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

Abstract

A proposal that serum testosterone concentration declines during aging In the male laboratory rat because it is diluted in a larger body mass (and larger blood plasma volume) was reexamined. Five age groups were studied: 4, 7, 13, 19, and 24 months of age. Testosterone was measured in both testicular vein and peripheral serum collected from ether‐anesthetized rats within 2.5 minutes of removal from the cage. Both testosterone concentrations fell significantly (P < 0.001) at 7 months of age and did not change further in older rats, although body weight continued to increase until 19 months of age. The ratio of testicular vein to peripheral serum testosterone did not change significantly within the age span, although both concentrations (and their ratio) were at their lowest values at 24 months of age. Serum LH did not change significantly at any age. It was concluded that the decline in peripheral serum testosterone in the aging male rat reflects a significant change in testicular function, which first can be observed by 7 months of age. The eflect of dilution on testosterone and possibly on LH is a minor factor during aging.

Gonadal Dysfunction in the Spontaneously Diabetic BB Rat: Alterations of Testes Morphology, Serum Testosterone and LH

“…The fall in testosterone in both controls and BB rats between 201-250 days is compatible with normal aging (Frankel and Mock 1982;Saksena and Lau 1979;Kaler and Neaves 1981). However, older non-diabetic rats are reported to have normal (Frankel and Mock 1982;Kaler and Neaves 1981); or low serum LH (Saksena and Lau l919;Pirkek, Krings and Vogt 1979) 1982). This increase in serum LH in the BB rat is compatible with primary Leydig cell failure.…”