The role of the renal vascular baroreceptor mechanism in the renin response elicited by acute respiratory acidosis was studied in 8 chloralose anesthetized dogs. Ventilation with 8% CO₂ in air for 10 minutes (constant minute ventilation) resulted in a significant increase (P <0.01) in plasma renin activity (PRA) with a small, but insignificant, decrease in mean arterial pressure and increase in renal blood flow. The smooth muscle relaxant, papaverine, was infused into the renal artery (2 mg/min) to produced renal vasodilation and thus inhibit the renal vascular receptor for renin release. During intrarenal papaverine, the renin response to 8% CO₂ inhalation was attenuated (P < 0.05) even though blood pressure fell (P < 0.01) by an average of 21 mmHg. The data indicated that the renin response during acute respiratory acidosis is papaverine sensitive and is mediated in part by the renal vascular baroreceptor mechanism.

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Alkaline phosphatase activity in the cerebral vessel wall of SHR was examined histochemically. In the control rats, the enzyme activity was observed in the adventitia and in the endothelial cells at the bifurcation on the arterial system and capillaries, while in SHR, positive alkaline phosphatase activity appeared in the endothelial cells also of places other than branchings. This positive activity was found in the early hypertensive stage 8 week old SHR and increased with age. The relationship of alkaline phosphatase activity and increased endothelial permeability and metabolism due to hypertension was discussed.

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High-speed cross-sectional echocardiography was performed along the long axis of the left ventricle in 24 patients with mitral stenosis. The anterior mitral leaflet (AML) showed two different echo patterns. In 22 patients, the AML had no particularly intensive echo in any parts or only a moderately increased echo at the tip. Two patients showed an extremely strong echo in a part or whole of the AML. The posterior mitral leaflet (PML) was variable in echo-intensity and showed an abnormal position. A comparison between early-diastolic mitral domes in cross-sectional echocardiogram and angiocardiogram in 12 patients, using the A- and E-angles, showed a good correlation coefficient of r= 0.85 (P < 0.001). Moreover, the dome angle in cross-sectional images was related to the left atrial dimension measured by the method of Hirata and associates on patients without the severely affected AML. Two-dimensional echocardiogram in 15 patients through leaflets, papillary muscles and chordae tendineae disclosed three different patterns : (a) column-like complex, (b) discrete chordae tendineae and (c) intermediate form. In two patients, the anterior and posterior papillary muscles showed different patterns from one other.

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The incidence of a notch on the T wave, a T(N), was investigated in 5610 cardiovascular normals (Group 1), 100 cases with right bundle branch block (RBBB) (Group 2), 100 cases with congenital heart disease (Group 3), and 100 cases with left ventricular hypertrophy (LVH) (Group 4). A T (N) was observed at a rate of 7.5% in Group 1, 26% in Group 2, 21% in Group 3, and 15% in Group 4. In Group 1, a striking parallelism was observed in the incidence of a T (N) and an inverted T wave in V₁ ("Juvenile T wave"). This indicates that a T (N) in normals may be associated with right ventricular preponderance. On the basis of the present study, it is suggested that RBBB and RVH may provide more suitable situations for the occurrence of a T (N) than LVH. Explanation of the genesis of a T (N) is provided on the assumption that a T (N) would be produced by a marked delay or marked inhomogeneity in the repolarization process of some part of the right or left ventricle.

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The ultrastucture of the myotendinous junction (MTJ) of the cardiac papillary muscle was studied in cat and bat. In both species findings were similar for either ventricle. Toward the tip of the papillary muscle, myocytes are oriented in parallel array and each cell is narrowed in diameter. Longitudinal or oblique segments of intercalated discs became more prevalent than transverse segments. The distal ends of the last myocytes exhibited finger-like invaginations of the sarcolemma. The lateral sarcolemmae were longitudinally creased, causing a cavernous appearance to the sarcoplasm. Subsarcolemmal cisternae and spherical microparticles were found near the sarcolemma. The basal lamina of myocytes was thick (about 0.7 μ) and was bound to numerous microfibrils. These microfibrils (170 Å wide) were enmeshed with collagen fibrils from the chorda and appeared to connect muscle and tendon. Myofilaments of the last sarcomeres terminated into subsarcolemmal dense mats at distal or lateral margins of narrowing myocytes. All margins of even the terminal myocytes could be penetrated with lanthanum. In papillary muscle tips the nerve fiber varicosities were filled with small mitochondria, of a type suggesting sensory neuroreceptors. In the MTJ of cat hearts narrowing myocytes terminated with occasional P cells which were not organized into multicellular clusters. In bat hearts the P cells did occasionally cluster in the MTJ, and in attached valve leaflets. P cells in the MTJ suggest possible local automaticity, decrement in conduction velocity of excitation and, perhaps, moderation of the jerk during papillary muscle contraction.

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The neurovascular function was evaluated in 7 hypotensive and 8 normotensive patients on the long-term hemodialysis and compared with the healthy control group. The vascular reactivity to a cold stress was found diminished significantly in these renal failure patients; most severely in the hypotensive group. A role of somatic nerve dysfunction for the diminished vascular reactivity was excluded from the measurements of nerve conduction velocity because the nerve conduction velocity was similar in the two groups. The rise of blood pressure following norepinephrine administration (I.V.) was similar in the two groups. The reactivity was found to be significantly correlated with the level of blood pressure in the uremic patients. (r = 0.52, p <0.05). The response of plasma dopamine-beta-hydroxylase both upon the cold stress and the postural change (450 head-up tilting) was found significantly diminised in the uremic patients. The present study suggests the role of the adrenergic nerve dysfunction in the diminished vascular reactivity and probably in the development of hypotension.

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