Regional expression of a gene encoding a neuron-specific Na(+)-dependent inorganic phosphate cotransporter (DNPI) in the rat forebrain

We have analyzed expression of a gene encoding a brain-specific Na(+)-dependent inorganic phosphate cotransporter (DNPI), which was recently cloned from human brain, in rat forebrain using in situ hybridization. The expression of DNPI mRNA showed a widespread but highly heterogeneous pattern of distribution in the forebrain, where hybridization signals were observed in neurons but not in any other types of cells. Neurons expressing the mRNA were far more numerous in the diencephalon than in the telencephalon. In the thalamus, a number of neurons with high levels of signals were localized to all nuclei of the dorsal thalamus, habenular nuclei and subthalamic nucleus, but not the reticular nucleus and zona incerta. Moderate signal levels were seen in many neurons throughout the hypothalamus, particularly the ventromedial, paraventricular, supraoptic and arcuate nuclei, lateral hypothalamic area and mammillary complex. In contrast, expression of DNPI mRNA in the telencephalon was generally at a low level and occurred locally in some restricted regions within the neocortex, retrosplenial cortex, piriform cortex, olfactory regions, hippocampal formation and medial amygdaloid nucleus. The present results suggest that DNPI functions in heterogeneous neuron populations as a neuron-specific Na(+)-dependent inorganic phosphate cotransport system predominantly expressed in the diencephalon of the rat.

A RUNX2/PEBP2alpha A/CBFA1 mutation displaying impaired transactivation and Smad interaction in cleidocranial dysplasia

Cleidocranial dysplasia (CCD), an autosomal-dominant human bone disease, is thought to be caused by heterozygous mutations in runt-related gene 2 (RUNX2)/polyomavirus enhancer binding protein 2alphaA (PEBP2alphaA)/core-binding factor A1 (CBFA1). To understand the mechanism underlying the pathogenesis of CCD, we studied a novel mutant of RUNX2, CCDalphaA376, originally identified in a CCD patient. The nonsense mutation, which resulted in a truncated RUNX2 protein, severely impaired RUNX2 transactivation activity. We show that signal transducers of transforming growth factor beta superfamily receptors, Smads, interact with RUNX2 in vivo and in vitro and enhance the transactivation ability of this factor. The truncated RUNX2 protein failed to interact with and respond to Smads and was unable to induce the osteoblast-like phenotype in C2C12 myoblasts on stimulation by bone morphogenetic protein. Therefore, the pathogenesis of CCD may be related to the impaired Smad signaling of transforming growth factor beta/bone morphogenetic protein pathways that target the activity of RUNX2 during bone formation.

Novel clonal strains from adult rat anterior pituitary producing S-100 protein

S-100 protein, one of the unique proteins found in the nervous system, has recently been discovered unexpectedly in the rat anterior pituitary. Immunocytochemistry reveals that stellate, follicular and folliculostellate cells, and marginal cells of the rat anterior pituitary contain this protein; however, as far as we know, there are no reports on the physiological role of this protein in the anterior pituitary. In the study reported here, three S-100 protein-producing clonal strains (JH-S3, JH-S8 and JH-S12) from adult rat anterior pituitaries were established by using the single cell-plating feeder layer method. These new clonal strains reveal that the S-100 protein-producing cell is an independent cell type of the anterior pituitary. Both cultures and grafts of the JH-S3 cells stain immunocytochemically with anti-S100 protein IgG fraction. Moreover, the S-100 protein and conditioned medium of JH-S3 clonal cells both stimulate release of prolactin from prolactin-secreting clonal cells (1G4) in vitro.

