[Thermography of collagen diseases with Raynaud's phenomenon]

In forty-four patients with collagen diseases accompanied with Raynaud's phenomenon(systemic lupus erythematosus(SLE)10, progressive systemic sclerosis(PSS)15, primary Sjögren's syndrome(PSJS)18 and mixed connective tissue disease(MCTD)1), we analyzed the thermography of fingers after thermal stimulation with cold water(15 degrees C, 30 seconds). In normal controls, the temperature of the distal points of fingers was higher and recovered more quickly than that of the proximal points(proximal interphalangeal joint; PIP). But in the patients with Raynaud's phenomenon, the temperature of distal point of fingers was lower and recovered more slowly than that of proximal points. Because the difference of the temperature between the distal and the proximal points (DP)is a good parameter to distinguish these two thermographic patterns, we analysed DP. DP is less influenced by room temperature than the temperature of fingers and the recovery temperature after thermal stimulation which have been used as indicators of Raynaud's phenomenon. DP in the normal controls was significantly higher than that in the patients. DP in PSS was lower than that in SLE and PSJS, and statistically associated with the markers of disease activities, such as erythrocyte sedimentation rate, titers of anti-RNP antibody and diffusing capacity of lung. These results show that thermographic pattern and the value of DP are the useful indicator of severity of Raynaud's phenomenon.

An electron microscopic study of acetylcholinesterase-activity and vasoactive intestinal peptide- and neuro-peptide Y-immunoreactivity of the intraepithelial nerve fibers in the nasal gland of the guinea pig

In combination with transmission electron microscopy (TEM), histochemistry for acetylcholinesterase (AChE) and immunohistochemistry for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) were carried out on the intraepithelial nerve fibers of the guinea-pig nasal gland. AChE-positive nerve profiles and VIP-immunoreactive nerve profiles were detected in abundance within the epithelium of the glandular acini and within the epithelium of intralobular excretory ducts including the intercalated and striated ducts. Intraepithelial NPY-immunoreactive nerve profiles were also considerably large in number in the nasal gland, but less frequent than the other two types of nerve profiles; furthermore, the NPY-immunoreactive nerve profiles appeared absent within the epithelium of the striated duct. All the intraepithelial nerve varicosities were in close spatial contact with the epithelial cells of the acinus and the duct and also with the myoepithelial cells, which were commonly seen in the acinus and the intercalated duct. Throughout the present study, however, no membranous specializations could be found between the nerve varicosities and the epithelial cells or the myoepithelial cells. The present results suggest an intense and delicate regulation through the collaboration among ACh, VIP and NPY of the secretory activity of the guinea-pig nasal gland, including the emission of acinar secretions into the duct through contraction of the myoepithelium and modification of the secretion contents by the duct epithelium.

Positional nystagmus due to alteration of the specific gravity in the labyrinth

Horizontal positional nystagmus having characteristics similar to ice water caloric nystagmus was induced by injecting heavy water into the rabbit middle ear cavity or facial nerve through the stylomastoid foramen. Furthermore, with general administration of glycerol to normal subjects, horizontal positional nystagmus as with general administration of heavy water to experimental animals was observed. It is possible that alteration of the specific gravity arising from infiltration of heavy water or glycerol into the labyrinth accounts for the manifestation of positional nystagmus. These studies on positional nystagmus may be one of the means to elucidate the mechanism of caloric nystagmus and to examine the function of the human blood-labyrinth-barrier.

Visual evoked potentials in macular hole

Pattern reversal visual evoked potentials (VEPs) with checks of 50' and 12' were recorded in 15 patients with idiopathic unilateral macular hole. VEPs from the affected eyes were reduced in amplitude compared with those from the fellow eyes, especially with checks of 12' (percentage of the amplitude in the affected eye to that in the fellow eye was 86% +/- 19% with checks of 50' and 61% +/- 35% with checks of 12'). The latencies showed no statistically significant difference between the affected and the fellow eyes, although a marked interocular delay was found in a few patients. The degree of amplitude reduction and interocular delay had no relation to the size of the macular hole or visual acuity. The effects of experimental scotomata of various sizes on the VEPs, which were evaluated in nine normal subjects, were also variable among the subjects. We conclude that although the macula predominantly participates in the pattern VEP, an estimation of the extent of macular pathology from the VEP changes may be difficult because the VEP changes induced by a macular hole have wide individual variation and have no relation to the size of the hole.

