Radioimmunoassay for mouse nerve growth factor (NGF). Effects of thyroxine administration on tissue NGF levels

Nerve growth factor inhibits HCO3- absorption in renal thick ascending limb through inhibition of basolateral membrane Na+/H+ exchange

Nerve growth factor (NGF) inhibits transepithelial HCO3- absorption in the rat medullary thick ascending limb (MTAL). To investigate the mechanism of this inhibition, MTALs were perfused in vitro in Na+-free solutions, and apical and basolateral membrane Na+/H+ exchange activities were determined from rates of pHi recovery after lumen or bath Na+ addition. NGF (0.7 nM in the bath) had no effect on apical Na+/H+ exchange activity, but inhibited basolateral Na+/H+ exchange activity by 50%. Inhibition of basolateral Na+/H+ exchange activity with ethylisopropyl amiloride (EIPA) secondarily reduces apical Na+/H+ exchange activity and HCO3- absorption in the MTAL (Good, D. W., George, T., and Watts, B. A., III (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 12525-12529). To determine whether a similar mechanism could explain inhibition of HCO3- absorption by NGF, apical Na+/H+ exchange activity was assessed in physiological solutions (146 mM Na+) by measurement of the initial rate of cell acidification after lumen EIPA addition. Under these conditions, in which basolateral Na+/H+ exchange activity is present, NGF inhibited apical Na+/H+ exchange activity. Inhibition of HCO3- absorption by NGF was eliminated in the presence of bath EIPA or in the absence of bath Na+. Also, NGF blocked inhibition of HCO3- absorption by bath EIPA. We conclude that NGF inhibits basolateral Na+/H+ exchange activity in the MTAL, an effect opposite from the stimulation of Na+/H+ exchange by growth factors in other systems. NGF inhibits transepithelial HCO3- absorption through inhibition of basolateral Na+/H+ exchange, most likely as the result of functional coupling in which primary inhibition of basolateral Na+/H+ exchange activity results secondarily in inhibition of apical Na+/H+ exchange activity. These findings establish a role for basolateral Na+/H+ exchange in the regulation of renal tubule HCO3- absorption.

The granular convoluted tubule (GCT) cell of rodent submandibular glands

The granular convoluted tubule (GCT) is a segment of the duct system of all rodents, situated between the striated and intercalated ducts. It has the peculiar property of synthesizing a large variety of biologically active polypeptides whose role in saliva remains unknown. The literature on the fine structure of GCT cells is critically reviewed. Some recent developments on endocrine regulation of the structure and contents of rodent GCT cells are summarized, with emphasis on EGF, NGF, renin, and kallikrein proteases. A survey of the distribution of GCT cells in several vertebrate families is presented.

Thyroid hormone and androgen regulation of nerve growth factor gene expression in the mouse submandibular gland

The nerve growth factor (NGF) content of the mouse submandibular gland (SMG) is under hormonal control and is modulated by both thyroid hormones (TH) and androgens. The sexual dimorphism of the gland is well documented. In the adult male mouse, the SMG contains 10 times more NGF compared to the female. Conversely, castration of male mice reduces the SMG NGF levels to those found in control females. In order to determine the locus at which androgens and TH exert their effect on NGF gene expression in the SMG, steady-state NGF mRNA levels were determined. Daily treatment of adult female mice with TH for 1 week increased NGF mRNA levels 6-fold. Androgen treatment produced a 20-fold increase in SMG NGF mRNA, which was comparable to levels detected in the control adult male SMG. The effect of TH on NGF mRNA levels was time-dependent and coincided with the increase in NGF protein concentrations. At 48 h after a single TH injection, NGF mRNA levels (measured in SMG total RNA) increased 2-4-fold, while heteronuclear (hn) RNA levels were increased 1.5-2-fold. The NGF gene transcription rate was determined by run-on assay following TH treatment. A small but significant 2-fold induction by TH of NGF gene transcription was found at 24-48 h. Cytoplasmic RNA prepared from the same SMGs used in the run-on experiments was tested by S1 nuclease protection; NGF cytoplasmic RNA was increased 7-fold in the SMGs of females treated with TH 48 h previously. These results demonstrate that the effect of TH on NGF gene expression is due in part to an induction of NGF gene transcription. The discrepancies observed between transcription rate and mRNA levels suggest that the major effect of TH is at the post-transcriptional level, possibly mRNA stabilization. The time required to observe an induction of TH on NGF gene transcription is suggestive of an indirect effect, possibly through the induction by TH of another protein which in turn activates the NGF gene.

