In vitro ovarian responses to pulsatile and continuous gonadotrophin administration on steroid secretion and oocyte maturation in the frogs, Rana pipiens and Rana catesbeiana

doi:10.1016/0016-6480(86)90227-3

General and Comparative Endocrinology

Volume 61, Issue 3, March 1986, Pages 417-423

https://doi.org/10.1016/0016-6480(86)90227-3 Get rights and content

Abstract

An in vitro superfusion system was used to study the relative effects of pulsatile and continuous gonadotrophin administration on steroid secretion and oocyte maturation in Rana pipiens ovaries. Pulsatile (10 min pulse/hr) delivery of pituitary extract (PE) resulted in a slightly (insignificantly) lower level of testosterone (T) secretion over a 12-hr period. Administration of a fivefold lower, subliminal amount of PE instead of hormone-free media between pulses did not change the pattern of T secretion. When the interpulse frequency was increased to 2 or 3 hr, there were notable oscillations in T secretion which corresponded to the peaks in luteinizing hormone associated with the PE. In four experiments ovarian fragments underwent oocyte maturation, but this occurred only in fragments that received continuous PE stimulation. Progesterone (P) secretion was measurable only when oocyte maturation was observed in the ovarian fragment. Rana catesbeiana ovarian fragments exposed to continuous superfusion with homologous PE produced more T than those receiving hourly pulses of PE over a 6-hr period. Oocyte maturation accompanied by P secretion was observed in one experiment under continuous, but not pulsatile administration of PE. These results suggest that the frog ovary may be more resistant than the mammalian ovary to “down-regulation” under continuous gonadotrophic stimulation. The implications of these results on the frog pituitary-gonadal axis are discussed.

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G.M. Hubbard

Hormonal Control and Dynamics of in Vitro Ovarian Steroid Secretion in Ranid Frogs

Cited by (6)

