Strain differences in testicular weight and spermatogenesis with special reference to C57BL-10J and DBA-2J mice

Marked differences were found in the absolute and relative weights of the testes of young adult mice from 11 strains. DBA/2J mice had large testes (936 ± 46 mg/100 g body weight) and C57BL/10J mice had small ones (389 ± 6 mg/100 g). Comparisons of mice from these two strains, raised under three different environmental conditions, showed that the difference between the strains was relatively unaffected by environmental variation. Measurements on hybrid mice confirmed that much of the observed difference between the two strains was genetic in origin.

The C57BL/10 mice were unlike those of any of the other strains in that both the relative and the absolute weights of the testis declined between the ages of 9 and 16 weeks.

Strain differences were also found when spermatogenesis was studied in four of the strains by counting the different types of germinal cells in seminiferous tubules in stage VII of spermatogenesis. There were about twice as many type A spermatogonia in DBA/2 mice as there were in C57BL/10 mice. The mean numbers of spermatocytes and spermatids were much greater in DBA/2 than in C57BL/10. These differences were sufficient to account for the observed differences between these strains in testicular weight.

Reciprocal F1 mice resembled their DBA/2 parents both in the weight of their testes and in the pattern of spermatogenesis.

It is suggested that, in comparison with mice of the other strains, C57BL/10J mice may be deficient in androgenic hormones.

Differences between mouse strains in testicular cholesterol levels and androgen target organs

The concentrations of esterified and free cholesterol in the testes, and the weights of the testes, seminal vesicles, kidneys and submandibular glands, were determined in mice of the C57BL/10J and DBA/2J inbred strains. Measurements were also made on reciprocal F1 hybrids. Cholesterol concentration and the weights of the testes and seminal vesicles were also studied in C57BL/6J and AKR/J inbred mice and in mice from two random-bred stocks. Considerable strain differences were found both in the concentration of esterified cholesterol and in gonadal weight. Since all the animals were maintained under the same environmental conditions the differences must have been genetic in origin. The decrease in absolute testicular weight which occurred in the C57BL/10 mice after the age of 8 weeks was accompanied by an increase in the percentage of total cholesterol present as ester. Groups of C57BL/10 males were treated with luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin-secreting pituitary isografts, pregnant mare serum gonadotrophin (PMS), testosterone propionate or pregnenolone. The concentration of esterified cholesterol was slightly decreased by LH and increased by pituitary grafts, confirming earlier studies in other strains. Treatment with PMS caused a drastic depletion of the high levels of esterified cholesterol usually found in the testes of these mice, and also caused marked growth of the seminal vesicles. Testosterone increased the weight of seminal vesicles while pregnenolone had no effect. None of the treatments stimulated spermatogenesis. A marked sex difference in the weight of the kidneys was absent in the C57BL/10 strain but was present in the DBA/2 strain. The kidneys of C57BL/10 males were significantly smaller than those of DBA/2 males. These findings, together with other studies on C57BL/10 mice, suggest that males of this strain are relatively androgen deficient. This could be due to inadequate production of FSH and LH, perhaps accompanied by a deficiency in the conversion of pregnenolone to androgenic steroids. The effect of the C57BL/10 genotype on spermatogenesis either is not hormone mediated or else is irreversible after the age of 6 weeks.

The role of prolactin in the regulation of testis function: the synergistic effects of prolactin and luteinizing hormone on the incorporation of (1- 14 C)acetate into testosterone and cholesterol by testes from hypophysectomized rats in vitro

Hypophysectomized adult male rats were treated twice daily for 3½ days with 0·9% NaCl solution, 200 μg ovine prolactin, 5 μg ovine luteinizing hormone (LH), or 200 μg prolactin +5 μg LH, starting 18 days after the operation. Minced testes from these animals were incubated in Krebs—Ringer bicarbonate buffer containing [1-14C]acetate for 3 h at 37 °C. The conversion of acetate into testosterone was calculated. It was not changed by prolactin treatment, was increased by LH (P < 0·01), and further increased by prolactin + LH (P < 0·01) to approximately the level observed in intact adult controls. The amount of testosterone in some of the incubates was measured by gas liquid chromatography. It was not changed in prolactin-treated animals and was increased in LH-treated animals (P < 0·02 compared with hypophysectomized controls). Treatment with prolactin+LH resulted in an increase in testosterone above that after treatment with LH alone (P < 0·01) and to a value similar to that in intact adult males. The incorporation of acetate into esterified cholesterol was decreased (P < 0·05) in groups treated with LH or prolactin + LH in which testosterone synthesis was increased. The incorporation of acetate into free cholesterol was not changed by any of the treatments. These results demonstrate synergistic action of prolactin and LH on the synthesis of testosterone in vitro confirming our earlier suggestions.

