Allergic eosinophil-rich inflammation develops in lungs and airways of B cell-deficient mice.

Immunoglobulins (Ig), particularly IgE, are believed to be crucially involved in the pathogenesis of asthma and, equally, in allergic models of the disease. To validate this paradigm we examined homozygous mutant C57BL/6 mice, which are B cell deficient, lacking all Ig. Mice were immunized intraperitoneally with 10 micrograms ovalbumin (OVA) plus alum, followed by daily (day 14-20) 30 min exposures to OVA aerosol (OVA/OVA group). Three control groups were run: OVA intraperitoneally plus saline (SAL) aerosol (OVA/SAL group); saline intraperitoneally plus saline aerosol; saline intraperitoneally plus OVA aerosol (n = 6-7). Lung and large airway tissues obtained 24 h after the last OVA or SAL exposure were examined by light microscopy and transmission electron microscopy (TEM). The Ig-deficient mice receiving OVA/ OVA treatment had swollen and discolored lungs and exhibited marked eosinophilia both in large airway subepithelial tissue (49.2 +/- 12.0 cells/mm basement membrane [BM] versus OVA/ SAL control 1.2 +/- 0.3 cells/mm BM; P < 0.001), and perivascularly and peribronchially in the lung (49.3 +/- 9.0 cells/unit area versus OVA/SAL control 2.6 +/- 0.6 cells/unit area; P < 0.001). The eosinophilia extended to the regional lymph nodes. TEM confirmed the subepithelial and perivascular localization of eosinophils. Mucus cells in large airway epithelium increased from 1.5 +/- 0.8 (OVA/SAL mice) to 39.5 +/- 5.7 cells/mm BM in OVA/OVA treated mice (P < 0.001). OVA/SAL mice never differed from the other control groups. Corresponding experiments in wild-type mice (n = 6-7 in each group) showed qualitatively similar but less pronounced eosinophil and mucus cell changes. Macrophages and CD4+ T cells increased in lungs of all OVA/OVA-treated mice. Mast cell number did not differ but degranulation was detected only in OVA/OVA-treated wild-type mice. Immunization to OVA followed by OVA challenges thus cause eosinophil-rich inflammation in airways and lungs of mice without involvement of B cells and Ig.

Natural killer cells determine development of allergen-induced eosinophilic airway inflammation in mice.

The earliest contact between antigen and the innate immune system is thought to direct the subsequent antigen-specific T cell response. We hypothesized that cells of the innate immune system, such as natural killer (NK) cells, NK1.1(+) T cells (NKT cells), and gamma/delta T cells, may regulate the development of allergic airway disease. We demonstrate here that depletion of NK1.1(+) cells (NK cells and NKT cells) before immunization inhibits pulmonary eosinophil and CD3(+) T cell infiltration as well as increased levels of interleukin (IL)-4, IL-5, and IL-12 in bronchoalveolar lavage fluid in a murine model of allergic asthma. Moreover, systemic allergen-specific immunoglobulin (Ig)E and IgG2a levels and the number of IL-4 and interferon gamma-producing splenic cells were diminished in mice depleted of NK1.1(+) cells before the priming regime. Depletion of NK1.1(+) cells during the challenge period only did not influence pulmonary eosinophilic inflammation. CD1d1 mutant mice, deficient in NKT cells but with normal NK cells, developed lung tissue eosinophilia and allergen-specific IgE levels not different from those observed in wild-type mice. Mice deficient in gamma/delta T cells showed a mild attenuation of lung tissue eosinophilia in this model. Taken together, these findings suggest a critical role of NK cells, but not of NKT cells, for the development of allergen-induced airway inflammation, and that this effect of NK cells is exerted during the immunization. If translatable to humans, these data suggest that NK cells may be critically important for deciding whether allergic eosinophilic airway disease will develop. These observations are also compatible with a pathogenic role for the increased NK cell activity observed in human asthma.

