Insulin-independent, MAPK-dependent stimulation of NKCC activity in skeletal muscle

Na(+)-K(+)-Cl(-) cotransporter (NKCC) activity in quiescent skeletal muscle is modest. However, ex vivo stimulation of muscle for as little as 18 contractions (1 min, 0.3 Hz) dramatically increased the activity of the cotransporter, measured as the bumetanide-sensitive (86)Rb influx, in both soleus and plantaris muscles. This activation of cotransporter activity remained relatively constant for up to 10-Hz stimulation for 1 min, falling off at higher frequencies (30-Hz stimulation for 1 min). Similarly, stimulation of skeletal muscle with adrenergic receptor agonists phenylephrine, isoproterenol, or epinephrine produced a dramatic stimulation of NKCC activity. It did not appear that stimulation of NKCC activity was a reflection of increased Na(+)-K(+)-ATPase activity because insulin treatment did not stimulate NKCC activity, despite insulin's well-known stimulation of Na(+)-K(+)-ATPase activity. Stimulation of NKCC activity could be blocked by pretreatment with inhibitors of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2) activity, indicating that activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) MAPKs may be required. These data indicate a regulated NKCC activity in skeletal muscle that may provide a significant pathway for potassium transport into skeletal muscle fibers.

Unique 5'-end of a Na(+)-K(+)-2Cl- cotransporter-like mRNA expressed in rat skeletal muscle

Functional evidence presented by others indicates that rat slow-twitch skeletal muscle lacks typical Na(+)-K(+)-2Cl- cotransporter activity, as determined by loop diuretic-sensitive potassium transport. This report presents a unique 5' mRNA sequence of a Na(+)-K(+)-2Cl- cotransporter-like molecule expressed in the rat soleus muscle and the deduced N-terminus of the protein. In addition to its unique 5' mRNA sequence, the coding region of the N-terminus is quite short compared with other known Na(+)-K(+)-2Cl- cotransporters. Nonetheless, the mRNA possesses conserved cotransporter-like membrane spanning domains, though one domains corresponding to a reported exon is divergent. Therefore, it appears that skeletal muscle does express a Na(+)-K(+)-2Cl- cotransporter-like mRNA that may code for a protein with atypical Na(+)-K(+)-2Cl- cotransporter properties.

Direct modulation of basal and angiotensin II-stimulated aldosterone secretion by hydrogen ions

Disturbances in acid-base balance in vivo are associated with changes in plasma aldosterone concentration, and in vitro changes in extracellular pH (pH(o)) influence the secretion of aldosterone by adrenocortical tissue or glomerulosa cells. There is considerable disparity, however, as to the direction of the effect. Furthermore, the mechanisms by which pH(o) independently affects aldosterone secretion or interacts with other secretagogues are not defined. Thus, bovine glomerulosa cells maintained in primary monolayer culture were used to examine the direct effects of pH(o) on cytosolic free calcium concentration ([Ca(2+)](i))( )and aldosterone secretion under basal and angiotensin II (AngII)-stimulated conditions. pH(o) was varied from 7.0 to 7.8 (corresponding inversely to changes in extracellular H(+) concentration from 16 nM to 100 nM). Whereas an elevation of pH(o) from 7.4 to 7.8 had no consistent effect, reductions of pH(o) from 7.4 to 7.2 or 7.0 caused proportionate increases in aldosterone secretion that were accompanied by increases in transmembrane Ca(2+) fluxes and [Ca(2+)](i). These effects were abolished by removal of extracellular Ca(2+). A decrease in pH(o) from 7.4 to 7.0 also enhanced AngII-stimulated aldosterone secretion. This effect was more pronounced at low concentrations of AngII and was manifested as an increase in the magnitude of the secretory response with no effect on potency. In contrast to its effect on AngII-stimulated aldosterone secretion, a reduction of pH(o) from 7.4 to 7.0 inhibited the Ca(2+) signal elicited by low concentrations (</=1x10(-10) M) of AngII, but did not affect the increase in [Ca(2+)](i) caused by a maximal concentration (1x10(-8) M) of AngII. These data suggest that pH(o) (i.e. H(+)) has multiple effects on aldosterone secretion. It independently increases aldosterone secretion through a mechanism involving Ca(2+) influx and an increase in [Ca(2+)](i). Also, it modulates the action of AngII by both decreasing the magnitude of the AngII-stimulated Ca(2+) signal and increasing the sensitivity of a more distal site to intracellular Ca(2+). The latter action appears to be a more important determinant in the effects of pH(o) on AngII-stimulated aldosterone secretion.

Molecular and functional evidence for Na(+)-K(+)-2Cl(-) cotransporter expression in rat skeletal muscle

Doubt has been raised about the expression of a functional Na(+)-K(+)-2Cl(-) cotransporter in rat skeletal muscle. In this study we present molecular and functional evidence for expression of a protein having the characteristics of a cotransporter. RT-PCR of RNA isolated from rat soleus muscle with primers to a conserved putative membrane-spanning domain resulted in a single product of predicted size. Sequencing of the product showed that it bears >90% homology with known rodent NKCC1 (BSC2) cotransporters. RNase protection assay of RNA isolated from the rat soleus muscle also identified this sequence. Immunologic detection of the cotransporter with two different antibodies indicated the presence of cotransporter protein, perhaps more than one, in blots of total muscle protein. Immunohistochemical detection by confocal microscopy localized the majority of expression of the protein to the muscle fibers. Functional studies of cotransport activity also indicate the appropriate sensitivity to inhibitors and ion dependence. Taken together, these data support the presence and function of Na(+)-K(+)-2Cl(-) cotransporter activity in the soleus muscle of the rat.

Potassium-induced aldosterone secretion involves a Cl(-)-dependent mechanism

Stimulation of aldosterone secretion by increases in extracellular potassium concentration is associated with increases in the volume of the adrenal glomerulosa cell. Because increases in cell volume have been associated with increases in aldosterone secretion, the effect of preventing the potassium-induced increase in cell volume by removal of chloride from the medium on the response of dispersed bovine glomerulosa cells grown in primary culture was determined. Totally replacing the chloride ion with the methylsulfate ion prevented the increase in cell volume and significantly suppressed the increase in aldosterone secretion normally associated with increasing [K] to 10 mM. In the absence of Cl-, the increase in cytosolic calcium concentration ([Ca2+]c) normally induced by increasing the [K] to 10 mM was also significantly suppressed. The replacement of 10 mM methylsulfate by Cl- restored the potassium-induced increase in both cell volume and aldosterone secretion to values not different from those found in the presence of 108 mM Cl-. The potassium-induced increase in cell volume was dependent also on the presence of extracellular calcium. Thus a component of the glomerulosa cell response to an increase in [K] may be caused by a chloride-dependent increase in cell volume that is triggered by the initial depolarization-induced increase in [Ca2+]c. The increase in cell volume enhances the increase in [Ca2+]c and amplifies the increase in aldosterone secretion.

