Ames Dwarf Mice Research Articles

Changes in lymphoid organs of Ames dwarf mice after treatment with growth hormone, prolactin or ectopic pituitary transplants.

This study was performed to obtain more insight into the roles of PRL and GH in the control of immune functions in hereditary dwarf mice characterized by severe immunodeficiency. Adult female Ames dwarf mice (df/df) were injected daily for 10 days with ovine PRL (oPRL), bovine GH (bGH), oPRL+bGH or were implanted with a normal pituitary under the kidney capsule for 5 days. Only the treatment with bGH resulted in significant increases in the gain of body weight, and in absolute and relative thymus and spleen weights. Treatment with oPRL alone did not affect body weight gain or thymus and spleen weights. Treatment with oPRL+bGH produced a significant increase in the gain of body weight and in absolute and relative spleen weight but these effects were smaller than those measured in dwarf mice treated with bGH alone. Only bGH therapy resulted in extensive recovery of the absolute number of lymphocytes in the thymus and spleen of dwarf mice, with the values in treated dwarf mice not significantly different from those found in normal non-dwarf females. However, when these values were corrected for body weight, both the splenic and the thymic indices exceeded the values found in normal mice. The absolute numbers of lymphocytes in the spleen were also increased by oPRL+bGH treatment, but did not reach the values found in normal mice; however, the splenic index exceeded the values found in normal animals. Surprisingly, the absolute and relative numbers of lymphocytes found in the thymus of dwarf mice under oPRL+bGH therapy were indistinguishable from those found in oPRL or vehicle treated dwarf mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Ectopic pituitary transplants restore immunocompetence in Ames dwarf mice

This work was undertaken to study the effects of prolactin on immune function in Ames dwarf mice. For that purpose, adult Ames dwarf mice were implanted with pituitaries from normal mice under the kidney capsule. Ectopic pituitary transplants produced the expected increase in plasma prolactin levels in male and female dwarf mice as compared to sham-operated dwarf or untreated normal mice. Body weight was significantly increased in pituitary-grafted dwarf mice of both sexes, but did not reach the values found in normal (non-dwarf) animals. Pituitary transplants induced an increase in thymus weight and in the number of lymphocytes in the thymus in dwarf mice of both sexes as compared to sham-operated dwarf controls. The weight of the thymus in grafted dwarf mice remained below values found in normal mice, while the number of thymic lymphocytes became indistinguishable from those recorded in normal mice. Effects of pituitary transplants on the spleen were similar to those described for the thymus; however, neither the weight nor the lymphocyte number in pituitary-grafted dwarfs reached the values found in normal animals. Natural killer activity of spleen lymphocytes from pituitary-grafted male and female dwarf mice was greatly enhanced as compared to lymphocytes from sham-operated dwarfs. This effect was greater in males than in females. The number of white blood cells in pituitary-grafted male dwarf mice was increased and indistinguishable from the values found in normal males. Surprisingly, this effect was absent in the females. These findings suggest that hormones secreted by the transplants, most likely prolactin and growth hormone, can enhance the immune response. This action may be mediated by direct action of prolactin and/or growth hormone on immune cells or by indirect effects.

Effects of Hyperprolactinemia on Ornithine Decarboxylase Activity and Polyamine Levels in Seminal Vesicles of Genetically Prolactin-Deficient Adult Dwarf Mice1

Prolactin (PRL) has been shown to exert many different actions in various biological systems. Polyamines are known to influence the growth and function of the seminal vesicles (SV). Furthermore, ornithine decarboxylase (ODC) is considered a key enzyme in the biosynthesis of polyamines and is regulated by PRL in certain target tissues. Adult Ames dwarf mice (df/df), genetically deficient in PRL, were used for this study. The experimental groups were as follows: Group 1, pituitary-grafted; Group 2, sham-operated; Group 3, castrated + testosterone propionate (TP)-treated (25 micrograms/mouse, 3 times/wk, s.c.) + grafted; and Group 4, castrated + TP as above. The animals were killed 40 days later, and polyamines and ODC activity in SV and liver were determined. Serum PRL, FSH, and testosterone (T) were also measured. In the grafted groups, there were significant elevations in serum PRL and FSH levels. In the gonad-intact, pituitary-grafted group, animals exhibited an elevation in plasma T levels, and similar levels were achieved in the castrated, androgen-replaced groups. In hyperprolactinemic mice, the weights of SV were significantly greater than in the corresponding control groups. The relative weights of the SV showed a similar pattern. An increase in ODC activity was observed in both SV and liver in hyperprolactinemic groups. In those animals in which serum T levels were held constant, an increase in the enzyme activity in SV was detected in hyperprolactinemic group whereas in liver, no significant difference was observed. Concentrations of polyamines in the SV were increased in hyperprolactinemic, castrated, TP-treated mice. The present results indicate that PRL can exert a direct stimulatory effect on the growth, ODC activity, and polyamine levels in the SV.

