Biomedical subjects

T E Wagner

Publications and source records attributed to T E Wagner.

At least 55 records · Page 3Linked to original sources

PubMed1993

Growth hormone transgenes regulate the expression of sex-specific isoforms of 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase in mouse liver and gonads.

The sexually dimorphic pattern of GH secretion regulates the expression of several steroidogenic enzymes in rat liver, including a male-specific 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase (3 beta HSD). Recently, we identified male-specific isoforms of immunoreactive 3 beta HSD in mouse liver [42 kilodaltons (kDa)] and gonads (47 kDa). To test whether GH can regulate the expression of these murine 3 beta HSDs, endogenous forms of 3 beta HSD were studied in transgenic mice expressing heterologous GH transgene products. Mice from five transgenic lines were used; two expressed GH transgenes encoding the phosphoenolpyruvate carboxykinase (PEPCK) promoter fused to either the human (h) GH (somatogenic and lactogenic) or bovine (b) GH (somatogenic) structural genes, and three expressed GH transgenes encoding the mouse metallothionein-1 (MT1) promoter fused to the hGH, hGH variant (hGHv), or bGH structural genes. Control mice were normal nontransgenic littermates. Expression of a male-specific (42 kDa) isoform of hepatic 3 beta HSD is dramatically suppressed in all transgenic mouse lines, as detected on Western immunoblots, without affecting a 47-kDa isoform expressed in livers of both male and female mice. This negative regulation was not observed in mouse kidney, which normally expresses two 3 beta HSD isoforms (in both sexes) with molecular masses similar to those in liver. Considering that PEPCK and MT1 promoters direct expression of GH fusion genes in both tissues, the inhibition of hepatic, but not renal, 3 beta HSD immunoreactivity suggests that GH affects sex-specific, rather than tissue-specific, expression of 3 beta HSD. As in the liver, sex-specific expression of 3 beta HSD in the testis is also suppressed by heterologous GH, but with one notable difference. Only human-derived GH (MT1-hGH and MT1-hGHv) effectively inhibits expression of the 47-kDa sex-specific isoform of testicular 3 beta HSD, without affecting the 44-kDa isoform expressed in gonads of both male and female mice. These results suggest that the negative effects of heterologous GH on sex-specific 3 beta HSDs may be mediated by PRL receptors in the testis and GH receptors in the liver. PEPCK-GH transgenes had little effect on testicular 3 beta HSD, possibly because this promoter (unlike MT1) is relatively inactive in this tissue. In the liver of male transgenics (PEPCK-hGH), loss of the sex-specific (42-kDa) 3 beta HSD has little effect on the Km for dehydroepiandrosterone (DHEA; 11 microM) compared with that in normal controls (16 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Specific somatotropic and lactogenic uptake in vivo in the livers of transgenic mice expressing bovine growth hormone gene.

The distribution of labeled hGH, oGH and mPRL in different tissues of MT-bGH transgenic and normal mice was investigated using an in vivo technique. This technique allows comparisons of tissue uptake of radioactivity after the labeled hormone was injected alone (20 ng/50 g BW) or together with an excess (300 micrograms/50 g BW) of unlabeled hormone. Liver, kidney and spleen are the organs that concentrate a significant amount of radioactivity 20 min after the injection of labeled hormones, but the uptake of radioactivity decreased in the presence of unlabeled hormones only in the liver. Graphical analysis showed that the disappearance curves were described by the sum of 3 compartments alpha, beta and gamma. The first two are similar in transgenic and in normal mice but the third had a t1/2 of 56 +/- 9 min in transgenic and 71 +/- 8 min in normal mice. The inhibition of liver uptake was related to the dose of unlabeled hormone injected and a half maximal displacement was obtained with 4 micrograms and 10 micrograms of hGH per 50 g of body weight for normal and transgenic mice, respectively. The 125I-hGH taken up in vivo by the liver of transgenic mice was bound to a molecular species with Stokes radius of approximately 64 A (which is consistent with the molecular size reported for the hormone-receptor complex).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Pituitary morphology of transgenic mice expressing bovine growth hormone.

