Relative Capillary Blood Flow and Leydig Cell Function in Old Rats

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Abstract
The incretory testicular function was investigated in young adult (3 months old) and old (24–27 months old) male Wistar rats. Plasma testosterone ranged from 72–1162 ng/100 ml in the young rats (average, 300 ng/100 ml; n = 35) and from 23–263 ng/100 ml (average, 120 ng/100 ml; n = 31) in the old animals. A significant reduction in plasma LH levels, which were, on the average, 54.4 ng/ml (range, 26.0–95.0) in the young rats and 36.9 ng/ml (range, 5.0–97.5) in the old animals, probably causes the decrease in testosterone secretion observed. To investigate further the consequences of reduced LH secretion in old rats, we have studied the relative testicular capillary blood flow by means of the inert gas clearance technique. A significantly reduced capillary blood flow was observed in the old rats (12.6–55.8; average 32.5 ml/100 g tissue-min; n = 17) when compared with the young rats (28.9–69.4; average, 50.5 ml/100 g tissue min; n = 18). The age-dependent fall in testicular blood flow was completely reversible by hCG treatment. After 2 days of hCG injection (50 IU/animal), the blood flow was 63.8 (range, 34.3–108.2 ml/100 g tissue-min; n = 14) in the young rats and 67.6 (range, 43.3–108.2 ml/100 g tissue-min; n = 13) in the old rats. Plasma testosterone in the stimulated young rats ranged from 700–2375 (average, 1086 ng/100 ml) and from 650–1700 (average, 1071 ng/100 ml) in the old rats. The data indicate that a reduced testicular blood flow in the aged rat, which probably occurs as a result of a decrease in LH secretion, may contribute to the failure of Leydig cell function in old age.

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