Transient deviation of closed eye on head torsion. A kind of neck-ocular reflex

Electrooculographically, torsion of the head with closed eyes causes little appearance of VOR, but a transient ocular deviation (TOD) of about 30 degrees and a maximum velocity of not less than 200 degrees/sec. TOD occurs more significantly during torsion of the head alone than during rotation of the whole body, with a two-fold greater degree of deviation, suggesting the importance of the input from the cervical afferent. TOD occurs even in a condition in which torsion of the head is made to try with the head fixed and as a result of this maneuver, a torsional force is put on the neck toward the direction of head torsion, but the head does not rotate (vestibular afferent is inoperative). Thus, it is supposed that TOD occurs as a result of the fact that the lateral gaze center is activated by perception of the directional information of head torsion from the cervical afferent.

The permeability of capillaries in the eustachian tube mucosa

The transendothelial passage of horseradish peroxidase (HRP) and diffusion of HRP into the pericapillary space, injected intravenously into cats, was studied at the light and electron microscopic level in the mucosa of the eustachian tube. The permeability of capillaries in the pharyngeal two-thirds of the tube was higher than in the tympanic one-third though all the subepithelial capillaries were of the continuous type. In the lamina propria of the subepithelium in the pharyngeal two-thirds much HRP was found 10 min after its intravenous injection, but in the tympanic one-third, it was absent in the perivascular spaces. The capillaries of the pharyngeal two-thirds had many projections and marginal folds inside the capillary lumen and large pinocytotic vacuoles containing HRP as well as many micropinocytotic vesicles. On the other hand, the capillaries in the tympanic one-third had many micropinocytotic vesicles too, but only a few large pinocytotic vacuoles.

[Effect of adhesion promoting monomers on adhesion to ground dentin]

Effect of adhesion promoting monomers dissolved in photocurable bonding agents on adhesion to ground dentin was investigated. They were MDP, Phosmer-M and 4-MET. The effect of those monomers was compared with that of Phenyl-P. The bonding agents contained campherquinone (CQ) as a photosensitizer, N-phenylglycine (NPG) as a reducing agent and TEGDMA as a base monomer. Phenyl-P was the best adhesion promoting monomer among those studied monomers. MDP could not polymerize well enough to give good bond strength. Phosmer-M could permeate through the smeared layer but could not make a stable resin reinforced dentin. 4-MET did not permeate through the smeared layer and did not adhere to ground dentin.

Time-lapse microscopy and DNA double-strand breakage of Chinese hamster cells under conditions promoting or preventing PLD repair after irradiation with 60Co gamma rays

We have confirmed previous time-lapse microscopic observations (Suzuki 1985) using Chinese hamster hai and V79 cells. The proportion of non-dividing to dividing cells was the same under conditions of potentially lethal damage (PLD) repair and non-PLD repair after irradiation with 60Co gamma-rays. This finding suggested that the radiation-induced damage to cellular DNA was similarly repaired so that cells undergo a first division to the same extent under both sets of conditions. In fact, direct measurement of double-strand breaks (dsb) in DNA from the two cell lines by the neutral elution technique showed no differences either in the initial amount of damage or in the time-course under conditions promoting or preventing PLD repair. These results indicate that PLD repair (i.e. an increase in cell survival) cannot be simply explained by a difference in the repair of dsb, but it can perhaps be explained by assuming that DNA damage is repaired with either fewer or more errors in the presence or absence of PLD repair respectively.

Central changes in hypothyroid myopathy: a case report

A muscle biopsy from a patient with hypothyroid myopathy showed striking central changes. "Cores" were seen in most type 1 fibers with oxidative enzyme preparations. Electron microscopy of these areas revealed Z disc streaming, myofilament disruption, and absent mitochondria. The myopathy rapidly improved with thyroxine treatment. This biopsy is of interest, as numerous "cores" have not previously been reported in hypothyroid myopathy.

[Retinitis pigmentosa with uveal effusion syndrome, a case report]

We reported a 65 year old female patient with retinitis pigmentosa accompanied by unilateral uveal effusion syndrome. Reduction in visual acuity and loss of depth of the anterior chamber were followed by peripheral choroidal detachment and then by retinal detachment. Subretinal fluid shifted to the lower part of the fundus for a short period and easily shifted to the posterior pole in a supine position. The axial length of both eyes was 21.3 mm. Fluorescein angiography revealed no definite points of leakage or abnormally dilated vessels. Chorioretinal detachment gradually disappeared with systemic steroid therapy. After that two recurrences, both of which were accompanied with loss of depth of the anterior chamber, we found during a follow-up period of two years. We thought this combination of retinitis pigmentosa and uveal effusion syndrome to be incidental. Since the exudative fluid easily accumulated in the subretinal space and shifted according to the head position, retinochoroidal adherence in retinitis pigmentosa may not be so strong as previously presumed.