BACKGROUND: In mice transgenic for growth hormone (GH), the ectopic production of foreign GH causes gigantism and strong inhibition of endogenous pituitary GH. In human (h) GH transgenics, morphologic changes occurred not only in somatotrophs but in lactotrophs, corticotrophs, and gonadotrophs as well. To distinguish between changes attributed to somatotrophic effect of hGH from those caused by its lactogenic effects, we studied the pituitary morphology of bovine (b) GH transgenics since bGH has no lactogenic activity. EXPERIMENTAL DESIGN: Pituitaries from transgenic mice and nontransgenic siblings were studied by immunocytochemistry for adenohypophysial hormones, in situ hybridization for GH, prolactin (PRL), and proopiomelanocortin mRNAs, and electron microscopy. RESULTS: Transgenic mice had an increased body weight and a significantly decreased pituitary mass. In both sexes, GH immunoreactive cells were markedly reduced in size and moderately decreased in number, and the GH mRNA signal was lower compared with controls; ultrastructurally, in somatotrophs, the cytoplasmic organelles involved in hormone synthesis were inconspicuous. Males were normoprolactinemic, and lactotrophs showed no morphologic changes. In transgenic females, PRL immunoreactive cells were hypertrophic and appeared to be more numerous. In transgenic males, a mild increase in size and number of follicle-stimulating hormone/luteinizing hormone immunoreactive cells was noted. No changes were evident in corticotrophs and thyrotrophs in either sex. In the intermediate and posterior lobes, many corticotrophs and pituicytes were GH immunoreactive, indicating expression of metallothionein-1 (MT)-bGH transgene. CONCLUSIONS: Pituitaries of MT-bGH transgenic mice contained somatotrophs with morphologic features of inhibition. Endogenous GH production was not completely suppressed as indicated by the presence of GH mRNA and GH immunoreactivity. Females had a mild increase in percentage of PRL immunoreactive cells, and previous biochemical data proved that they were hyperprolactinemic. Substantial differences in pituitary morphology between transgenic MT-bGH mice and MT-hGH animals studied previously can be due to the fact that bGH is purely somatotropic, whereas hGH is both somatotropic and lactogenic.

Adrenocorticotropic Hormone↗

PubMed1992

Neuroendocrine function in adult female transgenic mice expressing the human growth hormone gene.

Adult female transgenic mice expressing the human GH (hGH) gene with mouse metallothionein-I promoter are sterile. To evaluate the hypothalamic-pituitary function in these animals, adult female transgenic mice and nontransgenic normal littermates were ovariectomized. On days 7 and 8 after ovariectomy, mice were injected with either oil or primed with 0.5 micrograms estradiol benzoate (EB) in oil, 24 h later treated with 10 micrograms EB/100 g body wt and a day later bled for measurements of FSH, LH, and PRL levels. Plasma gonadotropin and PRL levels were also measured in ovary-intact transgenic and normal siblings at estrus. Additional ovariectomized EB-treated transgenic mice and normal siblings were injected with either saline or GnRH in saline (1 ng/g body wt) and were bled 15 min later for determination of circulating hormone levels. At estrus, in transgenic mice, circulating FSH and PRL levels were significantly lower (FSH:P less than 0.001; PRL:P less than 0.025), but plasma LH concentrations were higher (P less than 0.001) than those in nontransgenic mice. As expected, ovariectomy significantly increased (P less than 0.001) circulating FSH and LH levels in both groups of mice relative to ovary-intact animals, but the increase in plasma LH levels was attenuated in transgenic mice. The suppressive effect of estrogen on circulating FSH and LH levels were similar in transgenic and nontransgenic mice. Treatment with GnRH significantly increased plasma FSH and LH levels in both transgenic and normal mice. However, the plasma FSH and LH responses to GnRH administration were significantly reduced (P less than 0.001) in transgenic mice. The results of these studies indicate that adult female transgenic mice expressing the hGH gene are hypoprolactinemic. Yet due to PRL-like activity of hGH, the gonadotropin secretion is altered. Thus, endogenously secreted hGH modulates the hypothalamic-pituitary function of adult female transgenic mice bearing the hGH gene.

Animals↗

PubMed1992

Transgenic female mice with high human growth hormone levels are fertile and capable of normal lactation without having been pregnant.