Neuroendocrine Control of Reproduction in Amphibians
2011, Hormones and Reproduction of Vertebrates - Volume 2
The chapter provides an overview of the development, anatomy, and function of several reproductively relevant neuroendocrine systems. Further, their influences on the reproductive brain, pituitary gonadotropin (GTH) secretion, and peripheral organs such as the gonad are also discussed. It explains that the neurohormones secreted by the brain serve as important intermediaries that transduce environmental signals to peripheral tissues for reproductive regulation. The emerging evidence states that in mammals, the neuroendocrine regulation of amphibian reproduction is achieved principally through the actions of the gonadotropin-releasing hormone (GnRH) system. The chapter also discusses the ontogeny, function, and regulation of the amphibian GnRH systems. Additional roles of GnRH in peripheral reproductive regulation are also explored. Examining the neuroendocrine basis of amphibian reproduction provides an important means for understanding how disruption of the reproductive brain could occur under perturbed environmental conditions, leading to impaired fertility and declining population.
Expression profiles of LHβ, FSHβ and their gonadal receptor mRNAs during sexual differentiation of Xenopus laevis tadpoles
2010, General and Comparative Endocrinology
Citation Excerpt :
The LH-R and FSH-R mRNA expression profiles during ontogeny are the first data analyzed in an amphibian species. Until now, mostly the presence of gonadotropin receptors were demonstrated indirectly, e.g. by exposure of gonadal cultures in vitro to gonadotropins that increased androgen production in X. laevis (Fortune, 1983; Lecouteux, 1988) or R. catesbeiana (Hubbard and Licht, 1986; Pozzi et al., 2006). In bullfrog, it was suggested that only one gonadotropin binding site was present in the testis with the same affinity to LH and FSH (Yamanouchi and Ishii, 1990).
The gonadotropins, luteinising hormone (LH) and follicle stimulating hormone (FSH), are important hormones regulating reproductive biology in vertebrates, especially the processes of steroidogenesis and gamete maturation. Despite the role of gonadotropins during the reproductive cycle in amphibians is well established, much less is known about the functional maturation of the hypothalamus–pituitary–gonad axis during larval development. Therefore, the present study aimed to analyze the expression profiles of hypophyseal LHβ and FSHβ mRNA and of their corresponding gonadal receptors (LH-R, FSH-R) in Xenopus laevis tadpoles during their ontogeny and sexual differentiation. The first significant elevation of LHβ and FSHβ mRNA was observed at late premetamorphosis. A clear raise of LHβ mRNA was present during prometamorphic stages especially in males, while the LH-R only slowly increased during ontogeny with highest levels during metamorphic climax. In contrast, FSHβ mRNA expression only slightly increased during ontogeny, however in both sexes the FSH-R mRNA was considerably elevated at prometamorphosis and further at metamorphic climax. Our results suggest that LHβ and LH-R mRNA expression might be involved in initial maturation events of gametes, at least in males, while the gradually increase of FSH-R mRNA coincided with the advancing process of gamete maturation in both sexes. The present study provides for the first time evidence based on expression of gonadotropins and their corresponding gonadal receptors that the hypothalamus–pituitary–gonad axis evolves already at early stages of ontogeny and sexual differentiation in amphibians.
A nonsteroidal follicular factor is involved in maturation process of Xenopus laevis oocytes
1992, General and Comparative Endocrinology
Xenopus laevis postvitellogenic ovarian follicles release into conditioned medium nonsteroidal factor(s) that potentiate progesterone-induced oocyte maturation. The molecular weight of this factor is between 1000 and 10,000 Da. The potentiating activity is suppressed when follicles are incubated with cyanoketone to inhibit steroidogenesis, suggesting that the secretion of the potentiating factor can be modulated in vitro. These results indicate that the steroid-independent pathway in vitro, previously reported in oocytes exposed to insulin or IGF-1 to induce meiotic resumption, may be of physiological importance.
The dynamics of the steroidogenic response of perifused Xenopus ovarian explants to gonadotropins
1988, General and Comparative Endocrinology
Steroid release before and during maturation was studied in Xenopus ovarian follicles under various conditions of stimulation of LH in a perifusion system. Acute stimulation by 15 μg of LH induces a 10-fold increase in the androgen (testosterone and androstenedione) level which reaches a maximum 4 hr later and then slowly decreases until the 25th hour. Repeated stimulations every 2 or 4 hr are followed by the same androgen increase during the first 8 or 10 hr and then by a slow decrease in the secretion despite new LH injections. A significant increase in progesterone secretion is seen only after at least two stimulations (8 hr). Estradiol secretion slowly increases to a moderate level during the first 5 hr and then remains stable whatever the stimulation. During continuous stimulation (LH 0.5 μg/ml) androgen levels reach an initial maximum after 4 hr and then fluctuate with a 2-hr period. Addition of theophyllin to the medium enhances these fluctuations. After 12 hr when the progesterone has increased, androgen secretion diminishes to reach a basal level without fluctuations. Germinal vesicle breakdown occurs only in follicles that have been appropriately stimulated to secrete androgens and progesterone during the required time.
Seasonal plasma and intraovarian sex steroid profiles, and influence of temperature on gonadotropin stimulation of in vitro estradiol-17β and progesterone production, in Rana esculenta (Amphibia: Anura)
1987, General and Comparative Endocrinology
Seasonal plasma and intraovarian estradiol-17β (E) and progesterone (P) fluctuations were studied by specific radioimmunoassay in the frog, Rana esculenta. Moreover, incubations of ovine-luteinizing hormone (oLH)-stimulated ovarian pieces at two different temperatures (15 and 24°) have been carried out in order to evaluate the dependence of E and P output on this exogenous factor. Estradiol showed similar changes in plasma and ovaries, while P profile was better evidenced in the gonads since this hormone fluctuated in plasma, giving pulses of difficult interpretation. A shift from E to P production by the ovary near the ovulatory period (February–March) was noted. In vitro experiments were carried out using approximately equal-sized ovarian fragments containing follicles ranging from 0.7 to 1 mm and classified as early vitellogenic. High temperature induced oLH-stimulated P production within 6 h, while E increased after 24 h concomitantly with a P decline. At 15° the stimulatory effect of oLH was achieved only on E output in the incubation medium after 24 h. In conclusion, our results in the frog, R. esculenta, show that E and P intervene at peak values separately during the annual cycle and that the temperature has an important role in the regulation of the steroid hormone-releasing activity.
Effects of temperature and mode of delivery on responses to gonadotropin-releasing hormone by superfused frog pituitaries
1986, General and Comparative Endocrinology
An in vitro superfusion system was used to examine the effects of temperature on the responsiveness of frog, Rana pipiens, hemipituitaries to chronic superfusion with gonadotropin-releasing hormone (GnRH). The effects of pulsatile as opposed to continuous delivery of GnRH on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion were also studied at 30°. Secretion of both gonadotropins (FSH and LH) increased significantly in a dose-dependent manner in response to a brief exposure to 0.1–1000 ng/ml (nM) GnRH at both 18 and 32°, but the magnitude of response at each dose was temperature dependent. Moreover, the temporal pattern of the chronic response to a standard dose of GnRH (100 ng/ml) also varied markedly between 10 and 32°: Hemipituitaries superfused at 10 or 18° showed greatly attenuated responsiveness to GnRH after the first hour of GnRH treatment, whereas responsiveness was maintained or even continued to increase for many hours at higher temperatures. These temperature effects may be related to seasonal changes in reproductive activity. Pulsatile administration of GnRH was more effective in inducing elevated gonadotropin (GtH) secretion during the first few hours of superfusion, but continuous superfusion with GnRH was more effective at maintaining elevated GtH levels over long periods. The results support and extend previous studies by indicating that, unlike the situation in many mammals and birds, the frog pituitary is highly resistant to desensitization by even high doses of GnRH, and in fact, self-priming and maintained responsiveness to GnRH is better supported by chronic treatment than by pulsatile delivery of GnRH.

