Electrochemical stimulation of the preoptic area and release of luteinizing hormone in the rat: the effects of ferrous and ferric ions

It is well known that 'electrochemical stimulation' (ECS) of the medial preoptic area (MPOA) in the rat results in the release of LH. This neuroendocrine effect is associated with the deposition of iron cations from the electrode tip to the surrounding neural tissue. The present study was designed to investigate further the effect of depositing cations into the MPOA on the release of LH. To this end female rats were anaesthetized on the afternoon of vaginal pro-oestrus with pentobarbitone sodium and brain surgery was performed at 14.00–16.00 h. In one group ECS (100 μA anodal d.c. × 60 s) of the MPOA was carried out with a stainless-steel electrode. A platinum electrode was used to pass a current of 200 μA anodal d.c. × 60 s through another group. Other groups had 1 μl of one of the following solutions injected into the MPOA: FeCl2 (31, 47 and 62 mmol/l); FeCl3 (21, 42 and 83 mmol/l); FeCl2 + FeCl3 (15·5 and 10·5 mmol/l respectively); CuCl2 (62 and 120 mmol/l; MgCl2 (62 mmol/l); Ce(SO4)2 (16 mmol/l) and acid 0·9% NaCl (w/v) solution (pH 2·7). Blood samples for determination of LH were obtained from the jugular vein at 0, 1 and 2 h. The next morning the uterine tubes were examined for the presence of ova. The smallest concentrations of iron infused corresponded to the number of g equivalents (6·2 × 10−8) of iron deposited from the stainless-steel electrode during ECS. Only ECS and injection of the intermediate and highest concentrations of FeCl2 and FeCl3 resulted in a significant (P < 0·01) rise in plasma LH levels and ovulation when compared to the platinum-treated group. The plasma LH rise after the highest concentration of FeCl2 and FeCl3 was significantly (P < 0·01) less than that observed after ECS. The other solutions had no significant effect on LH release or ovulation. These data suggest that: (a) iron is the major component responsible for stimulating LH release during ECS although there may be others which potentiate the action of iron, (b) the effect of ECS on LH release is not due to tissue damage (c) other cations do not have a stimulatory effect on LH release.