Globulin-enriched protein supplements shorten the pre-compaction mitotic interval and promote hatching of murine embryos

PROBLEM

To determine whether Synthetic Serum Substitute (SSS), which contains human globulins in addition to Human Serum Albumin (HSA), is superior to HSA alone as a protein supplement for embryo culture.

METHOD

Development of mouse zygotes to eight-cell/compacting morulae and to hatching/hatched blastocysts was assessed in Human Tubal Fluid (HTF) medium containing either SSS of HSA.

RESULTS

Although there was no difference in the overall blastocyst rate at 120 h in HTF+SSS versus HTF+HSA, significantly more embryos at 54 h were at the eight-cell/compacting morula stage in HTF+SSS. At 120 h, there were more hatching/hatched blastocysts in HTF+SSS, and hatching correlated with SSS concentration. Addition of isolated globulins to HSA significantly stimulated the number of hatching/hatched blastocysts. Hatching could be "rescued" by transfer of embryos grown in HTF+HSA to globulin-containing media and prevented by removal of globulins as late as the compacted morula stage (54 h).

CONCLUSIONS

SSS is superior to HSA alone for embryo culture. The stimulatory effects on mitosis and hatching may be mediated directly by globulins or by other components in the globulin-enriched fraction.

Osmolality-induced changes in aldosterone secretion involve a chloride-dependent process

Alterations in extracellular osmolality have a powerful inverse effect on aldosterone secretion that is associated with sustained changes in cell volume. With dispersed bovine glomerulosa cells grown in primary culture, the effects of alterations in osmolality on cell volume measured by the distribution of [14C]urea and [3H]mannitol were determined in the presence and absence of chloride. In the presence of chloride, decreases in osmolality increased cell volume, whereas angiotensin II (< 4 x 10(-9) M) did not affect cell volume. When chloride was removed from the medium (replacing chloride with the impermeant methyl sulfate ion), cell volume decreased significantly, but basal aldosterone secretion was not altered. In the absence of chloride, the increases in cell volume, cytosolic calcium concentration, and aldosterone secretion induced by decreases in osmolality were significantly suppressed. The replacement of chloride with the methyl sulfate ion suppressed the increases in both cytosolic calcium concentration and aldosterone secretion induced by low (< 4 x 10(-9) M) but not high (4 x 10(-8) M) concentrations of angiotensin II. The results suggest that reductions in osmolality increase cell volume, partly by inducing an influx of chloride ions that contributes to the total net influx of water. Reductions in cell volume caused by an increase in osmolality or by replacing the chloride ion with the impermeant methyl sulfate ion may induce alterations in membrane stretch that may decrease the angiotensin II-induced increase in cytosolic calcium concentrations, which in turn suppresses aldosterone secretion.

Osmolality and potassium cause alterations in the volume of glomerulosa cells

Alterations in extracellular osmolality have a powerful inverse effect on aldosterone secretion and potassium- and angiotensin-stimulated aldosterone secretion. Whether alterations in extracellular osmolality produced sustained changes in cell volume that may contribute to the regulation of aldosterone secretion is not known. Using dispersed bovine glomerulosa cells grown in primary culture, the effect of alterations in osmolality on cell volume, measured by the distribution of [14C]urea and [3H]inulin and videometric analysis of the surface area of glomerulosa cells, was determined. Alterations in osmolality had an inverse effect on cell volume and surface area. Changes in cell volume induced by exposure to anisotonic medium were 52% greater (P > 0.02) than that predicted by the changes in osmolality. Increases in potassium concentration also caused sustained (1-h) concentration-dependent increases in cell volume and surface area. Angiotensin-II did not increase glomerulosa cell volume, but did produce a small dose-dependent transient increase in cell surface area. The results demonstrate that alterations in osmolality do cause sustained changes in cell volume, and thus, membrane stretch could be an important part of the cellular mechanism responsible for causing osmolality-induced changes in the cytosolic calcium concentration and subsequent alterations in aldosterone secretion. Alterations in membrane stretch may also be an important component of potassium-induced, but not angiotensin II-induced, aldosterone secretion.

Fatty acids may regulate aldosterone secretion and mediate some of insulin's effects on blood pressure

Experiments in vitro and observation made in humans suggest that some unesterified fatty acids (FA) participate, as inhibitors, in the regulation of aldosterone secretion. Removal of FA from adrenal glomerulosa cells with albumin increases the responses to angiotensin II (AII) and dibutyryl cyclic AMP. Micromolar concentrations of some FA including arachidonic, oleic, linoleic, eicosapentaenoic, and docosahexaenoic inhibit aldosterone secretion by adrenal glomerulosa cells. Inhibition is specific--some acids like stearic are inactive, and the adrenal fasciculata is relatively resistant to inhibition. Oleic acid rapidly and reversibly inhibits aldosterone secretion by perfused dog adrenals. Observations in vivo suggest a reciprocal relationship between plasma levels of FA and aldosterone: insulin infusion into dogs lowers plasma FA and increases adrenal responsiveness to All; salt infusions into humans increase plasma FA as aldosterone falls; plasma FA are low in low-renin essential hypertension where adrenal responsiveness to All is high; plasma FA are inversely correlated with ratios of aldosterone to renin in black hypertensives; and plasma FA are high in some seriously ill patients whose aldosterone levels are inexplicably low. All receptors and the final step of aldosterone biosynthesis, oxidation at the 18 position, are the adrenal sites most sensitive to FA. Insulin's antinatriuresis may be mediated in part by its ability to lower plasma FA and thereby enhance adrenal response to secretagogues.

