The hormonal and testicular effects of hemicastration have been examined using rodent models. When rats were hemicastrated at 5 days of age, significant testicular hypertrophy was noted within 5 days. Hypertrophy decreased as the age at hemicastration approached 20 days and did not occur in rats 45 days of age or older. The changes in testicular weight were associated with significant (P < 0.001) increases in serum FSH values from 10–20 days, but no significant alterations in the intratesticular concentration of testosterone occurred. Hemicastration also caused significant hypertrophy in testes depleted of germ cells. This was reflected by a substantial increase in testicular protein and DNA when compared to intact controls at 10, 15, and 20 days of age; however, the concentration of protein/ μg DNA was increased only at 15 days. These data indicate that 1) changes in serum FSH and not intratesticular testosterone are associated with the testicular hypertrophy which follows unilateral castration of immature animals; 2) a significant proportion of the hypertrophy can be attributed to non-germinal cells, the Sertoli cell being the prime candidate; 3) the increase in testicular weight is primarily the result of an increase in cell number.
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