The Pit-1 transcription factor gene is a candidate for the murine Snell dwarf mutation

Two nonallelic mouse mutations with severe dwarf phenotypes are characterized by a lack of growth hormone, prolactin, and thyroid stimulating hormone. The cells that normally synthesize these pituitary hormones express a common transcription factor called GHF-1 or Pit-1. Using an intersubspecific backcross, we have demonstrated tight linkage of the Pit-1 and Snell dwarf ( dw) genes on mouse chromosome 16. No recombination was observed between Pit-1 and dw in 110 individuals examined. Southern blot analysis of genomic DNA reveals that the Pit-1 gene is rearranged in C3H HeJ - dw 1 dw mice but not in coisogenic +/+ animals, providing molecular evidence that a lesion in the Pit-1 gene results in the Snell dwarf phenotype. Demonstration of low levels of Pit-1 expression in Ames dwarf ( df) mice implies that both Pit-1 and df expression may be required for pituitary differentiation.

Effect of Prolactin Replacement on the Number of Tyrosine Hydroxylase Expressing Neurons in the Arcuate Nuclei of Ames Dwarf and Normal Mice

Ames dwarf mice do not synthesize or release growth hormone or prolactin (PRL) and have very poorly developed tuberoinfundibular dopaminergic (TIDA) neurons. An antibody to tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of dopamine, and immunohistochemical procedures were used in this study to compare the numbers of TH-immuno-positive neurons observed in the arcuate nuclei of Ames dwarf mice compared to phenotypically normal mice of the same strain. In female dwarfs, the number of TH-immunopositive neurons in the arcuate nuclei but not the pars compacta was markedly reduced when compared to normal females. The elevation of circulating PRL either by the implantation of a normal pituitary under the kidney capsule or by the daily administration of ovine PRL increased the numbers of arcuate neurons which expressed immunochemically detectable TH to a level comparable to that observed in untreated normal mice. The number of TH-expressing neurons was also reduced in the arcuate nuclei of dwarf males although the deficiency was not as great as in females. Ovine PRL seemed to have little effect on the numbers of TH-immunopositive neurons observed in either dwarf or normal male mice. These results suggest that the postnatal absence of PRL in mice does not result in a major reduction in the total population of TIDA neurons. Rather these neurons appear to be present in nearly normal numbers but are in a dormant state in the absence of circulating PRL.

Identification of a placental lactogen in pregnant Snell and Ames dwarf mice.

Sera and placentas from pregnant dwarf mice contain a placental lactogen. This placental lactogen has immunological and electrophoretic properties similar to those of placental lactogen from normal mice.

Prolactin status of hereditary dwarf mice.

Snell (dw/dw) and Ames (df/df) dwarf mice of both sexes were evaluated for immunoassayable PRL in plasma and for the presence of PRL-containing cells in the hypophysis. Regardless of the method of blood collection (decapitation or cardiac or orbital puncture), minimal concentrations of PRL were detected in the plasma of hereditary dwarf mice. PRL secretion was not augmented in Snell or Ames female dwarfs after treatment with perphenazine or estradiol benzoate, stimuli which greatly increased PRL release in normal female littermates. Comparison of PRL levels in dwarf animals (dw/dw or df/df) using two different homologous RIAs substantiated the observation that male and female dwarfs are PRL deficient. Mammotropes, readily detectable in the pituitary glands of all normal siblings of Snell and Ames mice, were absent from the dwarf mouse hypophysis, which was markedly reduced in size. The lack of PRL-containing cells in the dwarf mouse pituitary may explain why peripheral PRL levels in this animal are below those measured in hypophysectomized mice.

Growth hormone and prolactin synthesis in normal and homozygous Snell and Ames dwarf mice.

The severe growth retardation and sterility characteristic of Snell and Ames dwarfs, two nonallelic, recessive mouse mutants, have been attributed to a deficiency in pituitary production of GH and PRL. We have investigated the synthesis of these hormones in normal and homozygous dwarf mice of both strains at various stage of development to determine whether the mutations prevent initial development of the pituitary capacity to produce these hormones. Synthesis of radiolabeled GH and PRL was assayed by two-dimensional electrophoresis and immunoprecipitation using goat antisera to mouse GH and PRL. Litters in which all pups were mutant were produced by mating adult dwarfs made fertile by implanting a normal pituitary under the kidney capsule. We found that GH and PRL synthesis was undetectable in Snell or Ames dwarfs at all stages of development examined, including the neonatal period when dwarf pups are indistinguishable from normal littermates. Furthermore, we detected no immunoprecipitable peptides which might represent mutant hormones in these animals. Assays of GH synthetic rates in heterozygous animals indicated that there may be a slight negative effect of the mutant gene on GH synthesis in Snell animals. It was concluded that in the homozygous condition, both types of dwarf alleles result in failure of the pituitary to initiate GH and PRL synthesis.

