AGE AND GENDER INFLUENCE BASAL AND STRESS-MODULATED HYPOTHALAMIC-PITUITARY-THYROIDAL FUNCTION IN FISCHER 344 N RATS/

To investigate possible gender- and age-associated changes of the hypo thalamic-pituitary-thyroid (HPT) axis at baseline and during stress, w e studied healthy young (3-month) and old (23-month) female 344/N Fisc her rats at the basal state and after 2 h of immobilization (IMMO), in parallel to age-matched male rats. At baseline, there were no major d ifferences of HPT axis functions between young female and male animals . Old age was associated with impaired central thyroid function in bot h genders, albeit to a much lesser extent in females than in males. Pl asma prolactin (PRL) levels were similar in young females and males bu t were higher in old females than males. IMMO inhibited HPT axis funct ions in both genders in young, but not old animals. Thus, plasma TSH a nd hypothalamic TRH mRNA levels were decreased by IMMO in young, but n ot in old rats of both genders. IMMO increased plasma PRL in young and old males, but did not have any effect in young and old females. In s ummary, these data indicate that age and gender exert diverse effects on HPT axis functions at baseline and after stress.