Search for Leptonic Decays of Dark Photons at NA62.

The NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of 1.4×10^{17} protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% confidence level, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV/c^{2} and coupling values in the range 10^{-6} to 4×10^{-5}. An interpretation of the e^{+}e^{-} search result in terms of the emission and decay of an axionlike particle is also presented.

Linkage between growth retardation and pituitary cell morphology in a dystrophin-deficient pig model of Duchenne muscular dystrophy.

OBJECTIVE: Human patients with Duchenne muscular dystrophy (DMD) commonly exhibit a short stature, but the pathogenesis of this growth retardation is not completely understood. Due to the suspected involvement of the growth hormone/insulin-like growth factor 1 (GH/IGF1) system, controversial therapeutic approaches have been developed, including both GH- administration, as well as GH-inhibition. In the present study, we examined relevant histomorphological and ultrastructural features of adenohypophyseal GH-producing somatotroph cells in a porcine DMD model. METHODS: The numbers and volumes of immunohistochemically labelled somatotroph cells were determined in consecutive semi-thin sections of plastic resin embedded adenohypophyseal tissue samples using unbiased state-of-the-art quantitative stereological analysis methods. RESULTS: DMD pigs displayed a significant growth retardation, accounting for a 55% reduction of body weight, accompanied by a significant 50% reduction of the number of somatotroph cells, as compared to controls. However, the mean volumes of somatotroph cells and the volume of GH-granules per cell were not altered. Western blot analyses of the adenohypophyseal protein samples showed no differences in the relative adenohypophyseal GH-abundance between DMD pigs and controls. CONCLUSION: The findings of this study do not provide evidence for involvement of somatotroph cells in the pathogenesis of growth retardation of DMD pigs. These results are in contrast with previous findings in other dystrophin-deficient animal models, such as the golden retriever model of Duchenne muscular dystrophy, where increased mean somatotroph cell volumes and elevated volumes of intracellular GH-granules were reported and associated with DMD-related growth retardation. Possible reasons for the differences of somatotroph morphology observed in different DMD models are discussed.

Acaricide treatment prevents adrenocortical hyperplasia as a long-term stress reaction to psoroptic mange in cattle.

In cattle, infestation with Psoroptes ovis mites may cause severe dermatitis (psoroptic mange) which compromises the health and welfare of the animals and may lead to significant economic losses. To investigate yet undocumented effects of psoroptic mange mite infestations and how successful therapy promotes animal health, the present study examined alterations of the skin, lymph nodes and adrenal glands of P. ovis infested Fleckvieh (Simmental) bulls treated with either ivermectin long-acting injection (IVM LAI; IVOMEC(®) GOLD, Merial; 3.15% ivermectin w/v) or saline (n=16 each). Approximately 8 weeks subsequent to experimental infestation with P. ovis, the bulls had developed mange and were administered either IVM LAI or saline once at 1 mL/50 kg body weight by subcutaneous injection. Mite counts were conducted in weekly intervals for determination of efficacy of treatment, and following humane euthanasia of the animals 8 weeks after treatment, skin samples from affected (mangy or previously mangy) and unaffected areas, prescapular lymph nodes and adrenal glands were collected for gross and pathohistological examination. In addition, four age-matching, uninfested Simmental bulls were sampled as controls for comparison. No P. ovis mites were detected on any IVM LAI-treated bull after 28 days following treatment whereas saline-treated bulls maintained infestation throughout the study. At sampling (approximately 16 weeks after experimental infestation and 8 weeks following saline or IVM LAI treatment), saline-treated bulls displayed a severe, exsudative dermatitis with significantly increased skin thickness and inflammatory cell infiltration, significantly enlarged, hyperplastic prescapular lymph nodes, as well as significantly increased adrenal gland weights and volumes as compared to P. ovis-infested, IVM LAI-treated bulls and uninfested controls. Quantitative stereological analysis revealed that the adrenal gland enlargement in P. ovis-infested, saline-treated bulls was due to a selective increase of the volume of the zona fasciculata in the adrenal cortex. Compared to uninfested controls and P. ovis-infested, IVM LAI-treated bulls, the number of epithelial cells in the zona fasciculata was significantly increased in P. ovis-infested, saline-treated bulls, while the zona fasciculata cell volumes did not differ between the three groups of cattle. While the single point determination of serum cortisol concentrations did not reveal significant differences between the three groups of cattle at tissue sampling, the hyperplastic growth of the adrenal cortex in the P. ovis-infested, saline-treated bulls provides morphologic evidence that a chronic stress reaction is one consequence of mange mite infestations that can be prevented by efficacious acaricidal treatment.