A beta cell-specific knockout of hormone-sensitive lipase in mice results in hyperglycaemia and disruption of exocytosis.

AIMS/HYPOTHESIS: The enzyme hormone-sensitive lipase (HSL) is produced and is active in pancreatic beta cells. Because lipids are known to play a crucial role in normal control of insulin release and in the deterioration of beta cell function, as observed in type 2 diabetes, actions of HSL in beta cells may be critical. This notion has been addressed in different lines of HSL knockout mice with contradictory results. METHODS: To resolve this, we created a transgenic mouse lacking HSL specifically in beta cells, and characterised this model with regard to glucose metabolism and insulin secretion, using both in vivo and in vitro methods. RESULTS: We found that fasting basal plasma glucose levels were significantly elevated in mice lacking HSL in beta cells. An IVGTT at 12 weeks revealed a blunting of the initial insulin response to glucose with delayed elimination of the sugar. Additionally, arginine-stimulated insulin secretion was markedly diminished in vivo. Investigation of the exocytotic response in single HSL-deficient beta cells showed an impaired response to depolarisation of the plasma membrane. Beta cell mass and islet insulin content were increased, suggesting a compensatory mechanism, by which beta cells lacking HSL strive to maintain normoglycaemia. CONCLUSIONS/INTERPRETATION: Based on these results, we suggest that HSL, which is located in close proximity of the secretory granules, may serve as provider of a lipid-derived signal essential for normal insulin secretion.

A substance P antagonist, [D-Pro2, D-Trp7,9]SP, inhibits inflammatory responses in the rabbit eye.

Neurogenic factors released by antidromic nerve stimulation are thought to be in part responsible for the vasodilation and breakdown of the blood-aqueous barrier that follows trauma to the eye. Substance P is one candidate for the mediation of the inflammatory response since it is thought to be a neurotransmitter in sensory afferents and since exogenous substance P is capable of eliciting a response characteristic of inflammation. In rabbits, intravitreal or topical application onto the eye of a specific substance P antagonist, [d-Pro2, D-Trp7,9]SP, inhibited not only the irritant effects of exogenous substance P but also the inflammatory response to a standardized trauma (infrared irradiation of the iris). These observations suggest that substance P, or a related peptide, is a neurogenic mediator of the inflammatory response in the eye.

Reconstructing the pancreas: restoration of normoglycemia, exocrine function, and islet innervation by islet transplantation to the pancreas.

Impaired function in transplanted islets may be ascribed in part to disturbed reinnervation. The objectives of this study were to determine whether islet transplantation to the pancreas in the presence of nerve growth factor (NGF) would restore islet innervation and endocrine and exocrine pancreatic function. Streptozotocin-diabetic Lewis rats received 800 syngeneic islets beneath the pancreatic capsule in the presence or absence of NGF (20 ng/d for 14 days). Fasting blood glucose was measured for 3 months. The pancreata were isolated and perfused in situ. Pancreatic juice was collected for amylase determination. The sympathetic trunks were isolated and stimulated electrically. The tissues were immunostained for nerve markers. All islet recipients remained euglycemic (4.2 +/- 0.6 mmol/L glucose). Ductal amylase concentrations were restored to near normal levels in contrast to diabetic controls (normal rat 98 +/- 8 U/L, islet transplant 78.4 +/- 9 U/L, diabetic control 14.5 +/- 8 U/L). NGF enhanced the innervation of transplanted islets in contrast to control islet transplants. Sympathetic adrenergic innervation was significantly increased by NGF (tyrosine hydroxylase [P < .001] and neuropeptide Y [P < .05]). No differences in parasympathetic innervation were observed (vesicular acetylcholine transporter). Electrical stimulation of the sympathetic trunks in the presence of 4 micromol/L phentolamine and 5 micromol/L atropine resulted in increased insulin secretion in NGF-treated islet transplants (164%) compared with control transplants (30%). The combination of growth factors and the pancreatic site may allow the use of fewer islets than conventional islet transplant sites and promote more normal transplanted islet function by the enhancement of islet reinnervation.