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General and Comparative Endocrinology

Abstract

References (22)

Immunochemical studies on the pituitary gonadotropins (FSH and LH) from the bullfrog, Rana catesbeiana

Gen. Comp. Endocrinol

In vitro study of the direct ovarian effects of gonadotropin-releasing hormone (GnRH) in the frogs, Rana pipiens and Rana catesbeiana

Gen. Comp. Endocrinol

Plasma 5α-dihydrotestosterone and testosterone in the bullfrog, Rana catesbeiana: Stimulation by bullfrog LH

Gen. Comp. Endocrinol

Hypothalamic control of gonadotropin release in amphibia: Evidence from studies of gonadotropin release in vitro and in vivo

Gen. Comp. Endocrinol

Action of pulsatile gonadotropic stimulation on the in vitro incorporation of vitellogenin by trout follicles in an open perifusion system

C.R. Acad. Sci. Ser. 3

Endocrine signaling and female reproduction

Biol. Reprod

Endocrine signaling and male reproduction

Biol. Reprod

Changing frequency of pulsatile luteinizing hormone and progesterone secretion during the luteal phase of the menstrual cycle of rhesus monkeys

Biol. Reprod

Ovarian progesterone levels during in vitro oocyte maturation in Xenopus laevis

Biol. Reprod

Pulsatile LH release during the ovulatory LH surge on proestrus in the rat

Biol. Reprod

Hormonal Control and Dynamics of in Vitro Ovarian Steroid Secretion in Ranid Frogs

Cited by (6)

Neuroendocrine Control of Reproduction in Amphibians

Expression profiles of LHβ, FSHβ and their gonadal receptor mRNAs during sexual differentiation of Xenopus laevis tadpoles

A nonsteroidal follicular factor is involved in maturation process of Xenopus laevis oocytes

The dynamics of the steroidogenic response of perifused Xenopus ovarian explants to gonadotropins

Seasonal plasma and intraovarian sex steroid profiles, and influence of temperature on gonadotropin stimulation of in vitro estradiol-17β and progesterone production, in Rana esculenta (Amphibia: Anura)

Effects of temperature and mode of delivery on responses to gonadotropin-releasing hormone by superfused frog pituitaries