Studies were performed to determine whether estradiol (E2) has a direct action on the release and disposition of norepinephrine (NE) from adrenergic nerve endings in isolated superfused canine saphenous veins. [3H]NE and is labeled metabolites were separated by column chromatography with measurement by liquid scintillation spectrometry. An increase in the spontaneous overflow of total 3H, [3H]NE, and [3H]dihydroxyphenylglycol ([3H]DOPEG) that occurred with 1 and 10 microgram/ml E2 in the superfusing medium suggested that E2 either induced NE release or interfered with intraneuronal NE storage. During electrical stimulation (ES), release of [3H]NE and [3H]DOPEG exceeded controls with 1 and 10 microgram/ml E2 in the superfusate, yet total 3H was little changed. The evoked release of [3H]DOPEG showed less of an elevation over its spontaneous efflux in E2-treated veins than in nontreated veins, suggesting that E2 may block neuronal reuptake of released NE. The efflux of O-methylated deaminated metabolites during and after ES was decreased by E2 treatment, suggesting also an inhibition of extraneuronal uptake of NE.
The influence of the anterior pituitary on tissue CRF was investigated in two sets of experiments using lesioned, hypophysectomized, adrenalectomized donor rats. Donors were injected with 1 or 0.5 anterior pituitary equivalents 3 h before transfer of plasma to recipient animals. Injection of 1 pituitary equivalent significantly reduced levels of corticosterone in recipient rats compared to saline injection at 3 different time intervals following the transfer. In a second series of experiments donor animals received replacement with saline, ACTH, TSH, or PRL at 0, 2 and 4 h following adrenalectomy; transfer of plasma to recipient animals was at 5 h. Of the three hormones injected only ACTH significantly reduced tissue CRF activity in donor animals. Recipients of these donors showed suppressed levels of corticosterone compared to recipient animals whose donors were injected with saline, TSH or PRL. The ACTH dose-response curve indicates that the effective dose for suppression of tissue CRF in donor animals is in the range of 1–10 mU/ml. Results of these experiments clearly show that tissue CRF is inhibited by the anterior pituitary hormone ACTH rather than by elevated levels of corticosterone. These experiments suggest that feedback regulation of tissue CRF release by ACTH may occur in response to prolonged physical stress.
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