THE BROWN-NORWAY RAT AS A MODEL OF MALE REPRODUCTIVE AGING - EVIDENCEFOR BOTH PRIMARY AND SECONDARY TESTICULAR FAILURE

In man, aging is associated with both primary and secondary testicular dysfunction. In contrast, most studies in male rat models of aging ha ve demonstrated only secondary testicular failure. We previously repor ted that testes from aging male F344 rats secrete excessive progestero ne (P), which may suppress gonadotropin secretion and confound aging s tudies. To determine whether the male Brown Norway (BN) rat is a more suitable aging model, trunk blood was collected from intact (sham-oper ated) and orchidectomized young (3 mo), middle-aged (13 mo), old (23 m o), and senescent (28-30 mo) animals. Testosterone (T), estradiol (E(2 )), P, prolactin (PRL), luteinizing hormone (LH), and follicle-stimula ting hormone (FSH) were measured by RIA. In intact rats, T levels decl ined with aging, while LH was unchanged, and FSH increased progressive ly with aging. In contrast to F344 rats, no age-related increases in P or E(2) occurred, nor did PRL or other steroid hormones increase. In the absence of testicular feedback (orchidectomized rats), FSH and LH declined progressively with aging. These findings suggest that, as in men, aging male BN rats manifest both primary and secondary testicular failure, and do not exhibit decreased gonadotropin levels secondary t o excessive steroid or PRL secretion. Therefore, the BN rat appears to be the best available rat model for studies of male reproductive agin g.