Thirst and salt appetite in horses treated with furosemide.

When a preliminary experiment in sodium-replete ponies revealed an increase, but not a significant increase, in salt consumption after furosemide treatment, the experiment was repeated using sodium-deficient horses in which aldosterone levels might be expected to be elevated to test the hypothesis that a background of aldosterone is necessary for salt appetite. Ten Standardbred mares were injected intravenously with furosemide or an equivalent volume of 0.9% sodium chloride as a control to test the effect of furosemide on their salt appetite and blood constituents. Sodium intake and sodium loss in urine, as well as water intake and urine output, were measured and compared to determine accuracy of compensation for natriuresis and diuresis. Plasma protein and packed cell volume showed significant increases in response to furosemide treatment (F = 29.31, P less than 0.001 and F = 11.20, P less than 0.001, respectively). There were no significant changes in plasma sodium concentration or osmolality in response to the treatment (P greater than 0.05). The furosemide-treated horses consumed 126 +/- 14.8 g salt, significantly more than when they were given the control injection (94.5 +/- 9.8 g; t = 2.22, P = 0.05). In response to furosemide, horses lost 962 +/- 79.7 and consumed 2,170 +/- 5 meq sodium; however, compared with control, they lost 955 meq more sodium and ingested only 570 meq more sodium, so they were undercompensating for natriuresis. The furosemide-treated horses drank 9.6 +/- 0.8 kg of water, significantly more than when they received the control injection (6.4 +/- 0.8 kg; t = 6.9, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous immune complex orchitis in Brown Norway rats

Immune complexes occur spontaneously in the testis of Brown-Norway (BN) inbred rats between the basal lamina of the seminiferous tubules and the outer lamina of the myoid testicular cells. The deposits can be detected immunohistologically (IgG; C3) and by electron microscopy. The immune complexes appear between the 8th and 12th weeks of life, increase in amount up to the 30th week and decrease thereafter. After about the 20th week, of life, 15% of the animals show destruction of the germinal epithelium accompanied by an infiltration of lymphocytes and plasma cells. The final stage of this disease, which initially shows no signs of inflammation, is characterized by diffuse tubular atrophy. However, up to the 70th week of life, 85% of the animals with immune complexes show no pathological alterations. Antibodies eluated from the testes react with spermatocytes I and structures close to the lumen of the seminiferous tubules, but not with mature sperms. Serum antibodies to sperms occur in about 25% of the BN rats, but the presence of these antibodies shows no correlation with the immunohistological findings. This newly described spontaneous immune complex orchitis is regarded as a further example of an in-situ-induced immune complex disease. The observations made here can be compared with those in (peri-) membraneous glomerulonephritis, another example of a disorder resulting from in-situ-formation of immune deposits.     

CD8+ T cells modulate late allergic airway responses in Brown Norway rats.

To test the hypothesis that CD8+ T cells may suppress the allergen-induced late airway response (LAR) and airway eosinophilia, we examined the effect of administration of Ag-primed CD8+ T cells on allergic airway responses, bronchoalveolar lavage (BAL) leukocytes, and mRNA expression for cytokines (IL-4, IL-5, and IFN-gamma) in OVA-sensitized Brown Norway rats. On day 12 postsensitization to OVA, test rats were administered 2 million CD8+ T cells i.p. isolated from either the cervical lymph nodes (LN group; n = 8) or the spleen (Spl group; n = 6) of sensitized donors. On day 14, test rats were challenged with aerosolized OVA. Control rats were administered PBS i.p. on day 12, and challenged with OVA (n = 10) or BSA (n = 6) on day 14. The lung resistance was measured for 8 h after challenge. BAL was performed at 8 h. Cytospin slides of BAL were analyzed for major basic protein by immunostaining and for cytokine mRNA by in situ hybridization. The LAR was significantly less in the LN group (1.8 +/- 0.5 U; p < 0.01) and BSA controls (1.4 +/- 0.7; p < 0.01), but not in the Spl group (6.7 +/- 2.2), compared with that in OVA controls (8.1 +/- 1.8). In BAL, the number of major basic protein-positive cells was lower in the LN and Spl groups compared with OVA controls (p < 0.05 and p < 0.01). IL-4- and IL-5-positive cells were decreased in the LN group compared with the OVA controls (p < 0.01). INF-gamma-positive cells were increased in the LN and Spl groups compared with the OVA controls (p < 0.01). Serum OVA-specific IgE levels were unaffected by CD8+ T cell transfers. These results indicate that Ag-primed CD8+ T cells have a potent suppressive effect on LAR.     

