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The Pineal Gland: A Supplemental Source of Hypothalamic-Releasing Hormones
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1974
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FertilityComparative EndocrinologyBovine MaterialNeuroendocrinologyGynecologyReproductive BiologyEmbryologyReproductive EndocrinologyNeuroendocrine MechanismTrh BioassayReproductive MedicinePublic HealthAnimal PhysiologyInfertilityHypothalamusAnimal NutritionCrude ExtractsMedicineNervous SystemEndocrinologyAnimal ReproductionAnimal SciencePhysiologyNeuroscienceHypothalamic FunctioningEndocrine ResearchPineal GlandReproductive Hormone
Crude extracts of commercially availa-ble ovine, bovine and porcine pineal glands were found to contain high levels of gonadotropin-releasing activity. The gonadotropin-releasing hor-mone (Gn-RH) radioimmunoassay values (porcine, 185 ng/gland; bovine, 500 ng/gland; and ovine, 490 ng/gland) were consistent with values obtained by in vitro Gn-RH bioassay. The pineal glands con-tained 4–10 times as much gonadotropin-releasing activity as that reported in hypothalami of the corresponding species. To verify this high ratio, fresh pineal glands and hypothalami were obtained from 4 ewes and similarly extracted. The pineal:hypothalamus activity ratio was found to be more than 20:1. The bovine and ovine pineal extracts were also tested for the induction of ovulation in the estrous rabbit. Ovulation occurred in all animals treated with the extract at a dose equivalent to 2μg Gn-RH (based on radioimmuno and bioassay results). One of the extracts was further characterized by gel filtration on Sephadex G-25 using 3H-pGlu-Gn-RH as tracer. The gonadotropin-releasing activity eluted coincident with the radioactive tracer. All crude extracts were examined for thyrotropin-releasing hormone (TRH) content by specific radioimmunoassay and the value for the bovine material was verified by TRH bioassay. The amounts of TRH found in the pineal glands were of the same order of magnitude as values previously reported for TRH hypothalamic content of the same species. Melatonin, a biogenic amine localized in the pineal gland, did not cross-react in either radioimmunoassay and was only active in the Gn-RH bioassay system at doses 4–20 times the reported pineal gland content. We conclude that the gonadotropin-releasing ac-tivity and thyrotropin-releasing activity of the pineal gland, in the species examined, is due to the presence of Gn-RH and TRH. Thus, the pineal gland is a supplemental source of at least two neurohumoral hormones previously believed to be specifically associated with the hypothalamus. (En-docrinology94: 1422, 1974)