Does reperfusion extend necrosis? A study in a single territory of myocardial ischemia--half reperfused and half not reperfused

The purpose of this study was to confirm or disprove the existence of reperfusion-induced extension of necrosis. To avoid the effect of the variability of collateral circulation when groups of dogs are compared, we compared the effect of reperfusion and nonreperfusion on myocardial necrosis in a single ischemic territory, half of which was reperfused and half of which was not. The left anterior descending coronary artery (LAD) territory between its last diagonal branch and the apex was studied because it was found to have uniform collateral blood flow. In 20 dogs, the LAD was occluded for 90-240 minutes to produce necrosis of different degrees of transmurality. Before release of this occlusion, the LAD was occluded distally halfway to the apex to keep the distal half nonreperfused. After 5 minutes of proximal reperfusion. Monastral blue dye was injected into the left atrium for demarcation of the reperfused region, and the heart was arrested, excised, cut parallel to the LAD, and placed into triphenyl tetrazolium chloride (TTC) solution for delineation of the region of necrosis. The validity of TTC staining under the conditions of this study was confirmed by light and electron microscopy. The transmurality of necrosis, measured within 1 or 0.5 cm on either side of the boundary, ranged from 30% to 88% of wall thickness and was not different in the reperfused compared with the nonreperfused region (paired t test). Reperfusion did not advance the epicardial edge of necrosis compared with the nonreperfused region. In conclusion, at 5 minutes after reperfusion, comparison of necrosis in the reperfused and nonreperfused halves of a single ischemic territory could not demonstrate an extension of necrosis by reperfusion.

[Two cases of abdominal bronchogenic cyst]

Two cases of abdominal bronchogenic cyst were reported. In the first case, the cyst was communicated with gastric fundus and existed as gastric abscess. In the second case, the cyst showed high CT number and chemical analysis of the contents revealed high range of Ca, Fe and Amylase levels.

Importance of retinal pigmentation as a subclinical marker in familial adenomatous polyposis

Surgery was performed in 35 patients with familial adenomatous polyposis (FAP) from 22 family trees. To clarify retinal pigmentation as an important subclinical marker in patients with FAP, precise retinal examinations were performed in 41 cases (82 eyes), including 23 patients and 18 family members including 12 second-generation and third-generation possible carriers. In 27 patients, precise studies were done on accompanying lesions, and the number of polyps was counted at the time of surgery in each patient in every family tree. The overall incidence of retinal pigmentation in patients was 82.6 percent. The incidence of retinal pigmentation in possible carriers was found to be 50 percent, which is comparable with the calculated expressibility of the polyps. The shape and distribution of pigmentations were classified into two categories--large and small. A total of 1984 control retinal examinations were performed, which revealed only six retinal pigmentations (0.3 percent). In the control group, all pigmentation was solitary and unilateral. No large pigmentations in bilateral eyes were found in the control group. In large pigmentation, the sensitivity and specificity were calculated as 0.652 and 0.999, respectively, and in small pigmentation, the sensitivity and specificity were calculated as 0.783 and 0.997, respectively. Small pigmentation appears to increase in number around the age of the appearance of the polyp. Earliest recognition of the pigmentation in this series was one year of age.

Bull's-eye maculopathy, negative electroretinogram and low plasma cyclic guanosine monophosphate level. A report of two cases

Two patients had bull's-eye maculopathy, negative electroretinograms and low level of plasma cyclic guanosine monophosphate. In these cases, single bright-flash electroretinograms were of a negative type and scotopic electroretinograms were reduced in amplitude, whereas photopic electroretinograms were normal or only slightly reduced in amplitude. The negative electroretinograms were considered to result from extensive abnormalities in the inner retinal layer or an abnormal cyclic guanosine monophosphate metabolism in the photoreceptor cells.