Effect of osmolality on cytosolic free calcium and aldosterone secretion

Alterations in extracellular osmolality have powerful inverse effects on basal and potassium- and angiotensin-stimulated aldosterone secretion. With the use of bovine glomerulosa cells grown in primary culture, the effects of alterations in osmolality on cytosolic calcium concentration ([Ca2+]c), efflux and uptake of 45Ca2+, and aldosterone secretion were determined. Alterations in osmolality, independent of sodium concentration, have inverse effects on aldosterone secretion, which are correlated with simultaneous changes in [Ca2+]c measured using fura-2. Reductions in osmolality cause dose-dependent biphasic increases in [Ca2+]c different from the monophasic increases in [Ca2+]c produced by increases in potassium concentration. Like potassium- and angiotensin-stimulated increases in [Ca2+]c, hypotonically induced increases in [Ca2+]c are associated with an increase in 45Ca2+ efflux. Reductions in osmolality also increased the uptake of 45Ca2+, an effect apparent at 2 min and persistent for at least 30 min. In the absence of extracellular calcium, reductions in osmolality, as increases in potassium concentration but not angiotensin, fail to increase [Ca2+]c, efflux of 45Ca2+, or aldosterone secretion. In conclusion, osmolality-induced alterations in aldosterone secretion are associated with parallel changes in [Ca2+]c, effects caused by alteration in the influx of extracellular calcium. On the basis of these and previous studies, we hypothesize that osmolality affects calcium influx by activating voltage-dependent or stretch-activated calcium channels.

Insulin prevents glucose induced inhibition of angiotensin II-stimulated aldosterone secretion

In humans with diabetes mellitus or in individuals given infusions of insulin or insulin plus glucose, plasma aldosterone levels have been reported to be suppressed. Whether insulin has a direct effect to suppress aldosterone secretion by the adrenal gland has not been established. The effect of insulin on glucose-induced inhibition of angiotensin II-stimulated aldosterone secretion was examined. The effect of glucose and insulin plus glucose on angiotensin II-stimulated aldosterone secretion was examined in isolated perfused canine adrenal glands. In the absence of insulin, 15.6 mM glucose decreased angiotensin II-stimulated aldosterone secretion by 35 +/- 7%, while in the presence of insulin the same glucose concentration had no significant effect on angiotensin II-stimulated aldosterone secretion. In contrast, insulin had no effect on NaCl-induced inhibition of angiotensin II-stimulated aldosterone secretion. Neither insulin alone nor saline vehicle affected angiotensin II-stimulated aldosterone secretion. These results (1) demonstrate that insulin can prevent inhibition of glucose-induced angiotensin II-stimulated aldosterone secretion, possibly by preventing a glucose-induced decrease in cell volume, and (2) suggest that the suppressed plasma level of aldosterone found in individuals with diabetes mellitus may in part be due to the direct effects of hyperglycemia on the adrenal gland secretion of aldosterone.

In Water Deprivation, Osmolality Becomes an Important Determinant of Aldosterone Secretion

The adrenal gland secretion of aldosterone is closely linked to the volume and composition of the plasma compartment via the renin-angiotensin II system. In contrast, alterations in the plasma concentration of potassium and in plasma osmolality significantly alter aldosterone secretion by a direct action on the adrenal gland.

Altered sensitivity of osmotically stimulated vasopressin release in quadriplegic subjects

Osmoregulation of vasopressin release was studied in 15 quadriplegic subjects (Quad) and 7 healthy control subjects (Con). Hypertonic NaCl (0.85 M) was infused intravenously (0.05 ml.kg-1.min-1) over 90 min in studies on supine subjects and in comparable studies on the same subjects erect (sitting). Erect posture in Quad, but not in Con, was accompanied by orthostatic reductions in arterial blood pressure and by significantly increased plasma aldosterone (P less than 0.001) and cortisol (P less than 0.001) concentrations and increased plasma renin activity (P less than 0.025). Changes in plasma arginine vasopressin concentration (PAVP) during hypertonic NaCl infusions were also greater in erect than in supine Quad (P less than 0.005), despite identical changes in plasma osmolality (Posm). Linear regression analysis of the PAVP/Posm relationship during hypertonic NaCl infusions showed highly significant correlations (P less than 0.0002) in both Quad and Con. Mean slope values for regression lines, however, were significantly higher in erect than in supine Quad (P less than 0.005) but did not differ in relation to posture in Con. Differences in posture were not associated with differences in abscissal intercepts in either Quad or Con. These studies show significant alterations in the sensitivity of osmotically stimulated vasopressin release related to differences in posture in Quad, characterized by enhanced sensitivity in erect posture due to nonosmotic stimuli not evident in Con.

Calcium dependence of osmolality-, potassium-, and angiotensin II-induced aldosterone secretion

Different calcium-dependent mechanisms may be involved in mediating stimulus-induced aldosterone secretion. Using isolated perfused canine adrenal glands, we determined the effect of reductions in extracellular [Ca2+] and of infusion of a voltage-dependent calcium channel antagonist, nifedipine, on aldosterone secretion induced by decreases in osmolality, by increases in [K+], or by infusion of angiotensin II (ANG II). Aldosterone secretion was stimulated to a similar level by reducing osmolality, by increasing [K+], or by infusing ANG II. After 50 min of stimulation, lowering [Ca2+] from 1.25 to 0.10 mM caused a marked and similar inhibition of osmolality- and [K+]-induced aldosterone secretion that was significantly greater than inhibition of ANG II-induced aldosterone secretion. Similarly, nifedipine at 3.3 X 10(-8) M caused marked and similar inhibition of osmolality- and [K+]-induced aldosterone secretion that was significantly greater than the inhibition of ANG II-induced aldosterone secretion. These data demonstrate that calcium-dependent processes are involved in osmolality-, [K+]-, and ANG II-induced aldosterone secretion. However, the calcium-dependent process(es) evoked by reductions in osmolality or increases in [K+] are considerably different from that evoked by ANG II. Osmolality and potassium appear to induce aldosterone secretion primarily by activating voltage-dependent calcium channels.

Absence of a direct effect of recombinant interleukins and cultured peritoneal macrophages on early embryonic development in the mouse

On the basis of their recent studies, several researchers have suggested that the infertility associated with mild endometriosis is due to the alteration of peritoneal fluid, resulting in impairment of the viability of gametes or embryos. Elevated numbers of macrophages and lymphocytes have been reported in the peritoneal fluid of patients with endometriosis. Interleukin-1 (IL-1) a major product of activated macrophages and Interleukin-2 (IL-2), a product of most activated T-cells, have been postulated to play a role in the infertility associated with this disease, possibly by acting as direct embryotoxic agents. We have examined the effect of purified recombinant IL-1 and IL-2, which are not species-specific, on in vitro development of mouse embryos. Both interleukins had no effect on development to the blastocyst stage or on early stages of implantation, as measured in vitro by attachment and outgrowth of blastocysts to fibronectin-coated dishes. Moreover, co-culture of mouse embryos with activated human peritoneal macrophages had no effect on embryogenesis. We conclude that neither IL-1, nor other products of human macrophages activated by lipopolysaccharide, nor IL-2 are directly toxic to early mouse embryonic development.