L-triiodothyronine stimulates growth by means of an autocrine factor in a cultured growth-hormone-producing cell line

L-Triiodothyronine (T3) stimulates DNA synthesis and replication of cultured GC cells, a T3-responsive growth hormone (GH)-secreting cell line. To determine whether T3 stimulates secretion of an autocrine growth factor, we compared the growth-promoting activity of medium conditioned by T3-stimulated and T3-depleted cells to that of unconditioned medium. Addition of polyclonal rabbit anti-T3 serum to T3-containing media decreased cellular T3 content by 50-70%. In unconditioned medium, anti-T3 serum decreased T3-induced cell growth and GH production by 40-70%. In conditioned medium, anti-T3 serum also effected a 45-70% decrease in induction of GH secretion but did not attenuate the growth-promoting activity. Growth-promoting activity was not detected in medium conditioned by T3-depleted cells. Thus, conditioned medium from T3-containing GC cell cultures contains growth-promoting activity that is independent of T3. Further, the induction of GC cel growth by T3 may occur, at least in part, by induction of an autocrine growth factor.

Nerve growth factor immunoreactivity in mouse kidney: an immunoelectron microscopic study

We have recently reported the immunolocalization of nerve growth factor (NGF) in mouse kidney by light microscopy. In the present study, we have investigated the ultrastructural localization of NGF by the preembedding immunoperoxidase method for electron microscopy. NGF immunoreactivity was present in the connecting tubule cells of the distal nephron. These cells showed immunostaining associated with the Golgi complex, vesicles, rough endoplasmic reticulum (RER), and polyribosomes. The intercalated cells, in contrast, lacked immunoreactivity.

Thyroid hormone induction of an autocrine growth factor secreted by pituitary tumor cells

Thyroid hormones stimulate the rate of cell division by poorly understood mechanisms. The possibility that thyroid hormones increase cell growth by stimulating secretion of a growth factor was investigated. Thyroid hormones are nearly an absolute requirement for the division of GH4C1 rat pituitary tumor cells plated at low density. Conditioned media from cells grown with or without L-triiodothyronine (T3) were treated with an ion exchange resin to remove T3 and were tested for ability to stimulate the division of GH4C1 cells. Conditioned medium from T3-treated cells was as active as thyroid hormone at promoting GH4C1 cell growth but did not elicit other thyroid hormone responses, induction of growth hormone, and down-regulation of thyrotropin-releasing hormone receptors, as effectively as T3 did. A substance or substances associated with T3-induced growth stimulatory activity migrated at high molecular weight at neutral pH and was different from known growth-promoting hormones induced by T3. The results demonstrate that thyroid hormones stimulate the division of GH4C1 pituitary cells by stimulating the secretion of an autocrine growth factor.

Beta-nerve growth factor measurements in mouse serum

Mouse serum beta-nerve growth factor (NGF) levels were measured using a newly developed competitive beta-NGF radioimmunoassay. The basal serum beta-NGF levels in male and female mice were consistently less than 2 ng/ml when these animals were maintained in individual cages for at least 7 days before they were killed. However, in male mice, serum beta-NGF levels were significantly elevated when they were housed 5 per cage. The rise in serum beta-NGF levels, presumably mediated by intermale aggression, was confirmed by grouping previously isolated mice together in one cage for 20 min before they were killed. In all aggressive male mice, serum beta-NGF levels were elevated by two orders of magnitude. The beta-NGF radioimmunoassay values were also validated by a neurite outgrowth bioassay system using the serum of aggressive male mice. In summary, both measurement techniques confirm that mouse serum beta-NGF levels undergo marked changes depending on animal handling conditions.

Immunocytochemical localization of nerve growth factor in mouse kidney

The presence of NGF in mouse kidney was investigated using immunocytochemical methods. Female and male adult Swiss-Webster mouse kidneys were fixed by perfusion with 4% paraformaldehyde or Zamboni's fixative. The kidneys were frozen, and serial sections were prepared. Rabbit NGF antiserum was used for the primary incubation, and the avidin-biotin complex immunoperoxidase procedure was utilized for immunostaining. NGF immunoreactivity was localized in the apical and perinuclear cytoplasm of cells lining the late distal nephron, in a portion that corresponds to the connecting tubule. This portion of the nephron has been consistently observed in close anatomical relationship with arterioles, which are known to be richly innervated. Some cells of the connecting tubule, corresponding to intercalated cells, lacked NGF immunoreactivity.