Differential localization and colocalization of two neuron-types of sodium-dependent inorganic phosphate cotransporters in rat forebrain

We studied by immunohistochemistry the distribution of differentiation-associated sodium-dependent inorganic phosphate (Pi) cotransporter (DNPI) in the rat forebrain, in comparison with brain-specific cotransporter (BNPI). DNPI-staining was principally seen in axonal synaptic terminals which showed a widespread but discrete pattern of distribution different from that of the BNPI-staining. In the diencephalon, marked DNPI-staining was seen in the dorsal lateral geniculate, medial geniculate, ventral posterolateral, ventral posteromedial, anterior, and reticular thalamic nuclei without the colocalization with BNPI-staining. DNPI-staining showed a strong mosaical pattern and overlapped well the BNPI-staining in the medial habenular nucleus. DNPI-staining was moderate over the hypothalamus and notably localized in neurosecretory terminals containing corticotropin-releasing hormone in the median eminence. In contrast, the BNPI-staining was region-related and strong in the ventromedial and mammillary nuclei. In the telencephalon, laminar DNPI-staining was seen over the neocortex, corresponding to the thalamocortical termination, and also found in the retrosplenial cortex and the striatum, with the highest intensity in the accumbens nucleus shell. The present results suggest that DNPI serves as a dominant Pi transport system in synaptic terminals of diencephalic neurons including thalamocortical and thalamostriatal pathways as well as the hypothalamic neuroendocrine system in the rat forebrain.

Score-dependent fertility model for the evolution of cooperation in a lattice

The evolution of cooperation is studied in a lattice-structured population, in which each individual plays the iterated Prisoner's Dilemma game with its neighbors. The population includes Tit-for-Tat (TFT, a cooperative strategy) and All Defect (AD, a selfish strategy) distributed over the lattice points. An individual dies randomly, and the vacant site is filled immediately by a copy of one of the neighbors in which the probability of colonization success by a particular neighbor is proportional to its score accumulated in the game. This "score-dependent fertility model" (or fertility model) behaves very differently from score-dependent viability model (viability model) studied in a previous paper. The model on a one-dimensional lattice is a analysed by invasion probability analysis, pair-edge method mean-field approximation, pair approximation, and computer simulation. Results are: (1) TFT players come to form tight clusters. When the probability of iteration w is large, initially rare TFT can invade and spread in a population dominated by AD, unlike in the complete mixing model. The condition for the increase of TFT is accurately predicted by all the techniques except mean-field approximation; (2) fertility model is much more favorable for the spread of TFT than the corresponding viability model, because spiteful killing of neighbors is favored in the viability model but not in the fertility model; (3) eight lattice games on two-dimensional lattice with different assumptions are examined. Cooperation and defects can coexist in the models of deterministic state change but not in the models of stochastic state change.

Molecular mechanism of growth hormone (GH) deficiency in the spontaneous dwarf rat: detection of abnormal splicing of GH messenger ribonucleic acid by the polymerase chain reaction

The spontaneous dwarf rat (SDR) is an experimental model for pituitary dwarfism with an autosomal recessive mode of inheritance. In the pituitary of the SDR, neither GH cells nor GH protein were detected by immunological methods, but SDR pituitary has a very small amount of GH mRNA. In the present study the effects of GH-releasing factor and an analog of its second messenger, (Bu)2cAMP, on the total accumulation and secretion of GH were studied in primary cultures from SDR pituitaries. GH-releasing factor and (Bu)2cAMP increased the amount of GH mRNA, but neither accumulation nor secretion of immunoreactive GH was detected. These results suggested that the mutation is not manifest during transcription, but at a later stage. The GH gene of SDR was cloned, and its sequence was determined. A point substitution was found in the consensus sequence of the 3' splice site of the third intron. Judging from this point mutation, one would predict an abnormal splicing and a 1-base deletion in the GH mRNA. Therefore, the fragment of SDR GH cDNA in which the deletion was predicted was amplified by the polymerase chain reaction. Its sequence analysis confirmed that the SDR GH mRNA had 1 base deletion which must cause a premature translational termination of GH mRNA. These results demonstrate that GH deficiency in SDR is caused by a point mutation in the GH gene producing an abnormal splicing of GH mRNA.

