Changes of LH level in the pituitary gland and plasma in hibernating frogs, Rana temporaria

Abstract

Pituitary and plasma luteinizing hormone (LH) levels were measured in female frogs, Rana temporaria, during and immediately after hibernation (0–4° in darkness; 22–25 weeks) to study regulation of gonadotropin leading to posthibernation ovulation. Pituitary LH content began to rise progressively during the last third of hibernation (e.g., from starting levels of 5.3 ± 0.09 μg/gland, 1.5 μ/mg between 8 and 11 weeks, to 18.6 ± 9.7 μg/gland, 5.0 ± 2.7 μg/mg at 19–22 weeks). Plasma LH increased in parallel, but with some delay (from 10 ± 8 to 25 ± 24 ng/ml). Frogs kept in light at low temperatures showed similar responses. Release of LH (rise in plasma levels with a drop in pituitary content) was observed during 32 hr immediately after termination of hibernation in association with the onset of ovulation. These data indicate the existence of regulatory mechanisms operating during hibernation under conditions of constant cold. Altogether, these and our previous results obtained after surgical deafferentiation of median eminence support the hypothesis of a progressive reduction of a CNS inhibition that results in the release of GnRH during hibernation in this frog.