Genetic dissection of IGF1-dependent and -independent effects of permanent GH excess on postnatal growth and organ pathology of mice.

To study insulin-like growth factor 1 (IGF1)-independent effects of permanent growth hormone (GH) excess on body and organ growth and pathology in vivo, hemizygous bovine GH transgenic mice with homozygous disruption of the Igf1 gene (Igf1(-/-)/GH) were generated, and examined in comparison to Igf1(-/-), Igf1(+/-), wild-type (WT), Igf1(+/-)/GH, and GH mice. GH mice and Igf1(+/-)/GH mice showed increased serum IGF1 levels and the well-known giant-phenotype of GH transgenic mice. In contrast, the typical dwarf-phenotype of Igf1(-/-) mice was only slightly ameliorated in Igf1(-/-)/GH mice. Similar to GH mice, Igf1(-/-)/GH mice displayed hepatocellular hypertrophy, glomerulosclerosis, and reduced volumes of acidophilic cells in the pituitary gland. However, GH excess associated skin lesions of male GH mice were not observed in Igf1(-/-)/GH mice. Therefore, development of GH excess induced liver-, kidney-, and pituitary gland-alterations in GH transgenic mice is independent of IGF1 whereas GH stimulated body growth depends on IGF1.

Enhanced oxidative stress and endocrine pancreas alterations are linked to a novel glucokinase missense mutation in ENU-derived Munich Gck(D217V) mutants.

In the large-scale Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project murine models recapitulating human diseases were generated. In one strain, a novel missense mutation (D217V) in the glucokinase (Gck) gene was identified, resulting in decreased glucokinase activity. Heterozygous mutants display mild hyperglycaemia, disturbed glucose tolerance, and decreased glucose-induced insulin secretion. In contrast, homozygous mutants exhibit severe but not survival affecting hyperglycaemia, mild growth retardation, diminished oxidative capacity, and increased abundance of CHOP protein in the islets. Furthermore, the total islet and ß-cell volumes and the total volume of isolated ß-cells are significantly decreased in adult homozygous mutants, whereas in neonatal mice, ß-cell mass is not yet significantly decreased and islet neogenesis is unaltered. Therefore, reduced total islet and ß-cell volumes of adult homozygous mutants might predominantly emerge from disturbed postnatal islet neogenesis. Thus, we identified a novel Gck mutation in mice, with relevance in humans, leading to glycaemic disease.

Early insulin therapy prevents beta cell loss in a mouse model for permanent neonatal diabetes (Munich Ins2(C95S)).

AIMS: Heterozygous male Munich Ins2(C95S) mutant mice, a model for permanent neonatal diabetes mellitus, demonstrate a progressive diabetic phenotype with severe loss of functional beta cell mass. The aim of this study was to investigate the influence of early insulin treatment on glucose homeostasis and beta cell destruction in male Munich Ins2(C95S) mutants. METHODS: One group of male Ins2(C95S) mutants was treated with subcutaneous insulin pellets, as soon as blood glucose levels began to rise; placebo-treated mutants and wild-type mice served as controls. An additional group of mutant mice received a sodium-dependent glucose transporter 2 (SGLT2) inhibitor (AVE2268) via rodent chow. RESULTS: Insulin treatment normalised blood glucose concentrations, improved oral glucose tolerance, preserved insulin sensitivity and inhibited oxidative stress of Munich Ins2(C95S) mutant mice. Pancreatic C-peptide content, as well as total beta cell and isolated beta cell volumes, of insulin-treated mutant mice were higher than those of placebo-treated mutants. In addition, alpha cell dysfunction and hyperplasia of non-beta cells were completely normalised in insulin-treated mutant mice. Treatment with the SGLT2 inhibitor lowered blood glucose, improved glucose tolerance and normalised insulin sensitivity as well as oxidative stress of Ins2(C95S) mutants. The abundance of the endoplasmic reticulum (ER) stress markers binding Ig protein (BiP) and phosphorylated eukaryotic translation initiation factor 2 alpha (P-eIF2α) was significantly increased in the islets of mutants, before onset of hyperglycaemia, vs wild-type mice. CONCLUSIONS: We conclude that early insulin treatment protects Munich Ins2(C95S) mutant mice from insulin resistance, alpha cell hyperfunction, beta cell loss and hyperplasia of non-beta cells, some well-known features of human diabetes mellitus. Therefore, insulin treatment may be considered early for human patients harbouring INS mutations.