Relation of serological- and CPE- classification of porcine enteroviruses to the classification by immunoperoxidase (IP) staining, and observation of CPE by IP staining method

Characteristics of CPE produced by porcine enteroviruses (PEV) were examined by Immunoperoxidase (IP) staining method. Viral antigens were detected earlier than appearance of CPE. Distinctive characteristics of the three CPE types were clearly showed by the method. In cross reactions by IP staining, the titers of the staining were high (1:6,400 to 1:25,600), even though neutralizing titers of PEV with CPE II or III were low (1:200 to 1:400). The very close relationship was detected between PEV with the same CPE type, but the very low relationships were detected between PEV with the different CPE type. The relationships in CPE I group were various. The results by IP staining were more relative to CPE type than the serotype. Thus, IP staining is one method to classify PEV clearly.

[HLA-DR positive T cells and CD45R positive CD4 cells in primary Sjögren's syndrome]

In 55 patients with primary Sjögren's syndrome (PSJS), we studied on peripheral HLA-DR positive T cells, suppressor inducer (CD4 + CD45R) cell and helper inducer (CD4 + CDw29) cells by 2-color analysis using flow cytometry system. As shown in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), progressive systemic sclerosis and myositis, the rate of pheripheral HLA-DR positive T cells in PSJS (5.9% +/- 3.9) was significantly higher than in normal (1.6% +/- 1.1). The rate of CD4 +/- CD45R + cells in PSJS (12.8% +/- 6.1) and SLE (12.8% +/- 8.2) were significantly lower than in normal (16.6% +/- 3.9). With respect to the disease pattern of PSJS, the increase of HLA-DR positive T cell and decrease of CD4 + CD45R cell were recognized in patients with leucopenia, high titer of anti-RNP antibody and/or abnormal findings of sialography, and the decrease of CD4 + CD45R + cell was not recognized in patients with kerato-conjunctivitis sicca alone. In either SLE or RA, there were no correlations between the rate of T cell subsets (HLA-DR positive T cells and CD4 + CD45R cells) and the degree of salivary gland damage. T cell subsets in PSJS were useful indicators of disease severity and it is also useful for classifying PSJS into several subtypes. To analyze T cell surface markers in PSJS is very important for investigation of functions of lymphocytes in this disease.

[Neuro-psychiatric symptom associated with primary Sjögren's syndrome]

Neuro-psychiatric complications of primary Sjögren's syndrome (SjS) were studied on their frequency and characteristics of clinical signs in 150 patients of our clinic. Clinical symptoms and laboratory examinations were compared in the patients group complicated with neuro-psychiatric symptoms and the non-complicated group. Neuro-psychiatric symptoms (neuro SjS) were complicated with 63 patients (42.0%). Central nervous system (CNS) involvement were occurred in 47 patients (31.3%). In this group (CNS SjS), psychiatric complications were observed in 43 patients (28.7%), consisted with 29 cases of neurosis, 7 cases of depression, 6 cases of presenile dementia, and others. Nine patients (6.0%) in this group had neurologic involvement that were 3 cases of aseptic meningitis, 3 cases of neurogenic bladder, and each case of multiple infarction, multiple sclerosis, and others. These 9 patients showed more frequently positive results for rheumatoid factor, anti-SSA antibody, leucopenia, and lymphopenia, so this subgroup might be consisted of a small group which was resemble to systemic lupus erythematosus. Cranial nerve involvement, mainly injured in trigeminal nerve, and peripheral nerve involvement were complicated with 5 patients (3.3%) and 24 patients (16.0%), respectively. In neuro-psychiatric complicated group, mean age was older and dry mouth were more frequent (p less than 0.05) than non-complicated group. In psychiatric complicated group, mean age was older (p less than 0.01) and dry mouth were more frequent (p less than 0.05). In any groups of neuro-psychiatric complications, the frequency of any autoantibodies was not statistically different from non-complicated group. But, in the group of cranial nerve involvement, anti-RNP antibody was 60.0% positive (in non-complicated group, 17.2%: p less than 0.05). In CNS SjS group, magnetic resonance imaging (MRI) abnormalities were occurred in 8 of 13 patients. High intensity lesions in white matter on the T2-weighted examinations was characteristic, which showed lacnar infarctions or demyelinated lesions in MRI abnormalities. In CNS SjS, corticosteroid or immunosuppressant was not always necessary, because this complication was self-limited or enough controlled by minor-tranquilizer or anti-depressant. The character of onset in neuro SjS was chronic and neuro SjS was insidiously developing disease. And more studies including treatment on neuro SjS were needed.

