Diethylstilbestrol regulates the number of alpha- and beta-adrenergic binding sites in incubated hypothalamus and amygdala.

Previous work has identified an effect of circulating estrogens on the number of central adrenergic binding sites. We have further characterized this effect by performing the experiments in vitro and have taken advantage of a well-described hypothalamic preparation in which diethylstilbestrol (DES), is known to elevate cAMP levels through a pathway which involves adrenoreceptors. We show that DES induces a reciprocal change in the numbers of alpha- and beta-adrenergic binding sites in incubated hypothalami obtained from intact immature female rats as well as from ovariectomized adult rats. The alpha-adrenergic binding sites are reduced by 25-30% whereas the beta-adrenergic sites are increased by 60-100%. The effect is maximal at 3 h in vitro (20 microM DES) and largely reversible following a 2 h wash in the absence of DES. Using the change in beta-adrenergic binding sites as a probe, we were further able to show that estradiol (100 microM) and 2-hydroxyestradiol (50 microM) had no effect. Further, the effect of DES was not blocked by the anti-estrogens clomiphene or tamoxifen. Since DES is able to elevate beta-adrenergic binding sites in hypothalamus and amygdala (brain areas known to contain high levels of estrogen receptors) but has no effect in cerebellum, we conclude that we have observed an effect of DES not shared by estradiol but which may be confined to estrogen target areas of the brain.

Effect of pentoxifylline on alpha- and beta-adrenoceptor sites in cerebral cortex medial basal hypothalamus and pineal gland of the rat.

The intraperitoneal injection of the methylxanthine derivative pentoxifylline (3,7-dimethyl-1-(5-oxo-hexyl)-xanthine] brought about, 3 hr later, a significant depression of alpha- and beta-adrenoceptor sites in the cerebral cortex, and of beta-adrenoceptor sites in medial basal hypothalamus and pineal gland, (assessed from the specific binding of radioactive dihydroergocryptine and dihydroalprenolol respectively). The changes in the density of binding sites were not accompanied by significant modifications of the Kd's. Sympathetic denervation of the pineal gland by superior cervical ganglionectomy (SCGx) abolished the changes of beta-adrenoceptor number in the pineal caused by pentoxifylline. The increase of alpha-adrenoceptor sites in the hypothalamus brought about by ganglionectomy was not affected by injection of pentoxifylline. Pentoxifylline did not compete in vitro for radioligand binding to brain membranes. These results suggest that methylxanthines depress brain adrenoceptor sites acutely, probably by down-regulation of receptors following the increase in catecholamine release caused by injection of the drug.

[3H]dihydroergocryptine binding in rat brain.

[3H]dihydroergocryptine (DHE) appears to bind to alpha-adrenergic receptor sites in rabbit uterine membranes. We have characterized the binding of [3H]DHE to membranes prepared from rat cerebral cortex. alpha-Adrenergic agents were less potent and dopamine and serotonin, more potent, in displacing brain DHE binding than in uterus. Furthermore brain DHE binding sites demonstrated less stereospecificity for catecholamines than sites in uterus. Dopamine displaced DHE binding with about the same potency in cerebellar and cerebral cortical membranes, but was 10 times as potent in displacing DHE binding in the striatum. The binding of [3H]DHE in brain is complex and differs significantly from the rabbit uterus. There are two possible explanations for this discrepancy. [3H]DHE may bind a single site in brain with properties differing from known peripheral adrenergic receptors or DHE may bind to multiple sites in brain, sites which may or may not represent other neurotransmitter receptors.