A group of membrane-associated guanine nucleotide binding proteins (G-proteins) are essential for transducing signals generated at cell-surface receptors into changes in cellular function and metabolism. These proteins are a complex of three subunits designated alpha, beta and gamma. The alpha-subunit is responsible for binding guanine nucleotides and seems to be characteristic of each protein. Transducin, a member of this protein family, mediates visual transduction by coupling the signal of photolysed rhodopsin with activation of a cyclic GMP phosphodiesterase. We have now cloned and sequenced the complementary DNA encoding the alpha-subunit of bovine retinal transducin and from this we have deduced the complete amino-acid sequence. The transducin alpha-subunit shares several homologous amino-acid sequences with ras gene products. The homologous segments correspond mostly to the regions thought to be involved in the guanine nucleotide binding and GTPase activity of ras proteins and to the ADP-ribosylation sites of the transducin alpha-subunit.

Adenosine Diphosphate Ribose↗

PubMedDate not supplied

Diminished reserve for cerebral vasomotor response to L-arginine in the elderly: evaluation by transcranial Doppler sonography.

BACKGROUND: Nitric oxide is pivotal in endothelially dependent vasodilatory regulation. An association of endothelial dysfunction with aging has been documented in the forearm and coronary vascular beds. However, the influence of aging in the human cerebral circulation, where regulation is particularly complex, is incompletely understood. OBJECTIVE: We systematically administered L-arginine, a precursor of nitric oxide, to evaluate the influence of aging on nitric oxide-mediated cerebral vasomotor regulation. METHODS: Among healthy volunteers, 20 older subjects (10 men, 10 women; age: 70.2 +/- 2.8 years) and 22 younger subjects (10 men, 12 women; age: 28.8 +/- 1.9 years) received intravenous infusions of L-arginine monochloride (500 mg/kg) over 30 min. Hemodynamic parameters were monitored continuously during and after infusion. The cerebral vasomotor response was estimated by transcranial Doppler sonography of the right middle cerebral artery. RESULTS: Infusion of saline as a control brought little change in the mean blood pressure, heart rate or cerebral blood flow velocity in either group. On administration of L-arginine, cerebral blood flow velocity increased and mean blood pressure decreased. After completion of infusion, both parameters rapidly normalized. While reduction of mean blood pressure did not differ between older and younger groups, the cerebral circulation in the older group showed a blunted, smaller, and more easily saturated vasomotor response compared to the younger group, though both groups had similar baseline values. CONCLUSION: Our results indicate a diminished nitric oxide-mediated cerebral vasomotor response in aging subjects. Additionally, transcranial Doppler sonography can be used to reliably evaluate age-related changes in the physiologic responses of the human cerebral circulation.

Adult↗

PubMedDate not supplied

Evaluation of cross-circulation through circle of Willis using an ultrasonic Doppler technique. Part I. Comparison between blood flow velocity by ultrasonic Doppler flowmetry and angiogram.

In 24 patients with cerebrovascular disease and 6 without organic brain lesions, the increased velocity of blood flow in both the internal carotid and vertebral arteries during a contralateral carotid compression was compared with the angiographic appearance of the circle of Willis. The flow velocity was measured using ultrasonic Doppler flowmetry. It was not possible to investigate fully the relationship between the increase of velocity of blood flow in the internal carotid artery and the anatomical variations of the circle of Willis, specifically the anterior cerebral and communicating arteries. The velocity of flow in the patients with an aplastic proximal portion of the anterior cerebral artery showed no increase. There were no differences in the increase of velocity of flow in the vertebral artery in patients with hypoplastic, normal and fetal posterior communicating arteries. It is considered that although anatomical variations of the circle vessels influence the cross-circulation via the circle of Willis, peripheral vascular factors distal to the circle also play an important role in the quantity of cross-circulation through the circle.

Adolescent↗

PubMedDate not supplied

Evaluation of cross-circulation through circle of Willis using an ultrasonic Doppler technique. Part II. Comparison between blood flow velocity by ultrasonic Doppler flowmetry and cerebrovascular resistance.

The correlation between the increase in velocity of blood flow in both the internal carotid and vertebral arteries during a carotid compression and the cerebrovascular resistance (CVR) was investigated in 11 patients with chronic ischemic cerebrovascular disease and 4 without organic brain lesions. The velocity of blood flow was measured by an ultrasonic Doppler flowmeter. CVR was calculated from cerebral blood flow and arterial blood pressure. There was no correlation between the increased velocity of blood flow in the internal carotid and vertebral arteries and CVR. The increased velocity of blood flow in patients with low CVR was, however, significantly higher than that of patients with high CVR. The investigation of cross-circulation by ultrasonic Doppler flowmetry is a useful non-invasive method for the detection of changes in cerebral vascular resistance.

Adolescent↗

PubMedDate not supplied

Ultrasonic evaluation of superficial temporal artery-middle cerebral artery anastomosis.

Ultrasonic Doppler studies were made pre- and postoperatively in 22 patients undergoing STA-MCA anastomosis. A quantitative evaluation of the bypass was attempted by determining the STA blood flow velocity and pattern. The STA velocity on the Doppler sonogram was compared with the degree of intracranial vascular filling via anastomotic channels and the STA diameter on angiogram. The STA velocity was increased and the blood flow pattern of STA altered from an external carotid pattern to an internal carotid pattern in a patent bypass. The results were in good agreement with angiographic findings. The are of intracranial vascular filling via a vewly formed bypass on angiogram was proportional to the increase in STA velocity. As the STA diameter enlarged, the STA velocity increased progressively. It is suggested the Doppler flowmetry is reliable as a semi-quantitative means of evaluationg the STA-MCA anastomosis.

Adult↗

PubMedDate not supplied

To-and-fro movement and external escape of carotid arterial blood in brain death cases. A Doppler ultrasonic study.

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Adolescent↗

PubMedDate not supplied

Interrelationships among regional cerebral blood flow, mean transit time, vascular volume and cerebral vascular resistance.

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Blood Flow Velocity↗

PubMedDate not supplied

Subclavian steal in Takayasu's arteritis. A hemodynamic study by means of ultrasonic Doppler flowmetry.

Blood flow in the vertebral artery and the upper extremity was studied in five cases of Takayasu's arteritis with subclavian steal by use of ultrasonic Doppler flowmetry and finger plethysmography. The diagnosis of subclavian steal was made by observation of flow reversal in the vertebral artery on the subclavian steal side during grip exercise and, in addition, the vertebral flow change with brachial artery occlusion. The blood flow increase of both internal cartotid and non-affected (non-subclavian steal side) vertebral arteries during a common carotid compression was almost normal in patients with Takayasu's arteritis in this study. During carotid compression on the side of the subclavian steal, ipsilateral vertebral blood flow greatly decreased, and the amplitude the ipsilateral finger plethysmogram decreased slightly or moderately. It is suggested that there are significantly important factors in suppressing sumptoms of vertebrobasilar ischemia in these patients with Takayasu's arteritis with subclavian steal. These factors are believed to be (1) good function of the circle of Willis, (2) good blood supply to the brain stem, and (3) collateral circulation to the distal subclavian artery not via the vertebral artery.

Aortic Arch Syndromes↗