Developmentally and regionally regulated expression of growth hormone secretagogue receptor mRNA in rat brain and pituitary gland

Distribution and development of growth hormone secretagogue receptor (GHS-R) mRNA expression in rat brain and pituitary gland were examined using ribonuclease protection assay. In adult male rats, GHS-R mRNA levels were highest in the pituitary gland, whereas those in the hypothalamus and hippocampus were 57 and 30% of those in the pituitary gland, respectively. Less abundant but detectable levels of GHS-R mRNA were found in the midbrain, pons, and medulla oblongata, but expression was barely detectable in the cerebellum and cerebral cortex. The expression of GHS-R mRNA was detected at late gestation (embryonic day 19) in the pituitary gland, hypothalamus, and brainstem. The mRNA levels increased with age in the pituitary gland, and decreased postnatally in the brainstem, while they remained constant in the hypothalamus during development. In contrast, GHS-R mRNA was not detectable in the hippocampus during the fetal period, but was first detected on postnatal day 7. Expression of GHS-R mRNA was also examined in the spontaneous dwarf rat (SDR), a model for isolated GH deficiency, to examine alterations in GHS-R mRNA expression in a GH-deficient state. GHS-R mRNA levels in the pituitary gland of SDRs were higher than those of control rats, suggesting negative regulation of GHS-R mRNA by GH in this region. GHS-R mRNA levels increased in the hypothalamus of female, but not in male SDRs. In contrast, GHS-R mRNA levels were not affected by GH in the brainstem and hippocampus. These results indicate that region-specific, developmentally regulated expression of GHS-R mRNA may reflect divergent physiological roles of GHS/GHS-R in distinct regions of the central nervous system and the pituitary gland.

Fine structural criteria of prolactin cells identified immunohistochemically in the male rat

Immunoreactive prolactin (PRL) cells in the adult male rat pituitary were observed by light microscopy to be scattered throughout the gland without special localization but sometimes to form small clusters consisting of five to ten cells. The cells had oval, polygonal, and cuplike shapes. Using the "superimposition technique," the fine structural properties of the PRL cells were examined on ultrathin sections just adjacent to the thick plastic section for immunostaining. Four cell types were distinguished: (1) oval, polygonal, and elongate cells with only small spherical granules, 130-200 nm in diameter; (2) oval or polygonal cells with both medium-sized spherical granules (250-300 nm) and about same size of polymorphic granules; (3) polygonal cells containing only large polymorphic granules (300-700 nm in maximal diameter); (4) cup-shaped PRL cells with spherical and small polymorphic granules. Furthermore, the prolactin immunoreactivity of these cell types was confirmed by the electron immunohistochemistry. Type 1 cells resemble, in fine structure, Kurosumi-Oota LH-gonadotrophs, but the former are not stained with anti-rat LH beta serum, but with anit-rat PRL serum. Although the functional relationship between these four types of cells is still unclear, it is concluded that the polymorphic shape of the granules is not necessarily an absolute criterion for identification of the PRL cell in the male.

Transmembrane bone morphogenesis across multiple-walled diffusion chambers. New evidence for a diffusible bone morphogenetic property

Bone generation and regeneration are associated with a bone morphogen that recruits mesenchymal cells for differentiation into bone. Experiments with particulate bone matrix gelatin implanted in multiple-walled diffusion chambers suggest that bone morphogen is a rapidly diffusible molecule, and consists of a noncollagenous bone morphogenetic protein (BMP). When particulate bone matrix gelatin is implanted inside of diffusion chambers constructed of two to five membranes, ranging from 300 to 750 cu micronm in total thickness, large deposits of bone develop on the outside. The volumes of the deposits of new bone are inversely proportional to the thickness (or distance) of transmission of the BMP. Transmission for long distances through interstitial fluid can be accounted for by a low molecular mass hydrophobic BMP, disseminated according to the laws of diffusion.

