IN THE MALE BROWN-NORWAY (BN) MALE-RAT, REPRODUCTIVE AGING IS ASSOCIATED WITH DECREASED LH-PULSE AMPLITUDE AND AREA

The Brown-Norway (BN) rat has been proposed as a rodent model for the study of human male reproductive aging. As in man, reduction in serum or plasma testosterone (T) and both testicular (primary) and hypothala mic-pituitary (secondary) reproductive dysfunction have been associate d with aging in male BN rats. However, the presence of secondary testi cular failure in this rodent, as indicated by low serum luteinizing ho rmone (LH) levels, needs further corroboration. The present study was designed to determine whether age-related differences in the pulsatile patterns of pituitary LH and follicle-stimulating hormone (FSH) secre tion occur in gonad-intact mate BN rats. Three age groups were examine d: young (3-4 months), middle aged (12-13 months), and old (21-22 mont hs). Using intra-atrial cannulae, serial 5-minute blood samples were w ith-drawn from conscious, unrestrained animals. Plasma LH concentratio ns were determined by a supersensitive immunofluorometric assay (FIA) and FSH and T by radioimmunoassay (RIA). Mean T levels were different among groups (young > middle age > old). In young rats, T levels were higher in the late morning/early afternoon than in the late afternoon; this variation was not found in older rats. Mean FSH concentrations w ere higher in the old than in the middle-aged and young rats. Signific ant differences in mean LH levels were not found among groups. Compare d to young rats, shortened pulse interval and reduced area of pulses c haracterized the secretory pattern of both gonadotropins in old rats. In addition, LH-pulse amplitude and total area of LH pulses were also significantly lower in old than in young rats. Besides the well-recogn ized primary testicular failure that occurs in the old BN rat, this st udy confirms a hypothalamic-pituitary deficiency that makes this roden t model ideal for studying human male reproductive aging.