The role of prolactin in the regulation of testis function: the effects of prolactin and luteinizing hormone on the plasma levels of testosterone and androstenedione in hypophysectomized rats

Testosterone and androstenedione levels in the plasma of hypophysectomized rats were measured by a protein-binding method (sensitivity 150 pg testosterone; precision, 10%).

Testosterone levels in the plasma of saline-treated hypophysectomized rats were undetectable (<0·3 ng/ml). Administration of 200 μg prolactin twice daily s.c. for a period of 3½ days caused a slight rise in testosterone in four rats (0·61 ± 0·35 ng/ml) while 5 μg luteinizing hormone (LH) administered in the same regimen increased testosterone levels to 1·42 ± 0·35 ng/ml (P < 0·05). Administration of prolactin ± LH (same doses) increased testosterone levels to 5·07 ± 0·51 ng/ml which is significantly higher than when LH was given alone and exceeds testosterone levels in intact adult males (4·12 ± 0·60 ng/ml).

Androstenedione levels in the plasma of saline-treated hypophysectomized rats were, in contrast to testosterone levels, very high and averaged 3·37 ± 0·60 ng/ml. This level is higher than that in saline-treated intact controls (1·89 ± 0·36 ng/ml). Treatment with prolactin, LH or prolactin + LH induced insignificant changes in androstenedione levels which were 1·80 ± 0·33, 2·02 ± 0·28 and 4·22 ± 0·75 ng/ml, respectively.

The ratio testosterone: androstenedione was calculated to be 0·37 ± 0·08 in the prolactin-treated group, 0·76 ± 0·20 in the LH-treated group and 1·47 ± 0·64 in the prolactin + LH-treated group compared with 2·36 ± 0·28 in intact control males.

Effect of hypophysectomy on cholesterol metabolism in the testes of rats and mice

Increased synthesis de novo of cholesterol by testes of rats and mice was found to be a contributing factor in the increased testicular cholesterol content after hypophysectomy. This was shown by increased [1-14C]acetate incorporation in vitro into free and esterified cholesterol by testicular tissue from rats and mice hypophysectomized 3 weeks earlier, as compared with intact controls.

In mice, testicular cholesterol content was significantly increased 1 day after hypophysectomy at which time there was no change in the testis weight. Three weeks after the operation there was a significant decrease in testis weight and a significant increase in the concentration of free, esterified and total cholesterol as well as in the percentage of esterified fraction. These changes were even more pronounced 1 month later.

The role of prolactin in the regulation of testicular function: the effect of prolactin and luteinizing hormone on 3 -hydroxysteroid dehydrogenase activity in the testes of mice and rats

Administration of 100 μg prolactin twice daily for 3 days increased 3β-hydroxysteroid dehydrogenase (3β-HSD) activity in the testes of dwarf mice compared with that found in the normal mouse. In hypophysectomized rats, prolactin (200 μg, same regimen) was without effect when given alone, whereas 5 μg luteinizing hormone (LH) alone injected twice daily, increased 3β-HSD activity to above normal. When prolactin and LH were administered in combination, 3β-HSD activity was raised to normal levels only.

