Sex differences in osmotic regulation of AVP and renal sodium handling.

To determine sex differences in osmoregulation of arginine vasopressin (AVP) and body water, we studied eight men (24 +/- 1 yr) and eight women (29 +/- 2 yr) during 3% NaCl infusion [hypertonic saline infusion (HSI); 120 min, 0.1 ml. kg body wt(-1). min(-1)]. Subjects then drank 15 ml/kg body wt over 30 min followed by 60 min of rest. Women were studied in the early follicular (F; 16.1 +/- 2.8 pg/ml plasma 17beta-estradiol and 0.6 +/- 0.1 ng/ml plasma progesterone) and midluteal (L; 80.6 +/- 11.4 pg/ml plasma 17beta-estradiol and 12.7 +/- 0.7 ng/ml plasma progesterone) menstrual phases. Basal plasma osmolality was higher in F (286 +/- 1 mosmol/kgH(2)O) and in men (289 +/- 1 mosmol/kgH(2)O) compared with L (280 +/- 1 mosmol/kgH(2)O, P < 0.05). Neither menstrual phase nor gender affected basal plasma AVP concentration (P([AVP]); 1.7 +/- 4, 1.9 +/- 0.4, and 2.2 +/- 0.5 pg/ml for F, L, and men, respectively). The plasma osmolality threshold for AVP release was lowest in L (x-intercept, 263 +/- 3 mosmol/kgH(2)O, P < 0.05) compared with F (273 +/- 2 mosmol/kgH(2)O) and men (270 +/- 4 mosmol/kgH(2)O) during HSI. Men had greater P([AVP])-plasma osmolality slopes (i.e., sensitivity) compared with F and L (slopes = 0.14 +/- 0.04, 0.09 +/- 0.01, and 0.24 +/- 0.07 for F, L, and men, respectively, P < 0.05). Despite similar Na+-regulating hormone responses, men excreted less Na+ during HSI (0.7 +/- 0.1, 0.7 +/- 0.1, and 0.5 +/- 0.1 meq/kg body wt for F, L, and men, respectively, P < 0.05). Furthermore, men had greater systolic blood pressure (119 +/- 5, 119 +/- 5, and 132 +/- 3 mmHg for F, L, and men, respectively, P < 0.05) than F and L. Our data indicate greater sensitivity in P([AVP]) response to changes in plasma osmolality as the primary difference between men and women during HSI. In men, this greater sensitivity was associated with an increase in systolic blood pressure and pulse pressure during HSI, most likely due to a shift in the pressure-natriuresis curve.     

Estrogen and progesterone effects on transcapillary fluid dynamics

The purpose of this study was to determine estrogen (E(2)) and progesterone (P(4)) effects on atrial natriuretic peptide (ANP) control of plasma volume (PV) and transcapillary fluid dynamics. To this end, we suppressed reproductive function in 12 women (age 21-35 yr) using a gonadotropin releasing-hormone (GnRH) analog (leuprolide acetate) for 5 wk. During the 5th week, the women either received 4 days of E(2) administration (17beta-estradiol, transdermal patch, 0.1 mg/day) or 4 days of E(2) with P(4) administration (vaginal gel, 90 mg P(4) twice per day). At the end of the 4th and 5th week of GnRH analog and hormone administration, we determined PV (Evans blue dye) and changes in PV and forearm capillary filtration coefficient (CFC) during a 120-min infusion of ANP (5 ng x kg body wt(-1) x min(-1)). Preinfusion PV was estimated from Evans blue dye measurement taken over the last 30 min of infusion based on changes in hematocrit. E(2) treatment did not affect preinfusion PV relative to GnRH analog alone (45.3 +/- 3.1 vs. 45.4 +/- 3.1 ml/kg). During ANP infusion CFC was greater during E(2) treatment compared with GnRH analog alone (6.5 +/- 1.4 vs. 4.9 +/- 1.4 microl. 100 g(-1) x min(-1) mmHg(-1), P < 0.05). The %PV loss during ANP infusion was similar for E(2) and GnRH analog-alone treatments (-0.8 +/- 0.2 and -1.0 +/- 0.2 ml/kg, respectively), indicating the change in CFC had little systemic effect on ANP-related changes in PV. Estimated baseline PV was reduced by E(2)-P(4) treatment. During ANP infusion CFC was approximately 30% lower during E(2)-P(4) (6.0 +/- 0.5 vs. 4.3 +/- 4.3 microl. 100 g(-1) x min(-1) mm Hg(-1), P < 0.05), and the PV loss during ANP infusion was attenuated (-0.9 +/- 0.2 and -0.2 +/- 0.2 ml/kg for GnRH analog-alone and E(2)-P(4) treatments, respectively). Thus the E(2)-P(4) treatment lowered CFC and reduced PV loss during ANP infusion.     