Ghrelin and insulin gene expression changes in streptozotocin-induced diabetic rats after rosiglitazone pretreatment.

The aim of the study was to evaluate the effect of rosiglitazone treatment on islet ghrelin and insulin gene expressions in streptozotocin (STZ)-induced diabetic rats. Animals were divided into four groups. 1. Intact controls. 2. Rosiglitazone-treated controls. 3. STZ-induced diabetes. 4. Rosiglitazone-treated diabetes. Rosiglitazone was given for 7 days at a dose of 20 mg/kg body weight. Ghrelin and insulin gene expressions were investigated by immunohistochemistry and in situ hybridization. There was no statistically significant difference in body weight between STZ-induced diabetic rats and rosiglitazone-treated diabetic rats during the experimental period. Furthermore, there were no significant differences in blood glucose levels and insulin immunoreactive cell numbers between STZ-induced diabetic rats and rosiglitazone-treated diabetic rats. There was a tendency towards a reduction of ghrelin gene expression in diabetic animals compared with intact controls. We found, in addition, that ghrelin immunoreactive and ghrelin mRNA expressing cells were frequent in the epithelial lining of the ducts suggesting ductal epithelium might be the source of the regenerating islet ghrelin cells, as is known for other islet cells. The results show that short-term rosiglitazone pretreatment had no significant effect on ghrelin and insulin gene expressions.

Procolipase is produced in the rat stomach--a novel source of enterostatin.

Procolipase was identified in the stomach by in situ hybridisation. A strong autoradiographic labelling of chief cells was seen in the fundus region, declining more distally and being almost absent in antrum. There was no labelling seen in the intestine. Colipase activity was estimated in rat gastric juice following pentagastrin stimulation and was found to average 2 microM. Furthermore, enterostatin, the N-terminal pentapeptide of procolipase, has been identified in the rat gut and pancreas. Extracts from gastric mucosa, intestinal mucosa and pancreas were purified by gel filtration (Sephadex G25), ion-exchange chromatography (CM-Sepharose) and HPLC (C18 reverse phase). Using an ELISA assay with antibodies directed against enterostatin, two forms of the peptide were identified both in the gut and in the pancreas, with the amino-acid sequences APGPR and VPGPR, respectively. APGPR was found to be the predominant form of enterostatin, whereas only a small amount had the structure VPGPR. Enterostatin in the form of APGPR, when injected intracerebroventricularly in female Sprague-Dawley rats, significantly reduced high-fat food intake in a two-choice situation of low-fat (14% fat by energy) and high-fat (38% fat) food. It is concluded that procolipase is produced in the stomach and secreted into the gastric juice. This is also a novel source of enterostatin.

The mouse trap.

Mouse models of asthma are now being used extensively in drug research. However, the successful unravelling of combinatorial interplays of cells and molecules in the murine airways may not be matched by equally successful demonstrations of an asthma-like pathophysiology. Here, Carl Persson, Jonas Erjefält, Magnus Korsgren and Frank Sundler discuss the fact that major features of asthma may still need to be demonstrated in the airways of allergic mice.

Dexamethasone-induced neuropeptide Y expression in rat islet endocrine cells. Rapid reversibility and partial prevention by insulin.

