The pubertal development of a novel GH-deficient mutant, the dwarf rat, has been evaluated. The establishment of normal spermatogenic function within small testes suggests that GH plays no role in spermatogenic function during puberty and adult life. However, a reduction in testicular size may reflect a reduced Sertoli cell population, suggesting that GH may be of importance in prepubertal testicular development.

Furthermore, marked differences between the homozygous dwarf rat and homozygous GH-deficient mouse mutants (e.g. Snell, Ames, pygmy and little mutants) have been demonstrated. It would appear that the GH deficiency in the rat mutant is far more specific for GH than those hitherto described in the mouse. In contrast to Snell dwarf mice mutants, pituitary and serum concentrations of FSH and LH are normal throughout pubertal development in the dwarf rat. Both spermatogenic function and seminal vesicle function develop normally, whilst in Snell dwarf mice spermatogenic function develops late in life and seminal vesicles remain infantile. Serum and testicular concentrations of androgen are also normal in dwarf rats. Homozygous dwarf rats have been shown to be fertile in previous studies; however, our observations suggest that despite spermatogenesis being qualitatively and quantitatively normal when assessed histologically, reduced testicular size seen in dwarf rats would lead to a reduced daily sperm output in these animals.

The dwarf rat represents a mutant in which the consequences of the selective depletion of GH may be studied on various endocrine systems. The reproductive axis appears to be only partially affected, at an early age, by GH deficiency.

Journal of Endocrinology (1990) 126, 193–201