Effects of gonadotropin‐releasing hormone on plasma sex hormones in rana esculenta. in vivo studies (original) (raw)
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Biology of Reproduction
Previous studies indicated that the chronic elevation in LH and FSH secretion from frog pituitaries stimulated with GnRH is dependent upon continued protein synthesis. To determine if GnRH is able to stimulate the de novo synthesis of gonadotropins (Gth: FSH and LH), anterior pituitaries from frogs were incubated in vitro with 35S-methionine in the presence or absence of 100 ng/ml GnRH. Glands stimulated with GnRH secreted elevated levels of FSH and LH, including higher amounts of newly synthesized Gth. Continual exposure to GnRH for 8 h did not affect the pituitary content of either immunoassayable Gth (labeled + unlabeled) or newly synthesized Gth. However, GnRH stimulation did increase the total amount (secreted + pituitary) of newly synthesized Gth. GnRH did not stimulate Gth synthesis in females. The temporal pattern of GnRH-stimulated secretion of newly synthesized Gth from male pituitaries was also determined. A lag period of 60-90 min occurred prior to appreciable secretion of radiolabeled Gth. Secretion of radiolabeled hormone then increased and reached a plateau before decreasing. After 6 h of stimulation, approximately 30% of the radiolabeled Gth still remained within the pituitary. These results are the first direct evidence that GnRH can stimulate the biosynthesis of Gth in a nonmammalian species.
The Journal of experimental zoology, 1992
The effects of vertebrate gonadotropin-releasing hormone (GnRH) variants on plasma and testicular androgen level in intact and hypophysectomized (PDX) male frogs, Rana esculenta, have been investigated. In intact animals, mammalian (m)-GnRH, m-GnRH analog (buserelin), salmon (s)-GnRH, chicken (c) I-GnRH, cII-GnRH, D-Arg6-cII-GnRH (cII-GnRHA), and lamprey (l)-GnRH (1.5 micrograms and 6 micrograms, total dose given on alternate days for 5 days) were able to enhance androgen production showing that specificity of pituitary responsiveness to GnRH variants appears to be low. Chicken II-GnRH was more effective than s-GnRH in eliciting testicular and circulatory androgen level increase. Moreover, in animals treated with 6 micrograms of cII-GnRH and s-GnRH in combination, androgens decreased as compared with animal treated with cII-GnRH only, suggesting that GnRH receptors bind preferentially the s-GnRH form. In PDX animals, buserelin (1.5 and 6 micrograms), cII-GnRH, and its analog (6 micr...
General and Comparative Endocrinology, 1984
The ability of mammalian and chicken gonadotropin-releasing hormones (GnRH) and their agonistic analogs to stimulate in vivo gonadotropin release were tested in a frog (Rana catesbeiana), snake (Naja naja), and turtle (Sternotherus odoratus). In the frog, chicken and mammalian GnRH were equipotent in stimulating the release of FSH and LH. Attendant increases in plasma androgen and the occurrence of spermiation confirmed the release of biologically active gonadotropin. Neither of the GnRH preparations or their agonists produced significant changes in plasma hormones in either of the reptiles. In light of comparable data for the actions of these GnRH preparations in mammals and birds, it appears that species specificity in the response to different GnRHs does not correlate well with the nature of the homologous hypothalamic GnRH molecule.
Biology of Reproduction, 1990
Previous studies indicated that the chronic elevation in LH and FSH secretion from frog pituitaries stimulated with GnRH is dependent upon continued protein synthesis. To determine if GnRH is able to stimulate the de novo synthesis of gonadotropins (Gth: FSH and Lu), anterior pituitaries from frogs were incubated in vitro with "S-methionine in the presence or absence of 100 ng/ml GnR}l. Glands stimulated with GnRH secreted elevated levels of FSH and LU, including higher amounts of newly synthesized Gth. Continual exposure to GnRH for 8 h did not affect the pituitary content of either immunoassayable Gth (labeled + unlabeled) or newly synthesized Gth. However, GuRU stimulation did increase the total amount (secreted + pituitary) of newly synthesized Gth. GnRH did not stimulate Gth synthesis in females. The temporal pattern of GnE}I-stimulated secretion of newly synthesized Gth from male pituitaries was also determined. A lag period of 60-90 mm occurred prior to appreciable secretion of radiolabeled Gth. Secretion of radiolabeled hormone then increased and reached a plateau before decreasin& After 6 h of stimulation, approximately 30% of the radiolabeled Gth still remained within the pituitary. These results are the first direct evidence that GnRH can stimulate the biosynthesis of Gth in a nonmammallan species. INTRODUCTiON Two distinct gonadotropins (Gth), having properties similar to mammalian FSH and U-I have been purified from pituitaries of ranid frogs [1,2,3]. These pituitaries are known
The Journal of experimental zoology, 1993
To further investigate the action of gonadotropin-releasing hormone (GnRH) on gonadotropin (Gth) secretion and synthesis, pituitaries from frogs, Rana pipiens, were incubated in the presence or absence of 100 ng/ml GnRH for 12 h. GnRH was then removed from the medium and glands were labeled with 35S-methionine either 12, 24, or 36 h after the conclusion of GnRH exposure. Immunoassayable LH and FSH (iLH and iFSH; both labeled and nonlabeled hormone) were determined by separate radioimmunoassays. Newly synthesized (radiolabeled) Gth was quantified by immunoprecipitation. When GnRH was present in the medium, it stimulated the secretion of both iLH and iFSH (compared to unexposed glands). Following withdrawal of the secretagogue, iLH and iFSH secretion diminished until they returned to control levels (within ca. 12 h). Previous exposure to GnRH enhanced the biosynthesis of Gth; this elevation was detectable up to 36 h after removal of the secretagogue. The magnitude of the elevation in ...