Neuropeptide Y (NPY) is a widely distributed neurotransmitter in the central and peripheral nervous system. In the normal rat pancreas, NPY is confined to neuronal elements, including fibers penetrating the islets. However, treatment of rats with the glucocorticoid dexamethasone (DEX) induces NPY expression also in islet cells. Previously performed double immunocytochemistry (ICC) and in situ hybridization (ISH) combined with ICC revealed that the majority of NPY-expressing islet cells are beta-cells. The present study, using ICC, ISH, and Northern blot, addressed the question whether the islet cell expression of NPY induced by DEX is affected by concomitant insulin (60 U/kg body wt daily for 12 days) treatment. Further, the time course of NPY expression in the islet cells after DEX withdrawal was examined. Treatment with DEX (2 mg/kg body wt daily for 12 days) confirmed the induction of NPY expression in numerous cells, most of which were beta-cells, dispersed within the islets. Northern blot analysis of RNA extracted from isolated islets of DEX-treated rats revealed a strong signal for NPY. Furthermore, DEX also induced NPY expression in isolated rat islets during a 5-day culture period in DEX (100 nmol/l). In vivo, the DEX-induced islet cell expression of NPY mRNA was rapidly reversed after cessation of DEX, being nondetectable 5 days post-treatment; NPY peptide was nondetectable 10 days post-treatment, indicating a slower turnover of the formed peptide. After combined treatment with DEX and insulin, the frequency of islet cells expressing NPY was markedly lower than after treatment with DEX alone. The vast majority of the NPY-expressing cells were beta-cells. In conclusion, DEX-induced NPY expression in rat islet cells is dependent on continuous DEX treatment and is partly prevented by exogenous insulin. The results suggest that the DEX-induced islet NPY expression is regulated by insulin.

Reinnervation of syngeneic mouse pancreatic islets transplanted into renal subcapsular space.

A syngeneic transplantation of 150 islets into the subcapsular renal space was performed on normoglycemic or alloxan-induced diabetic male C57BL/6 mice. Six, 8, 14, or 20-21 wk after transplantation, the graft-bearing kidney was removed and processed for microscopical examinations with indirect immunofluorescence for neuropeptides and tyrosine hydroxylase, and with acetylcholinesterase staining to visualize nerve fibers within the graft. Six weeks after implantation, only a few scattered nerve fibers were observed within the grafts. A progressive increase in the number of nerves was observed until 14 wk after transplantation, after which, a stable level was reached. Alloxan-induced diabetic mice showed quantitatively and qualitatively similar reinnervation to normoglycemic mice 20 wk after transplantation. The findings demonstrate the presence of sympathetic nerve fibers (containing tyrosine hydroxylase and neuropeptide Y), mainly accompanying ingrowing blood vessels; parasympathetic nerve fibers (containing acetylcholinesterase and vasoactive intestinal peptide), possibly reaching the graft from the adjacent renal capsule; and afferent nerve fibers (containing substance P and calcitonin gene-related peptide), which were less numerous. The data suggest that transplanted islets become reinnervated by ingrowth of nerve fibers from the implantation organ and that several types of nerves are present.

Hormone-sensitive lipase, the rate-limiting enzyme in triglyceride hydrolysis, is expressed and active in beta-cells.

Triglycerides in the beta-cell may be important for stimulus-secretion coupling, through provision of a lipid-derived signal, and for pathogenetic events in NIDDM, where lipids may adversely affect beta-cell function. In adipose tissues, hormone-sensitive lipase (HSL) is rate-limiting in triglyceride hydrolysis. Here, we investigated whether this enzyme is also expressed and active in beta-cells. Northern blot analysis and reverse transcription-polymerase chain reaction demonstrated that HSL is expressed in rat islets and in the clonal beta-cell lines INS-1, RINm5F, and HIT-T15. Western blot analysis identified HSL in mouse and rat islets and the clonal beta-cells. In mouse and rat, immunocytochemistry showed a predominant occurrence of HSL in beta-cells, with a presumed cytoplasmic localization. Lipase activity in homogenates of the rodent islets and clonal beta-cells constituted 2.1 +/- 0.6% of that in adipocytes; this activity was immunoinhibited by use of antibodies to HSL. The established HSL expression and activity in beta-cells offer a mechanism whereby lipids are mobilized from intracellular stores. Because HSL in adipocytes is activated by cAMP-dependent protein kinase (PKA), PKA-regulated triglyceride hydrolysis in beta-cells may participate in the regulation of insulin secretion, possibly by providing a lipid-derived signal, e.g., long-chain acyl-CoA and diacylglycerol.

