Reflex antidiuresis after occlusion of common carotid arteries in hydrated dogs

Common carotid arteries were occluded bilaterally for 5 min below the thyrocarotid arterial junctions in mildly hydrated, anesthetized dogs. Within 5–15 min after the occlusion, urine flow declined and remained below control values for 30–105 min. Concurrently, the urine became hypertonic to systemic plasma and there was no evidence for renal vasoconstriction or increased solute reabsorption. The decrement in urine flow was accounted for entirely by the decline in free-water clearance. Prolonged periods of occlusion or increased hydration altered the response. Bilateral occlusion of the common carotid arteries for 5 min above intact thyrocarotid arterial junctions (but below the carotid sinuses) or below denervated thyrocarotid arterial junctions did not affect urine flow. The time course of the response, the characteristics of the urine, and the absence of renal vasoconstriction suggest that the procedure induced a reflex release of antidiuretic hormone. Furthermore, the data indicate that the receptor area for this reflex is located in the region of the junction of the common carotid and thyroid arteries.

CAROTID SINUS REFLEX IN CAT: EFFECT OF PRIOR EXTERNAL CAROTID ARTERY CLAMPING

Intrasinusal and systemic arterial pressure changes resulting from occlusion of the common carotid arteries (CCO) in vagotomized cats were recorded and compared with those in which the external carotid arteries were previously clamped. The CCO responses were similar under chloralose and pentobarbital anesthesia, and were unaltered by positive-pressure respiration. Prior bilateral external carotid artery clamping (ECC) significantly reduced the initial fall in intrasinusal pressure and the reflex pressor response. Injections of acetic acid into the sinus region reduced the reflex pressor response despite a greater fall in intrasinusal pressure after CCO. Following acid treatment, prior ECC generally reduced the reflex pressor response to a lesser degree than before treatment. It is concluded that in vagotomized cats, there is no difference between chloralose and pentobarbital anesthesia or positive-pressure and spontaneous respiration on the CCO response. The magnitude of the reflex pressor response apparently depends on the degree of baroreceptor deactivation and chemoreceptor activation. The results are discussed further in terms of differences between the cat and the dog.

DETERMINANTS OF INTRAMYOCARDIAL PRESSURE IN THE CAT

Determinants of intramyocardial pressure in the cat were investigated by means of a small latex tube inserted into the wall of the left ventricle. Maximal intramyocardial pressures were generally below carotid systolic pressures. Rhythmic variations in intramyocardial pressure occurred and were related to pulmonary ventilation. There was no evidence of efferent vagal activity on the left ventricle. Sympathetic stimulation increased and sympathetic blockade (with Pronethalol) decreased intramyocardial pressure. Intramyocardial pressure was increased by venous infusions and by constriction of the aorta.

MECHANISMS OF HEMODYNAMIC CONTROL OF SECRETION OF ALDOSTERONE IN THE DOG

Changes in aldosterone and cortisol secretions were measured in response to constriction of the thoracic inferior vena cava and of the carotid arteries in intact and nephrectomized dogs. Aldosterone and cortisol secretions increased and decreased normally in response to caval constriction and release in nephrectomized animals. Carotid constriction in intact animals increased aldosterone secretion to the same extent as caval constriction, but without increasing cortisol secretion. Cortisol secretion rose after carotid constriction in vagotomized dogs. Nephrectomy led to transient low rates of aldosterone secretion in otherwise intact animals and prevented the increase of aldosterone secretion following carotid constriction in most, but not all, animals in which there was no evidence for ACTH release. Since carotid constriction decreases renin secretion, this effect of nephrectomy is probably independent of the renin-angiotensin system. The data suggest the presence of a mechanism involving the central nervous system, not mediated through ACTH release or the renin-angiotensin system, which is important in the physiologic control of aldosterone secretion, and which may involve an inhibitor of aldosterone secretion.

THE MICROSCOPICAL APPEARANCES OF HUMAN PERIPHERAL ARTERIES DURING GROWTH AND AGING

Twelve peripheral arteries are described in 59 patients of all ages. Accumulation of ground substance in the media, accompanied by small foci of calcification of the internal elastic lamina, was found in the large leg arteries of young adults, and progressively in a wider series of arteries throughout life. This picture showed no relationship to hypertension, to Mönckeberg's sclerosis, or to the development of atheroma. A notable quantity of ground substance may be a feature of early intimal development, and of a thickened intima in adult life, and probably the major constituent of an organizing thrombus. Organizing thrombi were apparently incidental findings at several sites even in young adults, and showed no association with the state of the arterial wall beneath the lesion, the wall being in fact normal, though accumulated mucopolysaccharide was always present. Atheroma increases with age, and its focal incidence gives way to confluence in the arteries of the leg. Occlusive peripheral artery atheroma was found only in cases where the cause of death was severe atheroma, e.g., coronary artery disease and abdominal aortic aneurysm, or in myxoedema, in which the incidence of occlusive lesions may differ from that in severe generalized atheroma. Elastic tissue is described in all coats of the artery wall, with some variants of the common pattern. The musculo-elastic cushion is not seen after adolescence, and it is suggested that the cushion represents the growing point of the artery. Longitudinal muscle bundles are almost confined to the popliteal artery, where they may form an essential buttress for a large branching artery subject to unusual external stresses. The functions and origin of the ground substance are discussed.