Testis Vein Testosterone Falls in the Aging Rat: Refutation of “Dilution” Hypothesis

Age-related deficits in brain androgen binding and metabolism, testosterone, and sexual behavior of male rats

Brain androgen binding and metabolism, serum testosterone (T), and sexual behavior were measured in old and young male Fischer 344 rats. After completion of sexual behavior tests, blood was collected for T assay and brains were removed for simultaneous measurements of cytosolic (ARc) and nuclear (ARn) androgen receptors and aromatase activity (AA) in the preoptic area (POA), hypothalamus (HYP) and amygdala (AMG). In Experiment 1, old and young intact males were examined. None of the old males ejaculated in any of the tests of sexual behavior whereas all of the young males ejaculated. The old males had lower levels of serum T, lower levels of ARn in the POA and HYP and lower levels of AA in the POA. The ARc levels of the old and young males did not differ. Experiment 2 was designed to determine if the deficits in brain androgen binding and metabolism were due to low levels of T. Old and young T-treated gonadectomized (GX-T) males and young intact (I) males were examined. T levels were comparable in the young and old GX-T males and were higher in each of these groups than in the young I males. In sexual behavior tests, all of the young but only 25% of the old GX-T males ejaculated. Although ARn levels in the old GX-T males were lower than in the young GX-T males, they were comparable to the young I male levels. No age-related differences in T induction of AA were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma testosterone levels are higher in old mating rats than in old non-mating rats

About one-half of 96 aged rats mated at 20 months of age. Their plasma LH and prolactin concentrations were similar to those in non-mating old rats, but their plasma testosterone concentrations were significantly higher. Exogenous testosterone administration failed to change the sexual status of the non-mating group.

The aging Leydig cell. VIII. Protein kinase activity

The effects of aging on cyclic AMP (cAMP) dependent protein kinase activity of purified Leydig cells were evaluated. Purified Leydig cells from 20-day-, 40-day-, 60-day- and 30-month-old rats were incubated with or without hCG for 1 hour. At the end of incubation, tubes were centrifuged and supernatants were saved for cAMP and testosterone determinations, and the pellets were prepared for protein kinase assay. Basal cAMP levels of Leydig cells from 20-day- and 40-day-old rats were lower than those of 60-day- and 30-month-old rats. In response to hCG stimulation, Leydig cells of 40-day-old rats produced the highest amounts of cAMP, while 30-month-old had the lowest levels. Testosterone responses of 30-month-old rates were also significantly lower than those of 60-day-old mature rats. When cAMP-dependent protein kinase activities were measured, 30-month-old rats had the lowest total kinase activity. These results suggest that reduced protein kinase activity might contribute to the decreased testosterone synthesis of aged rats.

Gonadal dysfunction in the spontaneously diabetic BB rat

Diabetes which occurs spontaneously in the BB Wistar rat is associated with reduced fertility, predominantly in breeding males. In the first month of diabetes, there is a significant (p less than 0.05) reduction in serum testosterone associated with a transient decrease of serum LH and the accumulation of lipid in Leydig cells. Between one and three months of diabetes, there is an increase in both serum testosterone and LH and a further deposition of lipid droplets in Leydig cells. From three to six months of diabetes, there is a reduction of serum testosterone similar to age-matched controls, but high serum LH levels persist. Similar levels of LH and testosterone are noted after six months of diabetes, and all BB rats show marked changes in seminiferous tubules. These morphological changes in tubules consist of increased tubular wall thickness, severe germ-cell depletion, and Sertoli-cell vacuolization. Similar morphological changes of testes associated with generalized atrophy are noted in all control rats after 16 months of age. Decreased fertility in the BB rat appears to be associated with a primary disorder of Leydig cells, which precedes changes in seminiferous tubules consistent with accelerated aging. Preliminary data in impotent diabetic men suggest that the BB rat may be a valuable model for investigating human diabetic impotence and infertility.