Microarray analysis of equine endometrium at days 8 and 12 of pregnancy.

Establishment and maintenance of pregnancy in equids is only partially understood. To provide new insights into early events of this process, we performed a systematic analysis of transcriptome changes in the endometrium at Days 8 and 12 of pregnancy. Endometrial biopsy samples from pregnant and nonpregnant stages were taken from the same mares. Composition of the collected biopsy samples was analyzed using quantitative stereological techniques to determine proportions of surface and glandular epithelium and blood vessels. Microarray analysis did not reveal detectable changes in gene expression at Day 8, whereas at Day 12 of pregnancy 374 differentially expressed genes were identified, 332 with higher and 42 with lower transcript levels in pregnant endometrium. Expression of selected genes was validated by quantitative real-time RT-PCR. Gene set enrichment analysis, functional annotation clustering, and cocitation analysis were performed to characterize the genes differentially expressed in Day 12 pregnant endometrium. Many known estrogen-induced genes and genes involved in regulation of estrogen signaling were found, but also genes known to be regulated by progesterone and prostaglandin E2. Additionally, differential expression of a number of genes related to angiogenesis and vascular remodeling suggests an important role of this process. Furthermore, genes that probably have conserved functions across species, such as CRYAB, ERRFI1, FGF9, IGFBP2, NR2F2, STC1, and TNFSF10, were identified. This study revealed the potential target genes and pathways of conceptus-derived estrogens, progesterone, and prostaglandin E2 in the equine endometrium probably involved in the early events of establishment and maintenance of pregnancy in the mare.

Phenotypic and pathomorphological characteristics of a novel mutant mouse model for maturity-onset diabetes of the young type 2 (MODY 2).

Several mutant mouse models for human diseases such as diabetes mellitus have been generated in the large-scale Munich ENU (N-ethyl-N-nitrosourea) mouse mutagenesis project. The aim of this study was to identify the causal mutation of one of these strains and to characterize the resulting diabetic phenotype. Mutants exhibit a T to G transversion mutation at nt 629 in the glucokinase (Gck) gene, leading to an amino acid exchange from methionine to arginine at position 210. Adult Munich Gck(M210R) mutant mice demonstrated a significant reduction of hepatic glucokinase enzyme activity but equal glucokinase mRNA and protein abundances. While homozygous mutant mice exhibited growth retardation and died soon after birth in consequence of severe hyperglycemia, heterozygous mutant mice displayed only slightly elevated blood glucose levels, present from birth, with development of disturbed glucose tolerance and glucose-induced insulin secretion. Additionally, insulin sensitivity and fasting serum insulin levels were slightly reduced in male mutant mice from an age of 90 days onward. While beta-cell mass was unaltered in neonate heterozygous and homozygous mutant mice, the total islet and beta-cell volumes and the total volume of isolated beta-cells were significantly decreased in 210-day-old male, but not female heterozygous mutant mice despite undetectable apoptosis. These findings indicate that reduced total islet and beta-cell volumes of male mutants might emerge from disturbed postnatal islet neogenesis. Considering the lack of knowledge about the pathomorphology of maturity-onset diabetes of the young type 2 (MODY 2), this glucokinase mutant model of reduced total islet and total beta-cell volume provides the opportunity to elucidate the impact of a defective glucokinase on development and maintenance of beta-cell mass and its relevance in MODY 2 patients.

Betacellulin overexpression in transgenic mice improves glucose tolerance and enhances insulin secretion by isolated islets in vitro.

Betacellulin (BTC), a ligand of the epidermal growth factor receptor, has been shown to promote growth and differentiation of pancreatic beta-cells and to improve glucose metabolism in experimental diabetic rodent models. We employed transgenic mice (BTC-tg) to investigate the effects of long-term BTC overabundance on islet structure and glucose metabolism. Expression of BTC is increased in transgenic islets, which show normal structure and distribution of the different endocrine cell types, without pathological alterations. BTC-tg mice exhibit lower fasted glucose levels and improved glucose tolerance associated with increased glucose-induced insulin secretion. Surprisingly, quantitative stereological analyses revealed that, in spite of increased cell proliferation, the islet and beta-cell volumes were unchanged in BTC-tg mice, suggesting enhanced cell turnover. Insulin secretion in vitro was significantly higher in transgenic islets in medium containing high glucose (11.2 or 16.7mM) as compared to control islets. Our results demonstrate that long-term BTC overabundance does not alter pancreatic islet structure and beta-cell mass, but enhances glucose-induced insulin secretion in vivo as well as in vitro.