Transgenic mice carrying the phosphoenolpyruvate carboxykinase promoter region-human growth hormone (PEPCK-hGH) fusion gene are characterized by accelerated growth and plasma hGH levels ranging from 100 to 700 ng/ml. Both sexes are fertile, in contrast to previous findings in metallothionein-I/hGH transgenic mice in which females are sterile, apparently due to luteal failure. Virgin transgenic PEPCK/hGH females from this line produce milk and can successfully raise foster litters to weaning. We conclude that the life-long presence of very large amounts of hGH in the circulation is compatible with ovulation, can override the effects of hGH-induced suppression of endogenous PRL release, and can support full lactation in animals that have not been primed by hormonal changes associated with pregnancy.

Animals↗

PubMed1992

Growth response and androgen receptor expression in seminal vesicles from aging transgenic mice expressing human or bovine growth hormone genes.

Previous work has shown that expression of human (h) GH in transgenic mice is associated with significant age-related enlargement of seminal vesicles. To further explore this aberrant growth activity, we have characterized seminal vesicles from various GH transgenic lines and examined their androgen receptor (AR) content and distribution. Six groups of animals were initially studied: young adult (3-5 months) control mice, old (greater than 12 months) control mice, young adult hGH transgenic mice, old hGH transgenics, young adult bovine (b) GH transgenics, and old bGH transgenic mice. Young transgenic mice (hGH and bGH) possessed seminal vesicles with similar relative weights, DNA and protein contents, and AR levels as nontransgenic littermates. Histologically, the glands appeared similar. With aging, the hGH transgenic seminal vesicles exhibited massive stromal hyperplasia, whereas the glands from controls and bGH transgenic mice did not show this response. Seminal vesicles from old hGH mice presented with a marked increase in cell number (DNA content) and a marked decrease in cell size and/or glandular secretions (protein/DNA ratio) compared to those from old controls and young hGH transgenic mice. Tissue AR content was markedly reduced in old hyperplastic hGH seminal vesicles compared to that in seminal vesicles from young hGH transgenics, old controls, and old bGH transgenic mice. Immunohistochemistry indicated the absence of AR in the proliferating stromal cells, whereas acinar epithelial cells showed similar or moderately reduced AR staining intensity compared to control seminal vesicles. To examine whether the above results may be due to insertional mutagenesis rather than hGH itself, two additional GH transgenic lines were examined. Aged transgenic mice expressing bGH with an alternate promoter possessed seminal vesicle weights that were not different from those of old controls, whereas aged transgenic mice expressing an hGH. V gene (variant gene, placental origin) possessed significantly larger vesicles than the controls, which further suggests that vesicular hyperplasia is specifically related to hGH. To assess androgen responsiveness, aged control and hGH transgenic mice were castrated and examined after 15 days. While control seminal vesicles significantly decreased in size, glands from transgenic mice did not. Regressive changes were observed in the remaining epithelium of hGH transgenic mice; however, stromal tissue exhibited no response to androgen withdrawal. The present results suggest that the aging-associated seminal vesicle hyperplasia in hGH transgenic mice is a result of a massive increase in stromal tissue that is low or devoid of AR, suggesting a loss of direct androgen regulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1992

Conversion of bovine growth hormone cysteine residues to serine affects secretion by cultured cells and growth rates in transgenic mice.

GHs have been found to possess two disulfide bonds. We set out to determine the importance of bovine (b) GH's disulfide bonds relative to the ability of the hormone to be secreted by cultured cells in vitro and to promote growth in transgenic mice. We have generated six mutated bGH genes that encode serine (Ser) substitutions for cysteines (Cys). These mutated genes were used to generate bGH analogs in which either one or both disulfide bonds are destroyed. When the small loop of bGH was destroyed (Cys181-Ser or Cys189-Ser), the bGH analogs were found to be secreted by mouse L-cells at levels comparable to those of wild-type bGH. However, secretion was drastically reduced when the large loop was abolished (Cys53-Ser or Cys164-Ser). An immunofluorescence study of these bGH analogs revealed two distinct patterns of subcellular localization. Bovine GH analogs with mutations in the small loop demonstrated a perinuclear distribution similar to that of wild-type bGH, but analogs containing a disrupted large loop revealed a uniform cytoplasmic distribution pattern. When these mutated bGH genes were individually introduced into transgenic mice, only those animals that expressed bGH analogs with the large loop intact demonstrated a growth-enhanced phenotype. Transgenic mice that expressed bGH analogs lacking the large loop showed growth rates similar to those of nontransgenic mice. These results suggest that the integrity of the large loop, but not that of the small loop, is essential for the growth-enhancing activity of bGH in transgenic mice.