Effects of prolactin on spermatogenesis in hypophysectomized mice

Hypophysectomized mice were treated daily for 28 days with 12 i.u. prolactin, 10 μg luteinizing hormone (LH), 10 μg LH plus 12 i.u. prolactin, 50 μg testosterone propionate (TP), or 50 μg TP plus 12 i.u. prolactin. The yield of spermatogenesis was studied quantitatively from the counts of spermatogonia, preleptotene and pachytene spermatocytes and spermatids in the seminiferous tubules at stage VII of spermatogenesis. Prolactin administered alone caused a small, but significant, increase in the yield of spermatogenesis. Treatment with a mixture of LH, follicle-stimulating hormone and growth hormone in amounts 1·5 times higher than those reported as contaminants of prolactin had similar effects. Injections of LH or TP caused partial restoration of spermatogenesis. The yield of spermatogenesis was significantly higher in animals given LH plus prolactin than in the animals given LH alone. Prolactin, however, did not augment the effects of TP on spermatogenesis. It is concluded that prolactin acts on the Leydig cells of the testis to increase their responsiveness to LH. More androgen appears to be produced under the influence of LH when prolactin is also present.

Effects of prolactin and luteinizing hormone on the cholesterol stores in the mouse testis

In intact adult male mice three injections, 2 h apart, of 3 μg luteinizing hormone (LH), 15 μg LH or 100 μg follicle-stimulating hormone (FSH) decreased the concentration of esterified cholesterol in the testes. Treatment with 35 μg testosterone propionate (TP)/day or 4 mg aminoglutethimide/day increased the concentration of esterified cholesterol. Single heterotopic pituitary homografts increased the concentration of esterified cholesterol; injecting 7·5 i.u. prolactin twice daily had similar effect. The concentration of free cholesterol showed little individual variation and little or no response to any of the above treatments. The concentration of testicular total cholesterol was increased in hypophysectomized mice. Administration of 10 μg LH or 50 μg TP daily for 28 days reduced the concentration of both esterified and free cholesterol in these animals to approximately the levels found in intact adult males. Prolactin (12 i.u./day) given alone or with TP had no effect, but it increased the concentration of esterified cholesterol in LH-treated animals. It is concluded that in the mouse testis the concentration of esterified, but not free, cholesterol tends to fluctuate with the apparent changes in the rate of androgen synthesis and that prolactin promotes accumulation of cholesterol esters. This could explain the synergism between prolactin and LH in stimulating spermatogenesis and the growth of androgen dependent tissues.

Influence of prolactin and pituitary isografts on spermatogenesis in dwarf mice and hypophysectomized rats

SUMMARY

This work was undertaken to study the influence of purified prolactin on spermatogenesis in hypophysectomized rats with or without testosterone propionate maintenance therapy and in prolactin-deficient hereditary dwarf mice. In addition some dwarf mice were given heterotopic isografts of non-dwarf mice pituitaries. In rats, 25 i.u. ovine prolactin given daily for 33 days had no effect on the maintenance of spermatogenesis. In untreated dwarf mice spermatogenesis progressed to completion but had a low yield due to cell loss, especially during premeiotic divisions. Both 10 i.u. prolactin daily for 28 days and pituitary grafts resulted in marked stimulation of spermatogenesis. The number of preleptotene and pachytene spermatocytes and step 7 spermatids was significantly increased in both inbred and F1 dwarf mice regardless of age. Since seminal vesicles were also considerably heavier in treated dwarfs, it was concluded that the observed stimulation of spermatogenesis was most likely due to elevated testicular androgen production indicating that, in the male mouse, prolactin may be involved in pituitary regulation of Leydig cell function.

The influence of pituitary homografts on the weight of the accessory reproductive organs in castrated male mice and rats and on mating behaviour in male mice

SUMMARY

The effects of heterotopic pituitary homografts on the weight of the accessory reproductive structures, submandibular glands and kidneys were studied in castrated, castrated—adrenalectomized and castrated—hypophysectomized male rats and mice. In rats no consistent effects were seen; in mice the weights of the seminal vesicles, submandibular glands and kidneys were increased. When castrated mice were treated with prolactin or growth hormone (GH), singly or combined, the seminal vesicles responded to all three treatments at certain dose levels, while the submandibular glands were affected by GH only. The effects of pituitary isografts were compared in castrated and in intact hereditary dwarf mice. The weight of the submandibular glands was increased in both groups but that of the seminal vesicles only in intact dwarfs. It was concluded that in male mice prolactin exerts a small testis-independent influence on the reproductive system, and may also increase the production of androgen by the testis. Pituitary grafts had no effect on the restoration of mating behaviour in either castrated or castrated—hypophysectomized male mice treated with testosterone propionate.