Insulin-like growth factor-binding protein-4 inhibits growth of the thymus in transgenic mice.

Numerous in vitro studies have demonstrated that IGF-binding protein (IGFBP)-4 is a consistent inhibitor of IGF actions. In order to investigate the functions of IGFBP-4 in vivo, transgenic mice were generated by microinjection of a transgene, in which the murine Igfbp4 cDNA is driven by the H-2K(b) promoter, and followed by a splicing cassette and polyadenylation signal of the human beta-globin gene. Transgene mRNA was expressed ubiquitously, and elevated IGFBP-4 protein was detected in the spleen, thymus, kidney and lung of transgenic mice. The activities of serum IGFBPs were not changed in transgenic mice. Immunohistochemical studies revealed transgene expression predominantly in the thymic medulla and red pulp of the spleen. Body weight and the weights of the spleen, kidney and lung of transgenic mice were not different from controls. In contrast, the thymus of transgenic mice showed a significantly reduced weight and cortex volume. In transgenic thymus and spleen, cell proliferation was inhibited and apoptosis was stimulated. Transgenic mice showed normal T- and B-cell development and normal basal plasma immunoglobulin levels. In conclusion, overexpression of IGFBP-4 inhibits growth of the thymus. IGFBP-4 excess inhibits cell proliferation and stimulates apoptosis in lymphoid tissues, but does not affect lymphocyte development. These findings suggest that IGFBP-4 is a potential growth inhibitor of lymphoid tissues.

Nuclear transfer in cattle with non-transfected and transfected fetal or cloned transgenic fetal and postnatal fibroblasts.

The efficiency of nuclear transfer (NT) using two primary cultures of fetal fibroblasts (FF1 and FF2) was compared vs. the same cultures transfected with an expression vector in which the bovine prochymosin coding sequence is placed under the control of the bovine alpha(S1)-casein promoter (TFF1 and TFF2). In addition, fibroblasts of a cloned transgenic fetus (TRFF1) derived from TFF1 and ear skin fibroblasts of a 1-month-old cloned transgenic calf (TRCF1) derived from TRFF1 were used as nuclear donors. Embryos reconstructed from FF1 (44%) and FF2 (52%) developed to the blastocyst stage at a significantly (P < 0.05) higher rate than those derived from TFF1 (24%) and TFF2 (27%). The proportions of cleaved embryos and blastocysts were significantly (P < 0.05) higher with TRFF1 than with TRCF1 used as nuclear donors (75 vs. 66% and 33 vs. 16%, respectively). Transfer of NT embryos derived from FF2 and TFF2 to recipients resulted in similar pregnancy rates on day 30 (52 and 48%, respectively). However, with TFF2 embryos, the majority of pregnancies (8/11; 73%) was lost in the first and second trimesters of gestation, whereas 4/11 (36%) pregnancies with FF2 embryos were lost during the full period of in vivo development. Of 11 FF2 and 6 TFF2 born calves (25 and 13% of transferred embryos, respectively), 6 and 3 survived including one oversized FF2 calf. After transfer of TRFF1 and TRCF1 NT embryos to recipients, initial pregnancy rate was as a tendency higher in the TRFF1 (49%) than in the TRCF1 group (30%). The majority (14/17) of TRFF1 pregnancies and all TRCF1 pregnancies were lost in the first and second trimester. A high proportion of TRFF1 calves (5/8) showed increased body weights, and only two calves which were also large survived. These findings demonstrate that (i) extended culture associated with transfection and selection procedures may induce changes of donor cells which markedly decrease the efficiency of nuclear transfer and (ii) these changes are not reversed by recloning.

Growth inhibition in giant growth hormone transgenic mice by overexpression of insulin-like growth factor-binding protein-2.

