Single-cell and spatial transcriptomics identify a macrophage population associated with skeletal muscle fibrosis

Macrophages are essential for skeletal muscle homeostasis, but how their dysregulation contributes to the development of fibrosis in muscle disease remains unclear. Here, we used single-cell transcriptomics to determine the molecular attributes of dystrophic and healthy muscle macrophages. We identified six clusters and unexpectedly found that none corresponded to traditional definitions of M1 or M2 macrophages. Rather, the predominant macrophage signature in dystrophic muscle was characterized by high expression of fibrotic factors, galectin-3 (gal-3) and osteopontin (Spp1). Spatial transcriptomics, computational inferences of intercellular communication, and in vitro assays indicated that macrophage-derived Spp1 regulates stromal progenitor differentiation. Gal-3+ macrophages were chronically activated in dystrophic muscle, and adoptive transfer assays showed that the gal-3+ phenotype was the dominant molecular program induced within the dystrophic milieu. Gal-3+ macrophages were also elevated in multiple human myopathies. These studies advance our understanding of macrophages in muscular dystrophy by defining their transcriptional programs and reveal Spp1 as a major regulator of macrophage and stromal progenitor interactions.

Single-cell and spatial transcriptomics identify a macrophage population associated with skeletal muscle fibrosis

The monocytic/macrophage system is essential for skeletal muscle homeostasis, but its dysregulation contributes to the pathogenesis of muscle degenerative disorders. Despite our increasing knowledge of the role of macrophages in degenerative disease, it still remains unclear how macrophages contribute to muscle fibrosis. Here, we used single-cell transcriptomics to determine the molecular attributes of dystrophic and healthy muscle macrophages. We identified six novel clusters. Unexpectedly, none corresponded to traditional definitions of M1 or M2 macrophage activation. Rather, the predominant macrophage signature in dystrophic muscle was characterized by high expression of fibrotic factors, galectin-3 and spp1. Spatial transcriptomics and computational inferences of intercellular communication indicated that spp1 regulates stromal progenitor and macrophage interactions during muscular dystrophy. Galectin-3 + macrophages were chronically activated in dystrophic muscle and adoptive transfer assays showed that the galectin-3 + phenotype was the dominant molecular program induced within the dystrophic milieu. Histological examination of human muscle biopsies revealed that galectin-3 + macrophages were also elevated in multiple myopathies. These studies advance our understanding of macrophages in muscular dystrophy by defining the transcriptional programs induced in muscle macrophages, and reveal spp1 as a major regulator of macrophage and stromal progenitor interactions.

Effect of biomaterials hydrophobicity and roughness on biofilm development

Most hospitalized patients are carriers of biomedical devices. Infections associated with these devices cause great morbidity and mortality, especially in patients in intensive care units. Numerous strategies have been designed to prevent biofilm development on biodevices. However, biofilm formation is a complex process not fully clarified. In the current study, roughness and hydrophobicity of different biomaterials was analyzed to assess their influences on the biofilm formation of four leading etiological causes of healthcare-associated infections, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis and Candida albicans, using a CDC biofilm reactor. Hydrophobic materials allowed the formation of more abundant and profuse biofilms. Roughness had effect on biofilm formation, but its influence was not significant when material hydrophobicity was considered.

Damping in yttrium iron garnet nanoscale films capped by platinum

Strong damping enhancement in nm-thick yttrium iron garnet (YIG) films due to Pt capping layers was observed. This damping is substantially larger than the expected damping due to conventional spin pumping, is accompanied by a shift in the ferromagnetic resonance field, and can be suppressed by the use of a Cu spacer in between the YIG and Pt films. The data indicate that such damping may originate from the ferromagnetic ordering in Pt atomic layers near the YIG/Pt interface and the dynamic exchange coupling between the ordered Pt spins and the spins in the YIG film.

Contribution of ion binding affinity to ion selectivity and permeation in KcsA, a model potassium channel

