Title: Effect of exogenous estradiol-17β on plasma vitellogenin levels in male and female Chrysemys and its modulation by testosterone and progesterone
Abstract: Injection of estradiol-17β into the freshwater turtle, Chrysemys picta induced hormone-specific and dose-dependent vitellogenic responses in both sexes. However, both the time course of induction and the magnitude of the responses showed marked sexual differences. No vitellogenin was detected in untreated males. Following a single injection of estradiol-17β (100 μg/100 g body wt) vitellogenin was first detected in the plasma 8 hr postinjection. Maximal levels (3.1 ± 0.8 mg/ml, n = 5) were obtained by Day 6. Multiple injections of estradiol-17β into males raised plasma vitellogenin levels to 10–20 mg/ml. The initial increases during the first 6 days post-hormone treatment were independent of the dose. Nonvitellogenic females have basal levels of 1–2 mg/ml vitellogenin in circulation. Female turles receiving equal amounts of estradiol-17β (100 μg/100 g body wt) as males demonstrated a response 10 times greater (32.6 ± 3.9 mg/ml, n = 5). Maximum levels were reached in 12–14 days. Multiple injections of the hormones brought plasma vitellogenin levels to concentrations attained during the natural vitellogenic season (40 mg/ml). When progesterone or testosterone were administered to male turtles in conjunction with estradiol-17β, both hormones inhibited the estrogen-induced vitellogenesis. The antagonistic effect of progesterone on estrogen was directly dose dependent; in contrast, the testosterone effect appeared to be inversely related to dose. Since both progesterone and testosterone concentrations reach high levels during the periovulatory phase of the gonadal cycle, it is suggested that these hormones may be of physiological significance in modulating vitellogenin level in the plasma.
Publication Year: 1981
Publication Date: 1981-04-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 87
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