Sexual maturation and sex differentiation comprise facets of a
common theme: reproduction. The endocrine system regulates many
of the critical physiological processes necessary for reproduction and
offers a framework within which technologies can be developed for
controlling sexual maturation and sex differentiation. The studies
described in this thesis were undertaken to improve the
understanding of the endocrine control of these critical stages of
development in salmonids.
Final ovarian maturation in salmon is accompanied by dynamic
changes in plasma hormone levels. Ovulation can be accelerated
through the use of hormones such as gonadotropin releasing hormone
or its analogs (GnRHa). The effectiveness of GnRHa often depends on
the timing of treatment. To determine if plasma concentrations of
steroids can be used to predict the sensitivity of adult female coho
salmon (Oncorhynchus kisutch) to GnRHa, circulating levels of
testosterone, 17α,20β-dihydroxyprogesterone (DHP), and estradiol
were measured before and after injection with GnRHa to accelerate
ovulation. We found that high levels of testosterone were predictive of
early response of coho salmon to GnRHa treatment.
The correlation between testosterone and ovulatory response to
GnRHa suggested a possible functional relation. However.
implantation or injection of testosterone. 17α-methyltestosterone
(MT), or the antiandrogen, cyproterone acetate (CA), before or with
GnRHa treatment did not affect the ovulatory response of coho or
chinook salmon ( 0. tshawytscha) to GnRHa. Chinook salmon treated
with MT alone had accelerated ovulation in comparison to controls.
If steroids are involved in sex differentiation. steroids must be
produced early in development. In vitro production of steroids in both
coho salmon and rainbow trout (0. mykiss) was assessed from hatch
through sex differentiation. Cortisol, androstenedione, testosterone,
and estradiol were produced just after hatching by tissue explants that
contained anterior kidneys and gonads of coho salmon. To circumvent
the problem of not knowing the sex of individuals until after sex
differentiation, single-sex populations of rainbow trout were produced
by gynogenesis or androgenesis. Tissue explants produced more
androstenedione than testosterone or estradiol. More androgens were
produced by testes and more estradiol was produced by ovaries within
6 to 10 weeks of hatching. Dietary treatment with estradiol or MT
inhibited gonadal steroid secretion.
Electrophoresis of gonadal homogenates from salmonids
revealed several sex-specific bands. In particular, a prominent band of
about 50,000 daltons was apparent in ovaries but not testes.
Production of sex-specific proteins may be affected by dietary steroid
treatment. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37097 |
| Date | 29 May 1990 |
| Creators | Fitzpatrick, Martin S. |
| Contributors | Schreck, Carl B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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