Ion permeation and selectivity, key features in ion channel function, are believed to arise from a complex ensemble of energetic and kinetic variables. Here we evaluate the contribution of pore cation binding to ion permeation and selectivity features of KcsA, a model potassium channel. For this, we used E71A and M96V KcsA mutants in which the equilibrium between conductive and nonconductive conformations of the channel is differently shifted. E71A KcsA is a noninactivating channel mutant. Binding of K(+) to this mutant reveals a single set of low-affinity K(+) binding sites, similar to that seen in the binding of K(+) to wild-type KcsA that produces a conductive, low-affinity complex. This seems consistent with the observed K(+) permeation in E71A. Nonetheless, the E71A mutant retains K(+) selectivity, which cannot be explained on the basis of just its low affinity for this ion. At variance, M96V KcsA is a rapidly inactivating mutant that has lost selectivity for K(+) and also conducts Na(+). Here, low-affinity binding and high-affinity binding of both cations are detected, seemingly in agreement with both being permeating species in this mutant channel. In conclusion, binding of the ion to the channel protein seemingly explains certain gating, ion selectivity, and permeation properties. Ion binding stabilizes greatly the channel and, depending upon ion type and concentration, leads to different conformations and ion binding affinities. High-affinity states guarantee binding of specific ions and mediate ion selectivity but are nonconductive. Conversely, low-affinity states would not discriminate well among different ions but allow permeation to occur.

Spin pumping at the magnetic insulator (YIG)/normal metal (Au) interfaces

Spin injection across the ferrimagnetic insulator (YIG)/normal metal (Au) interface was studied by ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping in bare YIG films with those covered by a Au/Fe/Au structure. The Fe layer in Au/Fe/Au acted as a spin sink as displayed by an increased Gilbert damping parameter α compared to that in the bare YIG. In particular, for the 9.0  nm  YIG/2.0 nm Au/4.3 nm Fe/6.1 nm Au structure, the YIG and Fe films were coupled by an interlayer exchange coupling, and the exchange coupled YIG exhibited an increased Gilbert damping compared to the bare YIG. This relationship between static and dynamic coupling provides direct evidence for spin pumping. The transfer of spin momentum across the YIG interface is surprisingly efficient with the spin mixing conductance g(↑↓) ≃ 1.2 × 10(14) cm(-2).

[T-L mucosa to mucosa pancreatojejunal anastomosis for pancreatic reconstruction following a duodenopancreatectomy]

INTRODUCTION

The pancreatojejunal anastomosis is considered the weak spot when carrying out a duodenopancreatectomy, because it causes most of the complications following a Whipple surgery. Here we present a series of cases using a single technique for performing this anastomosis.

MATERIAL AND METHODS

During the period between October 2002 and August 2005, 49 duodenopancreatectomies were performed at the 3AII Department of the National Hospital Edgardo Rebagliati Martins - H.N.E.R.M., in 31 of these cases a lateral mucosa to mucosa pancreatojejunal anastomosis was carried out by the same surgeon.

RESULTS

The most frequent complication was infection of the operating wound followed by pancreatic fistula and intra-abdominal hemorrhage and the overall morbidity was 29%. Pancreatic fistula developed in 13% of the cases; however, no patient required additional treatment and the fistula closed maximum twenty days after the surgery. On average, patients resumed oral food intake after 6 days and remained hospitalized for 16 days. Mortality was 3%, because a patient developed a pseudo-aneurism of the hepatic artery, which ruptured 17 days after the operation.

CONCLUSIONS

The mucosa to mucosa pancreatojejunal anastomosis is a safe technique with a low index of pancreatic fistula and mortality.

A survey for helminth parasites in feral New World non-human primate populations and its comparison with parasitological data from man in the region

A survey for helminth parasites in feral New World non-human primates was conducted and compared with parasitological data from man in the region. A total of 835 fecal samples were collected from feral Aotus nancymae, A. vociferans, Saguinus labiatus, S. mystax, Saimiri boliviensis peruviensis, S. sciureus macrodon, Lagothrix lagotricha and Cacajao calvus rubicundus. In addition, adult parasites were collected from necropsies performed on monkeys that died during quarantine and in captivity. Helminth parasites shared by non-human primates and man in Peru were Ancylostoma braziliensis and Ascaris lumbricoides, found in a captive L. lagotricha; Necator americanus, found in a captive C. calvus rubicundus; Hymenolepis diminuta, found in feral Aotus spp. and S. mystax; and a single Trichuris spp. specimen found in a feral S. sciureus macrodon.

Spontaneous terminal ileitis resembling Crohn disease in captive tamarins

Five tamarins (four Saguinus mystax and one S. labiatus) died with wasting syndrome characterized by chronic diarrhea at the Center for Reproduction and Conservation of Non-Human Primates in Iquitos, Peru. At necropsy, the terminal ileum of all affected tamarins was found to be markedly thickened. Histologically, the terminal ileal mucosa was completely ulcerated, and effaced by debris and mononuclear inflammatory cells. The submucosa and serosa were thickened by fibroplasia, mononuclear cell infiltrates and variable edema. No infectious agent was observed. The lesions were similar to those described previously for Crohn disease. This is to our knowledge the first report of terminal ileitis resembling Crohn disease in non-human primates.

