Category Archives: Gonadotropins

Effects of Gonadectomy and Androgen Treatments: DISCUSSION(4)

DISCUSSION(4)

In the present study, 11KA had a strong stimulatory effect on FSH. In most previous studies, however, 11-ketoan-drogens have been found to have no or weak feedback effects on the hypothalamus-pituitary-gonadal axis; some exceptions have been observed, but these all concern LH. Although 11KT is well known to have pronounced effects on many aspects of teleost reproduction, genomic steroid receptors for 11KT have not been found. Specific binding of 11KT has recently been shown in the membrane-organelle fraction of stickleback kidneys; the stickleback kidney is a target organ for 11KT. Specific binding sites of 11KT are also present in the membrane-organ-elle fraction of salmon brains (unpublished results). This specific binding may represent 11KT receptors through which feedback actions may be exerted. birth control pills

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Effects of Gonadectomy and Androgen Treatments: DISCUSSION(3)

Whereas effects of season and feedback on plasma and pituitary LH are largely parallel, this is not consistently so for FSH. For instance, plasma FSH levels in castrated llKA-treated fish are higher than in sham-operated fish in July, whereas the opposite is the case for pituitary content. Considering that pituitary content is controlled by synthesis and release, and plasma levels by release and clearance, it is not surprising that their patterns are not always the same. Negative feedback on FSH has previously been shown in adult coho salmon: gonadectomy caused rapid increases in plasma levels in maturing male and female fish.

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Effects of Gonadectomy and Androgen Treatments: DISCUSSION(2)

DISCUSSION(2)

Increased pituitary content of a hormone could be due to either increased synthesis or diminished release of the hormone. In the present study, plasma levels of LH in sham-operated fish were, though low, higher than in castrated males in autumn. This indicates that there is indeed a physiological positive feedback from the gonads to the pituitary in the regulation of LH secretion in salmon. This positive feedback could play a role in the temporal shift from predominantly androgen production to 17,20P production by the gonads over the reproductive cycle. Androgens, particularly T, eventually stimulate the secretion of LH, which in turn stimulates the production of 17,20P. In the present study, pituitary and plasma levels of FSH were also higher in sham-operated fish than in castrated ones. buy ortho tri-cyclen

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Effects of Gonadectomy and Androgen Treatments: DISCUSSION(1)

In the present study, plasma FSH levels in sham-operated fish displayed their highest levels in July, followed by a decline in autumn. Plasma and pituitary LH, on the other hand, increased from July to September and further in November. These seasonal changes are in general agreement with previous findings on other salmonids. In mature male Atlantic salmon parr in northern Sweden, plasma levels of T and 11KT peak in September-October, and the levels of 17,20P peak in November. Since plasma levels of FSH decreased over the breeding season also in castrated animals, this decline per se does not appear to be dependent on gonadal feedback mechanisms.

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Effects of Gonadectomy and Androgen Treatments: RESULTS(3)

RESULTS(3)

FSH plasma levels in experiments 1 and 2 are shown in Figures 5 and 6, respectively. Nondetectable plasma FSH levels (< 0.4 ng/ml, 0.04 ng/RIA tube) were counted as 0 for statistical analysis. Plasma levels of FSH were generally higher than for LH and were within the detection range in most fish in all groups except in T-treated fish sampled in July and September. In spring, plasma FSH levels were significantly higher in mature than in immature males (p < 0.01). levitra super active plus

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Effects of Gonadectomy and Androgen Treatments: RESULTS(2)

LH plasma levels are shown in Table 2. LH plasma levels were nondetectable (< 0.15 ng/ml, 0.015 ng/RIA tube) in all specimens sampled in spring or in July. In autumn, however, plasma LH levels reached the detection limit in most sham-operated males, being higher in November than in September (p < 0.001, experiment 2). Plasma LH levels were nondetectable in all castrated (significantly below the value in sham-operated fish; p < 0.01, experiment 1; p < 0.01, experiment 2, September; and p < 0.001 experiment 2, November) or llKA-treated males. Many T-treated males displayed detectable plasma levels of LH in September and November; these were, however, not significantly different from those for the castrated controls.

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Effects of Gonadectomy and Androgen Treatments: RESULTS(1)

RESULTS(1)

LH

The pituitary content of LH in the various groups in experiments 1 and 2 is shown in Figures 1 and 2, respectively. In spring, the LH content was significantly higher in mature than in immature males (experiment 2, p < 0.001). In autumn, pituitary LH levels in sham-operated fish increased above those found in the previous spring (experiment 1 and November sampling, experiment 2; p < 0.001 in both comparisons). In experiment 2, in which fish were sampled in July, September, and November, the levels were highest in November (p < 0.001, compared to both July and September). At all samplings, the pituitary LH content was far lower in castrated than in sham-operated fish (p < 0.001 in all four comparisons); this effect was more marked in autumn than in July.

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Effects of Gonadectomy and Androgen Treatments: MATERIAL AND METHODS(3)

ТЪе tubes were kept on ice (for up to 15 min) until centrifugation, after which the plasma was drawn off, frozen in plastic tubes on dry ice, and stored at -70°C until assay. Pituitaries were excised, frozen, and stored in the same manner as the plasma. Testes were weighed except in the case of immature fish that had threadlike testes too small (GSI < 0.1%) to be weighed with accuracy. All sham-operated fish rematured except for one male, which was excluded from further study. The completeness of castration and the presence and integrity of the Silastic capsules were always checked by visual inspection. Testicular remnants were found only in one fish, which was excluded from further study. Also, at the end of the experiments, the capsules were full of androgens. Lengths, weights, and GSI for the various groups of fish are shown in Table 1.

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Effects of Gonadectomy and Androgen Treatments: MATERIAL AND METHODS(2)

MATERIAL AND METHODS(2)

Louis, MO) or 11-ketoandrostenedione (11KA, Sigma) (androgens implanted into castrated fish only) or with empty capsules sealed with silicone glue, as well as with a passive integrated transponder tag (Destron, Boulder, CO) for individual identification (both experiments). 11KA is known to be converted extragonadally into 11-ketotestos-terone (11KT), and implantation of 11KA capsules to castrated salmon raises plasma 11KT levels. Plasma steroid levels were not measured, since the plasma volumes were sufficient for measuring FSH and LH only. However, in another study, similar capsules containing T and 11KA implanted into castrated salmon parr weighing ~50 g gave plasma levels of —20 ng/ml T and 11KT, respectively, values that are within the upper part of the natural range for mature salmon parr. In the present study, the fish grew considerably over the experimental period. At the autumn samplings, the fish weighed —100 g and at that time probably had somewhat lower androgen levels than in the earlier study. buy flovent inhaler

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Effects of Gonadectomy and Androgen Treatments: MATERIAL AND METHODS(1)

Experimental Animals and Treatments

Two experiments were conducted. In both, Atlantic salmon parr belonging to the Umealven (Ume River) stock were kept at the Norrfors hatchery (63°N, 20°E) in 2 X 2m tanks under standard hatchery conditions, with through-flowing river water at ambient temperature and under natural photoperiod. They were fed daily with commercial salmon food (Ewos Ltd., Westfield, Scotland). Two-year-old male parr that had matured in the previous autumn and still had running milt were castrated or sham operated on 25-28 March 1988 (experiment 1) and on 17-19 April 1989 (experiment 2) under —0.1% 2-phenoxyethanol (Flu-ka Chemie AG, Buchs, Switzerland) anesthesia. buy antibiotics online

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