Oxytocin secretion induced by osmotic stimulation in rats during the estrous cycle and after ovariectomy and hormone replacement therapy

Hyperosmolality is a potent stimulus for the secretion of oxytocin. Oxytocinergic neurons are modulated by estrogen and oxytocin secretion in rats varies according to the phase of the estrous cycle, with higher activity during proestrus. We investigated the oxytocin secretion induced by an osmotic stimulus (0.5 M NaCl) in female rats. Plasma oxytocin and the oxytocin contents in the neurohypophysis and the paraventricular and supraoptic nuclei were determined during the morning (8-9 h) and afternoon (17-18 h) of the estrous cycle and after ovariectomy followed or not by hormone replacement. Plasma oxytocin peaked in control animals during proestrus. Oxytocin content decreased in the paraventricular and supraoptic nuclei during proestrus and estrus compared to diestrus and increased in the neurohypophysis during proestrus morning. No significant difference was observed in the oxytocin content of the neurohypophysis, nuclei or plasma between ovariectomized animals and ovariectomized animals treated with estrogen or estrogen plus progesterone. Therefore, any ovarian factor other than estrogen or progesterone seems to play a direct or indirect role in the increase in oxytocin secretion. The osmotic stimulus caused an increase in plasma oxytocin throughout the estrous cycle. A reduction in oxytocin content during diestrus and an increase during proestrus were observed in the paraventricular nuclei. In ovariectomized animals, the treatment with estrogen potentiated the response of oxytocin to the osmotic stimulus, with the response being even stronger in the case of estrogen plus progesterone. In conclusion, the ovarian steroids estrogen plus progesterone could modulate the osmoreceptor mechanisms related to oxytocin secretion.     

Influence of osmotica and abscisic acid on triglyceride accumulation in peanut somatic embryos

Attempts were made to determine the influence of sucrose, mannitol, sorbitol and abscisic acid on accumulation of triglycerides in peanut (Arachis hypogaea L.) somatic embryos. The results revealed that 0.584 m sucrose in the medium produced increased triglycerides in the embryos compared to the control. At 0.730 m sucrose, embryos were necrotic although the triglyceride content was high. Sorbitol at 0.6 m or abscisic acid at 20 μm were effective in increasing triglycerides in the embryos. The increase in triglycerides on a fresh-weight basis observed with increasing concentration of osmoticium was not apparent when determined in terms of dry weight. However, an increase in triglyceride as percent fresh weight observed in the presence of 20 μm abscisic acid remained unaltered when determined in terms of percent dry weight. An increase in storage lipid did not improve conversion of peanut somatic embryos. Received: 4 April 1997 / Revision received: 15 February 1998 / Accepted: 2 March 1998     

Application of the osmotic virial equation in cryobiology

The multisolute osmotic virial equation is the only multisolute thermodynamic solution theory that has been derived from first principles and can make predictions of multisolute solution behaviour in the absence of multisolute solution data. Other solution theories either (i) include simplifying assumptions that do not take into account the interactions between different types of solute molecules or (ii) require fitting to multisolute data to obtain empirical parameters. The osmotic virial coefficients, which are obtained from single-solute data, can be used to make predictions of multisolute solution osmolality. The osmotic virial coefficients for a range of solutes of interest in cryobiology are provided in this paper, for use with concentration units of both molality and mole fraction, along with an explanation of the background and theory necessary to implement the multisolute osmotic virial equation.     

Regulation of the paracellular Na+ and Cl- conductances by the NaCl-generated osmotic gradient in a manner dependent on the direction of osmotic gradients