Differentiation of crypt epithelium in human palatine tonsils: the microenvironment of crypt epithelium as a lymphoepithelial organ

The differentiation of the keratinocytes of the human palatine tonsils were studied by means of light and electron microscopy and immunohistochemistry using a polyclonal (K) and two monoclonal antikeratin antibodies (PKK1, PKK2). In the surface epithelium, the basal cells, cuboidal or columnar in shape, undergo progressive terminal differentiation and are transformed into the flattened cells of the upper layers. K reacts with both the basal and spinous layers, while PKK1 and PKK2 mark exclusively the basal layer. In the neck portion of the crypt, cavities containing one or aggregated lymphocytes with amorphous substances are observed in the spinous layer. The cavities are surrounded by elongated cytoplasmic processes of transformed epithelial cells bearing surface microvilli. These transformed epithelial cells display intense PKK1- and PKK2-positive reactions, whereas other conventional polygonal cells in the vicinity remain PKK1- and PKK2-negative as do those in the surface epithelium. In the deep portion of the crypt, where numerous lymphocytes invade the epithelium, the epithelial cells are transformed into star-shaped reticulum cells showing PKK1- and PKK2-positive reactions. The extended and branched cytoplasmic processes interconnect with one another constituting a complex network of reticulum cells, the well known reticulation of the crypt epithelium. Ten-nm filaments are usually oriented parallel to the longitudinal axis of transformed epithelial cells. Our observations suggest that the cell-shape transformation, i.e., from conventional polygonal epithelial cells into epithelial reticulum cells, occurs when the epithelial cells are in close contact with the infiltrating lymphocytes, and that this transformation is accompanied by a change in keratin phenotype.

Audiological findings of prolonged Menière's disease

As Ménière's disease progresses, the fluctuations becomes less marked and the hearing level gradually declines. In the more established and advanced stages of the disease, a permanent and progressive hearing loss develops. It has been reported, however, that hearing acuity in some patients with Ménière's disease significantly improved after having had the disorder for many years. Such observation suggests that the inner ear pathology in late stages of Ménière's disease may not be necessarily irreversible. The purpose of this investigation was to assess whether or not various audiological evaluations including EcochG may be of value in predicting the irreversibility of hearing deficit in patients suffering from advanced stages of Ménière's disease. The audiological studies included pure tone audiogram, SISI test, Bekesy audiometry, glycerol (or urea) test, speech discrimination test, and electrocochleography. A combination of the recruiting type of response in the EcochG and the narrowing of the tracing width of continuous sound in the Bekesy pattern seemed to be indicative for irreversible hair cell damages. Patients who had a low score in the speech discrimination test as well as an absence of ABR response were suspected of having retrocochlear lesions. Our investigations suggest that the irreversibility of hearing impairment in patients with later stages of Ménière's disease may be predicted to some extent in the use of various audiological evaluations including the EcochG.

Aeration of the tympanomastoid cavity and the Eustachian tube

Physiological changes in body position affect the degree of opening and closing of human auditory tubes. Notable changes were observed in lateral body position concerning the opening rate of the auditory tubes, which corresponds to the changes in pressure within the lower portion of the middle ear cavity. This physiological mechanism seems to be related with the anatomical direction of the auditory tube and the natural mechanism for the protection of the middle ear cavity. When a change takes place which moves the compliance of the eardrum to the positive side (e.g. head position change or static lateral body position), observation suggests the possibility of venostatis and production of gas. Measurement of the oxygen tension in the middle ear cavity under atmospheric pressure revealed the existence of constant gas production which maintains the pressure in the middle ear cavity at the same level as atmospheric pressure. This result denies the influx of gas from the atmospheric environment into the middle ear cavity. These results stem from the intrinsic physiologic mechanism of the middle ear cavity, namely maintenance of effective auditory sound conduction (a function to keep eardrum compliance as close to zero as possible), by keeping the pressure within the middle ear cavity below the atmospheric pressure, either at the same level as or slightly higher than that of the environment pressure. Gas emission from the middle ear cavity in the atmospheric environment and a low oxygen tension are a natural physiologic mechanism to protect the middle ear cavity from infection and other hazards.

