Melatonin radioimmunoanalysis: evaluation of the pineal function in hyperprolactinemic male rats and controls

Abstract

A sensitive and specific radioimmunoassay for melatonin quantification in rat pineal and biological fluids is described.The assay utilizes a specific antibody and H3-melatonin as tracer.Bound and free fraction were separated by a saturated sulphate ammonium solution.The sensitivity of the method is 9 pg/ml.The intra and interassay variation coefficient were 10.4 and 13.6% respectively.By means of this RIA the content of melatonin in the pineal gland in male rats made hyperprolactinemic on day 30 of life and their respective sham-operated controls has been evaluated.The results showed that the melatonin content measured at 2 a.m.was reduced in the transplanted animals when compared to control group, not only shortly (48 hours) after the transplant operation, but also in the chronic situation; though suggesting that further investigations are necessary to deepen and understand the interrelationships between prolactin and pineal gland and their effect on the hypothalamic-pituitary-gonadal axis.