Cyclic Fluctuations in Ovarian FSH-Inhibiting Material in Golden Hamsters1

Abstract

The response of two pineal enzymes, serotonin N-acetyltransferase (SNAT; E.C.2.3.1.5) and hydroxyindole-O-methyltransferase (HIOMT; E.C.2.1.1.4) to the reduction of pineal norepinephrine (NE) content produced by systemic injections of 6-hydroxydopamine (6-OHDA) was examined in the present study twice daily, at 1200 and 2400 h, in the cyclic female rat. In rats sacrificed 3 days postinjection during the dark period (2400 h), injections of 6-OHDA that produced maximal inhibition of SNAT activity (58% of control values) also caused significant decreases in NE content in pineal, hypothalamic and cardiac tissues (48, 75 and 12% of control values, respectively). In rats sacrificed 17 days postinjection at 2400 h, SNAT activity and pineal NE content had returned to control levels, while hypothalamic and cardiac NE content remained significantly depressed (70 and 22% of control levels, respectively). These results confirm the role of NE in the induction of SNAT activity and reveal that 6-OHDA is more effective in decreasing cardiac than pineal NE content.