General and Comparative Endocrinology, 1983
Freshly captured female bullfrogs (Rana catesbeiana) were challenged with a standard dose (2 micrograms) of gonadotropin-releasing hormone (GnRH) shortly before and at the onset of the spawning season (in early April and mid-May) to examine the relationship between pituitary responsiveness and ovarian stage; males were also tested in April. As shown previously, increments in plasma gonadotropins induced by GnRH were consistently lower in females than in males. There was little difference in average responsiveness between the two collections of females and results for these were similar to those obtained at other times of the year. A wide range of ovarian stages was represented at both collection times as evidence by plasma steroid profiles, but there was no correlation between the GnRH-induced increments in plasma FSH and LH and plasma levels of androgens (testosterone and 5 alpha-dihydrotestosterone), estradiol-17 beta, or progesterone in the 71 females tested. Thus, there is no evidence of a feedback effect of ovarian steroids on the pituitary responsiveness to acute GnRH stimulation in the frog as has been demonstrated in mammals.
Gonadotropins and reproductive function in the anuran amphibian, Rana esculenta
Biology of Reproduction, 1998
In this study, the measurement both of peripheral gonadotropins (FSH and LH) and of sex steroids in male and female wild anuran, Rana esculenta, was performed during the annual reproductive cycle; moreover, the role of gonadotropins in the vitellogenic process and in ovarian steroidogenesis was investigated through in vitro experiments. LH plasma changes in males showed high values during autumn-winter months and during the mating period, when high androgen levels were found. Conversely, for the first time in male vertebrates, a clear correspondence between plasma FSH and estradiol-1710 (E 2) was shown. In females, FSH peak values were found at the beginning of the mating period in parallel with those of plasma vitellogenin (VTG) and E 2 ; in contrast, high LH levels went together with ovarian weight (gonadosomatic index), which is considered a good marker for the plasma sequestration of VTG by growing oocytes. The in vivo results are corroborated by in vitro studies showing the direct effects of both FSH and LH in inducing hepatic VTG synthesis and release in the culture media. Lastly, although it is not yet known whether or not FSH and LH have separate functions in amphibians, it was clearly shown that they induce ovarian steroid production. These results are discussed in terms of the high seasonality previously demonstrated in this wild frog.
Gonadotropins and Reproductive Function in the Anuran Amphibian, Rana Esculenta 1
Biology of Reproduction, 1998
In this study, the measurement both of peripheral gonadotropins (FSH and LH) and of sex steroids in male and female wild anuran, Rana esculenta, was performed during the annual reproductive cycle; moreover, the role of gonadotropins in the vitellogenic process and in ovarian steroidogenesis was investigated through in vitro experiments. LH plasma changes in males showed high values during autumn-winter months and during the mating period, when high androgen levels were found. Conversely, for the first time in male vertebrates, a clear correspondence between plasma FSH and estradiol-1710 (E 2) was shown. In females, FSH peak values were found at the beginning of the mating period in parallel with those of plasma vitellogenin (VTG) and E 2 ; in contrast, high LH levels went together with ovarian weight (gonadosomatic index), which is considered a good marker for the plasma sequestration of VTG by growing oocytes. The in vivo results are corroborated by in vitro studies showing the direct effects of both FSH and LH in inducing hepatic VTG synthesis and release in the culture media. Lastly, although it is not yet known whether or not FSH and LH have separate functions in amphibians, it was clearly shown that they induce ovarian steroid production. These results are discussed in terms of the high seasonality previously demonstrated in this wild frog.