Growth hormone and bone

It is well known that GH is important in the regulation of longitudinal bone growth. Its role in the regulation of bone metabolism in man has not been understood until recently. Several in vivo and in vitro studies have demonstrated that GH is important in the regulation of both bone formation and bone resorption. In Figure 9 a simplified model for the cellular effects of GH in the regulation of bone remodeling is presented (Fig. 9). GH increases bone formation in two ways: via a direct interaction with GHRs on osteoblasts and via an induction of endocrine and autocrine/paracrine IGF-I. It is difficult to say how much of the GH effect is mediated by IGFs and how much is IGF-independent. GH treatment also results in increased bone resorption. It is still unknown whether osteoclasts express functional GHRs, but recent in vitro studies indicate that GH regulates osteoclast formation in bone marrow cultures. Possible modulations of the GH/IGF axis by glucocorticoids and estrogens are also included in Fig. 9. GH deficiency results in a decreased bone mass in both man and experimental animals. Long-term treatment (> 18 months) of GHD patients with GH results in an increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with a normal GH secretion. Recent clinical studies demonstrate that GH treatment of patients with normal GH secretion increases biochemical markers for both bone formation and bone resorption. Because of the short duration of GH treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. Interestingly, GH treatment to GHD adults initially results in increased bone resorption with an increased number of bone-remodeling units and more newly produced unmineralized bone, resulting in an apparent low or unchanged bone mass. However, GH treatment for more than 18 months gives increased bone formation and bone mineralization of newly produced bone and a concomitant increase in bone mass as determined with DEXA. Thus, the action of GH on bone metabolism in GHD adults is 2-fold: it stimulates both bone resorption and bone formation. We therefore propose "the biphasic model" of GH action in bone remodeling (Fig. 10). According to this model, GH initially increases bone resorption with a concomitant bone loss that is followed by a phase of increased bone formation. After the moment when bone formation is stimulated more than bone resorption (transition point), bone mass is increased. However, a net gain of bone mass caused by GH may take some time as the initial decrease in bone mass must first be replaced (Fig. 10). When all clinical studies of GH treatment of GHD adults are taken into account, it appears that the "transition point" occurs after approximately 6 months and that a net increase of bone mass will be seen after 12-18 months of GH treatment. It should be emphasized that the biphasic model of GH action in bone remodeling is based on findings in GHD adults. It remains to be clarified whether or not it is valid for subjects with normal GH secretion. A treatment intended to increase the effects of GH/IGF-I axis on bone metabolism might include: 1) GH, 2) IGF, 3) other hormones/factors increasing the local IGF-I production in bone, and 4) GH-releasing factors. Other hormones/growth factors increasing local IGF may be important but are not discussed in this article. IGF-I has been shown to increase bone mass in animal models and biochemical markers in humans. However, no effect on bone mass has yet been presented in humans. Because the financial cost for GH treatment is high it has been suggested that GH-releasing factors might be used to stimulate the GH/IGF-I axis. The advantage of GH-releasing factors over GH is that some of them can be administered orally and that they may induce a more physiological GH secretion. (ABSTRACT TRUNCATED)     

A course in medical ethics--a pain in the neck for the clinicians?

Last year, a course in clinical medical ethics for paediatricians had to be cancelled owing to lack of interest. To find the reason for this, and to learn what ethical problems the physicians encountered in the course of their work, how they solved them, and their attitude towards education in medical ethics, a questionnaire was sent to all members of The Norwegian Paediatric Association, to be answered anonymously. The most frequent excuses for not attending the course were pressure of work and lack of time. 37% claimed that they very often or often encountered ethical problems during their work. 20% often solved these problems alone, and two out of three after discussing them with colleagues. 51% felt a need to improve their competence to solve ethical problems. Only 16% reported having no such need. The authors discuss the form and content of the education in medical ethics.     

Effect of nitrite on primary photosynthetic processes in isolated chloroplasts of wheat grown under various conditions of nitrogen supply

In wheat chloroplasts, NO2- (5 mM) inhibited non-cyclic phosphorylation coupled to the linear electron flow through both photosystems but stimulated cyclic phosphorylation with phenazine methosulfate (plus diuron) and electron flux from an artificial electron donor through PSI and methylviologen to oxygen. During light energization of chloroplasts, NO2- increased the F740/F695 ratio in the low-temperature fluorescence spectra, thus suggesting that the energy of absorbed quanta is redistributed in favor of PSI. Nitrite also stimulated the activity of Mg2+-dependent H+-ATPase. Changes in the slow component of the induction curve of delayed fluorescence also suggest that NO2- affects energy transformation processes that are coupled to electron transport in the chloroplasts. Nitrite had no effect on these functional characteristics of thylakoids and chloroplasts isolated from plants grown under nitrogen deficiency in the medium.     

Background gamma-oscillations in neuronal networks with interhemisphere connections

Results obtained in studies of the high-frequency components of EEG recordings and in modeling, determining the conditions for the appearance of gamma oscillations in interneuronal interactions, were compared with features of the background gamma oscillations recorded in the activity of interacting neurons located in symmetrical loci of the right and left hemisphere motor areas in anesthetized rats. Similarities in high frequencies extracted from EEG recordings and in the most commonly observed gamma oscillation frequencies suggested that these oscillations may represent one of the mechanisms underlying the high-frequency EEG component. Published modeling data indicating that the formation of these oscillations involves reciprocal inhibitory connections, along with our own data that interhemisphere oscillations are seen 1.5 times more commonly than ipsilateral oscillations, suggested that transcallosal inhibition is more effective than inhibition between neighboring cells. Simultaneously extracted background oscillations in the interacting activity of callosal cells and neighboring cells could be different, as could those characterizing the activity of individual neurons. It is suggested that these differences underlie the functional heterogeneity of local cortical neuronal networks and explain the fact that these networks contain various types of inhibitory neurons.     

Several aspects of occupational effects of lead compounds on the cardiovascular system

The article covers some results of complex sanitary, hygienic, clinical, functional and laboratory examinations of individuals working in main shops of storage battery production where lead and its inorganic compounds are principal occupational hazards. Lead and its compounds harm human health, being risk factors for vegetoneurosis and arterial hypertension. Hemodynamic studies using integral rheography revealed hemodynamic type of circulation, increase of general and peripheral vascular tone. The main causes of hemodynamic disorders are influence of lead compounds on autonomous nervous system, prevalence of the parasympathetic section and metabolic disorders in myocardium.     

Ferromagnetic resonance affected by a superconductor

The effect of a high-T _c superconductor on the uniform ferromagnetic resonance was experimentally studied using an YBa₂Cu₃O_7−δ film placed onto an yttrium-iron-garnet disk. A peak in the resonance-bandwidth-temperature characteristic is revealed. The peak value is attained at a temperature slightly above T _c. The maximum bandwidth exceeds that for liquid-nitrogen temperature by a factor of 6.