Mechanisms of neonatal increase in glomerular filtration rate

To investigate the mechanisms responsible for the neonatal increase in glomerular filtration rate (GFR), renal function studies (whole kidney and micropuncture) were carried out in anesthesized fetal sheep (133-140 days gestation; term = 150 days) and lambs (12-18 days). Fetuses were delivered and placed in a water bath (39.5 degrees C), keeping the umbilical cord moist and intact. Lambs were studied on a thermostatically controlled heating pad. Animals were prepared for either blood flow studies or micropuncture measurements. Expected differences in blood composition and cardiovascular and renal function were observed between fetuses and lambs, and values obtained for most variables were similar to those measured in chronically catheterized unanesthetized animals. Fetal GFR was much lower than that of lambs (0.20 vs. 0.62 ml.min(-1).g kidney(-1), P < 0.001). Free-flow, stop-flow, and net filtration pressures (NFP) were lower in the fetuses than the lambs (NFP 20.8 vs. 23.8 mmHg, P < 0.001), as was the calculated ultrafiltration coefficient (0.014 vs. 0.022 ml.min(-1).g(-1).mmHg(-1), P < 0.001). Thus, we conclude that rises in both net filtration pressure and the ultrafiltration coefficient contribute to the large increase in GFR between fetal life and approximately 2 wk after birth.     

Homocarnosine levels in repeated hypothermia and hibernation

Compulsory cooling of rats (20 degrees) and susliks (20 degrees-10 degrees) leads to a considerable decrease of homocarnosine in cerebral hemispheres in midbrain and diencephalon and cerebellum. When hypothermia is repeated 4 or 7 times (in every 24 h) a more considerable decrease in the homocarnosine quantity in the rat brain takes place and it is not normalized after self-warming of the organism. After 11-12-fold hypothermia, when a certain adaptation of animals to cooling is developed, the second increase of homocarnosine content with subsequent normalization of its level in great cerebral hemispheres and in cerebellum at self-warming is observed. In dynamics of the hibernation (1, 7 and 30 days) either preservation of normothermal level or a certain increase of the homocarnosine content in all areas of the suslik brain under examination is observed.     

Comparative physiological and biochemical aspects of hypothermia as a model for hibernation

It is obvious that research is far from the last chapter in developing a model for natural hibernation. The relationships and comparative mechanisms for thermogenesis and survival in hibernation and experimental hypothermia are still unclear. Yet, two primary areas appear to be most promising, namely, the control of thermogenesis via the glucocorticoids and the specific role of the central nervous system (CNS) in survival of hypothermic subjects and arousal of hibernating subjects. Although there have been several approaches to understanding the role of the CNS in terms of circulation, integrity of the blood-brain barrier (BBB) system, and CNS sites of activity, it may appear that more questions have been raised than have been answered. However, a more optimistic view can also be taken. The development of a laboratory model, using experimental hypothermia for natural hibernation, is progressing. This view is justified in terms of results from the use of glucocorticoids in metabolic regulation of available carbohydrates, i.e., available glucose in hypothermia, and the continued promising parallel studies of physiological and biochemical integrity of areas of the CNS in hypothermic and hibernating subjects.     

Visualisation studies and glomerular filtration in early diabetic rats

The purpose of this mini-review is to show that more modern multi-photon microscopy approaches allow quantitative glomerular filtration experiments. Modern science has now entered a transition period from light microscopy to multi-photon confocal microscopy. Since the late 20th century, multi-photon microscopy has been applied in the study of organ function. In keeping with observations made in renal physiology and other representative studies throughout this transition period, and in the context of advancing microscopy techniques, this review has been presented as a comment on the glomerular filtration barrier, with a focus on the early aetiopathogenesis of diabetes.     

Mechanisms responsible for the curative effect of phosphen-electrostimulation

We studied the effect of electrical stimulation of the visual analyzer (evoking a phosphen phenomenon, the phosphen-electrostimulation, PES) on the visual functions, hemodynamics in the eye and brain, and general immune reactivity; the examined group Included patients afflicted with myopia. It was shown that the main visual functions, like visual keenness under normal and mesopial illumination conditions, accommodation reserves, and light sensitivity, improved under the influence of PES. Circulation in the eye and brain was intensified, as was shown by improvement of the brain blood supply via the main arterial pools and blood supply of the eye via the uveal tract, with a simultaneous decrease In the vascular tone. In addition, PES caused evident total optimization of the immuno-regulatory Processes in an organism.     

Mechanisms responsible for the cardiotoxic effects of cocaine

Cocaine can induce lethal cardiovascular events, including myocardial infarction and ventricular fibrillation. The mechanisms responsible for these cardiotoxic effects of cocaine remain largely to be determined. Cocaine has both sympathomimetic (inhibition of neuronal uptake of norepinephrine) and local anesthetic (Na+ channel blockade) properties. Neurotransmitters released from cardiac sympathetic nerves bind to both alpha- and beta-adrenergic receptors eliciting a cascade of intracellular responses. Stimulation of beta-adrenergic receptors activates adenylate cyclase, increasing cyclic AMP levels, whereas alpha-adrenergic receptor stimulation activates phospholipase C, increasing inositol trisphosphate. These second messengers, in turn, elicit increases in cystolic calcium. Elevations in cystolic calcium can provoke oscillatory depolarizations of the cardiac membrane, triggering sustained action potential generation and extrasystoles. Cocaine also acts as a local anesthetic by inhibiting sodium influx into cardiac cells, which impairs impulse conduction and creates an ideal substrate for reentrant circuits. Thus, the adrenergic and anesthetic properties of cocaine could act synergistically to elicit and maintain ventricular fibrillation. Adrenergic receptor activation would trigger the event whereas sodium channel blockade would create the reentrant substrate to perpetuate the malignant arrhythmias.     

Mechanisms responsible for autocrine regulation of the epiphysis function

The effect of injection of exogenous melatonin on formation of the nocturnal peak of the melatonin concentration and intrapineal hormonogenesis was studied on mature male rats. It was shown that³H-melatonin is selectively uptaken by pinealocytes, and the uptake intensity depends on the degree of saturation of an organism with exogenous melatonin. Exogenous melatonin exerts an inhibitory influence on the hormone self-production, at the same time apparently stimulating synthesis of epiphyseal peptides. The results can be considered an indication of the existence of an ultra-short connection between the mechanisms of production of epiphyseal indoles and peptides, which apparently plays an important role in autocrine regulation of the epiphyseal functions.