In the present study, we investigated the effect of osmolality on the paracellular ion conductance (Gp) composed of the Na⁺ conductance (G_Na) and the Cl⁻ conductance (G_Cl). An osmotic gradient generated by NaCl with relatively apical hypertonicity (NaCl-absorption-direction) induced a large increase in the G_Na associated with a small increase in the G_Cl, whereas an osmotic gradient generated by NaCl with relatively basolateral hypertonicity (NaCl-secretion-direction) induced small increases in the G_Na and the G_Cl. These increases in the Gp caused by NaCl-generated osmotic gradients were diminished by the application of sucrose canceling the NaCl-generated osmotic gradient. The osmotic gradient generated by basolateral application of sucrose without any NaCl gradients had little effects on the Gp. However, this basolateral application of sucrose produced a precondition drastically quickening the time course of the action of the NaCl-generated osmotic gradient on the Gp. Further, we found that application of the basolateral hypotonicity generated by reduction of NaCl concentration shifted the localization of claudin-1 to the apical from the basolateral side. These results indicate that the osmotic gradient regulates the paracellular ion conductive pathway of tight junctions via a mechanism dependent on the direction of NaCl gradients associated with a shift of claudin-1 localization to the apical side in renal A6 epithelial cells.     

Effects of warm acclimation on serum osmolality,cortisol and hematocrit levels in the Antarctic fish, <Emphasis Type="Italic">Trematomus bernacchii</Emphasis>

Antarctic fish, such as the Trematomus bernacchii, living at −1.9°C maintain a serum osmolality of around 600 mOsm kg⁻¹, nearly twice that of temperate fish. Upon warm acclimation, Antarctic fish significantly lower their serum osmolality. It has been suggested that this response to warm acclimation is due to stress. The purpose of this study was to determine, whether upon warm acclimation there was a change in the levels of the stress hormone cortisol and hematocrit associated with the decrease in serum osmolality. T. bernacchii were warm acclimated up to 4 weeks and serum osmolality, cortisol and hematocrit were measured. Upon warm acclimation to +1.6 and +3.8°C over the course of 4 weeks, T. bernacchii significantly lowered their serum osmolality (from 547 ± 4 mOsm kg⁻¹ to 494 ± 6 and 489 ± 4 mOsm kg⁻¹, respectively), yet did not alter their serum cortisol (29 ± 6 nl ml⁻¹) or hematocrit (22 ± 1%) levels. These results suggest that warm acclimation does not induce a stress response in T. bernacchii.     

Influences of isotonic, hypertonic and hypovolemic treatments on vasopressin response and fluid-electrolyte balance in l-thyroxine-induced hyperthyroid rat

The present study was performed to determine how l-thyroxine-induced hyperthyroidism affects the vasopressin response to different stimulations (isotonic, hypertonic and hypovolemic) in rats. Spraque-Dawley rats were initially separated into 3 groups; control (n=24), sham hyperthyroidism (n=24, hyperthyroidism (n=24). At the end of the experiment additional sub-groups were formed before decapitation. These sub-groups were formed as; without stimulation (n=6), isotonic stimulation (n=6), hypertonic stimulation (n=6) and hypovolemic stimulation (n=6). Total T3, total T4 and AVP levels were evaluated in the plasma. Haematocrit and osmolality levels were also determined. When the parameters related to thyroid hormones were evaluated, it was determined that total T3 and T4 levels were higher in hyperthyroid group than the other groups. Plasma AVP levels showed more increase in hyperthyroid group both in basal grade and against to hypertonic and hypovolemic stimulations than the other groups (P<0.001). The results of the present study indicate that l-thyroxine-induced experimental hyperthyroidism increased basal and stimulated AVP release in rats.     

Extension of sperm motility leads to increased rates of fertilization and hatching in curimba,Prochilodus lineatus

The objective of this study was to evaluate the effects of six activating solutions on duration of sperm motility, fertilization rate (FR), and hatching rate (HR) of Prochilodus lineatus (Valenciennes, 1837). The activating solutions (SA) used were: SA₀ (199 mOsm kg^?1, pH 8.5), SA₁ (138 mOsm kg^?1, pH 7.5), SA₂ (256 mOsm kg^?1, pH 7.5), SA₃ (131 mOsm kg^?1, pH 10), NaCl (92 mOsm kg^?1, pH 7.5) and distilled water (32 mOsm kg^?1, pH 7.5). SA₁ induced the highest motility, FR and HR, compared with the other activating solutions. The lowest motility was obtained with SA₀, with no fertilization or hatching, whereas motility was zero with SA₂ and SA₃. It is possible to conclude that the solution SA₁ can be used for the activation of gametes during fertilization in induced reproduction of curimba to achieve higher fertilization and hatching rates. Thus, it was found that the osmolality and pH of activating solutions, probably with the participation of dissolved substances therein, are the main factors acting on semen motility after activation.     