Expression analysis of the thyrotropin-releasing hormone receptor (TRHR) in the immune system using agonist anti-TRHR monoclonal antibodies

Monoclonal anti-rat thyrotropin-releasing hormone (TRH) receptor (TRHR)-specific antibodies (mAb) were generated by immunization with synthetic peptides of rat TRHR partial amino acid sequences; one (TRHR01) was directed against a sequence (84-98) in the extracellular portion of the rat TRHR reported to be constant among different species, including man, and the second (TRHR02) recognizes the C-terminal region sequence 399-412. In lysates from GH4C1 cells, a clonal rat pituitary cell line, both mAb recognize the TRHR in Western blot analysis, and TRHR02 immunoprecipitates the TRHR. Incubation of GH4C1 cells with the mAb causes a fluorescence shift in fluorescence-activated cell sorting analysis. The cells were stained specifically by both mAb using immunocytochemical techniques. Furthermore, TRHR01 is agonistic in its ability to trigger Ca2+ flux, and desensitizes the TRH receptor. We tested for TRHR in several rat organs and found expression in lymphoid tissues. TRHR01 recognizes the human TRHR, and analysis of human peripheral blood lymphocyte and tonsil-derived leukocyte populations showed receptor expression in non-activated and phytohemagglutinin-activated T and B cells.

[Acute pancreatitis and acquired immunodeficiency syndrome]

Viral acute pancreatitis in Human Immunodeficiency Virus (HIV) infected patients has been occasionally described. We studied nine patients with HIV antibodies and acute pancreatitis attributed to Cytomegalovirus and/or Cryptosporidium infection. In four patients the clinical picture was consistent with acute pancreatitis while in five clinical manifestations were unspecific, and diagnosis was based on ultrasonography and/or computed tomography findings. In the HIV infected patient pancreatic evaluation by imaging techniques may disclose acute pancreatitis even in the absence of abdominal pain.

Autolytic effect of the antibiotic produced by Myxococcus coralloides D

Myxococcus coralloides D secretes an antibiotic, named corallolysin, when grown on a rich medium. When a critical concentration is reached, this antibiotic lyses the producer bacterium either during vegetative growth or during morphogenesis. Corallolysin has not effect on resting cells nor on myxospores. The autolytic effect is caused by the early inhibition of RNA synthesis.

Primary renal hemangiosarcoma in a moustached tamarin

A wild-caught adult female Saguinus mystax died after 54 months in captivity. At necropsy, a small reddish zone in the renal cortex of one kidney was shown histologically to be a hemangiosarcoma.

Divergence between biochemical and cytogenetic differences in three species of the Callicebus moloch group

Specimens from three species of the Callicebus moloch group--C. moloch (N = 80), C. brunneus (N = 166), and C. cupreus (N = 23)--were studied. Twenty genetic loci were investigated through electrophoresis, genetic distances were estimated, and the results compared with the available cytogenetic data. Low values of genetic distance were encountered, contrasting with relatively large chromosome differences. We propose that recent karyotypic rearrangements, rather than other Pleistocene events, were the major evolutionary mechanisms determining speciation in these three taxa.

Spontaneous cardiomyopathy resembling acute rheumatic heart disease in an owl monkey

A wild-caught male Aotus vociferans died spontaneously during quarantine. Histologic examination of the heart showed several small myocardial arteries replaced with fibrinoid necrosis and adjacent inflammation that included lymphocytes and large histiocytic cells. Less often, similar inflammatory foci were observed in the myocardium interstitium. The lesions observed in the heart of the owl monkey resembled Aschoff bodies.

Pasteurella haemolytica infection in a Goeldie's monkey

An adult male Callimico goeldii died spontaneously. At necropsy, small whitish foci were found randomly distributed on the liver surface. Histologically, the foci were composed of mixed inflammatory cells with predominant polymorphonuclear cell infiltration and central areas of necrosis. Microbiological cultures revealed a Gram-negative coccoid-bacilli with bipolar staining. Biochemical analysis revealed that the microorganism was Pasteurella haemolytica.

Spontaneous cardiomyopathy and nephropathy in the owl monkey (Aotus sp.) in captivity

Clinical and pathologic data were reviewed for 72 owl monkeys that died between January 1987 and May 1990 at the Center for Reproduction and Conservation of Nonhuman Primates in Iquitos, Peru. Tissue samples from 39 animals were examined. Hypertrophic cardiac disease (51% of animals examined), dilative cardiomyopathy (26%), and nephropathy (87%) were the most common diagnoses. The incidence of all three diseases appeared to increase with time in captivity. Nephropathy was less severe in colony-born animals.