Behavioral and electrophysiological responses to NaCl in young and old Fischer-344 rats

This study compared both behavioral and electrophysiologicalresponses to NaCl in young and old Fischer-344 rats. These comparisonswere made in the same individuals. Preference for NaCl solutionsversus water was assessed using two-bottle preference tests.The integrated response of the chorda tympani nerve to NaClwas recorded. NaCl neural-response magnitude and correspondingbehavioral sensitivity appear to decrease with age in the Fischer-344rat at concentrations > 0.15 M and neural-response magnitudesincrease at lower concentrations.     

Acute phase plasma proteins in kininogen-deficient Brown Norway rats

We examined whether Brown Norway rat plasma (BN/May Pfd f) contains alpha 1-cysteine proteinase inhibitor (alpha 1-CPI), also called major acute phase alpha 1-protein or T-kininogen. T-kininogen is a low molecular weight kininogen from which kinin can be released by trypsin but not by kallikreins. The BN plasma reacted with rabbit anti-alpha 1-CPI gamma globulins. Purified alpha 1-CPI released a kinin-like activity with trypsin and with homogenate of salivary glands, as Brown Norway rat plasma did. High concentration of added rat urine induced a small release (10%) of kinin from alpha 1-CPI. Preincubation of Brown Norway rat plasma with rabbit anti-rat alpha 1-CPI gamma-globulins nearly suppressed the kinin-forming substrate of trypsin in this plasma. These results indicated that plasma of our Brown Norway rats contains only alpha 1-CPI as kinin-forming substrate. This plasma contains low amount of alpha 2-macroglobulin, while its content in orosomucoid and haptoglobin was a little larger than that of Wistar rat plasma.     

Plasma prekallikrein deficiency in a strain of Brown Norway rats

Plasma of a strain of Brown Norway rats has a prolonged partial thromboplastine time while its Quick time is normal. With kaolin, this plasma does not form kinins. These results are the consequence of a lack of plasmatic prekallikrein-like activity.     

L-NAME differentially alters ventilatory behavior in Sprague-Dawley and Brown Norway rats.

Nitric oxide (NO) is a regulating factor in respiration. The question was whether NO synthase (NOS) blockade would affect posthypoxic ventilatory behavior similarly in two rat strains with known differences in steady-state hypoxic and hypercapnic responses and in posthypoxic ventilatory behavior. Ventilatory behavior [respiratory frequency (f) and minute ventilation (VE)] was measured by body plethysmography on unanesthetized, unrestrained adult male Sprague-Dawley (SD; n = 8) and Brown Norway rats (BN; n = 8) at baseline and 1 min after rapid transition to 100% O(2) after 5 min of isocapnic hypoxia (10% O(2)-3% CO(2)-balance N(2)). Testing was performed 30 min after intraperitoneal injection of either saline (vehicle) or 100 mg/kg of N(G)-nitro-L-arginine methyl ester (L-NAME). Resting f and VE increased after L-NAME in both strains, more markedly in SD compared with BN (77 vs. 47% for f, and 42 vs. 16% for VE, respectively; P < 0.05). With vehicle, posthypoxic f and VE decline (Dejours phenomenon) was present only in BN and was absent in SD. With L-NAME, the Dejours phenomena were still present in BN but also were apparent in SD (f: 95.3 vs. 134.4 beats/min at baseline; VE: 66.3 vs. 88.8 ml/min at baseline; P < 0.05). Thus NOS blockade results in a strain-specific alteration in resting ventilation and uncovers the Dejours phenomenon in the SD strain.     

