Effects of 6-methoxy-2-benzoxazolinone on the pineal melatonin generating system.

6-Methoxy-2-benzoxazolinone (6-MBOA) at concentrations greater than 20 microM stimulates serotonin N-acetyltransferase (NAT) activity of rat pineal glands in 48-hr organ culture as well as of glands freshly cultured, indicating that 6-MBOA acts postsynaptically. The effects of 6-MBOA on NAT activity can be blocked by propranolol but not by prazosin, suggesting that 6-MBOA acts on the beta receptor. At the doses used 6-MBOA stimulation does not block or enhance NAT stimulation by norepinephrine, but is additive with vasoactive intestinal polypeptide which stimulates NAT activity at a site different than the beta receptor. This study demonstrates that 6-MBOA stimulates rather than inhibits melatonin biosynthesis and does not prevent stimulation of melatonin synthesis by norepinephrine. The progonadal association with eating plants containing 6-MBOA in the Montane vole may be due to over stimulation of melatonin receptor sites. Other possible explanations include an extrapineal action such as a blockade of melatonin receptors in the central nervous system, a blockade of receptors on the gonads or to a direct action of this agent on the gonads.