Spontaneous seminoma in an owl monkey in captivity

An adult male Aotus nancymae maintained for breeding purposes was submitted for surgery and the left testicle was removed. The surgically removed mass was about two to three times the size of a normal adult owl monkey testicle. Grossly, on cut surface, the mass was soft, white to pale gray, and bulged above the adjacent tissue. Microscopically, the morphology of the tumor cells was consistent with a seminoma.

Mortality causes of the moustached tamarin (Saguinus mystax) in captivity

From January 1987 to November 1990, 125 adult Saguinus mystax died at the CRCP. Enteritis/colitis (26%), hypoglycemia/cachexia (19%), and parasitic enteritis (13%) were the most common causes of death. Less common were purulent peritonitis (9%), lobular pneumonia (8%), and hemorrhagic gastroenterocolitis (6%). These results confirm the high frequency of gastroenteric lesions reported in Callitrichidae in captivity.

Sensitivity of thyrotropin secretion to TSH-releasing hormone in food-restricted rats

The aim of the present study was to identify the mechanisms involved in the reduction of TSH secretion during prolonged food restriction. The basal TSH secretion rate, the TSH secreted in response to TRH, both in vivo and in vitro, and the TSH, nuclear T3, and plasma membrane TRH binding sites in the pituitary were determined in rats receiving 75% (FR75), 50% (FR50) and 25% (FR25) of the food consumed by the ad libitum fed rats (controls). The basal TSH secretion rate (microgram.h-1.(100 g)-1) in FR75, FR50 and FR25 groups were decreased by 19, 42 and 74% of control values, respectively, whereas the TSH secreted in response to TRH in vivo and in vitro was reduced by 21 and 13% in FR50, and 55 and 44% in FR25, respectively, of the corresponding control values. Food restriction increased the TRH binding sites from 229 in controls to 322, 479 and 521 (fmol/mg protein), in FR75, FR50 and FR25 groups, respectively, whereas the opposite was seen in nuclear T3(controls 862, FR75 841, FR50 342 FR25 233 fmol/mg DNA). Moreover, a decrease in the pituitary TSH concentration was observed in FR50 and FR25 rats. The data suggest that an alteration in the amount of TRH reaching the pituitary gland is probably the main responsible for the low plasma TSH values during food restriction. However, an inhibitory effect at the pituitary level cannot be ruled out.

Effect of phosphate on antibiotic and extracellular protein production by Myxococcus coralloides D

The effect of inorganic phosphate concentrations on antibiotic and extracellular protein production by Myxococcus coralloides D have been examined. Antibiotic production by growing cells of this myxobacterium was maximal at phosphate concentrations of 10-20 mM, but was inhibited by concentrations higher than 20 mM. The total extracellular protein and the extracellular protein per cell ratio were independent of phosphate levels in the culture broth.

Production of acid and alkaline phosphatases by Myxococcus coralloides

Acid and alkaline phosphatase of Myxococcus coralloides were examined during vegetative growth in a liquid medium. Two extracellular phosphatases and two cell-bound phosphatases, acid and alkaline in both cases, were produced. The phosphatase production was unaltered by the presence of high concentrations of inorganic phosphate. Both enzymes were produced constitutively. These two hydrolases were released into the growth medium during the exponential growth phase (approximately 10% of total activity). The production of these enzymes was modified by the presence of organic acids and metal ions in the medium.

Mechanism of action of somatostatin

The chain of events leading to the manifestation of the biological action of somatostatin are described. Internalization is mediated by cytoskeletal proteins in the presence of calmodulin. Transduction of the somatostatin message at the membrane level takes place through inhibition of cyclic AMP accumulation and blockade of cytosol calcium increases. The influence of central and peripheral factors upon these processes is discussed and the importance of the Ni/Ns components is stressed. Thus, somatostatin also suppresses phosphoinositide turnover and stimulates soluble phosphodiesterase, thus reinforcing its negative effect on cyclase generation.

The effect of dopaminergic blockade on thyrotrophin response to thyrotrophin-releasing hormone and somatostatin

Using a large number of animals we have been able to demonstrate that somatostatin administration (20 micrograms/100 g bw) significantly reduces both basal serum thyrotrophin (TSH) levels and the response to thyrotrophin-releasing hormone (TRH) in the normal rat. Pretreatment with the dopaminergic antagonist domperidone resulted in increased TSH levels, increased response to TRH but no modification in the response to somatostatin.