Amino Acid Sequence↗

PubMed1992

Effects of expression of human or bovine growth hormone genes on sperm production and male reproductive performance in four lines of transgenic mice.

Reproductive performance was studied in transgenic males from lines expressing and transmitting four hybrid genes: mouse metallothionein-I/human growth hormone (GH) (MT/hGH), MT/hGH placental variant (MT/hGH.V), MT/bovine GH (MT/bGH) and phosphoenolpyruvate carboxykinase/bGH (PEPCK/bGH). Each male was exposed to three normal females for 1 week and to three different normal females for another week. Females were examined for vaginal plugs and necropsied on day 14 of pregnancy. Males were killed for analysis of organ weights, numbers of testicular spermatids, numbers of epididymal sperm and measurements of plasma glucose concentration. Fertility of MT/hGH and MT/hGH.V transgenic males was significantly lower than in normal males, primarily because most males failed to impregnate any females. In females that became pregnant, the numbers of corpora lutea, total fetuses and live fetuses did not differ from those in females mated to normal (nontransgenic) males. Fetal crown-rump length on day 14 of pregnancy did not differ between litters sired by normal or by transgenic males. Weights of testes and seminal vesicles were significantly greater in all four types of transgenic male, but daily sperm production per unit weight (g-1) of testis was not affected and epididymal sperm reserves were either normal or slightly higher than normal. Plasma glucose concentrations were significantly higher in PEPCK/bGH mice than in other mice. Average or individual reproductive performance of transgenic males from the various lines did not correlate with any of the parameters examined except for significantly heavier seminal vesicles in MT/hGH and MT/hGH.V males than in normal males; these transgenic males exhibited a high incidence of infertility. Since hGH and hGH.V, but not bGH, are lactogenic in rodents, it was concluded that chronic stimulation of GH and prolactin receptors by ectopically produced human GHs in transgenic mice compromises male fertility by an unknown mechanism. Reduced fertility of transgenic males with MT/hGH or MT/hGH.V hybrid genes is due to failure to inseminate or impregnate females rather than to reduced numbers of spermatozoa or gross changes in the male reproductive system.

Animals↗

PubMed1991

High-sulfur protein gene expression in a transgenic mouse.

We analyzed the effect of minoxidil on hair follicles isolated from transgenic mice. These transgenic animals synthesize the reporter enzyme CAT in their hair follicles only during the active phases of hair growth. The recombinant gene used to generate these mice contained the bacterial enzyme CAT under the control of the promoter from the gene of UHS protein. Studies using in situ hybridization showed that UHS proteins are expressed specifically in the matrix cells of the hair follicle during the terminal stages of hair differentiation. Hence the expression of the UHS proteins is a clear sign of active hair growth. With other in situ hybridization studies we demonstrated that CAT mRNA is expressed in differentiating matrix cells of the hair shaft in a location similar to that in which mRNA encodes UHS proteins. Thus we can use the levels of CAT activity as a measure of hair growth. We have confirmed that expression of the transgene is found in hair that is high in anagen and low in catagen follicles. The usefulness of our model was further demonstrated by showing that minoxidil, a drug that stimulates hair growth, increased the expression of CAT in cultured hair follicles. Thus we have demonstrated that expression of this reporter gene is sensitive, hair specific, and also useful for monitoring effects in cultured hair follicles. Hence these transgenic mice provide a model system for studying the biology of hair growth.

Aging↗

PubMed1991

Expression of truncated forms of the bovine growth hormone gene in cultured mouse cells.

