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Castration or treatment with exogenous follicle-stimulating hormone (FSH) both increase the turnover of 3H-norepinephrine in rat brain. The effect of castration is greatest in the hypothalamus and midbrain, and is probably mediated by endogenous FSH. The action of FSH is independent of the gonads, and is not shared by luteinizing hormone. (Endocrinology 84: 1489, 1969)

Brain norepinephrine synthesis rate in gonadectomized and control rats treated with alpha-methyl paratyrosine

MELATONIN (5-methoxy N-acetyltryptamine) is synthesized in the pineal glands of mammals through the action of the enzyme hydroxyindole-O-methyltransferase (HIOMT) (refs. 1 and 2). Because the activity of this enzyme varies diurnally among rats kept in cyclic lighting conditions, it has been suggested that melatonin secretion follows a similar rhythmic pattern3. Melatonin has been identified in urine and in peripheral nerve4. Neither the kidney nor nervous tissue contains measurable HIOMT activity, however, and this has been taken as evidence that the indole is secreted from the pineal. It has not yet been possible to demonstrate melatonin in blood or cerebrospinal fluid (CSF); this inability may result from the absence of melatonin in body fluids, a very rapid rate of inactivation once the indole leaves the pineal, or the lack of sensitive techniques for assaying melatonin. For this reason, it is not known whether melatonin is normally secreted into the blood or the CSF.

The rate at which (3)H-norepinephrine disappears from rat braint increases after gonadectomy; the effect is observed 6 days after the operation and 24 hours after introduiction of the labeled mnaterial; it is not reprodluced by hypophysectomy. The content of endogenouis brain norepinephrinie does not decline after removal of the ovaries or testes; thus synlthesis of the catecholamine is probably increased by these procedures.

The intraperitoneal administration of melatonin to rats caused an increase in brain serotonin concentration, especially in the midbrain. This effect could be demonstrated within 20 minutes of melatonin administration and was not associated with changes in norepinephrine concentration.