CART knock out mice have impaired insulin secretion and glucose intolerance, altered beta cell morphology and increased body weight.

CART peptides are anorexigenic and are widely expressed in the central and peripheral nervous systems, as well as in endocrine cells in the pituitary, adrenal medulla and the pancreatic islets. To study the role of CART in islet function, we used CART null mutant mice (CART KO mice) and examined insulin secretion in vivo and in vitro, and expression of islet hormones and markers of beta-cell function using immunocytochemistry. We also studied CART expression in the normal pancreas. In addition, body weight development and food intake were documented. We found that in the normal mouse pancreas, CART was expressed in numerous pancreatic nerve fibers, both in the exocrine and endocrine portion of the gland. CART was also expressed in nerve cell bodies in the ganglia. Double immunostaining revealed expression in parasympathetic (vasoactive intestinal polypeptide (VIP)-containing) and in fewer sensory fibers (calcitonin gene-related peptide (CGRP)-containing). Although the expression of islet hormones appeared normal, CART KO islets displayed age dependent reduction of pancreatic duodenal homeobox 1 (PDX-1) and glucose transporter-2 (GLUT-2) immunoreactivity, indicating beta-cell dysfunction. Consistent with this, CART KO mice displayed impaired glucose-stimulated insulin secretion both in vivo after an intravenous glucose challenge and in vitro following incubation of isolated islets in the presence of glucose. The impaired insulin secretion in vivo was associated with impaired glucose elimination, and was apparent already in young mice with no difference in body weight. In addition, CART KO mice displayed increased body weight at the age of 40 weeks, without any difference in food intake. We conclude that CART is required for maintaining normal islet function in mice.

Localization of ornithine decarboxylase in mutant CHO cells that overproduce the enzyme. Differences between the intracellular distribution of monospecific ornithine decarboxylase antibodies and radiolabeled alpha-difluoromethylornithine.

The intracellular localization of ornithine decarboxylase (ODC), a key enzyme in polyamine synthesis and cell growth, is a matter of present debate. Using two independent methods of analysis, we have attempted to determine the actual distribution of ODC in a mammalian cell. To overcome the problem of a normally very low cellular ODC content, we have used ODC overproducing mutant CHO cells. These mutant cells exhibit a 10-fold higher ODC activity than do the wild type cells. The localization of ODC protein in exponentially growing cells, was determined by indirect immunofluorescence microscopy (permeabilized whole-cell preparations and 1 micron sections), using a monospecific ODC antibody. The intracellular localization of catalytically active ODC was determined by light and electron microscope autoradiography following pulselabeling of cells with alpha-difluoromethyl(5-3H)ornithine (3H-DFMO) at the time of peak ODC activity. alpha-Difluoromethylornithine (DFMO) is an enzyme-activated irreversible inhibitor of ODC and binds covalently to the active enzyme. The specificity of this reaction in the cell was ascertained by immunoprecipitation of 3H-DFMO-labeled ODC. ODC (as determined by both methods) was present in all the cells of a serum-stimulated monolayer culture. The highest concentration of ODC protein and of catalytically active ODC was observed in the smallest and most rapidly proliferating cells. Polyploid and multinuclear cells always exhibited the lowest concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence and influence of cholinergic nerves in the mouse thyroid.

The presence and influence of cholinergic nerves in the mouse thyroid was studied by histochemistry and measurements of changes in blood radioiodine (BRI) levels. Numerous nerve fibers displaying specific acetyl choline esterase activity were found, not only as a dense network around vessesl but also as single fibers running around and between thyroid follicles. In stress-adapted normal mice, injection of carbamyl choline (CCh) reduced the BRI levels. In mice whose TSH secretion was suppressed by L-T4, neither CCh nor atropine had any measurable influence on the BRI levels when given alone. However, CCh pretreatment reduced and atropine pretreatment enhanced the TSH-induced BRI increase in such animals. It is concluded that the murine thyroid contains numerous cholinergic nerves that may influence not only thyroid blood flow but also thyroid hormone secretion directly. This direct influence appears to be an inhibitory one, mediated via muscarinic receptors in the follicle cells.