A synthetic oligonucleotide, 5'-d(CTAGT-CTAGACTAG)-3' which encodes translational termination codons in three reading frames, was inserted into either exon IV (pbGH-4A) or V (pbGH-5A) of the bovine growth hormone gene. The resultant plasmids, under the transcriptional regulation of the mouse metallothionein 1 promoter, were introduced into cultured mouse L-cells or rat GH3 cells. Compared to wild type bGH RNA, bGH-specific RNA transiently expressed from pBGH-5A or pBGH-4A DNA in mouse L-cells was similar or slightly smaller in size, respectively. Unexpectedly, bGH-4A RNA lacked exon IV sequences. Immunofluorescence and immunoprecipitation analyses revealed that wild type bGH was localized to the Golgi apparatus, while truncated hormones were confined to the cytoplasmic compartment of transfected cells. In addition, truncated hormones were shown to be secretion-defective albeit the bGH signal peptide was efficiently and precisely processed. Thus, structural alterations in the bGH gene can dramatically affect bGH precursor mRNA processing and hormone localization within cultured mouse fibroblast or rat pituitary cells.

Animals↗

PubMed1991

Inhibition of Moloney murine leukemia virus-induced leukemia in transgenic mice expressing antisense RNA complementary to the retroviral packaging sequences.

Recombinant plasmids pLP psi as and pCP psi as were constructed by positioning the Moloney murine leukemia virus (M-MuLV) proviral packaging (psi) sequences in reverse orientation under the transcriptional regulation of lymphotropic promoter/regulatory elements from the M-MuLV long terminal repeat or the cytomegalovirus immediate-early region. Linear fragments containing the antisense psi and the appropriate transcriptional regulatory sequences from these plasmids were introduced into the mouse germ line by zygote microinjection. The chromosomal integration, germ-line transmission, and lymphocyte-directed expression of the antisense psi RNA were confirmed. Control (nontransgenic) and transgenic mice containing either the pLP psi as or the pCP psi as sequences were infected with M-MuLV on the day of birth and assayed for signs of leukemia between 12 and 14 weeks of age with standard assay procedures. While 31% (11 of 36) of the control, nontransgenic, mice developed leukemia, none of the antisense psi transgenic mice developed any symptoms of leukemia. The pCP psi as sequences were also introduced into mouse NIH 3T3 cells and stably transformed cell lines were isolated. When infected with M-MuLV these cells were shown to produce virus devoid of packaged viral RNA.

Animals↗

PubMed1991

Mutations in the third alpha-helix of bovine growth hormone dramatically affect its intracellular distribution in vitro and growth enhancement in transgenic mice.

To investigate the relationship between the secondary structure of the third alpha-helix (amino acids 109-126) of bovine growth hormone (bGH) and the biological activity of the molecule, proline or glycine residues have been used as substitutes for native amino acids at positions 114, 118, 121, and 126, respectively. Mutations at the positions 114, 118, and 121 resulted in a dramatic decrease in bGH secretion by transiently transfected mouse L cells whereas the substitution of glycine for glutamate at position 126 (bGH-E126G) did not affect secretion. Immunofluorescence staining revealed that those nonsecretory bGH mutations possessed a different intracellular location as compared with wild-type bGH or the mutated secretory forms of bGH. Similar results were seen in the distribution of these mutated bGH molecules in transfected rat GH-3 cells. Transgenic mice that express wild-type bGH or bGH-E126G grew to approximately 1.6 times the mass of nontransgenic littermates. Transgenic mice that express two nonsecretory forms of mutated bGHs were found to lack the enhanced mouse growth phenotype in spite of elevated levels of serum bGH. These results suggest that the secondary structure in the third alpha-helix of bGH may be important for efficient intracellular targeting in vitro and in growth promotion in transgenic mice.

Animals↗

PubMed1991

Interactions of human growth hormone and prolactin on pituitary and Leydig cell function in adult transgenic mice expressing the human growth hormone gene.

Adult male transgenic mice expressing the human growth hormone (hGH) gene are hypoprolactinemic. To evaluate the effects of exogenous prolactin (PRL) and endogenously secreted hGH on pituitary and Leydig cell function, adult male transgenic and nontransgenic mice (10-16 wk of age) were treated s.c. with either saline-polyvinylpyrrolidone (PVP) or oPRL (100 micrograms/mouse) in saline-PVP. Animals were treated twice daily; a total of 7 injections were given. One hour after the last injection, each group of mice was treated i.p. either with saline or oLH (0.3 microgram/g BW); 2 h later, blood was obtained via heart puncture. Plasma FSH, LH, PRL, androstenedione (A-dione), and testosterone (T) levels were measured by validated RIAs. Basal PRL levels were significantly lower (p less than 0.001) and basal LH concentrations were significantly higher (p less than 0.01) in transgenic than in nontransgenic mice. Administration of PRL significantly decreased (p less than 0.01) plasma LH levels in transgenic mice, whereas similar treatment of nontransgenic mice increased (p less than 0.01) circulating LH concentrations. Plasma FSH levels were unaffected in transgenic and nontransgenic mice treated with saline or PRL. Basal plasma A-dione and T levels were similar in both groups of animals and were significantly increased after treatment with LH. Administration of PRL increased T levels in transgenic and nontransgenic mice, but the T response to LH treatment was greater in PRL-treated transgenic mice, indicating the synergistic effect of hGH in the biosynthesis of T.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗

