Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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The effect of melatonin injection on Freund's adjuvant-induced changes in levels and 24-hour rhythms of circulating prolactin (PRL), ACTH, luteinizing hormone (LH) and growth hormone (GH) was assessed in rats. Animals received sc injections of melatonin (30 micrograms) or vehicle, 1 h before lights off for 12 days. Ten days after melatonin treatment they were injected with Freund's complete adjuvant or its vehicle sc, and after 3 days, rats were killed at six different time intervals throughout a 24-hour cycle to measure the different hormones by RIA. Immunization augmented circulating PRL while conserving its diurnal rhythmicity. Melatonin-injected rats showed significant diurnal variations of serum PRL after immunization only. Following Freund's adjuvant injection, an increase in serum ACTH with maintenance of ACTH diurnal rhythm were found. In immunized rats, melatonin treatment increased the amplitude of serum ACTH rhythm. Immunization decreased circulating LH and suppressed its 24-hour rhythmicity patter n. The effect of immunization on LH was counteracted by melatonin injection. For GH, a depressive effect of immunization on circulating levels, together with absence of diurnal rhythmicity, were found. The data indicate that several early changes in levels and 24-hour rhythms of circulating PRL, ACTH and LH in Freund's adjuvant-injected rats were sensitive to treatment with pharmacological amounts of melatonin.

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Poster Number PAesquifino0197
Keywords: MELATONIN, PROLACTIN, ACTH, LH, GH