Effects of streptozotocin-induced experimental diabetes on the morphology and function of the zona fasciculata of rat adrenal cortex

The effects of a severe streptozotocin (STZ)-induced diabetes on the morphology and function of the adrenal zona fasciculata were examined in rats with intact or pharmacologically interrupted hypothalamic-hypophyseal-adrenal axis. In animals with an intact hypothalamic-hypophyseal axis, STZ-diabetes induced hypertrophy of the cells of the zona fasciculata and a rise in the plasma corticosterone concentration. Conversely, in rats in which the hypothalamic-hypophyseal axis had been interrupted, experimental diabetes provoked atrophy of the zona fasciculata cells, and a lowering in the plasma corticosterone level. The effects of STZ-diabetes were completely reversed by insulin infusion in both groups of rats. The hypothesis is discussed that the chronic lack of insulin may directly inhibit the growth and steroidogenic capacity of the rat zona fasciculata and that this effect of experimental diabetes may be masked in rats with an intact hypothalamic-hypophyseal axis by the concurrent enhancement of ACTH release due to chronic stress resulting from the metabolic consequences of prolonged diabetes.     

Relationship between efflux of ionic calcium and phosphorus during excitation of pancreatic islets with glucose

Simultaneous rates of [³²P]orthophosphate and ⁴⁵Ca²⁺ efflux from prelabeled rat pancreatic islets have been evaluated to assess whether these ions move in concert throughout all phases of “stimulus-secretion coupling”. Perifusion with stimulatory concentrations of glucose elicited immediate but transitory increases in ³²P outflow accompanied by initial retardations and subsequent augmentations in net ⁴⁵Ca²⁺ outflows. These monophasic ³²P and biphasic ⁴⁵Ca²⁺ responses to secretory stimulation were abolished completely by membrane stabilization with tetracaine. However, certain manipulations enabled individual components to be modified separately. During stimulation with glucose, inhibition of insulin release by Ni²⁺ abolished the late increases in ⁴⁵Ca²⁺ outflow without affecting the initial retentions of ⁴⁵Ca²⁺ or the increased releases of ³²P. Under basal conditions, the ionophore A23187 “triggered” increased releases of ⁴⁵Ca²⁺ and insulin without prior retentions of ⁴⁵Ca²⁺ or enhancements of ³²P efflux. Thus, the immediate retardations of ⁴⁵Ca²⁺ outflow and heightened efflux of ³²P may reflect early events in stimulus-secretion coupling which can be dissociated from the augmented release of ⁴⁵Ca²⁺ accompanying activated emiocytosis.     

Role of beta 1- and beta 3-adrenoceptors in the regulation of lipolysis and thermogenesis in rat brown adipocytes

To evaluate the physiological functions of₁-,₂-, and₃-adrenoceptors (ARs) in brownadipose tissue, the lipolytic and respiratory effects of variousadrenergic agonists and antagonists were studied in rat brownadipocytes. The -agonists stimulated both lipolysis and respiration(8-10 times above basal levels), with the following order ofpotency (concentration eliciting 50% of maximum response):CL-316243 (₃) > BRL-37344(₃) > isoproterenol (mainly₁/₂) > norepinephrine (NE; mainly₁/₂) > epinephrine (mainly₁/₂) dobutamine (₁)  procaterol (₂). Schild plot coefficients of competitive inhibition experiments using ICI-89406 (₁ antagonist) revealed thatmore than one type of receptor mediates NE action. It is concluded fromour results that 1) NE, at low plasma levels (1-25 nM), stimulates lipolysis and respiration mainly through ₁-ARs,2) NE, at higher levels, stimulateslipolysis and respiration via both₁- and₃-ARs,3)₂-ARs play only a minor role,and 4)₃-ARs may represent thephysiological receptors for the high NE concentrations in the synapticcleft, where the high-affinity₁-ARs are presumablydesensitized. It is also suggested that lipolysis represents theflux-generating step regulating mitochondrial respiration.

     

The effect of total inorganic nitrogen and the balance between its ionic forms on adventitious bud formation and callus growth of ‘Węgierka Zwykła’ plum (<Emphasis Type="Italic">Prunus domestica</Emphasis> L.)