PubMed1991

Fertility of transgenic female mice expressing bovine growth hormone or human growth hormone variant genes.

Although growth hormone (GH) exerts various direct and indirect stimulatory effects on gonadal development and function, excessive levels of GH in acromegalic patients and in transgenic animals are often associated with reproductive disorders. We have examined reproductive performance of transgenic female mice expressing the following hybrid genes: mouse metallothionein-1 (MT)/human placental GH variant (hGH.V), MT/bovine GH(bGH), and phosphoenolpyruvate carboxykinase (PEPCK)/bGH. This allowed us to evaluate the effects of chronic GH excess in three animal models and to obtain some information on the significance of the lactogenic activity of the foreign GH (hGH.V vs. bGH) and on the developmental stage of transgene expression (MT vs. PEPCK). Transgenic animals from each line had elevated plasma insulin-like growth factor-I levels and greatly increased adult body weight. Plasma bGH levels were significantly higher in PEPCK/bGH than in MT/bGH transgenic mice. Approximately 20% of transgenic MT/hGH.V and MT/bGH females and over 60% of transgenic PEPCK/bGH females were infertile. Transgenic females that did reproduce ovulated either a normal or increased number of eggs but exhibited a variety of reproductive disorders including increased interval between pairing with a male and conception, increased interval between litters, reduced number of litters, reduced fetal growth, increased pre- and postnatal mortality, and alterations in sex ratio. Among adult offspring of these females, the proportion of transgenic animals was significantly less than the expected 50%. While some characteristics (e.g., fetal crown-rump length and weight on Day 14 of pregnancy) were affected to a comparable extent in transgenic females from all three lines, MT/hGH.V and PEPCK/bGH females were, in general, more severely affected than the MT/bGH animals. Sterility of PEPCK/bGH females appeared to be due to luteal failure since treatment with progesterone led to pregnancy. Greatly increased intervals between successive litters appeared to be due to failure to mate during postpartum estrus and to sterile matings during this period. Reduced fetal size and weight may have been due to chronic glucocorticoid excess because comparable changes could be induced in normal females by injections of dexamethasone during pregnancy, and plasma corticosterone levels were previously shown to be elevated in transgenic mice from each of these lines. Comparison of these results with data obtained from matings of normal female mice to transgenic males from the same lines suggests that reduced fetal growth is due primarily to maternal genotype, while reduced "transmission" of the hybrid genes is not, and presumably reflects increased mortality of transgenic progeny at various stages of development.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Elevated corticosterone levels in transgenic mice expressing human or bovine growth hormone genes.

Ectopic expression of human or bovine growth hormone (GH) genes in 6 lines of transgenic mice was associated with a significant increase in plasma corticosterone levels. Elevated corticosterone levels were detected in both sexes under basal conditions and after ether stress. The adrenal activity of 3 beta-hydroxysteroid dehydrogenase was measured in two of these lines and was found to be significantly increased in transgenic animals. Plasma corticosterone levels in transgenic mice did not correlate with known differences between the various lines in male and female fertility or in the life span.

3-Hydroxysteroid Dehydrogenases↗

PubMed1991

Effects of heterologous growth hormones on hypothalamic and pituitary function in transgenic mice.

