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

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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.

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