Inhibitory regulation of adenylyl cyclases. Evidence inconsistent with beta gamma-complexes of Gi proteins mediating hormonal effects by interfering with activation of Gs

The possible effect of cholera toxin (CTX) on hormonal inhibition of adenylyl cyclase in somatostatin (SST)-sensitive GH3 cells was quantitatively evaluated. The toxin treatment employed led to an essentially complete ADP ribosylation of all alpha s subunits of the stimulatory regulatory component (Gs) of the system and to ca. 5- to 7-fold increases in the activity measured, yet it failed to affect the inhibitory action of SST regardless of whether analyzed in terms of degree of inhibition (ca. 60%) that is attainable or in terms of the apparent Kact with which the inhibitory hormone elicits its action. In absolute terms the activity inhibited after CTX was ca. 6 times larger than that inhibited under control conditions, indicating that SST is equally effective in regulating control and CTX-stimulated adenylyl cyclase system and that interpretations are independent of possible intramembraneous compartmentalizations of adenylyl cyclase and its various regulatory components. Since CTX-mediated ADP ribosylation of the alpha-subunits of Gs has been demonstrated to result in an at least 10-fold decrease in the potency (i.e. EC50) with which the beta gamma-complexes of G proteins act to stabilize preactivated purified alpha-subunits of Gs and in an approximately 300-fold decrease in the potency with which exogenously added beta gamma-complexes act to prevent activation of Gs in intact membranes, the present data indicate that beta gamma-complexes cannot be mediating the inhibitory effects of hormones by interfering with activation of the Gs of adenylyl cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of the hypothalamus-pituitary-thyroid axis in streptozotocin-diabetic rats during adaptation to a low iodine diet

Newer methods of radiation therapy for treating oligodendroglioma after surgical resection have produced promising results using high doses of radiation, However, these doses are close to those that cause necrosis of normal brain, making the accurate spatial localization of tissue at risk for containing tumor cells more important. Because MR imaging is superior to CT in detecting some types of intracranial disease, nine patients with oligodendroglioma were studied with both MR and CT, Results were compared with surgical findings. In six cases, MR identified some tumor volume found during surgery that was not detected by CT. In addition, the interface between abnormality (tumor plus edema) and normality was depicted much more clearly by MR than by CT in most cases. Such superior depiction of the margins of abnormality is important for radiation therapy planning because of the known tendency of oligodendroglioma to infiltrate adjacent edema, making all areas of abnormality potential tumor-bearing tissue. Finally, MR showed normal brain tissue in areas considered suspicious by CT, because they were not well seen on CT in several patients. In these cases of low-grade oligodendroglioma, MR was believed to be superior to CT in providing information needed for radiation therapy planning because of its ability to distinguish tumor and adjacent edema (considered tissue at risk for containing microscopic tumor) from contiguous normal brain.

Characterization and partial purification of a broad spectrum antibiotic AS-48 produced by Streptococcus faecalis

Streptococcus faecalis S-48 produces a broad spectrum antibiotic, active against Gram-positive and Gram-negative bacteria. This substance is produced in solid and liquid media and also in a defined basal medium. It is sensitive to protease, pronase, or trypsin, heating at 70 degrees C, and alkaline pH, but resistant to treatment with lipase, lysozyme, alkaline phosphatase, DNAase, RNAase, acidic or neutral pHs, and also lower temperatures (60 degrees C). Several organic solvents cause precipitation, but not inactivation. This antibiotic has been partially purified by gel filtration and further ion-exchange chromatography. Its molecular weight has been estimated close to 2000. The biological activity of this antagonistic substance against the selected indicator strains, Streptococcus faecalis S-47 and Escherichia coli U-9, is bactericidal. The characterization of this substance, initially classified as a bacteriocin, indicates that it is an antibiotic of peptidic nature. The significance of antibiotic occurrence in group D of the genus Streptococcus is also discussed.