[Effect of different kinds of toothbrushes on toothbrushing pressure and plaque removal in the scrubbing method of toothbrushing (5). Toothbrushes with nylon bristles arranged in different lengths along the toothbrush shank and with different types of toothbrush bristle tip]

The purpose of this study (Report 5) was to investigate the effect of difference in the length of toothbrush shank and type of tip of toothbrush bristle on toothbrushing pressure and plaque removal in the scrubbing method. Four kinds of toothbrushes which were different in length of shank (30 mm, 40 mm) and type of bristle tip (round type, tapered type respectively) were used in this study. Referring to the results of our previous reports (1-4), the dimension of new toothbrushes were determined as follows, nylon bristles: 40 mm long and 0.20 mm in diameter, brushing surface: 30 mm long, bristles: 3 rows with 26 tufts, and a straight handle. Twelve subjects participated in this experiment. Plaque scores were measured before and after toothbrushing. Then plaque removal rates were calculated. Toothbrushing pressure was determined using Watanabe's method. The average toothbrushing pressure of the toothbrush with a 40 mm long shank (301.6 +/- 84.1 g/cm2) was higher than that with a 30 mm long shank (294.7 +/- 74.8 g/cm2), and that with a tapered bristle type (316.7 +/- 90.4 g/cm2) was higher than that with a round type bristle (279.6 +/- 61.7 g/cm2). However statistically significant differences were not found among the four toothbrushes in brushing pressure and in plaque removal on total teeth surfaces and on distal surfaces of the most posterior teeth (P less than 0.05; two-way ANOVA).

Oligonucleotide probe for detection and identification of Campylobacter pylori

We have developed a novel and practical DNA-RNA hybridization assay for the detection and identification of Campylobacter pylori in the gastric mucosa. This technique utilizes a [32P]ddATP-labeled synthetic oligonucleotide probe complementary to a nucleotide sequence present in C. pylori 16S rRNA. This probe is very sensitive and reacted with all 23 strains of C. pylori tested. It is also highly specific, since there was no cross-reactivity with the heterologous organisms Campylobacter coli, C. fetus subsp. fetus, C. jejuni, and C. laridis or with Escherichia coli. Hybridization of the oligonucleotide probe with C. pylori RNA was completely inhibited by treatment of the membrane filters with RNase but not DNase. Although a gastric mucosa tissue homogenate slightly inhibited the hybridization, as few as 10(4) C. pylori cells could be detected even in the presence of 5 mg of gastric mucosa. Gastric biopsy specimens obtained from patients referred for upper gastrointestinal tract endoscopy were tested for C. pylori infection by direct oligonucleotide hybridization, and the results were compared with those of bacteriological cultures, the urease test, and histological observations. A comparison of the urease test and the oligonucleotide hybridization results showed an excellent correlation between the two methods. The clinical usefulness of this oligonucleotide-RNA hybridization method is discussed.

Differential vasodilator effect of nitroglycerin on systemic capacitance and resistance vessels in anesthetized dogs, and the mechanism of its action--a study by measuring mean circulatory pressure and total peripheral resistance

The aim of our studies was to examine if the baroreceptor reflex induced by intravenous injection of nitroglycerin (NG) nearly nullifies the vasodilator action of NG on the systemic capacitance vessels in dogs anesthetized with pentobarbital. We performed total spinal anesthesia (TSA) in open-chest dogs to eliminate the baroreceptor reflex. Dogs in which mean blood pressure (MBP) was maintained at about 100 mmHg by continuous intravenous infusion of epinephrine formed the TSA 100 group, and those in which MBP was maintained at about 70 mmHg formed the TSA 70 group. Dose-response curves relating 5-6 different doses (0.8 to 200 micrograms/kg) of intravenous NG, to changes in mean circulatory pressure (% delta MCP) and to changes in total peripheral resistance (% delta TPR), were constructed. These data were compared with those from untreated dogs. In addition, we also studied plasma catecholamine (CA) concentrations before and after the intravenous injection of NG. (1) There was no significant difference in the dose-response curves of NG for % delta TPR between the 3 groups. (2) There was no significant difference in the dose-response curves for % delta MCP between the 2 TSA groups. However, there was significant difference in the dose-response curves for % delta MCP between the TSA groups and the untreated dogs. The dose-response curves for % delta MCP in the TSA groups shifted upwards as compared with that of the untreated dogs. (3) In the TSA 100 group, there was no significant increase in the plasma CA concentrations with 100 micrograms/kg of NG. In the untreated group, intravenous injection of 12.5 micrograms/kg and 100 micrograms/kg of NG caused a dose-related fall in MBP and a dose-related rise in the plasma norepinephrine and epinephrine concentrations. Our results suggest that the vasodilator action of NG on the systemic capacitance vessels in the untreated dogs was counterbalanced partly by the vasoconstriction produced by the baroreceptor reflex, with its direct vasodilator effect masked when the hypotensive doses of NG were given acutely.