SEXUALLY DIMORPHIC EFFECTS OF AGING ON TUBEROINFUNDIBULAR DOPAMINERGIC-NEURONS AND LACTOTROPES OF RATS

The effect of aging on plasma prolactin (PRL) levels, hypothalamic tub eroinfundibular dopaminergic (TIDA) neurons and pituitary lactotropes was evaluated in prolactinoma-free young (5-month-old) and old (23- to 24-month-old) Long-Evans rats of either sex. The young female rats we re in diestrus, the old ones in recurrent pseudo-pregnancy, The tyrosi ne hydroxylase (TH)-labelled neurons in the arcuate nucleus (AN) and a xons in the median eminence (ME) as well as the PRL-labelled lactotrop es in the pituitary gland were studied by morphometry and densitometri c immunohistochemistry. Further, we investigated the secretory functio n of isolated lactotropes by reverse hemolytic plaque assay (RHPA) and by cell culture in comparable animal groups. Compared with young anim als, the plasma PRL levels of old rats of both sexes were similar or r educed. All morphometric and densitometric measurements of the AN neur ons, ME axons (except number) and pituitary lactotropes were comparabl e in young and old female rats. In old male rats the AN and ME measure ments were mostly decreased, while the lactotropes remained almost unc hanged. The RHPA generally showed a reduced PRL release from lactotrop es of old animals of both sexes. The PRL release from the cultured lac totropes, on the contrary, was greatly increased in old female rats an d unchanged in old male rats. Our functional and morphological data su ggest that the in vivo function of lactotropes in old prolactinoma-fre e female and male rats does not seem to be strongly influenced by the mildly reduced TIDA neuron activity, yet emphasize the differences of the aging process in the two sexes.