The growth of the testicular artery was restricted on one side in young bulls and subsequent testicular development was monitored. After the animals had been killed, the testes were studied histologically and compared with testes from hypoplastic bulls. The growth rate of testes from the experimental side was significantly lower than that of testes from the sham-operated side over a period of 578 days. At death, the experimental testes had a mean (+/- SD) mass of 76 (+/- 41) g compared with 220 (+/- 31) g for the control testes. The sham-operated testes accounted for 0.071 (+/- 0.008)% of live body mass compared with 0.025 (+/- 0.014)% for the experimental testes. The seminiferous tubules in the sham-operated testes had a mean diameter (+/- SD) of 211 (+/- 25) microns, whereas those of the artery-restricted testes and hypoplastic testes were significantly smaller (152 (+/- 37) and 145 (+/- 45) microns, respectively). In the artery-restricted and hypoplastic testes, the interstitial tissue accounted for a significantly greater proportion of the testicular tissue than in the sham-operated testes and spermatogenesis was either totally absent or present in only a small proportion of tubules. It is suggested that the artery-restricted testes could be used as a model for testicular hypoplasia.
The biased unilateral occurrence of heritable gonadal hypoplasia was investigated by examining the gross- and microanatomy of the testicular artery and vein, testicular blood flow and testicular testosterone secretion in normal Nguni bulls and in Nguni bulls showing unilateral left, unilateral right and bilateral hypoplasia of the testis. A high incidence of branching of the testicular artery was found ipsilateral to hypoplastic testes. The branching occurs a short distance from the dorsal aorta: one branch proceeds to the testis, the other to the ipsilateral kidney. The association between arterial branching to the kidney and ipsilateral hypoplasia of the testis held for both unilaterally left and unilaterally right hypoplastic bulls. Variations in the anatomy of the testicular vein occurred in both normal and hypoplastic bulls but there was no specific association between the variations and ipsilateral hypoplasia. The lumen diameter of the testicular artery or branch correlated with testis mass. Wall thickness of the artery ipsilateral to hypoplastic testes was not different from that in normal bulls, discounting hyperplasia of the endothelium. Total blood flow to the testis correlated with testis mass. The secretion rate of testosterone from hypoplastic testes was lower than that of normal testes but there was no difference when compared on a unit mass basis.
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