Efficiency,thermodynamic and kinetic stability of marketed gadolinium chelates and their possible clinical consequences: a critical review

Gadolinium-based contrast agents are widely used to enhance image contrast in magnetic resonance imaging (MRI) procedures. Over recent years, there has been a renewed interest in the physicochemical properties of gadolinium chelates used as contrast agents for MRI procedures, as it has been suggested that dechelation of these molecules could be involved in the mechanism of a recently described disease, namely nephrogenic systemic fibrosis (NSF). The aim of this paper is to discuss the structure-physicochemical properties relationships of marketed gadolinium chelates in regards to their biological consequences. Marketed gadolinium chelates can be classified according to key molecular design parameters: (a) nature of the chelating moiety: macrocyclic molecules in which Gd3+ is caged in the pre-organized cavity of the ligand, or linear open-chain molecules, (b) ionicity: the ionicity of the complex varies from neutral to tri-anionic agents, and (c) the presence or absence of an aromatic lipophilic residue responsible for protein binding. All these molecular characteristics have a profound impact on the physicochemical characteristics of the pharmaceutical solution such as osmolality, viscosity but also on their efficiency in relaxing water protons (relaxivity) and their biodistribution. These key molecular parameters can also explain why gadolinium chelates differ in terms of their thermodynamic stability constants and kinetic stability, as demonstrated by numerous in vitro and in vivo studies, resulting in various formulations of pharmaceutical solutions of marketed contrast agents. The concept of kinetic and thermodynamic stability is critically discussed as it remains a somewhat controversial topic, especially in predicting the amount of free gadolinium which may result from dechelation of chelates in physiological or pathological situations. A high kinetic stability provided by the macrocyclic structure combined with a high thermodynamic stability (reinforced by ionicity for macrocyclic chelates) will minimize the amount of free gadolinium released in tissue parenchymas.     

Schistosoma mansoni: emergence of progeny-daughter sporocysts in monoxenic culture

Daughter sporocysts of Schistosoma mansoni released from mother sporocysts from Biomphalaria glabrata were cultured monoxenically for 21 days at 27.4 C in a medium consisting of a balanced salt-sugar solution supplemented with lactalbumin hydrolysate, inactivated fetal calf serum, serum Fraction A, and egg ultrafiltrate. The sporocysts were retained in transparent porous membranes so that their germinal development could be observed without interference from the underlying cells of Aedcs albopictus tissue cultures; the membrane permitted interchange of medium between sporocysts and cell cultures. The greatest increase in length, fivefold, occurred by 18 days. Progeny-daughters began to emerge at 9 days.The effects of pH, osmolality, and antibiotics were evaluated in axenizing solutions. Optimal conditions were a pH range of 6.5–7.6 and 113–153 mOsm. Antibiotics were not toxic.     

Osmotic and ionic regulation in response to salinity variations and cold resistance in the Arctic under-ice amphipod <Emphasis Type="Italic">Apherusa glacialis</Emphasis>

Amphipods living at the underside of Arctic sea ice are exposed to varying salinities due to freezing and melting, and have to cope with the resulting osmotic stress. Extracellular osmotic and ionic regulation at different salinities, thermal hysteresis, and supercooling points (SCPs) were studied in the under-ice amphipod Apherusa glacialis. The species is euryhaline, capable to regulate hyperosmotically at salinities S _R < 30 g/kg, and osmoconforms at salinities S _R ≥ 30 g/kg. Hyperosmotic regulation is an adaptation to thrive in low-salinity meltwater below the ice. Conforming to the ambient salinity during freezing reduces the risk of internal ice formation. Thermal hysteresis was not observed in the haemolymph of A. glacialis. The SCP of the species was −7.8 ± 1.9°C. Several ions were specifically downregulated ([Mg²⁺], [SO₄ ²⁻]), or upregulated ([K⁺], [Ca²⁺]) in comparison to the medium. Strong downregulation of [Mg²⁺], is probably necessary to avoid an anaesthetic effect at low temperatures.