Induction of atherosclerosis in Brown Norway rats by immunization with ovalbumin

A study was carried out to establish an animal model that would be suitable for evaluating the role of the diet in immune cell-mediated atherogenesis. Brown Norway rats were initially treated with hypervitamin D2 for 4 days and then fed on an atherogenic diet for 3 months, during which period the rats were either immunized with ovalubumin plus Al(OH)3 (OVA group) or with Al(OH)3 alone (control group) every 3 weeks. Aortic lesions were mainly composed of foam cells, the lesions evaluated by the intimal thickness of the ascending aorta being more severe in the OVA group than in the control group. The OVA group, in comparison with the control group, showed prominently increased serum levels of OVA-specific IgG and rat chymase, an indicator of mast cell degranulation. The intimal thickness was positively correlated with the level of chymase. Immunization had no effect on the serum lipid levels. These results support the hypothesis that mast cells play a role in the early stage of atherosclerosis and suggest that this animal model could be useful for evaluating the role of the diet in immune-related atherogenesis.     

Regeneration and transplantation of muscles in old rats and between young and old rats.

In order to compare the regenerative ability of skeletal muscle between young (5 month) and old (26 month) rats, sliced or intact extensor digitorum longus muscles were freely autografted into young and old rats and also reciprocally grafted from young to old inbred animals and vice versa. Sixty days after grafting, the transplants were analyzed for contractile and histochemical properties. There was a relative similarity between the contraction times of both normal control muscles and of all groups of transplants, although the contraction time tended to be prolonged and histochemical fiber pattern was more often found to be uniform in grafts of senescent animals. All groups of transplants possessed histochemically heterogeneous fiber types at 60 days. The experiments demonstrate that skeletal muscle in old rats possesses a substantial degree of regenerative ability and that the free tranpllantation of entire muscles in old animals is feasible.     

Airway remodeling in allergen-challenged Brown Norway rats: distribution of proteoglycans

Proteoglycans (PG) have important effects on the mechanical properties of tissues and the phenotype of various structural cells. Little is known about changes in PG deposition in the airways in animal models of asthma. We studied changes in PG in the airway wall of Brown Norway rats sensitized to ovalbumin (OA) and exposed to repeated OA challenge. Control (Sal) animals were sensitized and challenged with saline. After the 3rd challenge, animals were killed and lungs fixed in formalin. Tissue sections were incubated with antibodies to the small, leucine-rich PG, decorin, and biglycan and collagen type I. Airways were classified according to basement membrane perimeter length (< or =0.99, 1-2.99, and > or =3 mm). Decorin, biglycan, and collagen type I were increased in the airways of OA vs. Sal rats. Remodeling was most prominent in central airways. The distribution of PG differed with respect to the subepithelial vs. airway smooth muscle (ASM) vs. adventitial layer. Whereas biglycan was readily detected within the ASM, decorin and collagen were detected outside the ASM and especially in the adventitial layer. Differences in the distribution of these molecules within the layers of the airway wall may reflect their specific functional roles.     

Ovalbumin sensitizes vagal pulmonary C-fiber afferents in Brown Norway rats.