To clarify the role of insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) in postnatal growth regulation, we crossed hemizygous CMV-IGFBP-2 transgenic mice with hemizygous PEPCK-bGH transgenic mice, which are characterized by serum GH levels in the range of 2 microgram/ml. Four genetic groups were obtained: animals carrying both transgenes (GB), the GH (G) or the IGFBP-2 transgene (B), and nontransgenic controls (C). Male offspring were analyzed for serum levels of IGF-I, for serum and tissue levels of IGFBP-2, and for body and organ growth. Serum IGF-I levels were 2- to 3-fold increased (P < 0.001) in the GH-overexpressing groups, with no difference between G and GB mice. Serum IGFBP-2 levels were 4- to 9-fold (P < 0.001) increased both in B and GB vs. C and G mice. Western immunoblot analysis did not reveal differences in tissue IGFBP-2 levels between B and GB mice. IGFBP-2 levels were highest in pancreas, followed by skeletal muscle, heart, kidney, brain, skin, and spleen. No elevation of IGFBP-2 was found in the liver. Body weight gain of G and GB mice was significantly increased vs. C and B mice, resulting in almost 2-fold increased body weights at the age of 15 weeks. However, there was a significant reduction in body weight of GB vs. G mice (17%; P < 0.001) and of B vs. C mice (13%; P < 0.05). This was primarily caused by a marked reduction of carcass weight (GB vs. G, 27%; B vs. C, 21%; P < 0.001). Measurements of nose-rump-length, organ (brain, heart, spleen, liver, pancreas, kidney), and tissue weights (skin, carcass, abdominal fat) in 5- and 15-week-old mice revealed several indications that the growth-inhibiting effect of IGFBP-2 overexpression was more marked in high-GH/IGF-I mice: 1) At 5 weeks of age, GB mice displayed a significant reduction of all growth parameters except for the weight of abdominal fat, when compared with G mice, whereas only brain weight was significantly reduced in B vs. C mice. 2) In 15-week-old animals, a significant reduction in all growth parameters, except for spleen and abdominal fat weights, was seen in GB vs. G mice, whereas only nose-rump-length and the weights of carcass and brain were significantly reduced in B vs. C mice. Our study demonstrates, for the first time, the potential of IGFBP-2 to inhibit GH-stimulated growth in giant transgenic mice, providing further evidence for an inhibitory effect of this IGFBP in vivo.

[Occurrence and economic importance of congenital hernia in German Fleckvich calves]. / Vorkommen und wirtschaftliche Bedeutung des angeborenen Nabelbruchs beim Deutschen Fleckvieh.

The frequency of congenital hernia was investigated in German Fleckvieh calves being driven up for sale on livestock markets for breeding and fattening calves in Miesbach and Traunstein. Data were collected on 77 livestock auctions in the years 1996 and 1997. Altogether 53,105 calves were examined and 1.8% of these calves showed a congenital umbilical hernia. The incidence of umbilical hernia was significantly influenced by the sex of the calf, the occurrence of multiple births, the market place/market date, the sire and the sire line. Red Holstein blood proportion, lactation number, duration of pregnancy and 305 day milk performance were not of significant importance. Herd milk level did not influence the incidence of congenital umbilical hernia, however, herdmate averages for calves differed significantly in their incidence. The average difference of the market price between male calves affected by congenital umbilical hernia and not affected male calves amounted to 75 DM, in female calves, however, only to 38 DM. The risk, that a congenital umbilical hernia is not closing within an age of 15 months, depends on the width of the hernial opening in the newborn calf. An opening of 4 cm and more has only a healing chance of 50% and less. However, negative effects on fattening and carcass traits could be not found. The genetic influence on congenital umbilical hernia was obvious. The analyses indicated that the incidence of congenital umbilical hernia observed could not be explained by one autosomal recessive gene locus, but it seemed much more likely that more than one gene locus is involved or a mixed multifactorial monogenic mode of inheritance may be the underlying genetic mechanism. Breeders should be aware of the implications of congenital hernias and thus, congenital hernia should get more attention in the selection process of young sires.

[Role of podocyte damage in the pathogenesis of glomerulosclerosis and tubulointerstitial lesions: findings in the growth hormone transgenic mouse model of progressive nephropathy]. / Zur Bedeutung der Podozytenschädigung in der Pathogenese glomerulosklerotischer und tubulointerstitieller Läsionen: Am Modell der progressiven Nephropathie der Wachstumshormon-transgenen Maus erhobene Befunde.

