Ageing and melatonin influence on in vitro gonadotropins and prolactin secretion from pituitary and median eminence

The effect of ageing and/or melatonin (MEL) on in vitro gonadotropins, lute inizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL ) release and tissue content from pituitary and median eminence (ME) were i nvestigated. Gonadotropins and PRL basal release (I-1) from hemipituitaries of young cyclic-rats was decreased by MEL to levels shown in old acyclic r ats. Pituitary tissue content of LH and PRL were not affected by ageing or MEL treatment. However, pituitary FSH tissue content was decreased by agein g and MEL, suggesting a different regulatory mechanism. MEL inhibitory infl uence on pituitary hormones is mainly exerted on the secretory process. Thi s effect is only exerted in young rats. ME LH and PRL release and content w ere significantly lower than in pituitary. However, FSH release and content in ME showed values similar to those found in the pituitary. This study co nfirms that the functional capacities of pituitary gland and ME are maintai ned during reproductive senescence. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.