Dehydration and fluid balance: central effects of angiotensin

Central effects of dehydration are stimulated by osmotic stimuli, the reduced input of volume receptors, and angiotensin II. The subfornical organ (SFO) and organum vasculosum laminae terminalis (OVLT) have become accepted as putative receptor sites for angiotensin II in the brain. The exact quantitative relationship between the hours of water deprivation and the amount of angiotensin generated peripherally and whether that amount is sufficient to induce thirst centrally have not been established, but there is no question that when animals are dehydrated their angiotensin levels rise and the animals are thirsty. Attempts to block centrally the contribution of angiotensin II to thirst have been variable and cholinergic inputs have to be blocked at the same time. Various stimuli for thirst interact in a parallel fashion, and when one stimulus is blocked the other stimuli are still effective. Plasma angiotensin II may induce natural thirst, but how it enters the brain still remains to be explained. Although the SFO and OVLT have no blood-brain barrier, the blood supply to these organs acts as a limited perfusion system whereby blood-borne proteins cannot diffuse far from the capillary bed. A second set of receptors is found on the ventricular surface of the OVLT, as shown by fluorescence labeled angiotensin II. The connection between the SFO and OVLT was cut by discrete knife cuts. Drinking to angiotensin II intraventricularly was not significantly altered but the pressor response was reduced by 50%. These results can be explained by a circuit for drinking passing down below the level of the knife cut and a separate pressor pathway passing dorsally through the area that was cut by the knife. Thirst and pressor neural circuits beginning with angiotensin receptors could explain some of the data accumulated with the AV3V syndrome that occurs when the OVLT and nucleus medianas are destroyed.     

The regulation of osmotic and ionic balance in fish reproduction and in the early stages of ontogeny

On the basis of the modern literature data we analyzed the influence of the level of salt concentration and ion composition in a fish habitat during the processes of reproduction. The results of studies of the mechanisms of the reaction of fish to gamete hypo- and hyperosmotic stimulus in the external aqueous environment, as well as the role of mineral and organic osmolytes in the adaptation of mature eggs of fishes in the external environment, depend on the hydrochemical and hydrological conditions of the spawning grounds. The paper provides information about the features of the endocrine regulation of oocyte maturation in fish spawning in different hydrological conditions and the importance of humoral factors in the pathological process of the maturation of fish oocytes. The main scientific and practical aspects of the formation of the phys mechanisms that regulate the water-salt balance is the early ontogeny of fishes are discussed.     

Estrogen and androgen influence hypothalamic AVP and CRF concentrations in fetal and adult sheep

The present study tested the hypothesis that action of sex steroids on the hypothalamus-pituitary-adrenal (HPA) axis is measurable in the hypothalamus. Late-gestation fetal sheep were treated (5 mg/21 days) with either estradiol, androstenedione, or tamoxifen and compared to age-matched control fetuses. Tamoxifen significantly increased hypothalamic corticotropin releasing factor (CRF) and arginine vasopressin (AVP) concentrations, and androstenedione significantly decreased hypothalamic CRF concentration. Adult sheep were treated with estrone (10 mg/21 days), and responded with significant increases in hypothalamic AVP concentration, but not in immunoreactive ACTH concentration or processing within the pituitary. The results demonstrate that the effect of estrogen on the HPA axis is measurable in the hypothalamus, and is therefore not primarily at the anterior pituitary.     

Turnover of galactosylglycerol and osmotic balance in ochromonas

Osmotic balance in Ochromonas malhamensis is mediated directly by fluctuations in the pool size of α-galactosylglycerol (isofloridoside). Chase experiments with glucose-¹⁴C indicate that the pool is in rapid turnover even at constant size. The turnover rate is related to the pool size. Regulation of the pool size seems to occur at enzymic steps involved in the formation, as well as those involved in the degradation of isofloridoside.     

Stress and water balance: the roles of ANP, AVP and isatin

Stress is often associated with water retention and its resolution with diuresis. The biological systems for the control of stress and water balance are very closely related. Corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) are co-localised in the hypothalamus and often act synergistically. Atrial natriuretic peptide (ANP) can exert a feedback control on the hypothalamic/pituitary/adrenal axis. ANP has been shown to be anxiolytic, whereas AVP may be anxiogenic. AVP and ANP levels have been found to be abnormal in a range of stress disorders and psychiatric illnesses. Isatin is an endogenous anxiogenic factor which is also a potent inhibitor of the ANP receptor. It may provide a link between the function of monoamines during stress, and the control of water balance by ANP.     