Pituitary hollow fiber units in the dwarf mouse.

Body weights of Snell (dw/dw) and Ames (df/df) dwarf mice doubled after intracranial implantation of hollow fiber units containing mouse pituitary cells. Recipients showed increased long bone growth, increased fat deposition, and marked loss of body hair. Recipients injected with thyroxine grew but did not develop increased fat deposition or hair loss. The results suggest that both somatotrophs and corticotrophs function in the fiber implants.

Effects of growth hormone and thyroxine on pituitary and testicular function in two types of hereditary dwarf mice.

AbstractHereditary dwarf mice are growht hormone (GH)‐ and prolactin (PRL)‐deficient and hypothyroid. Administration of PRL, GH, or thyroxine (T4) can induce fertility inmale dwarf mice. The mechanism of action of PRL appears to involve stimulation of FSH release, increased ability of the testes to bind LH, and increased production of testosterone (T) and spermatozoa. To obtain some information on the action of GH and T4 on the pituitary‐testicular axis in these animals, we have examined spermaogenesis, plasma hormone levels, and testicular T production in vitro in Snell (dw) and Ames (df) dwarf mice treated with GH or T4. Treatment with T4 (2μg/day for 2 weeks; 1μg/day for 4 weeks or 4–6μg 3 ×/wk for 6 weeks) or with GH (125 μg/day for 2 weeks; or 38–150 μg/day for 4 weeks) increased body weight, stimulated spermatogenesis, and increased the weight of the testes and seminal vesicles. Treatment with T4 had no significant effects on plasma hormone levels, while treatment with GH for 2 weeks increased plasma levels of LH, FSH, and T in Ames but not in Snell dwarf mice. The ability of the testes to produce T in vitro in the presence of hCG was not affected by in vivo treatment with GH or T4 in either df or dw dwarf mice. These results indicate that the stimulatory effect of T4 and GH on testicular function of dwarf mice does not involve increased responsiveness to gonadotropins or major chages in gonadotropin release. Comparison of the present results with those obtained earlier with PRL indicates that the ability of PRL to induce fertility in dwarf mice may be a specific action of this hormone on the pituitary‐testicular axis, rather that a result of its inherent somatotropic activity.

Immunodeficiency of the Thymus-Dependent System of the Ames Dwarf Mouse

Abstract The autosomal recessive pituitary Ames dwarf mouse was immunodeficient as shown by lymphocyte depletion and involution of thymus and peripheral lymphoid tissue, lymphopenia and a wasting syndrome with subsequent death at a young age. The appearance of 19S and 7S hemolytic plaque-forming cells after immunogenic stimulation with sheep erythrocytes was delayed and considerably less in Ames dwarf mice than in normal littermates. The graft-vs-host reactivity of spleen cells, measured by the Simonsen splenomegaly assay in young (Ames × AKR)F1 hybrid mice, was significantly lower in Ames dwarf mice. On the other hand, the Ames dwarf mouse did not have marked deficiencies in the serum levels of immunoglobulin. The normal colony-forming capacity of bone marrow cells measured with the spleencolony assay of Till and McCulloch (see Ref. 13), suggested a normal stem cell population in the bone marrow of Ames dwarf mice. The earliest degenerative change of the thymus of the Ames dwarf mouse was a depletion of thymocytes from the thymus cortex frequently accompanied by an increased number of lymphoid cells in the medulla. This was followed by a loss of lymphoid cellularity of the medulla, thereby causing a complete involution of the thymus. These results suggest that the Ames dwarf mouse has an immunodeficiency of the thymus-dependent lymphoid system as a consequence of defective thymotropic influences by the pituitary.

Reproduction of female dwarf mice treated with prolactin.

Summary. Genetically dwarf female mice are sterile but reproduction and lactation can be induced with prolactin-producing heterotopic pituitary homografts. To test if prolactin deficiency is the sole cause of the sterility, female dwarf mice were treated with purified prolactin. Dwarf (dwdw) and Ames dwarf (dfdf) mice in which the vaginae opened spontaneously were mated to non-dwarf males and injected with sheep prolactin starting on the day of plug formation. Pregnancy, delivery and lactation were obtained in both kinds of dwarf mouse indicating that, in the stocks used, the addition of prolactin alone is sufficient for reproduction.