Dependence of fragmentation behavior of colloidal aggregates on their fractal structure

The fragmentation dynamics of aggregate of non-Brownian particles in shear flow is investigated numerically. The breakup behaviors of aggregates having the same connectivity but the different space-filling properties are examined. The Lagrangian particle simulation in a linear flow field is performed. The effect of surrounding fluid on the motion of multiple particles is estimated by Stokesian dynamics approach. The inter-particle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The results obtained in this work indicate that the fragmentation behavior of colloidal aggregates depends on their fractal structure. However, if the resultant aggregate size is smaller than the critical one, the fragmentation behavior shows the universality regardless of their original structure. Furthermore, the restructuring of aggregate in shear flow and its effect on the fragmentation process are also discussed.

BAY u3405, a thromboxane A2 antagonist, reduces bronchial hyperresponsiveness in asthmatics

OBJECTIVE

Thromboxane A2 (TXA2) is reported to induce bronchial hyperresponsiveness along with the well-documented bronchoconstrictor action on smooth muscles. We examined the effect of the TXA2 antagonist, BAY u3405, on bronchial hyperresponsiveness to methacholine (MCh) in asthmatics.

PATIENTS

Twelve adult asthmatics were studied in a randomized, double-blind, placebo-controlled, crossover fashion.

DESIGN

Following a 2-week run-in period, the subjects were administered 75 mg of BAY u3405 or placebo orally, twice a day for 2 weeks each in a crossover design, interposing a 2-week washout period. Bronchial hyperresponsiveness was measured by the astograph method. Briefly, the respiratory resistance (Rrs) was measured by the forced oscillation method during continuous inhalation of MCh in stepwise incremental concentrations, until Rrs reached twice the baseline value. Bronchial hyperresponsiveness was evaluated as the minimum cumulative dose (Dmin) of MCh that induced an increase in Rrs. Dmin was calculated so that 1 U of Dmin equals to 1 min of inhalation of aerosol solution at 1.0 mg/mL during quiet breathing.

RESULTS

Three subjects were withdrawn from the evaluation because they had asthmatic attacks or wheezing during the study. The Dmin value of 0.533 U (GSEM 1.675) after the BAY u3405 treatment was significantly greater than that of 0.135 U (GSEM 1.969) after the placebo treatment (p = 0.0139). There were no safety concerns in either treatment group.

CONCLUSION

We conclude that BAY u3405 may be a useful drug for attenuating bronchial hyperresponsiveness in bronchial asthma.

PEBP2alphaA/CBFA1 mutations in Japanese cleidocranial dysplasia patients

Cleidocranial dysplasia (CCD) is an autosomal dominant human bone disease whose genetic locus has been located on chromosome 6p21, where the PEBP2alphaA/CBFA1 gene essential for osteogenesis also maps. Previously, several heterozygous mutations in PEBP2alphaA/CBFA1 were found in CCD patients. In this study, we identified six different types of mutations in PEBP2alphaA/CBFA1 in Japanese CCD patients. Four cases were similar to those reported previously: two were nonsense mutations in the Runt domain, one was a hemizygous deletion, and the other was a missense mutation in the Runt domain which abolished the DNA-binding activity of Runx2/PEBP2alphaA/CBFA1. The remaining two mutations were novel: one had a heterozygous gt-to-tt mutation at the splice donor site (gt) between the exon3-intron junction, which resulted in abnormal exon3 skipping, and the other had a mutation in exon7, which led to the introduction of a translational stop codon in the middle of the transactivation domain. Thus, defects in either the DNA-binding domain or transactivation domain of Runx2/PEBP2alphaA/CBFA1 can cause CCD. The results not only provide a strong genetic evidence that mutations involving in PEBP2alphaA/CBFA1 contribute to CCD, but also provide a useful tool to study how Runx2/PEBP2alphaA/CBFA1 plays its pivotal role during osteoblastic differentiation.

