STREPTOZOTOCIN-INDUCED DIABETES BLOCKS THE POSITIVE FEEDBACK RELEASE OF LUTEINIZING-HORMONE IN THE FEMALE RAT

The effects of streptozotocin-induced (STZ) diabetes on the release of gonadotropins was studied in female rats. In the first experiment, rats were ovariectomized and 2 days later were injected with STZ. Three weeks later rats were treated with estrogen and progesterone and blood samples were taken via intraatrial cannulae for luteinizing hormone (LH) assay. Afternoon surges of LH were seen in 4/5 control but 0/8 STZ rats. Pituitary responses to LH-releasing hormone in vitro did not differ. In the 2nd experiment, ovariectomized estrogen-primed rats were killed prior to and during a progesterone-induced LH surge. As in Experiment 1, STZ-treatment inhibited the LH surge but did not effect the afternoon rise in median eminence norepinephrine turnover which has previously been shown to be important in stimulating LH release. Turnover of norepinephrine in the anterior hypothalamus was depressed in the diabetic rats both prior to and during the expected time of the LH surge. Dopamine turnover was depressed in all three brain regions studied. It can be concluded that the positive feedback control of LH release is severely attenuated in diabetic rats but the mechanism explaining the loss is not clear. Diabetes-induced alterations in hypothalamic catecholamine metabolism may be involved but further work is needed to more carefully define these relationships.