Sensitization of vagal lung C fibers has been postulated to contribute to the development of asthma, but support for this notion is still lacking. We investigated the characteristics and function of pulmonary C fibers (PCFs) in ovalbumin (OVA)-sensitized Brown Norway rats, an established animal model of asthma. Rats were sensitized with intraperitoneal injection of OVA or were treated with saline (control). In study 1, with the use of open-chest and artificially ventilated rats, inhalation of 5% OVA aerosol evoked an augmented increase in total lung resistance in the OVA-sensitized rats, compared with the control rats. Bilateral vagotomy or subcutaneous pretreatment with a high-dose of capsaicin for blocking of C-fiber function equally attenuated this augmented total lung resistance response, suggesting the involvement of PCFs. In study 2, with the use of anesthetized, spontaneously breathing rats, right atrial injection of capsaicin (1 microg/kg; a PCF stimulant) evoked an augmented apneic response in the OVA-sensitized rats, compared with the control rats. In study 3, with the use of open-chest, paralyzed, and artificially ventilated rats, the afferent PCF responses to right atrial injection of capsaicin (0.5 and 1.0 microg/kg), phenylbiguanide (8 microg/kg; a PCF stimulant), or adenosine (0.2 mg/kg; a PCF stimulant) were enhanced in the OVA-sensitized rats, compared with the control rats. However, the baseline activities of PCFs and their afferent responses to mechanical stimulation by lung hyperinflation in the OVA-sensitized and control rats were comparable. Our results suggested that OVA-sensitized Brown Norway rats possess sensitized vagal PCFs, which may participate in the development of the airway hyperreactivity observed in these animals.     

Fever and behavioral thermoregulation in young and old rats

At standard laboratory ambient temperatures (T(a)) of 20-24 degrees C, peripheral injections of lipopolysaccharide (LPS) reliably produce fever in young rats. In contrast, old rats may show a blunted fever, no fever, or even hypothermia after LPS. In the present study we hypothesized that old rats might use behavioral thermoregulation to help them develop a fever. Young and old rats were implanted with temperature transmitters. At least 1 wk postoperatively they were placed in a thermally graded alleyway (T(a) 10-40 degrees C). On the third and sixth day they were taken out of the gradient, placed at an T(a) of 23 degrees C, injected intraperitoneally with LPS or saline, and left at 23 degrees C for 3 h. At the end of that time, all young rats had become febrile, whereas the old rats had not. When the rats were replaced in the thermal gradient, the young animals continued to develop a fever that was similar to fever in young rats left at 23 degrees C. The old animals chose significantly warmer positions in the thermal gradient than did the young animals and only then became febrile. Although there was a tendency for the young rats to prefer higher T(a) after LPS than after saline, these differences were not significant. However, the differences in the old rats were significant. These results suggest that the LPS had increased the thermal set point in the old rats, but they could develop febrile responses only at the warm T(a) they selected.     

Neuroendocrine factors in salt appetite.

We dedicate this paper to Curt P. Richter, father of the study of salt appetite, who died recently at the age of 94. Richter first demonstrated that the adrenalectomized rat's voracious appetite for salt kept it alive (1936) and showed the same in humans (1940). Our first paper in 1955 demonstrated that salt appetite was an innate response to salt depletion. Since then, we have pursued the notion that the neuroendocrine consequences of sodium depletion create a brain state that raises salt appetite. In Epstein's laboratory, it was shown that angiotensin and aldosterone, the hormones of salt retention in the periphery, act synergistically in the brain to produce salt appetite in the rat. Block either hormone and the appetite is reduced by half; block both and the appetite is eliminated despite severe bodily need. With repeated depletions or treatments of the brain with angiotensin and aldosterone, salt ingestion increases, reaching an asymptote by the third depletion. Need-free intake of NaCl also increases, especially in female rats which ingest more NaCl than male rats. In Stellar's laboratory, running speed to salt solutions in a runway is used as a measure of salt appetite. When the appetite is raised with large doses of DOCA, a mimic of aldosterone, rats run rapidly for a taste of strong salt solutions as high as 24% (almost 4 molar). Using ingestion as a measure, the role of the atrial natriuretic peptide (ANP), an antagonist of angiotensin's physiological effect, was investigated as a modulator of salt appetite. When angiotensin is involved is producing salt appetite, following sodium depletion by a diuretic combined with a low-salt diet, ANP reduced salt intake by 40%. When salt appetite was raised by DOCA, however, ANP either had no effect or reduced salt ingestion by only 10%. The subfornical organ, the lateral preoptic area, and the central and medial nuclei of the amygdala are being investigated as major components of the limbic circuit underlying salt appetite produced by the actions of angiotensin, aldosterone and ANP in the brain.