Effect of vasopressin on adrenal steroidogenesis

The direct effect of vasopressin on adrenal steroidogenesis and its effect on angiotensin II- and adrenocorticotropic hormone (ACTH)-stimulated steroidogenesis was evaluated by using an isolated perfused canine adrenal gland preparation. Infusions of vasopressin alone (50, 100, or 250 pg/ml perfusate) had no significant effect on the secretion of either aldosterone or cortisol. Infusions of vasopressin at 75 or 250 pg/ml perfusate during stimulation of steroidogenesis by angiotensin II or by ACTH did not cause a consistent increase in aldosterone secretion. In contrast, infusion of 250 but not 75 pg vasopressin/ml perfusate caused a consistent enhancement of ACTH-stimulated cortisol secretion. The infusion of a vasopressin V1-receptor agonist, but not of either a vasopressin V2-receptor agonist or oxytocin, also caused a significant enhancement of ACTH-stimulated cortisol secretion. These results suggest that the sensitivity of fasciculata cells to vasopressin is greater than that of glomerulosa cells. Finally, levels of vasopressin reported to occur in plasma during severe hemorrhage appear to be capable of enhancing cortisol secretion by a direct action on the adrenal gland via a V1-receptor mechanism.

Dissociation of osmotic and ionic modulation of aldosterone secretion

Although other investigators have suggested that reductions in either Na or chloride concentration stimulate aldosterone secretion, we previously found that small reductions in NaCl (3-7 mM) that enhanced angiotensin II-(ANG II) and [K]- but not adrenocorticotropic hormone (ACTH)-stimulated aldosterone secretion are due to a change in osmolality. In the present study, aldosterone secretion by an isolated perfused canine adrenal gland was stimulated by low doses of ANG II or ACTH or by small increases in perfusate [K], and during this stimulation, replacing 25 mM NaCl with an isosmotic amount of mannitol enhanced aldosterone secretion induced by each of the above secretagogues. Choline chloride significantly enhanced ANG II-stimulated aldosterone secretion when used in place of 25 mM NaCl, but sodium methylsulfate did not. Large isosmotic reductions in [NaCl] failed to alter ACTH-stimulated cortisol secretion or the conversion of either exogenous corticosterone or 11-deoxycorticosterone to aldosterone. Thus, reductions in Na, but not in chloride concentration, specifically enhance the ability of the adrenal glomerulosa to secrete aldosterone in response to ANG II, K, and ACTH by an action on some site in the steroidogenic cascade that is sensitive to ANG II, potassium, and ACTH.

Specificity of effect of osmolality on aldosterone secretion

Small (3-7 mM) changes in [NaCl] have a marked inverse effect on angiotensin II- or K-stimulated aldosterone secretion by the isolated, perfused canine adrenal gland. The effect is due to the accompanying changes in osmolality rather than to the changes in [Na] or [Cl]. The present study was undertaken to determine whether osmolality is a specific and discrete signal that modulates the secretion of aldosterone only or is simply a nonspecific physical factor that alters the secretion of other adrenocortical hormones as well. The study also determined whether small changes in osmolality affect the conversion of corticosterone to aldosterone. The secretion of both cortisol and aldosterone by isolated canine adrenal glands responded in a dose-dependent fashion to adrenocorticotropin (ACTH), but in contrast to the rapid and potent modulating action of osmolality reported previously for angiotensin II- or K-stimulated aldosterone secretion, changes in osmolality at the midpoint of ACTH infusion had no detectable effect on either cortisol secretion or, unexpectedly, aldosterone secretion. This indicates that osmolality is a highly specific signal that modulates responsiveness of the zona glomerulosa to the factors, angiotensin II and K, which are considered to be most important in the acute regulation of aldosterone secretion, but does not influence secretion of cortisol by inner zones of the adrenal cortex. In glands treated with agents that block aldosterone production from endogenous precursors, small changes in osmolality had no detectable effect on the conversion of exogenous corticosterone to aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake and metabolism of nucleosides by embryos of the sea urchin Strongylocentrotus purpuratus

Uptake and metabolism of thymidine and adenosine have been studied in embryos of the sea urchin Strongylocentrotus purpuratus. Uptake of these nucleosides is found to be mutually competitive, with the Km for uptake of thymidine similar to its Ki for inhibition of adenosine uptake and vice versa. The metabolic studies show that adenosine is rapidly and completely phosphorylated upon entry, even at high exogenous concentrations which saturate the uptake mechanism. In contrast, at concentrations which saturate nucleoside uptake, thymidine becomes appreciably catabolized (up to 60%) to thymine and beta-amino-isobutyric acid in addition to its phosphorylation to thymine nucleotides. Negligible amounts of endogenous thymidine appear to remain unmetabolized following uptake in these embryos. The data provide strong in vivo evidence for separate metabolic pathways for thymidine and adenosine which have not previously been described in this organism. The observation of mutual competition during uptake, together with different routes of metabolism for these nucleosides, would suggest that the rate-limiting step in the uptake process is transport rather than metabolism. The specificity of this transport system for its nucleoside substrate has been examined in some detail in the present report. All naturally occurring nucleosides but only a limited number of nucleoside analogs are recognized by this membrane carrier. Neither purine nor pyrimidine bases are substrates for this transport system. Previous work by this laboratory has demonstrated the strict Na+-dependence of this carrier, its high affinity for nucleoside substrate, and its activation at fertilization. These observations and the substrate specificity studies of the present work together describe a unique transport system for nucleosides in sea urchin embryos which is quite different from those previously described in mammalian cells.

Effect of osmolality on angiotensin-stimulated aldosterone production by primary cultures of bovine adrenal glomerulosa cells

Studies were performed to examine the relationship between osmolality and aldosterone production using primary cultures of bovine adrenal glomerulosa cells. Cell monolayers were incubated under hypo- (234 mOsm), iso- (274 mOsm), or hyperosmotic (318 mOsm) conditions in the absence or presence of angiotensin II (10(-12) M to 10(-9) M). Although basal steroidogenesis was unaffected, angiotensin II-stimulated aldosterone production was inversely related to osmolality. Mannitol and NaCl were equally effective as osmotic particles. Thus, modulation of angiotensin II-stimulated aldosterone secretion produced in vivo by changes in plasma osmolality result, in part, from a direct effect on the glomerulosa cells.