The expression of the mouse metallothionein-I (mMT) promoter/human growth hormone (hGH) fusion gene in transgenic mice leads to female sterility and major alterations in the function of the hypothalamic-adenohypophyseal system. These alterations include increases in median-eminence norepinephrine turnover and plasma LH levels, and a decrease in plasma prolactin levels in intact males, and an increase in median-eminence dopamine turnover combined with the suppression of plasma prolactin levels in ovariectomized females. To further characterize these changes and to determine whether they are due to the lactogenic or somatotropic activity of hGH, we have studied hypothalamic and pituitary function in transgenic mice expressing mMT/hGH, mMT/hGH.B 'variant', or mMT/bGH fusion genes. In males, the expression of the hGH.B gene was associated with a reduction in pituitary prolactin release in vitro and an increase in LH response to LHRH stimulation, while the bGH transgene did not affect any of the examined parameters of LH and prolactin release. Median-eminence norepinephrine turnover was increased in each of the three lines of transgenic males, while median-eminence dopamine turnover was reduced only in animals expressing the hGH.B gene. In ovariectomized females, plasma LH was suppressed by hGH variant expression, while median-eminence norepinephrine turnover was suppressed in both hGH.B and bGH animals. The turnover of dopamine was increased in the median eminence of females expressing either of the human genes (hGH or gHG.B) and reduced in the median eminence of ovariectomized bGH females. We conclude that the hGH.B gene is weakly lactogenic in mice, and that the chronic stimulation of either GH receptors (by bGH) or both GH and prolactin receptors (by hGH or hGH.B) can lead to profound alterations in the metabolism of hypothalamic neurotransmitters and pituitary hormone release.

Animals↗

PubMed1991

Effect of immunoneutralization of neuropeptide Y on gonadotropin and prolactin secretion in normal mice and in transgenic mice bearing bovine growth hormone gene.

Immunoneutralization of endogenous neuropeptide Y (NPY) with specific antibodies was used to evaluate the possible physiological role of this neuropeptide in the regulation of gonadotropin and PRL secretion in the mouse. Because regulation of anterior pituitary function can be profoundly altered by chronic GH excess, we felt it was also of interest to have examined the effects of immunoneutralization of NPY in transgenic mice expressing bovine (b) GH gene with mouse metallothionein-I promotor. Intact or castrated transgenic and normal (nontransgenic) littermate adult male mice were injected with control rabbit serum or anti-NPY rabbit serum (anti-NPY). Blood samples were obtained 24 h later for hormone measurements. In intact transgenic mice expressing bGH gene, plasma LH levels were reduced and plasma PRL levels were increased, as compared to their normal littermates. Plasma levels of FSH were similar in normal and transgenic animals. Injection of anti-NPY increased plasma LH levels significantly in both intact normal and intact transgenic mice. However, plasma levels of FSH and PRL were increased significantly after anti-NPY treatment only in intact normal mice. In both normal and transgenic males, castration lead to the expected increase in plasma FSH and LH levels, whereas plasma levels of PRL remained unaltered. Administration of anti-NPY to castrated animals was followed by a significant increase in circulating LH levels in both transgenic and normal mice, whereas plasma levels of PRL were not changed. The results suggest that NPY plays a physiological role in the control of gonadotropin and PRL release in the adult male mouse, and that expression of the bGH gene in transgenic mice is associated with altered role of endogenous NPY in the control of pituitary function.

Animals↗

PubMed1991

Functional antagonism between endogenous mouse growth hormone (GH) and a GH analog results in dwarf transgenic mice.

A dwarf transgenic mouse (DTM) line has been established in which mice express relatively high levels of a mutated bovine (b) GH gene. This bGH analog binds to mouse liver membrane preparations with an affinity similar to that of wild-type bGH. The mean growth ratio of these mice is approximately 0.7 relative to that of their nontransgenic littermates. Serum insulin-like growth factor-I (IGF-I) levels of DTM were found to be approximately half those in nontransgenic littermates. Liver GH receptor levels were up-regulated in DTM or wild-type bGH transgenic mice. Pituitary GH levels were negatively correlated with serum IGF-I concentrations. Wild-type bGH transgenic mice contain relatively high serum IGF-I and low pituitary GH levels, whereas DTM possess low serum IGF-I and high pituitary GH levels. The decrease in serum IGF-I resulting from the interaction between the bGH analog, the endogenous mouse GH, and GH receptor(s) apparently leads to a dwarf phenotype. These data suggest that this bGH analog has uncoupled GH ligand-receptor binding from IGF-I production and acts as a functional antagonist to the action of endogenous mGH.

Animals↗