Effects of hypothyroidism on the DNA, carbohydrate, soluble protein and sialic acid contents of rat submandibular glands

Submandibular glands are a target organ of thyroid hormones. This study examined the effects of hypothyroidism on the biochemical characteristics of these glands in the rat. There were no effects on the neutral sugar and DNA contents. However, soluble protein concentrations (micrograms/mg wet weight) were significantly decreased and sialic acid concentrations micrograms/mg soluble protein) were significantly elevated.

Artifactual presence of beta-nerve growth factor in adult mouse brain

Adult male mouse brain extracts were determined to contain 0.7 ng beta-nerve growth factor (NGF)/mg total protein in a one-site radioimmunoassay (RIA) and 3.6 ng NGF/mg protein in a competition radioreceptor assay using PC 12 cells. When brain extracts were immunoprecipitated with antiserum to NGF prior to use in a radioreceptor assay, no reduction in measured NGF content resulted, whereas immunoprecipitation of submaxillary gland extract reduced the NGF level by 83-100%. The immunoassay and radioreceptor assay were then modified by incubating antisera or PC 12 cells first with brain extract, and then, after washing, with 125I-labeled authentic mouse NGF. In the modified assays, no NGF was detected in the extracts, indicating that adult mouse brain does not contain NGF itself but does contain an NGF-binding component that causes false positive results in standard one-site RIAs and competition radioreceptor assays.

Insulin and insulin-like growth factors/somatomedins in fetal and neonatal development

In this presentation we have attempted to review the status of knowledge of the hormonal regulation of fetal and neonatal growth, and have placed particular emphasis on the roles of insulin and somatomedin in fetal growth. The inaccessibility of the fetus and the physical and ethical constraints on study of its growth have resulted in slow progress. Furthermore, the opportunity for the fetus to benefit from homologous hormones from a variety of sources has made it difficult to assess the effect of withdrawal of individual hormones. Many of the advances made have resulted from attempts to determine hormone concentrations in fetal blood, identify hormone binding by fetal tissues, and examine the effects of natural or experimentally induced deviations in hormone availability. In the future, attention should be focused on developing study models which better isolate the fetus from the influence of multiple, homologous hormones. Progress should also come as the result of more detailed study of the influence of individual growth factors on in vitro growth of fetal cells and tissues, assessment of control mechanisms for growth factors in the fetus, and experiments directed at recognizing the complex interactions between individual growth factors and between growth factors and hormones.

Acquisition of submandibular gland nerve growth factor (SMG-NGF) responsiveness to thyroxine administration in neonatal mice

The growth of the submandibular gland (SMG) was studied in newborn mice from birth to 15 days of age. Progressive changes in wet weight were observed to accompany changes in biochemical constituents such as RNA, protein, and lipid. Thyroxine (T4) administration from days 0-6 produced changes in SMG growth and SMG accumulation of RNA, protein, and lipid components relative to control pups treated with a similar volume of vehicle. This hormone regimen produced no measurable changes in SMG nerve growth factor (SMG-NGF) concentration. T4 responsiveness also was studied from days 0-15. Three patterns of T4 injection (from days 0-6, 7-14, and 0-14) were found to elicit a differential response in the three biochemical constituents measured, but treatment from days 7-14 and 0-14 elicited precocious increments in SMG-NGF concentrations on day 15. The effect of T4 injection from birth was more effective in augmenting SMG-NGF concentration than hormone treatment initiated from days 7-14. A persistent T4 effect on SMG-NGF also was observed on day 21 following hormone treatment from days 7-14 or 0-14. In summary, the acquisition of SMG-NGF responsiveness to T4 appears to develop during the neonatal period. The administration of T4 during this period also precociously stimulates the mechanisms that govern the normal ontogeny of SMG-NGF at the time of weaning.