Effect of hydrogen ion concentration on aldosterone secretion by isolated perfused canine adrenal glands

The direct effects of changes in extracellular hydrogen ion (H+) concentration on aldosterone secretion under basal, angiotensin II- and potassium-stimulated conditions were studied in isolated, perfused canine adrenal glands. Changes in extracellular H+ concentration were induced by altering either the partial pressure of CO2 (pCO2) or the HCO3- concentration of the perfusate. Acid-base disturbances had a more pronounced effect on aldosterone secretion under stimulated than under basal conditions. Increasing H+ concentration enhanced angiotensin II- and potassium-stimulated aldosterone secretion, whereas decreasing H+ concentration markedly inhibited the secretory response to these stimuli. Because changes in H+ concentration, whether produced by varying extracellular pCO2 or extracellular HCO3- concentration, had similar effects on angiotensin II-stimulated aldosterone secretion, the data suggest that H+ concentration per se is the important determinant of the aldosterone secretory rate. Interestingly, during the immediate recovery period from pCO2-induced alkalosis under both angiotensin II- and potassium-stimulated conditions, aldosterone secretion always returned to a value significantly higher than that obtained just before alkalosis. The results of this study demonstrate that changes in extracellular H+ concentration influence the rate of aldosterone secretion, possibly via changes in intracellular pH, by a direct action on the canine adrenal gland. Therefore, when evaluating the control of aldosterone secretion, the acid-base status of the whole animal or of in-vitro adrenal tissue must be considered.

Effect of hydrogen ion concentration on corticosteroid secretion

The direct effects of changes in extracellular hydrogen ion (H+) concentration on corticosteroid secretion under basal and ACTH-stimulated conditions were studied in isolated, perfused canine adrenal glands. Changes in extracellular H+ concentration were produced by altering either PCO2 or [HCO-3] of the Krebs-bicarbonate perfusate. Alkalosis markedly inhibited ACTH-stimulated aldosterone secretion. Moreover, within the range of pH from 7.19 to 7.85, there was a positive correlation between H+ concentration and the fractional secretion of aldosterone but a negative correlation between H+ concentration and the fractional secretion of corticosterone and 18-hydroxycorticosterone in response to ACTH. In contrast, neither acidosis nor alkalosis had a significant, direct effect on basal or ACTH-stimulated cortisol secretion. We conclude that 1) H+ concentration modulates the stimulatory effect of ACTH on aldosterone secretion by a direct action on the adrenal cortex, 2) acid-base disturbances are specific to the zona glomerulosa of the canine adrenal gland, and 3) H+ concentration may influence events occurring late in the pathway for aldosterone biosynthesis.

Effect of osmolality on aldosterone secretion

The purpose of these experiments was to determine if the powerful effect of sodium chloride concentration on angiotensin II- and potassium-stimulated aldosterone secretion by isolated perfused adrenal glands is mediated by the sodium or chloride ion or by the obligatory change in osmolality. We used isolated Ringer's bicarbonate perfused canine adrenal gland preparations to determine the effects of a variety of isosmotic, hyperosmotic, and hyposmotic solutions on angiotensin II- and potassium-stimulated aldosterone secretion. When we increased the osmolality of the perfusion medium (8-10 mosmol) by the addition of NaCl, sucrose, mannitol, or glucose, angiotensin II-stimulated aldosterone secretion was inhibited to a similar extent, whereas urea addition had no effect. Similarly, when we increased the osmolality of the perfusion medium (8-10 mosmol) by the addition of NaCl, sucrose, or mannitol, potassium-stimulated aldosterone secretion was also inhibited to a similar extent. In contrast to the increase in angiotensin II- and potassium-stimulated aldosterone secretion observed during hyposmotic reductions in NaCl concentration, (addition of sucrose) did not increase angiotensin II- or potassium-stimulated aldosterone secretion. Even the marked increase in aldosterone secretion caused by large hyposmotic reduction in NaCl concentration did not occur with an equivalent isosmotic reduction in NaCl concentration. These results clearly demonstrate that changes in NaCl concentration affect aldosterone secretion by a mechanism sensitive to the osmolality. Moreover, since hyperosmolality caused by urea addition had no effect on angiotensin II-stimulated aldosterone secretion, changes in intracellular volume or composition appear to be an important modulator of aldosterone secretion.

Activation of Na+-dependent transport at fertilization in the sea urchin: requirements of both an early event associated with exocytosis and a later event involving increased energy metabolism

Transport of glycine, phosphate, and thymidine has been studied in parallel in eggs and embryos of Strongylocentrotus purpuratus. Uptake of each of these substrates is shown to be sodium dependent and expressed at fertilization in this species. The data indicate that activation of unfertilized eggs by ammonia does not result in significant expression of any of these transport systems compared to fertilized eggs. Activation of unfertilized eggs by sperm or by ionophore A-23187 in seawater results in complete development of these transport systems. However, if eggs are activated by ionophore in sodium-free seawater or fertilized by sperm in complete seawater and transferred to sodium-free seawater, Na+-dependent transport does not develop. Ammonia reverses the inhibitory effect of sodium-free seawater on development of these transport systems. This reversal is sensitive to 2,4-dinitrophenol. The data suggest that transport of glycine, phosphate, and thymidine share a common mechanism of activation. Moreover, this activation requires both an early event (less than 5 min postinsemination) and a later event involving increased energy metabolism.

Plasma corticosterone and volume after preoptic recess lesions and volume depletion

The effects of extracellular fluid volume depletion on plasma corticosterone concentration (Pcort) and plasma volume in rats were determined after recovery from either electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V region) or control surgery. Rats received either furosemide injections and sodium-free chow or isotonic saline injections and continued access to sodium-replete food. One week after these injections some animals were decapitated and trunk blood collected for analysis of Pcort by radioimmunoassay. The remainder of the rats were implanted with femoral arterial catheters to obtain blood samples for measurement of plasma and blood volumes by calculating dilution of 125I-labeled serum albumin. Volume-replete rats with AV3V lesions had significantly higher Pcort concentrations and smaller plasma and blood volumes than volume-replete control-operated animals. Furthermore, volume depletion induced by furosemide caused a significant increase in Pcort concentration only in rats with AV3V ablations, whereas plasma and blood volumes were significantly lowered in both groups. These data demonstrate that AV3V periventricular ablation results in a chronic elevation of Pcort in the volume-replete animals and an exaggerated glucocorticoid response to volume depletion. These data show that decreased PV characteristic of animals with AV3V lesions is not due to glucocorticoid insufficiency.