The effect of different ammonium NH ₄ ⁺ and nitrate NO ₃ ^? ratios (4:1, 2:1, 1:1, 1:2, 1:4, 1:6) on organogenesis of ‘W?gierka Zwyk?a’ leaf explants cultivated on media with nitrogen levels equalling full- or half-MS was investigated. On media with total nitrogen equal to ½ MS, explant regeneration increased significantly and was highest on media with 1:2 or 1:4 NH ₄ ⁺ :NO ₃ ^? ratio. An excess of ammonium versus nitrate ions had a negative effect on both regeneration and biomass. Addition of potassium to the medium increased the fresh weight of explants and the number of adventitious buds.     

Sex differences in adrenocortical structure and function

Summary The cytological aspects of sexual dimorphism in the rat adrenal cortex and its relationship to the gonads have been investigated. The adrenal glands of mature female rats were heavier than those of males, and morphometry showed that this was almost exclusively due to conspicuous differences in the volume of cells of the zona fasciculata (ZF) and zona reticularis (ZR). Stereology demonstrated that the volume of the mitochondrial and lipid droplet compartments, as well as the surface area per cell of mitochondrial cristae and smooth endoplasmic reticulum tubules, were markedly higher in the ZF and ZR cells of female animals. Orchiectomy increased and ovariectomy decreased the adrenal weight, by eliciting hypertrophy and atrophy, respectively, of ZF and ZR cells; these effects of gonadectomy were reversed by the appropriate gonadal hormone replacement. It is suggested that the sexual dimorphism of the rat adrenal cortex may depend upon the inhibitory action of testosterone and the stimulatory effect of estradiol on the hypothalamo-hypophyseal-adrenal axis.     

Über experimentell hervorgerufene strukturelle Veränderungen des Golgi-Apparates und der Mitochondrien sowie über Bildung von Myelinfiguren in Spermatocyten und Spermatiden von Helix lutescens

Zusammenfassung Es wird versucht, die Strukturveränderungen der Spermatocyten und Spermatiden vonHelix, welche sich unter der Einwirkung verschiedener hypo- und isotonischer Salzlösungen einstellen, physikalisch-chemisch zu erklären. In destilliertem Wasser blähen sich die Mitochondrien stark auf, während der Golgi-Apparat fast unverändert bleibt. Dagegen bleiben in isotonischen NH₄Cl- und in ammoniakhaltigen isotonischen NaCl-Lösungen die Mitochondrien unverändert, während der Golgi-Apparat sehr bald einer starken strukturellen Veränderung unterliegt. Die Gestaltveränderung des Golgi-Apparates kommt durch Verflüssigung seiner Substanz zustande, was durch Wasseraufnahme ermöglicht wird. Offenbar wird der Golgi-Apparat erst dann zur stärkeren Wasseraufnahme fähig, wenn seine Lipoid-Eiweiß-Verbindungen durch Ammoniak zum Teil aufgespalten werden. Die inHelix- Spermatiden experimentell hervorgerufenen strukturellen Veränderungen des Golgi-Apparates sind den normalen physiologischen Strukturveränderungen derselben Plasmakomponente in Insekten-Spermatiden sehr ähnlich. In Spermatiden lösen sich von den Hüllen der Golgi-Apparat-Elemente ihre Binnenkörper los und verschmelzen miteinander zu einer großen Kugel, welche in das Cytoplasma ausgestoßen wird. Dies ist einer Akrosombildung sehr ähnlich. Diese Strukturveränderungen sind zwar vital aber irreversibel. Bei langdauernder Einwirkung von NH₄Cl und NaHCO₃ bilden sich, schon nekrobiotisch, strang- und fibrillenförmige Myelinfiguren. Die letzteren entstehen aus dem Grundcytoplasma und bilden Knäuel, welche sich zu großen Kugeln verflüssigen. Auf der Zelloberfläche entstehen geißeiförmige Fortsätze, welche auch als Myelinfiguren gedeutet werden.     

Nitrate reductase activity in high-mountain plants: a test across species,growth form and habitat type

Aims For many terrestrial plants, nitrate is the most important form of available soil nitrogen for growth. However, many plant species, which grow on acidic, ammonium-dominated soils, exhibit a constantly low level of nitrate reductase activity (NRA). Little is known about NRA in high-mountain vascular plants in similar conditions. We tested the hypothesis that high-mountain vascular plants in acidic and ammonium-dominated habitats have low levels of NRA.