The sequence of structural changes terminating in glomerulosclerosis, tubular atrophy and interstitial fibrosis was analyzed in the growth hormone (GH) transgenic mouse (TM) model of progressive renal disease. The investigation was performed in TM expressing the bovine GH gene under the control of the murine metallothionein-1-promoter and non-transgenic controls (CM) of different age groups. The kidneys were studied by light microscopy, transmission and scanning electron microscopy, and were analyzed with stereological methods. Early-stage renal lesions were characterized by glomerular hypertrophy and mesangial expansion. In 7-week-old TM the mean glomerular volume was twice that of age-matched CM. The number of endothelial and of mesangial cells per glomerulus was increased in TM vs. CM, while the number of podocytes did not change. The podocytes demonstrated hypertrophy and foot process effacement. Concomitant with an age-related further increase of glomerular size in TM, severe maladaptive podocyte lesions including detachment of podocytes were observed. The resultant denudation of the glomerular basement membrane was associated with severe proteinuria, glomerular hyalinosis, synechia formation and collapse of glomerular capillaries. These lesions progressed to glomerular obsolescence that was associated with atrophy of the adjacent tubule and interstitial fibrosis. The progressive kidney lesions in this model appear to be attributable to a considerable extent to podocyte damage resulting from the limited capacity of this cell type to keep up with progressing overall tuft growth. The findings provide further evidence that mature podocytes are unable for effective cell replication in vivo, and that podocyte damage plays a significant role in the pathogenesis of progressive glomerulosclerosis with tubular atrophy and interstitial fibrosis.

Chronic tubulointerstitial nephropathy in six okapis (Okapia johnstoni).

Renal tubular atrophy with conical and medullary interstitial fibrosis with severe thickening of the basement membranes of atrophic tubules was found in six okapis (Okapia johnstoni). Focal glomerular atrophy, probably secondary to ischemic collapse of the glomerular capillary tuft, was also observed. Although the etiologies and pathogeneses of these nephropathies are unclear, primary damage of the tubular epithelium appears to be the most likely cause, and toxicity from ingested plant material, possibly willow (Salix sp.), is a possibility.

Effects of IGFBP-2 overexpression in vitro and in vivo.

Insulin-like growth factor-binding proteins (IGFBPs) are important modulators of IGF actions and may have both stimulatory and inhibitory effects. Expression of IGFBP-2 is increased after fasting and in a variety of pathological conditions. However, the specific role of IGFBP-2 in growth physiology remains to be determined. In this review, we summarize data from in vitro and in vivo models suggesting that IGFBP-2 has mainly inhibitory effects on IGF actions. Since the growth hormone (GH)/IGF system is involved in a number of pathological alterations of the kidney and these changes may--at least in part--be due to increased IGF-I, local overexpression of inhibitory IGFBP-2 in the kidney might prevent IGF-I-induced lesions. This hypothesis will be tested by crossing GH transgenic mice, a common model of glomerulosclerosis, with transgenic mice characterized by systemic and renal overexpression of IGFBP-2.

Overgrowth of skin in growth hormone transgenic mice depends on the presence of male gonads.

Growth hormone has been shown to possess stimulatory effects on various connective tissues. We observed that skin growth in male rat phosphoenolpyruvate carboxykinase-bovine growth hormone transgenic mice (serum growth hormone levels: 740-1940 ng per ml) is progressive with age, resulting in an "oversized coat" phenotype with a marked increase in absolute and relative skin weight and surface area, and in thickness of the dermis. Histologic changes include severe dermal fibrosis and replacement of subdermal adipose tissue by fibrous tissue. Apart from an increase in skin surface area, these changes were not noted in female transgenic mice, arguing for a specific interaction of growth hormone with male sex hormones. To clarify this point, 6 wk old male transgenic mice and control mice were castrated and compared with their noncastrated counterparts in parameters of skin growth at an age of 8 mo. The skin weight of castrated transgenic mice was smaller (p < 0.01) than that of intact transgenic mice both absolutely and relative to body weight. The relative skin weight of castrated transgenic mice was in the same range as in intact and castrated control mice. Absolute and relative skin area of castrated transgenic mice was greater (p < 0. 001 and p < 0.05) than in controls but lower than in intact transgenic mice (p < 0.001 and p < 0.05). When compared with control mice, intact transgenic mice displayed an increase (p < 0.01) in the thickness of dermis. In castrated transgenic mice the thickness of the dermis was in the same range as in control mice. Our findings demonstrate a specific interaction of growth hormone with male sex hormones resulting in a marked stimulation of skin growth.