Sodium-dependent transport of inorganic sulfate by rabbit renal brush-border membrane vesicles. Effects of other ions

A Na+ gradient (extravesicular greater than intravesicular) increased the rate of inorganic sulfate (SO24-) uptake into renal brush-border membrane vesicles and energized the transient accumulation of the anion against its concentration gradient, indicating a secondary active transport system. Stimulation of SO24- uptake was specific for Na+. The anions, SO23-, S2O23-, SeO24-, MoO24-, CrO24-, and WO24-, but not HPO24-, cis-inhibited and trans-stimulated SO24- uptake, suggesting that these divalent anions shared the SO24- carrier. The Na+/SO24- co-transport and Na+. The apparent Km for SO24- was 0.6 mM at 100 mM Na+. The relationship between Na+ concentration and rate of SO24- uptake was sigmoidal. From a Hill analysis of the data a [Na+]0.5 of 36 mM and an n value of 1.6 were calculated. Comparisons of the effects of a K+ diffusion potential (inside positive), of a H+ diffusion potential (inside negative), of Na+ salts of anions of different conductances on the Na+-dependent uptakes of SO24- and D-glucose, and of the responses of a membrane potential-sensitive fluorescent probe concomitant with the uptakes indicate that Na+/SO24- co-transport was electroneutral. The simplest stoichiometry consistent with an electroneutral mechanism would be the co-transport of two Na+ and one SO24-. Na+ gradient-dependent SO24- uptake was enhanced by intravesicular Cl-. cis-Cl- inhibited the efflux as well as the influx of SO24-. These findings suggest that Cl- was an inhibitor of SO24- transport. Intravesicular K+ stimulated Na+ gradient-dependent SO24- uptake. The co-transport of Na+/SO24- appeared not to be coupled to the transmembrane flux of K+. It is hypothesized that the co-transport system contained an internal site activated by K+.

Effect of sodium concentration on aldosterone secretion by isolated perfused canine adrenal glands

Small changes in sodium concentration [( Na]) are not generally considered to have a major direct effect on aldosterone secretion. However, a marked disruption in the renin-aldosterone relationship has been observed in a variety of hypernatremic and hyponatremic states. Therefore, we evaluated the hypothesis that small changes in [Na] have a potent direct effect on angiotensin II- and potassium-stimulated aldosterone secretion. The left adrenal gland, abdominal aorta, and surrounding periadrenal tissue were surgically isolated from mongrel dogs and perfused with Ringers bicarbonate solution at a pressure of approximately 57 mm Hg. Infusion of a KCl test solution at the beginning and end of most experiments produced similar increases in aldosterone secretion, thus documenting the stability of these preparations. After a stable response was established to either a low dose of angiotensin II or a small increase in perfusate [K], the [Na] was changed by adding or removing NaCl. Changing perfusate [Na] from 152 to 139 mM during the infusion of either angiotensin II or potassium caused 20- to 25-fold increases in aldosterone secretion. Increasing perfusate [Na] from 145 to 152 mM inhibited aldosterone secretion to a greater extent during stimulation by lower doses (40-50 pg/ml) than by higher doses (80-100 pg/ml) of angiotensin II. These data demonstrate that during moderate stimulation by angiotensin II or potassium, small changes in [Na] have a powerful inverse effect on aldosterone secretion by a direct action on the canine adrenal gland.

Preoptic recess lesions, body fluid compartments, and the renin-aldosterone system

The effects of electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V) of the rat brain on body fluid distribution and the renin-aldosterone system were determined. Rats underwent either ablation of AV3V periventricular tissue or control surgeries. After recovery, animals were implanted with femoral arterial and jugular venous catheters, and sodium space and plasma volume were measured by calculating the dilution of intravenous injections of 22Na- and 125I-labeled serum albumin, respectively. Total body water was determined in separate groups of rats by desiccation. Other animals with AV3V lesions and control rats were used to measure urinary sodium excretion and plasma renin (Prenin) and aldosterone (Paldo) concentrations while volume replete and after volume depletion. Animals with AV3V lesions had expanded extracellular fluid volume and decreased plasma volume, but total body water was comparable with control-operated rats. Volume-replete and volume-depleted rats with AV3V lesions had significantly higher Prenin than control animals in similar volume states. Although Paldo was not different between groups in the volume-replete state, it was significantly greater in rats with AV3V lesions than in control animals after volume depletion. These data demonstrate that AV3V periventricular ablation results in chronic alterations in the normal body fluid distribution but does not diminish the rats' ability to increase Prenin and Paldo or decrease sodium excretion during volume depletion.

Effect of water deprivation on urinary excretion of PGE2 in the dog

We examined the influence of the state of hydration on the urinary excretion of prostaglandin E2 (PGE2) and kallikrein in the dog. Immunoreactive PGE2 and kallikrein were measured in the urine of conscious dogs during periods of water deprivation and periods of free access to drinking water and in the urine of time-control dogs that had free access to water throughout the study. During water deprivation the excretion of kallikrein did not change significantly, but PGE2 excretion increased by 50 and 75% (P less than 0.05) after 2 and 4 days, respectively, associated with reductions of body weight and urine flow and with elevation of plasma renin activity, plasma sodium, and both plasma and urine osmolality. Dehydrated dogs drank copiously when allowed free access to water, and over the following 4 days both PGE2 excretion and plasma renin activity fell significantly, associated with elevation of body weight and urine volume and with lowering of plasma sodium and plasma and urine osmolality. In contrast, if after 4 days of water deprivation the dogs were kept at a constant level of dehydration by restricting their water allotment on subsequent days to 300 ml/day, PGE2 excretion and most other variables remained at the dehydration level. In conclusion, these results suggest that renal PGE2 production is dependent on the state of hydration in the dog.

Effects of converting enzyme inhibition with captopril on renal function in normal and ACTH treated sheep

1. The effect on renal function in sheep of inhibiting converting enzyme with captopril was examined before and after 5 days ACTH administration. 2. Glomerular filtration rate, effective renal plasma flow, effective renal blood flow, mean arterial pressure and plasma sodium were all significantly increased by ACTH treatment and plasma potassium was decreased. Captopril (20 mg i.v.) had no effect on renal function or blood pressure before or after ACTH treatment, although urinary potassium excretion decreased following captopril on day 6 of ACTH treatment. 3. The increase in glomerular filtration rate and effective renal plasma flow seen with ACTH treatment in sheep does not appear to be mediated by the reninangiotensin system.