Heat moisture treatment of high amylose cornstarch increases its resistant starch content but not its physiologic effects in rats

To examine whether the physiologic effects of high amylose cornstarch (HACS) are affected by gelatinization or heat moisture treatment, male rats were fed for 21 d a fiber-free purified diet containing 40 g/100 g gelatinized normal cornstarch (G-CS), HACS, gelatinized high amylose cornstarch (G-HACS) or heat moisture-treated HACS (HMCS). Dietary fiber (DF) content in G-HACS was 87% lower than that in HACS. The apparent starch and protein digestibilities were higher in the G-HACS group than in the HACS group. Fecal wet weight and fecal bile acid excretion were lower in the G-HACS group than in the HACS group. The cecal tissue weight, cecal surface area, cecal content weight and cecal pH were lower in the G-HACS group than in the HACS group. The cecal n-butyric acid and succinic acid concentrations were higher and lower, respectively, in the G-HACS group than in the HACS group. The plasma cholesterol and triacylglycerol concentrations did not differ between the G-HACS group and the HACS group. On the other hand, the DF content in HMCS was 330% higher than that in HACS, but the HMCS and HACS groups generally did not differ except in cecal surface area. Dietary starch did not affect fecal moisture, fecal neutral sterol (cholesterol + coprostanol) excretion, liver cholesterol level, total short-chain fatty acid (SCFA) concentration or apparent Ca, Fe, Mg and Zn absorptions. These results show that the heat moisture treatment of HACS for the most part does not alter its physiologic effects despite the greater DF content.

Possible sensory receptor of nonadrenergic inhibitory nervous system

To determine the sensory receptor of the nonadrenergic inhibitory nervous system (NAIS), 22 cats were anesthetized and serotonin was continuously administered (50-250 micrograms.kg-1.min-1 iv) to increase pulmonary resistance (RL) to 377 +/- 57% (SE) of the control value. We then 1) mechanically irritated the trachea, 2) intravenously administered capsaicin (5 micrograms/kg), or 3) induced hypoxia (arterial PO2 30-40 Torr) to stimulate irritant and bronchial C-fiber receptors, pulmonary C-fiber receptors, or the carotid body (chemoreceptors), respectively. After treatment with atropine (3 mg/kg iv) and propranolol (2 mg/kg iv), the serotonin-induced change in RL was reduced by 58.6 +/- 14.3% by mechanical irritation and 63.3 +/- 12.1% by intravenous capsaicin. However, hypoxia produced no dilatation of the airways. In further experiments, we employed capsaicin inhalation to stimulate bronchial C-fiber receptors. Inhaled capsaicin (0.1%, for 5 breaths) also reduced RL by 79.2 +/- 9.2% of the elevated value, after atropine and propranolol. Treatment with a ganglionic blocking agent, hexamethonium (2 mg/kg iv), abolished bronchodilator responses, implying that a reflex pathway through vagal nerves is involved in this phenomenon. These results suggest that pulmonary and bronchial C-fiber receptors may be involved as sensory receptors in NAIS reflex bronchodilatation.

Cigarette nicotine yields and nicotine intake among Japanese male workers

OBJECTIVES

To analyse brand nicotine yield including "ultra low" brands (that is, cigarettes yielding less-than-or-equal 0.1 mg of nicotine by Federal Trade Commission (FTC) methods) in relation to nicotine intake (urinary nicotine, cotinine and trans-3'-hydroxycotinine) among 246 Japanese male smokers.

DESIGN

Cross sectional study.

SETTING

Two companies in Osaka, Japan.

SUBJECTS

130 Japanese male workers selected randomly during their annual regular health check up and 116 Japanese male volunteers taking part in a smoking cessation programme.

MAIN OUTCOME MEASUREMENTS

Subjects answered a questionnaire about smoking habits. Following the interview, each participant was asked to smoke his own cigarette and, after extinguishing it, to blow expired air into an apparatus for measuring carbon monoxide concentration. Urine was also collected for the assays of nicotine metabolites.

