micrograms/kg) from the day of surgery. The blood was sampled twice a week, and the GTH measured by RIA. At the end of vitellogenesis, castration induced a significant rise in the gonadotropic hormone level (P less than 0.001 from post-surgical day 5), and that response, unimpeded by E2, was homogeneous in all the fish. During germinal vesicle migration, the response to castration and to supplementary E2 varied with the individual. Ovariectomy induced a significant increase in GTH (P less than 0.005 from day 3), but that increase was immediate in 5 females and delayed in the other 4; E2 prevented GTH rise in only 6 females. At the post-ovulatory period we found no significant difference between the control fish and the castrates and E2, at least temporarily, prevented the post-ovulatory rise in GTH which is usually found in trout.

Animals↗
PubMed1980

Temperature and reproduction in tench: effect of a rise in the annual temperature regime on gonadotropin level, gametogenesis and spawning. I. The male.

During a 9-month period (corresponding to a sexual cycle), the adult male tench, Tinca tinca, was kept in fish farm ponds receiving heated water from a power plant. In 1974, the males were submitted to three different temperature regimes: group I: ambiant temperature; group II: ambiant temperature +3 degrees C; group III: ambiant temperature + 6 degrees C. The experiment was repeated in 1975, but only using groups I and III. The reproductive cycle and thermal treatment were studied from a quantitative analysis of spermatogenesis, the duration of the spawning cycle and radioimmunoassay (RIA) measurement of gonadotropin (GTH) in plasma and pituitary, using a carp RIA system turned out to be sensitive enough to assay tench GTH, which was expressed in a c-GTH equivalent. Spermatogenesis in the tench was a discontinuous process, starting in the spring and finishing in the summer. It began earlier in heated water in which the spawning period was also considerably longer (3 months in group III against 1 month in group I). At the beginning of spermatogenesis, pituitary and plasma GTH was low, but rose rapidly when spermatogenesis was initiated (appearance of type B spermatogonial cysts and meiosis). The highest GTH levels in the blood were recorded during the spawning period, with important fluctuations probably due to discharges from the pituitary.

Animals↗
PubMed1980

Temperature and reproduction in tench: effect of a rise in the annual temperature regime on gonadotropin level, gametogenesis and spawning. II. The female.

Female tench were bred for two consecutive years under different thermoperiods; the effect of the thermoperiods on vitellogenesis, spawning, plasma and pituitary gonadotropin (GTH) levels was studied. The temperature did not affect development during the preparatory period. We found no ovarian development below 10 degrees C. The temperature accelerated vitellogenesis only if the mean daily average was more than 10 degrees C, and the rate of increase of that parameter from 10 to 23 degrees C (spawning temperature) determined female fertility. The date of first spawning may be predicted by the summation of degree-days higher than 10 degrees C. GTH secretion increased during vitellogenesis to reach maximal values during spawning. The data indicate a gonadotropin surge at the beginning of each spawning. There was no difference between plasma GTH levels at the various temperatures, but pituitary GTH was higher in the groups bred under the highest temperatures.

Animals↗
PubMed1979

Stimulation of milk synthesis in the rabbit by fish pituitary extract.

The lactogenic properties of extracts of the pituitary glands of salmon and trout were evaluated by using the organ culture technique with rabbit mammary explants. Crude extracts and fractions obtained after chromatography on Ultrogel and selected for their capacity to compete with ovine prolactin in a rabbit mammary gland radioreceptor assay were added to the culture medium. The criteria of lactogenesis were lactose synthetase activity, casein synthesis, measurements of the concentration of casein messenger RNA and the histology of mammary glands. All these tests led to the conclusion that salmon and trout pituitary glands contain a prolactin-like principle capable of initiating milk synthesis in the rabbit mammary cell.

Animals↗
PubMed1976

[Effect of 17 alpha hydroxy-20 beta dihydroprogesterone and progesterone on maturation and ovulation in vivo and on the plasma level of gonadotropic hormone t-GtH in rainbow trout Salmo gairdneri].

Ovulation occurred 5 to 9 days after injection of 2 mg/kg 17 alpha-hydroxy-20 beta dihydroprogesterone (17 alpha-20 beta Pg) in rainbow trout with oocytes in which the germinal vesicle was subperipheral. Whereas oocyte maturation was initiated by 17 alpha-20 beta Pg without an immediate increase in the concentration of t-GtH, in controls an increased level was found to coincide with initiation of the process and the concentration of t-GtH was higher at all stages. Progesterone treatment was less effective.

20-alpha-Dihydroprogesterone↗
PubMed1976

[Stimulation of pituitary gonadotropin secretion after castration in rainbow trout: variation of the response during the reproductive cycle].

Bilateral castration of male rainbow Trout resulted in increased levels of circulating gonadotropin, as measured by radioimmunoassay, but the response varied depending on the season. In early May the increase was 12 ng/ml after 30 days, when compared to the intact control but later in the month at the time when a peak of gonadotropin level is observed in normal fish, the increase was 25 ng/ml after 13 days. At the beginning of August, when spermatogenesis commences, the increase was 9 ng/ml after 12 days. In September, when spermatogenesis is ending, an increase of 20 ng/ml was found after 7 days, but only 50% of the animals responded. In December, during spermiation, an increase of 90 ng/ml was found after 7 days.

Animals↗
PubMed1975

[The response of the hypophysis to exogenous Gn-RH during the annual reproductive cycle of the carp Cyprinus carpio L].

The response of the hypophysis to injection of homologous hypothalamic extract and of LH-RH was studied during the reproductive cycle of the Carp Cyprinus carpio L. It is maximal during the summer months, during the reproductive period. It is nil or weak during winter, the period of sexual inactivity. It appears in April-May when gametogenesis is initiated and the water temperature increase.

Animals↗
PubMed1975

[Reproductive cycle of trout and tench: effect of experimental variations of the temperature (author's transl)].

10 In the rainbow trout and the tench, at the time of spermatogonia divisions a rise in the plasma gonadotropin levels was observed. Just before or during the spawning period, E217 beta and plasma gonadotropin reach their maximum levels. 20 When the effects of raising the natural cycle temperature of the tench were studied (deltat + 3 degrees C and + 6 degrees C), in conditions where nycthemeral and seasonal rythmicity were maintained, a significant increase in fertility was observed with the increase in temperature (the first spawning period was earlier and there was a rise in the number of spawnings). This effect of temperature seems to act at the level of the hypothalamo-pituitary system.

Animals↗