Involvement of central catecholamines in the feedback actions of 17β-estradiolbenzoate on luteinizing hormone secretion in the ovariectomized female rat

Abstract

(1) Evidence has been presented, based on quantitative microfluorimetric estimations of dopamine (DA) and noradrenaline (NA) levels and turnover, and on radioimmunological measurements of serum luteinizing hormone (LH), and follicle-stimulating hormone (FSH) and prolactin levels, that the central inhibitory feedback action of estradiol on LH secretion mainly involves a marked increase in DA turnover of the lateral palisade zone (LPZ) of the median eminence and also involves a reduction of NA turnover, mainly located in the medial preoptic area (MPOA) and in the subependymal layer (SEL). (2) The mechanism for these changes in catecholamine (CA) turnover is discussed. The possibility is favored that they involve the stimulation of central cytosol estrogen receptors which may even be located in the arcuate DA and possibly reticular NA cell bodies themselves. (3) The marked and long-lasting hypersecretion of prolactin caused by estrogen could be involved in mediating the sustained increase of DA turnover in the median eminence and the sustained reduction of NA turnover. (4) The central facilitatory feedback action of estrogen, on the other hand, may be mainly responsible for the sharp increase of NA turnover in the MPOA and SEL and also the associated reduction of DA turnover in the LPZ in the critical period of both adult cyclic rats and of immature female rats treated with PMS. (5) We take the view that these latter NA and DA turnover changes take precedence over cytosol estrogen receptors, which previous evidence indicates (see Sawyer, 1975) are located in preoptic and amygdaloid regions. (These estradiol concentrating neurons then directly and/or indirectly make connections with the NA and DA pathways). (6) FSH secretion is not controlled by DA and NA pathways. (7) The hypothesis given above is based on the assumption that different estradiol concentrating neurons are involved in the central inhibitory and facilitatory feedback action of estradiol and that the estrogen receptors of these respective neurons have differences which allow their differential activation, the inhibitory feedback leading mainly to a marked increase in the ratio DA activity/NA activity in the median eminence, whereas the facilitatory feedback causes a marked reduction of this ratio.