Estrogen regulation of testicular function

Evidence supporting a role for estrogen in male reproductive tract development and function has been collected from rodents and humans. These studies fall into three categories: i) localization of aromatase and the target protein for estrogen (ER-alpha and ER-beta) in tissues of the reproductive tract; ii) analysis of testicular phenotypes in transgenic mice deficient in aromatase, ER-alpha and/or ER-beta gene; and, iii) investigation of the effects of environmental chemicals on male reproduction. Estrogen is thought to have a regulatory role in the testis because estrogen biosynthesis occurs in testicular cells and the absence of ERs caused adverse effects on spermatogenesis and steroidogenesis. Moreover, several chemicals that are present in the environment, designated xenoestrogens because they have the ability to bind and activate ERs, are known to affect testicular gene expression. However, studies of estrogen action are confounded by a number of factors, including the inability to dissociate estrogen-induced activity in the hypothalamus and pituitary from action occurring directly in the testis and expression of more than one ER subtype in estrogen-sensitive tissues. Use of tissue-specific knockout animals and administration of antiestrogens and/or aromatase inhibitors in vivo may generate additional data to advance our understanding of estrogen and estrogen receptor biology in the developing and mature testis.     

Estrogen effects on MMP-13 and MMP-14 regulation of left ventricular mass in Dahl salt-induced hypertension

Background:Female Dahl salt-sensitive (DS) rats fed a low-salt diet develop hypertension at 6 months of age. Ovariectomy at 2 months of age accelerates the development of hypertension, and estrogen replacement delays it. Although acute pressure overload induces structural changes in the left ventricle (LV) further effects of gradual hypertension on LV remodeling have not been examined in the DS rat model.Objective: The purpose of this study was to test the hypothesis that aging and estrogen loss in hypertensive DS rats are accompanied by changes in LV remodeling.Methods: Four groups of DS rats were examined: young intact, middle-aged (MA) intact, MA ovariectomized (MA-OVX), and MA-OVX with 17β-eestradiol (E₂) supplementation (MA-OVX+E²). Myocardial matrix metalloproteinases (MMPs),tissue inhibitors of metalloproteinases (TIMPs),and extracellular matrix (ECM) proteins were assessed by immunoblotting.Results: Each of the 4 groups comprised 6 animals. Mean (SEM) LV mass was significantly greater in the MA-intact and the MA-OVX groups (1257 [31] mg and 1199 [25] mg, respectively; both, P < 0.05) compared with the young-intact group (697 [6] mg). LV mass in the MA-OVX+E₂ group was significantly lower compared with the MA-intact and MA-OVX groups (both, P < 0.05), suggesting that estrogen may attenuate LV remodeling.Fibronectin and collagen III and IV concentrations increased significantly in the MA-intact and MA-OOVX groups (all, P < 0.05),indicating increased fibrosis. Multiple MMPs also increased in the MA-intact an nd MA-OVX rats, including MMP-3, -7, -99, -113, and -114, and all TIMPs. In contrast, estrogen attenuated fibrosis by increasing MMP-8 concentrations and increasing collagen III fragments. From good-fit regression modeling, MMP-13 and MMP-14 concentrations correlated positively with LV mass for the MA-intact and MA-OVX groups, respectively.Conclusions: Gradual hypertension stimulated ECM turnover by increasing both MMP/TIMP production and ECM degradation.Estrogen loss or gain resulted in a shift in MMP profiles, suggesting that MMP-13 and MMP-14 may be differentially regulated in postmenopausal hypertension.     

Effects of starvation and dehydration on osmotic and ionic balance in Carausius morosus

This study describes the effects that prolonged desiccation has on osmotic and ionic balance in Carausius morosus, an insect with a rather unusual haemolymph composition (it is rich in divalent cations and has a low sodium content). After 7 days at 0% r.h., there is a 50 per cent decrease in water content of the animal. This loss is largely confined to the haemolymph, which declines in volume to about one-seventh of its previous value. In spite of these drastic changes, the osmotic concentration of the haemolymph increases only by about 20 per cent while the concentrations of the main blood ions increase by similar or smaller amounts. So, as with other insects so far examined, Carausius turns out to have very effective control of the osmotic and ionic concentrations of its internal milieu in the face of severe stress upon it.     

Model study of the effects of interactions between systemic and peripheral circulation on interstitial fluid balance

Interstitial fluid balance is severely altered in microgravity, but the mechanisms underlying the fluid shift from lower to upper body are still partially unclear. A lumped parameter model of the arterial tree with active and non linear modulation of peripheral resistances and capillary fluid exchange was adopted to simulate the response of microcirculation to pulsatility and edema. Results suggest that myogenic regulation not only impinges on arteriolar radius, but it also indirectly affects interstitial fluid balance. Non linear dynamics of blood pressure (BP) and flow in capillary beds are influenced by systemic pulsatility, hinting that local activity is involved in the response to peripheral edema as well.     