RESULTS

We found wide variation in urinary nicotine metabolite concentrations at any given nicotine yield. Based on one way analysis of variance (ANOVA), the urinary nicotine metabolite concentrations of ultra low yield cigarette smokers were significantly lower compared to smokers of high (p = 0.002) and medium yield cigarettes (p = 0.017). On the other hand, the estimated nicotine intake per ultra low yield cigarette smoked (0.59 mg) was much higher than the 0.1 mg indicated by machine.

CONCLUSIONS

In this study of Japanese male smokers, actual levels of nicotine intake bore little relation to advertised nicotine yield levels. Our study reinforces the need to warn consumers of inappropriate advertisements of nicotine yields, especially low yield brands.

Studies on prolactin and growth hormone gene expression in the pituitary gland of spontaneous dwarf rats

The spontaneous dwarf rat (SDR) is a newly established experimental model for pituitary dwarfism with an autosomal recessive mode of inheritance. GH and PRL gene expressions were studied in the pituitary gland of this animal. Immunocytochemistry failed to detect any immunoreactive GH cells in SDR pituitary gland, whereas numerous PRL cells were encountered throughout the anterior lobe. Similarly, GH was not detectable in the pituitary cytosol from SDR of 7, 20, and 80 days of age. PRL of the same mol wt as the authentic rat PRL was found in the pituitary glands in all SDRs examined. Since these results were thought to be due to the absence of GH mRNA in the SDR's pituitary gland, we attempted to detect GH mRNA by dot hybridization. Very small amounts of GH mRNA were found in the pituitary glands of both male (2.6% of normal) and female (6.0% of normal) SDRs. Reduced levels of PRL mRNA were also found in the pituitary glands of male (50%) and female (30%) SDRs. Northern blot analyses of total RNA extracts revealed that the GH mRNA of the SDR was similar in size to the mature GH mRNA found in the pituitary glands of control rats. PRL mRNA from the SDR also migrated to the same position as normal PRL mRNA. Nuclear DNA preparations were prepared from normal and SDR livers, and the genomic organizations of the GH and PRL genes were examined using restriction mapping. The DNA fragment length patterns obtained with the cDNA probes for GH or PRL using several restriction enzyme digestions were identical. The results suggest that the GH deficiency in SDR is not due to a gross deletion or rearrangement of the GH gene. It is proposed that SDR may be an excellent experimental model for the study of isolated GH deficiency in the human.

Fine-structural heterogeneity and morphologic changes in rat pituitary prolactin cells after estrogen and testosterone treatment

This study was conducted to determine the functional and/or developmental relationships among three heterogeneous types of prolactin cells (I, II and III) in rats. Rats were injected subcutaneously daily with estradiol or testosterone propionate on days 10-20 after birth. Estradiol increased the proportion of cell types II and III, increased serum PRL levels 12-fold in males and 15-fold in females, and increased pituitary levels of prolactin 12-fold in males and 5-fold in females. Testosterone mainly increased the proportion of the Type-II cells, decreased serum levels of prolactin in males only, and did not change pituitary levels of prolactin. In a second experiment, treatment of rats with nafoxidine for five days after E2 treatment (days 10-20 after birth) increased the proportion of Type-I cells and decreased the proportion of Type-III cells and decreased serum and pituitary levels of prolactin by 50% in females and by 15 and 45% in males. In a third experiment utilizing adult male rats, estradiol and testosterone were found to modulate the relative ratios of the different types of PRL cells as they did in immature animals. The data taken as a whole suggest the possibility of an estrogen-stimulated conversion of one cell type to another, which may be a reflection of prolactin secretory activity.

