Effects of short postcapture confinement on plasma reproductive hormone and corticosterone profiles inRana esculentaduring the sexual cycle

Abstract

The effects of short-term confinement (24 hours) on the plasma levels of gonadal hormones and corticosterone have been evaluated in Rana esculenta, which is widely used in amphibian reproductive physiology studies. A 24-h confinement has been chosen since this is the time that usually elapses from frog capture to utilization. Although short confinement does not influence the morphological aspect of gonads, genital tracts (oviduct in the female) and secondary sexual characters (thumbpads in the male), it causes a significant decrease of testosterone in both sexes, and of progesterone and estradiol in the female only. The confinement effects vary depending on the sexual cycle phase, but plasma hormonal patterns during the year are, on the whole, maintained. Plasma hormonal drop in captive frogs is coupled with an increase of circulating corticosterone, the administration of which strengthens the captivity effects. The results were considered to support the fact that, like in other vertebrates, plasma hormonal changes in short-term confined frogs depend on a stress-related increase of circulating corticosterone. This hormone, in fact, inhibits sex hormone synthesis and/or release either by a local action on the gonads or by a depression of hypothalamus-pituitary axis. Capture effects, therefore, should be considered in any study of relationships between circulating sex hormone profiles and gonadal activity during the annual cycle.

Effect of 17β-Estradiol and Testosterone Treatment on Sex Steroid Binding Proteins in the Female of the Green Frog Rana esculenta

“…On the contrary, in Rana esculenta testosterone affected EBP binding capacity. Since our previous studies show that in Rana esculenta circulating sex steroid changes paralleled EBP fluctuations throughout the reproductive cycle, with the highest levels of EBP coinciding with the resumption of reproductive activity (Paolucci and Di Fiore, 1994), it is plausible that both 17β-estradiol and testosterone sustain EBP concentration in the female of this species, characterized by, as with other lower vertebrates, very high levels of circulating androgens (Delrio et al, 1979;Paolucci et al, 1990;Stuab and De Beer, 1997). Whether or not androgens act as estrogens, after their aromatization to 17β-estradiol we do not know at present.…”

“…Although our previous observations (Paolucci and Di Fiore, 1994) indicate that TBP binding capacity fluctuations in the female of Rana esculenta did not show any relationship with the reproductive cycle, we decided to monitor the possible changes in TBP binding capacity following the sex steroid treatment, since androgen plasma levels are, in the female of Rana esculenta, higher than in the male (Paolucci et al, 1990). Up to now a role for such high levels of circulating androgens in the females has not been demonstrated with certainty (Del Rio et al, 1979).…”

Reproductive activity and plasma androgen concentrations in the male ofRana dalmatina

“…Although potential effects on plasma hormone levels following capture and short-term confinement have not been investigated, we are confident that the changes in plasma hormone levels detected in this study have given a reliable plasma hormone profile of R. dalmatina throughout the sexual cycle. In fact, in Rana esculenta the annual pattern of plasma androgens, as well as their correlation with the secondary sexual character cycle, is not significantly different in just captured and short-term captive frogs (Paolucci et al, 1990). In R. dalmatina, T peaks during the breeding season.…”

Possible roles for prostaglandins E2 and F2 in seasonal changes in ovarian steroidogenesis in the frog (Rana esculenta)

“…In contrast, the lowest release of PGF2a and oestradiol from ovarian tissues was found in June, despite the fact that concentrations of plasma PGF2a and oestradiol are high during this month. In previous studies it was suggested that the major source of these two hormones, during June, may be the interrenal gland (Pavgi and Licht, 1989;Fasano et al, 1991 (Mori et al, 1989 (Salthe and Mecham, 1974 (Paolucci et al, 1991;, in Rana catesbeiana (Licht et al, 1983), in rough skinned newt, aricha granulosa (Moore efe Zoeller, 1985), and in crested newt, Triturus carnifex (Gobbetti et al, 1991b, c . In addition, in Triturus carnifex, treatment with PGE2 decreased androgen secretion, which was modified by captivity (Gobbetti and Zerani, 1992b), whereas a progesterone secretion which was not modified by captivity was increased after treatment with PGE2 This work was supported by a grant to A. Gobbetti from M.U.R.S.T.…”