A comparison of the effects of aspirin and histamine on fluid balance in the recruited lung

Salicylate administration has been reported to increase the flow of protein-rich lymph from lungs of animals, however, the mechanism of this response is unclear. In the present study we measured pulmonary hemodynamics and lung fluid and lung fluid and protein flux in anesthetized sheep, surgically prepared for the collection of lung lymph, in order to examine the possible effect of aspirin (ASP) on lung vascular permeability. ASP was given during recruitment of pulmonary microvascular surface area induced by sustained elevation of left atrial pressure (Pla) (Group 1) or continuous infusion of adenosine triphosphate (ATP) (Group 2). We compared the results of ASP administration to those found in similarly prepared animals given histamine (H) during like periods of increased Pla (Group 3) or ATP infusion (Group 4). ASP administration resulted in increased lymphatic protein clearance (Cp) in both Groups 1 and 2. In Group 1, following the characteristic increase in lung lymph flow (Q1) and fall in the ratio of lung lymph to plasma protein concentration (L/P) produced by Pla elevation, ASP administration resulted in a further increase in Q1 and a significant increase in L/P. The results found in ASP animals are qualitatively similar to those observed in Groups 3 and 4 after H. While we cannot specifically rule out a hemodynamic effect of the drug, our results suggest the increased protein flux observed following ASP administration was mediated at least in part through and increase in lung microvascular permeability.     

Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption

Shirreffs, Susan M., and Ronald J Maughan. Restorationof fluid balance after exercise-induced dehydration: effects of alcoholconsumption. J. Appl. Physiol. 83(4):1152-1158, 1997.The effect of alcohol consumption on therestoration of fluid and electrolyte balance after exercise-induceddehydration [2.01 ± 0.10% (SD) of body mass] wasinvestigated. Drinks containing 0, 1, 2, and 4% alcohol were consumedover 60 min beginning 30 min after the end of exercise; a differentbeverage was consumed in each of four trials. The volume consumed(2,212 ± 153 ml) was equivalent to 150% of body mass loss. Peakurine flow rate occurred later (P = 0.024) with the 4% beverage. The total volume of urine produced overthe 6 h after rehydration, although not different between trials(P = 0.307), tended to increase as thequantity of alcohol ingested increased. The increase in blood(P = 0.013) and plasma(P = 0.050) volume with rehydrationwas slower when the 4% beverage was consumed and did not increase tovalues significantly greater than the dehydrated level(P = 0.013 andP = 0.050 for blood volume and plasmavolume, respectively); generally, the increase was an inverse functionof the quantity of alcohol consumed. These results suggest that alcoholhas a negligible diuretic effect when consumed in dilute solution aftera moderate level of hypohydration induced by exercise in the heat.There appears to be no difference in recovery from dehydration whetherthe rehydration beverage is alcohol free or contains up to 2% alcohol,but drinks containing 4% alcohol tend to delay the recovery process.

     

Comparison of the effects of surface tension and osmotic pressure on the interfacial hydration of a fluid phospholipid bilayer

The effects of three so-called kosmotropic solutes, namely, betaine, sucrose, and choline chloride on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine large unilamellar vesicles, were studied by measuring the generalized polarization (GP) for the fluorescence emission of the membrane partitioning probe Laurdan. The latter has been shown to be sensitive to the depth of water penetration into phospholipid bilayers. At equal osmotic pressures the three solutes produced different increments in GP, with a qualitative positive correlation. However, the increments in GP correlated also quantitatively with the increase of air-water surface tension caused by the three kosmotropes. Our findings suggest surface tension to determine the impact of these solutes on the lateral packing of the lipid bilayer. Based on the changes in area/lipid at different surface tensions, the equilibrium lateral pressure for a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer at 25 degrees C was estimated to be approximately 34 mN/m.     

Novel regulation of aquaporins during osmotic stress

Aquaporin protein regulation and redistribution in response to osmotic stress was investigated. Ice plant (Mesembryanthemum crystallinum) McTIP1;2 (McMIPF) mediated water flux when expressed in Xenopus leavis oocytes. Mannitol-induced water imbalance resulted in increased protein amounts in tonoplast fractions and a shift in protein distribution to other membrane fractions, suggesting aquaporin relocalization. Indirect immunofluorescence labeling also supports a change in membrane distribution for McTIP1;2 and the appearance of a unique compartment where McTIP1;2 is expressed. Mannitol-induced redistribution of McTIP1;2 was arrested by pretreatment with brefeldin A, wortmannin, and cytochalasin D, inhibitors of vesicle trafficking-related processes. Evidence suggests a role for glycosylation and involvement of a cAMP-dependent signaling pathway in McTIP1;2 redistribution. McTIP1;2 redistribution to endosomal compartments may be part of a homeostatic process to restore and maintain cellular osmolarity under osmotic-stress conditions.