The effect of dietary sodium on the blood pressure response to dopamine infusion in the conscious rat

1. The influence of dietary sodium intake on the pressor response to intravenously infused dopamine in the conscious rat was studied. 2. Chronic sodium restriction significantly reduced the pressor response to infused dopamine, whereas high sodium diet enhanced the response. 3. Sodium intake is an important determinant of the pressor response to dopamine.

Dietary sodium intake: a determinant of postprandial plasma sodium concentration in the dog

1. The effect of dietary sodium intake on pre- and post-prandial plasma sodium concentrations and on the pattern of sodium and potassium excretion was determined in conscious female dogs, who were allowed free access to water and were fed on commercial low sodium diets supplemented with 0, 50, 100 or 250 mmol of sodium chloride/day for 6 days. 2. The preprandial plasma sodium concentration was not altered by the dietary sodium intake. However, the 4 h postprandial plasma sodium concentration was linearly related to the magnitude of dietary sodium intake, whereas the 8 h postprandial plasma sodium concentration was elevated only in dogs receiving 250 mmol of sodium/day. 3. The (0-8 h/0-24 h) ratio for urinary sodium excretion was significantly correlated with both the dietary sodium intake and the postprandial increase in plasma sodium concentration. 4. The 24 h excretion of potassium was not markedly affected by the dietary sodium intake; however, the (0-8 h/0-24 h) ratio for potassium excretion was significantly correlated with both the dietary sodium intake and the (0-8/0-24 h) ratio for sodium excretion. 5. These data indicate that: (a) postprandial increases in plasma sodium concentration need to be considered when evaluating the mechanisms involved in the daily regulation of sodium balance; (b) the daily pattern of potassium excretion is closely linked to the dietary sodium intake.

Renal and endocrine response to water deprivation in dog

Plasma and urine sodium, potassium, osmolality, aldosterone, and plasma renin activity (PRA) were measured in time controls and during control dehydration and rehydration periods in conscious dogs fed a 50 mmol NaCl diet. During 4 days of water restriction, plasma sodium and osmolality and PRA were elevated, whereas plasma potassium and aldosterone were not affected. Urinary potassium excretion was elevated above intake levels during the entire dehydration period, whereas Na excretion was only elevated during the first 2 days of dehydration. Unrestricted rehydration was associated with a marked fall in plasma sodium and osmolality, a decrease in PRA, and no change in plasma potassium or aldosterone. In addition, during the 1st day of rehydration, there was marked retention of sodium and potassium. Thus, in the dog, dehydration and subsequent rehydration cause significant alterations in sodium and potassium balance and marked alterations in PRA that are not associated with changes in either plasma aldosterone concentration or urinary aldosterone excretion.

Aldosterone and the enhanced natriuresis of hypertonic infusions in the dog

The purpose of this study was to determine whether small elevations in plasma sodium concentration (PNa) were effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in dogs fed normal sodium diets. Ten dogs fed a normal sodium diet, six DOCA-treated dogs, and four adrenalectomized dogs were given the same sodium load (2.5 mmol/kg) either as a hypertonic (1 M NaCl) or hypotonic (0.1 M NaCl) infusion. In all three groups of dogs, PNa was greater after the hypertonic than after the hypotonic infusion during most of the 22-h experiment. The dogs fed a normal sodium diet responded to the elevation in PNa (hypertonic infusion) with decreased aldosterone excretion and an exaggerated natriuresis. When aldosterone levels were maintained constant by either DOCA treatment or adrenalectomy, the exaggerated natriuresis that accompanied the hypertonic infusion was prevented. Therefore, elevation of PNa appears to be an important determinant of aldosterone secretion and, hence, of sodium excretion in conscious dogs fed normal sodium diets.

Stimulation of the efflux of L-glutamate from renal brush-border membrane vesicles by extravesicular potassium

The rate of efflux of L-glutamate from renal brush-border membrane vesicles was enhanced by Na+ and by extravesicular L-glutamate, but not by D-glutamate nor analogs of L-glutamate that do not share the Na+-L-glutamate co-transport system. These results suggest that efflux was mediated by the Na+-L-glutamate carrier. The efflux of L-glutamate was increased by extravesicular K+ or Rb+ but not by Li+, choline+, or Tris+. These findings, together with previous results showing that intravesicular K+ or Rb+ increased L-glutamate uptake and that a K+ gradient energized the concentrative uptake of the acidic amino acid in the absence of other gradients, provide evidence consistent with the hypothesis that the co-transport of Na+-L-glutamate is coupled to the transmembrane flux of K+.

Effect of hypertonic and hypotonic infusions on aldosterone in conscious sodium-depleted dogs

1. The role of the plasma sodium concentration in the regulation of aldosterone secretion and sodium excretion was investigated by comparing in 13 conscious sodium-depleted dogs the effects of the same sodium load (2.5 mmol/kg) given as either a hypertonic or hypotonic infusion. 2. The plasma sodium concentration was significantly higher and the plasma aldosterone concentration and urinary aldosterone excretion were significantly lower after the hypertonic infusion as compared with the hypotonic infusion. 3. The cumulative urinary sodium excretion during the 22 h after beginning the infusion was significantly greater after the hypertonic infusion, but this difference was not observed in five sodium-depleted dogs who were treated with deoxycorticosterone acetate before the infusions were given. 4. These data suggest that elevations in plasma sodium concentration are effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in conscious sodium-depleted dogs.

Lack of evidence for gastrointestinal control of sodium excretion in unanesthetized rabbits

Experiments were performed to determine whether unanesthetized rabbits exhibit a greater natriuresis after oral administration of a hypertonic sodium chloride solution (1.5 mmol NaCl/kg) than after the intravenous administration of the same solution. Male rabbits (New Zealand) were placed on a low sodium diet for 4 days, and on the fifth day a hypertonic NaCl solution (616 mM) was given either by stomach tube (GI) or intravenously (IV), while an equal volume of a hypotonic NaCl solution (31 mM) was given by the alternate route. The studies were repeated on each rabbit so that paired observations were obtained. No differences in plasma Na concentration, peripheral hematocrit, or urinary sodium excretion were observed between the GI and IV groups after administration of the hypertonic NaCl solution. In seven rabbits that were permitted access to food and water following NaCl administration by either route, urinary sodium excretion tended to be reduced (P = 0.08), but, again, no significant differences in plasma sodium concentration, peripheral hematocrit, or urinary sodium excretion were observed between the GI and IV routes of sodium administration. Accordingly, we could find no evidence to support the existence of a GI or portal Na receptor system that regulates urinary sodium excretion in the unanesthetized rabbit.