Time-dependent effects of oral thyrotropin-releasing hormone in hyperthyroid female rats

We have studied the thyrotropin (TSH) and thyroid hormone (T3) response to acute thyrotropin-releasing hormone (TRH) administration in rats previously rendered hyperthyroid by daily ip injection of 25 micrograms L-T4/100 g bw for 30 days. Animals were thereafter put on distilled water or TRH (2 mg/10 ml) as drinking solution for another 18 days, continuing T4 administration. On days 3 and 10 on oral TRH, the serum TSH and T3 response to TRH was studied by administering 2 micrograms of the tripeptide iv. After 3 days, neither the animals on oral DW, nor those on oral TRH showed any response. Nevertheless, after 10 days, animals on oral TRH had a measurable, significant thyrotropin response. At sacrifice (18 days), animals on oral TRH had increased pituitary TSH content. These results confirm and extend a recent report from our laboratory (Iglesias, Llobera and Montoya 1985). We conclude that TRH-mediated thyrotropin accumulation in pituitary is the primary cause for the presence of this response.

Long-term effects of TRH administration on food intake and body weight in the rat

The effect of long-term TRH administration through drinking water (0.2 mg/ml) on food and water intake and body weight has been studied in three groups of female rats: (1) thyroidectomized, (2) thyroidectomized receiving daily 250 micrograms/kg of L-T4, (3) sham-operated. Treatment with oral TRH for 30 days decreased body weight and increased food intake in sham-operated rats. No TRH effects on body weight or food consumption were observed in either of the other groups of thyroidectomized rats. TRH administration increased circulating T3 levels in sham-operated animals, but had no effects in either hypo- or hyperthyroid, thyroidectomized rats. It can be concluded that the TRH-induced increase on food intake is mediated through the pituitary-thyroid axis.

Postnatal development of brain TRH, serum TSH and thyroid hormones in the male and female rat

The postnatal development of immunoreactive TRH in the central nervous system (CNS), serum TSH and thyroid hormones was studied in both male and female normal rats. While in most structures of the CNS, TRH increased until day 20-30, serum TSH values peaked at day 15 as did T4. Significant differences were also obtained between both sexes in these parameters. These data further support the fact that pituitary-thyroid axis maturation is independent of brain TRH.

In vivo effects of gamma-aminobutyric acid and beta-alanine on thyrotrophin secretion in the normal and hypothyroid rat

The effect of pharmacological doses of two amino acids neurotransmitters, gamma-aminobutyric acid (GABA) and beta-alanine (beta-Ala), on thyrotrophin (TSH) secretion was studied in normal and hypothyroid (PTU-treated) male rats. Inhibition of TSH secretion was observed in normal rats treated with the drugs, 30 min after their administration. Hypothyroid animals responded only to GABA administration, decreasing their serum TSH at 30 min. Response to thyrotrophin-releasing hormone (TRH) after 15 min of drug administration was blunted in GABA injected animals, as compared to saline-injected controls. When TRH was injected at the same time as GABA and beta-Ala, the response was significantly lower than in controls. It is suggested that beta-Ala and GABA act at the pituitary by impairing the TSH response to TRH. The possibility that beta-Ala actions may be due to decreased GABA catabolism is considered, since beta-Ala administration increased GABA synaptosomal levels.

Sequential changes in the pituitary thyroid axis after chronic TRH administration: effects on euthyroid and thyroxine treated female rats

The effect of chronic oral thyrotrophin-releasing hormone (TRH) administration on thyrotrophin (TSH), L-triiodothyronine (T3) and L-thyroxine (T4) serum levels, pituitary TSH concentration and serum response to acute TRH injection, has been studied in female rats under different thyroidal conditions: sham-operated control animals, and thyroidectomized animals receiving 25 micrograms L-T4/100 g body weight/day. After 30 days, these groups were divided into two subgroups (6-10 animals per group), one receiving the aforementioned treatment and the other the same plus 2 mg TRH/10 ml distilled water (DW), as drinking water. TRH-treated sham-operated animals showed significantly reduced serum and pituitary TSH levels and increased serum T3 levels at most of the times studied (1, 6, 10, 18 and 34 days of oral TRH or DW administration), and a transient elevation in serum T4 between day 1 and 6. Thyroidectomized-L-T4-treated animals showed increased serum and pituitary TSH levels throughout the treatment and reduced T3 and T4 serum levels at the beginning, as compared to thyroidectomized-L-T4-treated animals. TSH response to iv TRH administration on the 10th day of oral TRH administration was reduced in controls chronically treated with oral TRH as compared to non-treated controls, and was increased in thyroidectomized-L-T4-treated animals on chronic TRH vs the same group on oral DW. These results suggest that chronic TRH administration can stimulate TRH synthesis in vivo, bypassing the inhibitory effects of thyroid hormones, the increased pituitary TSH reserve being responsible for the partial restoration of a response to acute TRH injection in the thyroidectomized-L-T4-treated animals.