Autoregulation System Research Articles

Effects of synthetic LH-RH and TRH on pituitary function in anencephalic infants.

The pituitary endocrine function in 4 anencephalic infants was studied by measuring the concentrations of growth hormone, prolactin, thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in umbilical venous serum. There was no significant difference in hormone levels between the anencephalic and normal infants. The response of FSH and LH was negative after administration of 10 micrograms of luteinizing hormone-releasing hormone. The TSH levels after administration of 50 micrograms of TRH elevated about 4- to 6-fold over pre-administration levels. These results indicate that the hypothalamo-pituitary axis of the human fetus initiates its function from mid-pregnancy; TSH may have an autoregulating system of the pituitary itself.

Effect of angiotensin II antagonist infusion on autoregulation of renal blood flow.

The role of the renin-angiotensin system in the autoregulation of renal blood flow was examined in the anesthetized dog. The angiotensin II antagonist, [1-sarcosine, 8-isoleucine]angiotensin II, was continuously infused into the renal artery at rates of 1 and 3 mug/min, and renin secretion rate and intrarenal distribution of blood flow as well as total renal blood flow were measured during acute reductions in renal perfusion pressure within and below the range of autoregulation. Renal autoregulation and redistribution of blood flow by pressure reduction were not disturbed by the angiotensin II antagonist. This result does not provide any evidence for a primary role of the renin-angiotensin system in renal autoregulation. Redistribution of blood flow by pressure reduction occurred independently of the renin-angiotensin system. It might depend on the differences in the resting tone among the zones.

Effect of beta-adrenergic blockade and inhibitors of angiotensin II and prostaglandins on renal autoregulation.

The role of the renin-angiotensin system and prostaglandins in renal autoregulation was investigated in dog kidneys in situ. Renal autoregulation during decreases in renal arterial pressure (RAP) was examined in animals pretreated with a competitive antagonist of angiotensin ii, [1-sarcosine, 8-glycine] angiotensin II, or one of two chemically dissimilar inhibitors of prostaglandin synthetase, indomethacin and meclofenamate. Because of recent evidence suggesting a role for an intrarenal beta receptor in regulating renin release, renal autoregulation was also examined in animals treated with the beta-adrenergic blocking agent propranolol. In all groups of animals constancy of glomerular filtration rate (GFR) and renal blood flow (RBF) was observed after substantial decreases in RAP to a range of 70-90 mmHg. These studies therefore do not provide evidence in support of a role for angiotensin II, prostaglandins, or an intrarenal beta receptor as mediators of the renal autoregulation of GFR or total RBF.

The Role of the Peripheral Sympathetic Nervous System in Cerebral Blood Flow Autoregulation

The effect of chronic, unilateral superior cervical ganglionectomy on cerebral blood flow and blood flow autoregulaiton to changes in perfusion pressure was examined in seven phencyclidine anesthetized monkeys. Ten to 14 days prior to the experiments Doppler ultrasonic flow transducers were placed on both carotid arteries after ligation of the external carotid branches and removal of one superior cervical ganglion. Autoregulation was tested by exsanguination and metaraminol infusion with the monkeys inspiring from air, 9% and 12% carbon dioxide in air. Immediately following experimentation the cerebral vessels were examined for the presence of noradrenergic fibers. The results of the study demonstrate that: (1) superior cervical ganglionectomy produces a significant reduction in the noradrenergic innervation of ipsilateral extraparenchymal arteries: (2) the peripheral sympathetic nervous system contrivutes to overall cerebral vascular resistance primarily by affecting resistance in extraparenchymal arteries; and (3) as a result, it determines the contribution of the extraparenchymal arteries to overall cerebral blood flow autoregulation.

The autoregulation of the microcirculation.

The paper reviews August Krogh's contribution to capillary physiology stressing his formulation of useful new concepts such as "tissue cylinder model", capillary intermittency and the intimate matching of capillary perfusion and cellular metabolism. Looked upon from a control theory viewpoint. Krogh was very early in considering the microcirculation as an autoregulated system with tissue oxygen tension as the controlled parameter. Recent work on Krogh's theories is briefly summarized.

Role of autonomic nervous system in autoregulation of human cerebral circulation.

Role of autonomic nervous system in autoregulation of human cerebral circulation.

Cerebral circulation in experimentally-induced cerebrovascular accidents

The cerebral blood-flow changes and their relation to the systemic blood pressure were studied on two experimental models of cerebrovascular accidents (intracerebral hematoma and cerebral softening). The cerebral blood flow measured with thermistores was found to be significantly increased in both hemispheres for either experimental model. Concomitant recording of the arterial systemic blood pressure showed that, unlike the conspicuously increased cerebral blood flow, the systemic arterial pressure remained unaltered after the experimental accident. This phenomenon may be considered a result of the suppression of the cerebral blood flow autoregulation system following the cerebrovascular accident.