Sympathetic innervation of the thyroid: variation with species and with age.

Fluorescence histochemistry was used to study the sympathetic innervation of the thyroids from adult individuals of six different species; mouse, rat, hamster, dog, sheep, and pig. In addition, thyroids from very young rats and from very old mice were examined. Generally, thyroidal sympathetic, adrenergic nerve terminals were found not only as a network around vessels, but also as single terminals between, and sometimes around, follicles. Interfollicular terminals were numerous in thethyroids of adult mice, sheep and hamsters, but they were few in the thyroids of adult rats and dogs, and even fewer in the porcine thyroid. In contrast to the findings in thyroids from adult mice and rats, several interfollicular terminals were found in thyroids from very young rats while very few such terminals were detected in the thyroids from very old mice. The observations suggest that there is a pronounced interspecies variation in the number of thyroidal interfollicular sympathetic nerve terminals and that, at least in the rat and the mouse, there is also a variation with age. Since, in mice, sympathetic activation appears to induce thyroid hormone secretion by a direct action of norepinephrine released from intrathyroidal sympathetic fibers, the recorded variations are presumed to have functional importance.

Beta2-adrenergic stimulation of thyroid hormone secretion.

The influence on thyroid hormone secretion of the nonselective beta-adrenergic stimulant isoproterenol (IPNE), of a selective beta1-adrenergic stimulant, 1-isopropylamino-3-(2-thiazoloxy)-2-propanol (ITP), and of a selective beta2-adrenergic stimulant, terbutaline, was investigated in mice. A combination of light microscopy (colloid droplet formation) and bioassay (blood radioiodine--BRI--measurements) was used. IPNE and terbutaline induced formation of colloid droplets and increased BRI levels, whereas ITP was ineffective. The responses to IPNE and terbutaline were abolished or reduced by pretreatment with L-propranolol, but were not inhibited for pretreatment with D-propranolol or phentolamine. The results indicate that secretion of thyroid hormone can be induced through the mediation of beta2-adrenergic receptors.

Calcitonin gene-related peptide: occurrence in pancreatic islets in the mouse and the rat and inhibition of insulin secretion in the mouse.

The intrapancreatic cellular distribution and effects on basal and stimulated insulin secretion of the 37-amino-acid polypeptide, calcitonin gene-related peptide (CGRP), were investigated in the mouse. The cellular localization of CGRP was also studied in the rat pancreas. In both species, CGRP was demonstrated in pancreatic islet cells and nerve fibers. Immunocytochemical double staining experiments revealed the CGRP-immunoreactive cells in the mouse to be identical with a majority population of the insulin cells. In the rat, on the other hand, CGRP-immunoreactive cells were identical with somatostatin cells. CGRP-immunoreactive nerve fibers were observed, in both species, running in the exocrine parenchyma, particularly around blood vessels, and they were occasionally seen also within the islets. In in vivo experiments, CGRP was found to inhibit both basal and stimulated insulin secretion in the mouse. Thus, 6 min after the iv injection of CGRP (0.85 nmol/kg), plasma insulin levels were 13 +/- 2 (SE) microU/ml compared to 30 +/- 4 microU/ml in controls (P less than 0.01). At this dose level, CGRP inhibited the insulin secretory response to carbachol, leaving that to glucose unaffected. However, at a higher dose level (4.25 nmol/kg), CGRP inhibited glucose-induced insulin secretion as well. We conclude that CGRP occurs in islet cells and in intrapancreatic nerve fibers of both the mouse and the rat, and inhibits both basal and stimulated insulin secretion in vivo in the mouse.

Neurokinin A and galanin in the thyroid gland: neuronal localization.