Haemodynamic effects of increasing extracellular potassium concentration in ACTH-induced hypertension in sheep

1. ACTH administration (20 microgram day-1 kg-1) to sheep produces hypertension associated with a raised cardiac output and hypokalaemia. 2. The aim of the present experiments was to detail the haemodynamic changes associated with restoration of the extracellular potassium concentration in sheep with ACTH-induced hypertension. 3. After 7 days of ACTH treatment potassium chloride (10 mmol/h) was infused for 3 days to restore plasma [K+] to the pre-ACTH value. 4. ACTH reduced plasma [K+] from 4.4 +/- 0.1 to 3.2 +/- 0.2 mmol/l but 3 days of potassium chloride infusion returned plasma [K+] to 4.3 +/- 0.2 mmol/l. 5. ACTH increased mean arterial pressure from 67 +/- 2 to 88 +/- 1 mmHg in the first 7 days and it remained elevated during potassium chloride infusion (91 +/- 5 mmHg on day 10). 6. Cardiac output rose with 7 days ACTH treatment from 4.9 +/- 0.2 to 6.0 +/- 0.6 l/min but fell progressively with potassium chloride infusion to 4.9 +/- 0.3 l/min on day 10. 7. These studies suggest that potassium status or extracellular [K+] may play a role in determining the haemodynamic profile associated with steroid-induced hypertension.

Evidence for a peritubular-to-luminal flux phosphate in the dog kidney

The possible presence of a direct influx of phosphate into the tubular lumen of the dog kidney was examined by two different techniques. A 0.3-ml bolus of 32PO4 and [3H]inulin was injected into the renal artery of dogs with and without phosphate loading. The mean urinary transit time (TT) for PO4 was consistently less than the TT for inulin in nonphosphate-loaded dogs. Following phosphate loading the TT for phosphate approached but did not equal the TT for inulin. In contrast, after microinjections of 32PO4 and [3H]inulin into proximal tubules, the urinary TT of PO4 was significantly longer than the TT of inulin. The application of 32PO4 and [3H]inulin to the surface of the left kidney was associated with a greater recovery of 32PO4 from the left kidney compared to that from the right kidney. The recovery of [3H]inulin was proportional to the glomerular filtration rate for both kidneys. Application of the 32PO4 and [3H]inulin to the surface of a muscle resulted in an equal recovery of phosphate and inulin from both kidneys. The results demonstrate the presence of a detectable tubular influx of phosphate.

Partial purification and properties of diglyceride kinase from Escherichia coli

Diglyceride kinase (diacylglycerol kinase, E.C. 2.7.1.-), an enzyme localized in the inner membrane of Escherichia coli, has been purified about 600-fold. The purified enzyme exhibits an absolute requirement for magnesium ion; its activity toward both lipid and nucleotide substrates is stimulated by diphosphatidylglycerol or other phospholipids. Adenine nucleotides are much better substrates for the enzyme than are other purine or pyrimidine nucleotides. The purified enzyme preparation catalyzes the phosphorylation of a number of lipids, including ceramide and several ceramide and diacylglycerol-like analogs. The broad lipid substrate specificity of diglyceride kinase suggests that this enzyme may function in vivo for the phosphorylation of an acceptor other than diacylglycerol.

Isolation and characterization of the liponucleotides of Saccharomyces cerevisiae

The liponucleotide fraction of Saccharomyces cerevisiae was isolated from cells grown on tritiated uracil and identified as CDPdiacylglycerol on the basis of (1), its behavior as a single compound upon DEAE-cellulose and thin-layer chromatography; (2), its extreme lability to mild alkaline methanolysis; and (3), its hydrolysis by the CDPdiacylglycerol hydrolase of Escherichia coli to yield tritiated 5'-CMP. At most, only about 5% of yeast liponucleotide could be dCDPdiacylglycerol, in contrast to the presence of nearly equimolar amounts of CDP-and dCDPdiacylglycerols in E. coli. Although no CDPceramide could be detected in the liponucleotide fraction of this organism, the possibility still exists that it may be an intermediate in the biosynthesis of sphingolipids in systems yet to be examined.

Effect of parathyroid hormone secretion on sodium reabsorption by the proximal tubule

To determine if an increase in the endogenous secretion of parathyroid hormone could decrease sodium reabsorption by the proximal tubule, the ionized calcium concentration of blood perfusing the parathyroid gland of eight unilaterally thyroid parathyroidectomized dogs (TPTX) was reduced by infusion of an isotonic sodium citrate plus sodium chloride solution into the blood supply of the parathyroid gland. The fractional clearance of phosphate increased significantly (+9.3 +/- 2.8 ml/min per 100 ml GFR), while fractional sodium reabsorption by the proximal tubule decreased (-.06 +/- .02; P less than .025). In seven normal control dogs that received isotonic sodium chloride infusion, neither fractional sodium reabsorption by the proximal tubule nor the fractional clearance of phosphate was significantly altered. In five bilaterally TPTX dogs that received a sodium citrate plus sodium chloride infusion, sodium reabsorption by the proximal tubule was not significantly altered. There were no significant changes in glomerular filtration rate or renal plasma flow in any of these groups. The data demonstrate that alterations in endogenous parathyroid hormone secretion can play a significant role in the regulation of sodium reabsorption by the proximal tubule.

Role of parathyroid hormone in the phosphaturia of extracellular fluid volume expansion

Role of parathyroid hormone in the phosphaturia of extracellular fluid volume expansion. Acute expansion of the extracellular fluid volume increases the urinary excretion of phosphate. The present study examined the importance of increased plasma parathyroid hormone concentration in the phosphaturia accompanying acute extracellular fluid volume expansion (ECVE). Infusion of a calcium-free Ringer's solution into dogs was associated with increased urinary phosphateexcretion and serum immunoreactive parathyroid hormone concentration (iPTH), the latter being significantly correlated with a decrease in plasma ionized calcium concentration. Prevention of the fall in plasma ionized calcium concentration by infusion of a calcium containing Ringer's solution prevented the increase in serum iPTH but the magnitude of the phosphaturia was not affected.