Demonstration of an organ-specific mitotic inhibitor in amphibian kidney. The effects of adult Xenopus tissue extracts on the mitotic rate of embryonic tissue (in vitro)

Growth, differentiation, and function of the testes in the toad Bufo bufo bufo (L.), with special reference to regulatory capacities: effects of unilateral castration, hypophysectomy, and excision of Bidder's organs

Function and compensatory growth of the testis have been studied in male toads of varying ages, ranging from postmetamorphosis to adults. All experiments lasted 2 months, starting about September 1. Spermatogenesis was normal in sexually immature, 1-year-old toads. The fastest growing young toads developed secondary sex characteristics, the thumbpads, during the experiment. The data suggest that size is more influential than age in determining the onset of sexual maturation. But body size is not the only factor which influences sexual maturation. The growth response of the remaining testis to unilateral castration decreased with increasing age and size of the toads. Two months after operation the remaining testis had reached the size of two testes in the young toads, whereas the testis showed no significant compensatory growth in the adult-sized toads, whether sexually immature or mature. Hypophysectomy reduced body growth in young toads and prevented a testicular growth response to unilateral castration. Young toads, but no adults, with excised Bidder's organs had larger testes than the control toads. In hypophysectomized, young toads spermatogenesis was still active 2 months after the operation.

Stimulation of cell division in ectopic kidney grafts following unilateral removal of the lung

Small fragments of kidney tissue were grafted into the right lung (Xenopus laevis) and the left lung was subsequently removed. This stimulated compensatory hyperplasia (increased mitotic rate) in alveolar tissue of the right lung and in the kidney graft. This suggests that the stimulus to compensatory hyperplasia is location-specific rather than tissue- or organ-specific. After implantation into the lung the kidney grafts are revascularized by the surrounding pulmonary supply. Damage or functional impairment of an organ usually produces a localized increase in the rate of blood flow and we therefore propose that this may lead to an increased rate of cell division in one of two ways: by permitting an increased functional capacity in the tissue concerned, or by causing a more rapid local clearance of mitotic control factors.

Effects of kidney extract on the folic acid induced proliferation of the rat kidney

Single injection of a high dose of folic acid causes a proliferation of the kidney with an increase of the 3H-thymidine incorporation into the DNA of kidney cortex slices in rats. An aqueous extract from rat kidneys inhibits the increase of 3H-thymidine incorporation. The inhibition begins after 4 hours. The maximum effect is observed between 11 and 17 hours after injection of the kidney extract. The kidney extract also inhibits the increase of the DNA content per kidney after folic acid injection. Heart, lung, spleen and liver extracts and bovine serum albumin do not lead to inhibition of the 3H-thymidine incorporation into the DNA of kidney cortex sclices.

Effect of a spermatogonial chalone on the growing rat testis

Immature rats were used in an experiment to test the possible influence of a spermatogonial chalone on the expanding spermatogonial population in their developing testes. An extract from adult rat testes was injected intraperitoneally into 33-day-old rats and control animals were injected with an equal amount of saline. Two groups of normal adult rats similarly injected with the testicular extract and saline solutions served as additional controls. Following these injections, all animals were administered a dose of 3H-thymidine 10 hr before sacrifice. An analysis of the labeling indices of the various types of spermatogonia revealed that in young rats injected with testicular extract the percentage of labeled type A spermatogonia was significantly lower than in control animals. In contrast, the labeling indices of Intermediate and type B spermatogonia were similar in the two groups of young rats. In the two groups of adult animals, there was no difference in the labeling indices of type A or of other types of spermatogonia. These data indicated that the saline extract of adult testes contained a substance, a spermatogonial chalone, inhibiting specifically the proliferation of some type A spermatogonia. The results also support the concept that a spermatogonial chalone may intervene, through its action on the spermatogonial stem cell population, to arrest the growth of the seminiferous tubules as the animal reaches maturity.