The distribution of neurokinin A (NKA) and galanin (GAL) in the thyroid gland of several species was examined with immunocytochemistry. NKA-immunoreactive fibers were observed around blood vessels and follicles in all species examined, whereas GAL-immunoreactive fibers were found in mice and rats only. NKA-containing fibers were more numerous than GAL-containing fibers. All thyroid NKA-containing fibers harbored substance P (SP), and the majority of them stored calcitonin gene-related peptide (CGRP) as well. Most thyroid GAL-immunoreactive fibers contained NKA, SP, and CGRP; in a minor population GAL coexisted instead with vasoactive intestinal peptide. Cervical vagotomy (extirpation of the nodose ganglion) reduced the number of NKA- and GAL-containing fibers in the thyroid by approximately 50%. The jugular ganglion and cervical dorsal root ganglia are fairly rich in GAL-, NKA/SP-, and CGRP-containing cell bodies, which presumably represent the source of GAL-, NKA/SP-, and CGRP-containing fibers in the thyroid. The thyroid ganglion is rich in vasoactive intestinal peptide nerve cell bodies, which presumably project to the thyroid gland; a minor proportion of these cell bodies was found to contain GAL as well. Although the distribution of NKA and GAL fibers in the thyroid suggests that the two peptides are involved in the regulation of local blood flow and follicular cell activity, neither NKA nor GAL had any influence on thyroid hormone release as tested in conscious mice.

Neuropeptide Y in the thyroid gland: neuronal localization and enhancement of stimulated thyroid hormone secretion.

Nerve fibers displaying neuropeptide Y (NPY) immunoreactivity occurred around blood vessels and follicles in the thyroid gland of several mammals, including man. Removal of the superior cervical ganglia or chemical sympathectomy (6-hydroxydopamine treatment) markedly reduced the number of NPY-containing nerve fibers in the thyroid and eliminated norepinephrine-containing fibers. NPY-immunoreactive nerve cell bodies were numerous in the superior cervical ganglia of mouse, rat, and guinea pig. Not unexpectedly, therefore, immunocytochemistry involving sequential staining with antibodies against dopamine-beta-hydroxylase (an enzyme marker for adrenergic neurons) and NPY revealed that most of the NPY fibers were adrenergic. As tested in mice in vivo, NPY did not affect basal or norepinephrine-stimulated thyroid hormone secretion, but enhanced isoprenaline-, TSH-, and vasoactive intestinal polypeptide-induced iodothyronine release. These findings suggest a modulatory role for NPY in the control of thyroid hormone secretion.

Immunocytochemical studies of the peptidergic innervation of the thyroid gland in the Brattleboro rat.

An indirect immunofluorescence technique was used to study the peptidergic innervation of the thyroid gland in homozygous Brattleboro rats (DI) and normal Long-Evans rats (LE). The primary goal of this study was to determine whether the previously demonstrated decrease in thyroid responsiveness to TSH in DI might be due to an abnormality in the innervation of the thyroid. Thyroids from both types of rats were found to contain nerve fibers containing immunoreactivity for vasoactive intestinal peptide (VIP), substance P (SP), neuropeptide Y (NPY), and peptide HI (PHI). All four types of fibers were found in close association with both follicle cells and blood vessels. Well developed networks of fibers surrounding blood vessels were particularly apparent in the case of NPY. The density of fibers associated with follicle cells in DI was at least as great as that in LE in regard to SP, NPY, and PHI. Fibers containing VIP were found in greater abundance in DI than in LE. Additional studies revealed no evidence of thyroid fibers containing either somatostatin or neurophysin, which was used as a marker for vasopressin. We conclude that the reduced responsiveness of the thyroid in DI is not due to an inadequate supply of any of the neuropeptides included in this study. Since VIP is known to enhance thyroid secretion, we suggest that the apparent proliferation of VIP-containing fibers in DI may be a reflection of a neural mechanism attempting to compensate for a thyroid gland deficiency analogous to the humoral mechanism by which TSH secretion increases in response to thyroid deficiency.