A new method of inhalation challenge with propranolol: comparison with methacholine-induced bronchoconstriction and role of vagal nerve activity

To establish a safe procedure for examining propranolol-induced bronchoconstriction, we have developed a new method for performing inhalation challenge with propranolol. Monitoring respiratory resistance during tidal breathing with continuous inhalation of propranolol in 1.5-fold increasing concentrations from 0.78 to 30 mg/ml for 1 minute at each concentration, we tested 43 subjects with stable asthma and 10 normal subjects. We also compared bronchial responsiveness with responsiveness to inhaled methacholine on separate days. In addition, to determine the role of vagal nerve activity in propranolol-induced bronchoconstriction, we studied the effect of atropine. Inhaled propranolol caused dose-related bronchoconstriction in all subjects with asthma but not in normal subjects. None of the subjects suffered severe asthmatic attack during the test, which was performed in 15 minutes or less. The minimum cumulative dose of methacholine and of propranolol, at the point where respiratory conductance began to decrease, was not significantly correlated. Increased respiratory resistance was reversed by atropine in 70% of the subjects with asthma with marked individual differences. These data suggest that, although in most subjects with asthma, vagal nerve activity contributes in varying degree to bronchoconstriction, other constricting factors may contribute in the remaining subjects. It is also suggested that the mechanism of bronchial response to propranolol differs from that of the nonspecific airway reactivity estimated by methacholine challenge.

Involvement of glucocorticoid-induced factor(s) in the stimulation of growth hormone expression in the fetal rat pituitary gland in vitro

The mechanism by which glucocorticoids induce GH expression between embryonic days 18 and 19 (E18-19) in the fetal rat pituitary gland was examined with an in vitro organ culture system. Twenty-four hour incubation of E18 pituitary glands in serum-free medium containing either dexamethasone (DEX, 5-50 nM) or corticosterone (0.55 microM) resulted in a conspicuous accumulation of GH messenger RNA (mRNA), whereas no spontaneous expression of GH mRNA was noted without glucocorticoid. Triiodothyronine (1 nM) alone weakly induced GH mRNA but increased the effect of DEX 2-fold. The GH mRNA accumulation was not observed after 5 or 10 h incubation with DEX. However, a 10-h incubation with DEX followed by 14 h chase incubation without DEX resulted in apparent induction of GH mRNA. The induction of GH mRNA by DEX was completely inhibited by puromycin. These data, taken as a whole, suggest that the induction of GH mRNA by DEX in the fetal pituitary gland is not a direct effect of DEX on the GH gene but is mediated by a factor that is synthesized in the pituitary gland in response to DEX. Both immunoblot and RNase protection assays suggested that this factor is not pit-1, which is known to be required for GH mRNA expression.

Tubular hypertrophy due to work load induced by furosemide is associated with increases of IGF-1 and IGFBP-1

We have examined the expression of insulin-like growth factor 1 (IGF-1), IGF binding protein-1 (IGFBP-1), and IGF binding protein-3 (IGFBP-3) in the rat distal nephron during increased cell work load and hypertrophy, induced by the diuretic, furosemide. Furosemide was given for six days to increase distal sodium delivery and uptake. To mitigate salt loss, the animals drank 0.8% NaCl and 0.1% KCl. Control rats were infused with vehicle (0.9% saline) and drank tap water. Furosemide increased urinary volume (13-fold) and sodium excretion (eightfold), and decreased urine osmolarity (fourfold). By immunocytochemistry, staining for IGF-1 and IGFBP-1 was markedly increased in distal convoluted tubules and cortical collecting ducts; both segments also underwent hypertrophy. Increased staining for the peptides was evident early (1 hr, 18 hr) after furosemide, prior to hypertrophy of cells. Whereas transcripts of IGF-1 and IGFBP-3 mRNA showed little or no increase in extracts from furosemide-treated kidney cortices, IGFBP-1 mRNA was increased threefold 18 hours after furosemide. Alterations of IGF-1 and IGFBP-1 were independent of changes in plasma aldosterone, glucocorticoids or arginine vasopressin. That IGFBP-1 mRNA increased threefold without significant changes in IGF-1 mRNA suggests that hypertrophic stimuli might initially induce the synthesis of IGF binding protein followed by the trapping of extracellular IGF-1. The present study raises the possibility of IGF-1 and IGFBP-1 being involved in processes that lead to tubular hypertrophy. IGFBP-1 may regulate these effects by binding to and interaction with IGF-1.