Nerve growth factor in sympathetic ganglia and corresponding target organs of the rat: correlation with density of sympathetic innervation

A two-site enzyme immunoassay is described which does not suffer from artifacts inherent in previous assays and has the necessary high sensitivity to determine the endogenous levels of nerve growth factor (NGF) in the sympathetic nervous system and its target organs. Monoclonal and affinity-purified polyclonal antibodies against mouse NGF (mNGF) were covalently linked to glass beads as the first site and coupled to the enzyme beta-galactosidase as the second site. Detection of the fluorescent beta-galactosidase reaction product permitted the determination of 0.01-0.02 fmol of mNGF per assay. The recovery of mNGF added to homogenates varied between 50% and 100%, depending on the tissue. Rat superior cervical and stellate ganglia were found to contain (mean +/- SEM) 25 +/- 4 and 19 +/- 3 ng of NGF per g wet weight, respectively, and the densely innervated submandibular gland, heart atrium, and iris contained 0.5 +/- 0.1, 1.0 +/- 0.1, and 1.9 +/- 0.3 ng of NGF per g wet weight, respectively. Heart ventricle and skeletal muscle, which are poorly innervated by the sympathetic nervous system, did not contain detectable levels of NGF (less than 0.3 ng/g wet weight). Serum contained less than 0.05 ng of NGF per ml. The correlation between NGF levels and density of innervation is consistent with the concept that the production of NGF in target organs determines their density of innervation by the sympathetic nervous system.

Effect of experimental thyrotoxicosis on oxidative phosphorylation in rat liver, kidney and brain mitochondria

Coupled phosphorylation was examined in liver, kidney and brain mitochondria from rats made thyrotoxic by injecting repeated doses of triiodothyronine. Liver and kidney mitochondria were maximally affected under these conditions, whereas effects on brain mitochondria were marginal. State-3 respiration rates with succinate decreased considerably in all the tissues, whereas glutamate oxidation increased in liver, but decreased in kidney and brain mitochondria. Oxidation rates of beta-hydroxybutyrate decreased in kidney and brain mitochondria but were not significantly affected in liver mitochondria. Oxidation of ascorbate + TMPD was not affected. State-4 respiration rates increased in general with all the substrates resulting in lowering of the RCI. The ADP/O ratios decreased in a site-specific manner in the mitochondria from the three tissues. The content of cytochrome b decreased in all three tissues, whereas the content of cytochrome c + c1 increased in liver and kidney but decreased in brain. The content of cytochrome a, however, was not significantly affected. Basal and Mg2+-stimulated ATPase activities increased in mitochondria of liver and kidney but not in those of brain; total ATPase activities, however, were not altered. The results imply that excessive levels of thyroid hormones over normal in the serum can lead to impairment of mitochondrial energy metabolism in a tissue-specific manner.

Hypertrophic and hyperplastic effects of thyroxine on the submandibular gland of the mouse

The nature of the trophic response of the mouse submandibular gland to thyroxine (T4) was examined. Adult female Swiss-Webster mice were given daily subcutaneous injections of T4 (1 microgram/gm body weight) for two or four days; two injections of tritiated thymidine (3H-TdR) were given 24 and 29 hours after the last injection of hormone, and the mice were killed one hour after the last injection of 3H-TdR. One gland was analyzed chemically for DNA content and for incorporation of 3H-TdR, while the other was used to prepare autoradiograms. The cellular composition of each gland was analyzed by counting 1000 nuclei, and the frequency and labelling index (LI) of six cell types were established. A rise in specific activity of DNA and a fall in its concentration were seen in response to T4. The LI for the entire gland more than doubled. The LIs and frequencies of granular convoluted tubule and granular intercalated duct cells were increased more than those of acinar and nongranular intercalated duct cells; striated and excretory duct cells were not affected. It is concluded that the enlargement of the submandibular gland of the mouse caused by T4 is due to both hyperplastic and hypertrophic effects.

Bioassay detection of mouse nerve growth factor (mNGF) in the brain of adult mice

Two pools of seven brains each from adult Swiss-Webster mice were homogenized, and supernatants were collected for bioassay. PC-12 cells were placed in a bioassay plate at time zero, at a concentration of 10(4) cells per well, and primed for 48 hours in a medium containing 50 ng/ml of mNGF. The PC-12 cell bioassay for neurite outgrowth was conducted after primed cells were exposed to an NGF-free medium for 24 hours. Suitable controls for serum toxicity and cell viability were established. The sensitivity of the bioassay approximates 100 pg NGF/ml. The results showed 80-100% neurite outgrowth in wells exposed to brain pool supernatant (BPS) alone, and control level outgrowth (3-8%) in wells containing BPS and specific anti-beta-NGF antibody. Therefore, the brains of Swiss-Webster adult mice contain an NGF-like substance which promotes neurite outgrowth in PC-12 cells. The substance probably is NGF itself, since the effect is blocked by specific NGF antiserum.