Male kidney-specific BMAL1 knockout mice are protected from K+-deficient, high-salt diet-induced blood pressure increases

The circadian clock protein basic helix-loop-helix aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a transcription factor that impacts kidney function, including blood pressure (BP) control. Previously, we have shown that male, but not female, kidney-specific cadherin Cre-positive BMAL1 knockout (KS-BMAL1 KO) mice exhibit lower BP compared with littermate controls. The goal of this study was to determine the BP phenotype and immune response in male KS-BMAL1 KO mice in response to a low-K+ high-salt (LKHS) diet. BP, renal inflammatory markers, and immune cells were measured in male mice following an LKHS diet. Male KS-BMAL1 KO mice had lower BP following the LKHS diet compared with control mice, yet their circadian rhythm in pressure remained unchanged. Additionally, KS-BMAL1 KO mice exhibited lower levels of renal proinflammatory cytokines and immune cells following the LKHS diet compared with control mice. KS-BMAL1 KO mice were protected from the salt-sensitive hypertension observed in control mice and displayed an attenuated immune response following the LKHS diet. These data suggest that BMAL1 plays a role in driving the BP increase and proinflammatory environment that occurs in response to an LKHS diet.NEW & NOTEWORTHY We show here, for the first time, that kidney-specific BMAL1 knockout mice are protected from blood pressure (BP) increases and immune responses to a salt-sensitive diet. Other kidney-specific BMAL1 knockout models exhibit lower BP phenotypes under basal conditions. A salt-sensitive diet exacerbates this genotype-specific BP response, leading to fewer proinflammatory cytokines and immune cells in knockout mice. These data demonstrate the importance of distal segment BMAL1 in BP and immune responses to a salt-sensitive environment.

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Circadian clocks of the kidney: function, mechanism, and regulation

An intrinsic cellular circadian clock is located in nearly every cell of the body. The peripheral circadian clocks within the cells of the kidney contribute to the regulation of a variety of renal processes. In this review, we summarize what is currently known regarding the function, mechanism, and regulation of kidney clocks. Additionally, the effect of extrarenal physiological processes, such as endocrine and neuronal signals, on kidney function is also reviewed. Circadian rhythms in renal function are an integral part of kidney physiology, underscoring the importance of considering time of day as a key biological variable. The field of circadian renal physiology is of tremendous relevance, but with limited physiological and mechanistic information on the kidney clocks this is an area in need of extensive investigation.

Acclimation to a High-Salt Diet Is Sex Dependent

Background Premenopausal women are less likely to develop hypertension and salt-related complications than are men, yet the impact of sex on mechanisms regulating Na+ homeostasis during dietary salt challenges is poorly defined. Here, we determined whether female rats have a more efficient capacity to acclimate to increased dietary salt intake challenge. Methods and Results Age-matched male and female Sprague Dawley rats maintained on a normal-salt (NS) diet (0.49% NaCl) were challenged with a 5-day high-salt diet (4.0% NaCl). We assessed serum, urinary, skin, and muscle electrolytes; total body water; and kidney Na+ transporters during the NS and high-salt diet phases. During the 5-day high-salt challenge, natriuresis increased more rapidly in females, whereas serum Na+ and body water concentration increased only in males. To determine if females are primed to handle changes in dietary salt, we asked the question whether the renal endothelin-1 natriuretic system is more active in female rats, compared with males. During the NS diet, female rats had a higher urinary endothelin-1 excretion rate than males. Moreover, Ingenuity Pathway Analysis of RNA sequencing data identified the enrichment of endothelin signaling pathway transcripts in the inner medulla of kidneys from NS-fed female rats compared with male counterparts. Notably, in human subjects who consumed an Na+-controlled diet (3314-3668 mg/day) for 3 days, women had a higher urinary endothelin-1 excretion rate than men, consistent with our findings in NS-fed rats. Conclusions These results suggest that female sex confers a greater ability to maintain Na+ homeostasis during acclimation to dietary Na+ challenges and indicate that the intrarenal endothelin-1 natriuretic pathway is enhanced in women.

Circadian Rhythm Effects on the Molecular Regulation of Physiological Systems

Nearly every system within the body contains an intrinsic cellular circadian clock. The circadian clock contributes to the regulation of a variety of homeostatic processes in mammals through the regulation of gene expression. Circadian disruption of physiological systems is associated with pathophysiological disorders. Here, we review the current understanding of the molecular mechanisms contributing to the known circadian rhythms in physiological function. This article focuses on what is known in humans, along with discoveries made with cell and rodent models. In particular, the impact of circadian clock components in metabolic, cardiovascular, endocrine, musculoskeletal, immune, and central nervous systems are discussed. © 2021 American Physiological Society. Compr Physiol 11:1-30, 2021.

Endothelin B receptors impair baroreflex function and increase blood pressure variability during high salt diet

Baroreflex function is an integral component maintaining consistent blood pressure. Hypertension is often associated with baroreflex dysfunction, and environmental risk factors such as high salt diet exacerbate hypertension in subjects with baroreflex dysfunction. However, the interactions between high salt diet, baroreflex dysfunction, and hypertension are incompletely understood. The endothelin system is another potent mediator of blood pressure control especially in response to a high salt diet. We hypothesized that the endothelin B (ETB) receptor activation on adrenergic nerves decreases baroreflex sensitivity. We utilized male ETB receptor deficient (ETB-def) rats that express functional ETB receptors only on adrenergic nerves and transgenic (TG) controls to evaluate baroreflex function during normal (0.49% NaCl) and high (4.0% NaCl) salt diets. In conscious rats equipped with telemetry, ETB-def rats had an increased lability of systolic blood pressure (SBP) compared to TG controls as indicated by higher standard deviation (SD) of SBP under both normal (10.2 ± 0.6 vs. 12.4 ± 0.9 mmHg, respectively, p = 0.0001) and high (11.7 ± 0.6 vs. 16.1 ± 1.0 mmHg, p = 0.0001) salt diets. In anesthetized preparations, ETB-def rats displayed reduced heart rate (p genotype = 0.0167) and renal sympathetic nerve (p genotype = 0.0022) baroreflex sensitivity. We then gave male Sprague-Dawley rats the selective ETB receptor antagonist, A-192621 (10 mg/kg/day), to block ETB receptors. Following ETB receptor antagonism, even though SBP increased (131 ± 7 before vs. 152 ± 8 mmHg after, p < 0.0001), the lability (standard deviation) of SBP decreased (9.3 ± 2.0 vs. 7.1 ± 1.1 mmHg, p = 0.0155). These data support our hypothesis that ETB receptors on adrenergic nerves contribute to baroreflex dysfunction.

Diurnal Control of Blood Pressure Is Uncoupled From Sodium Excretion

The diurnal rhythms of sodium handling and blood pressure are thought to be regulated by clock genes, such as Bmal1. However, little is known about the regulation of these factors by Bmal1, especially in rats. Using a novel whole-body Bmal1 knockout rat model (Bmal1-/-), we hypothesized that time of day regulation of sodium excretion is dependent on Bmal1. Using telemetry to continuously record mean arterial pressure, we observed that male and female Bmal1-/- rats had significantly reduced mean arterial pressure over the course of 24 hours compared with littermate controls. The circadian mean arterial pressure pattern remained intact in both sexes of Bmal1-/- rats, which is in contrast to the Bmal1-/- mouse model. Male Bmal1-/- rats had no significant difference in baseline sodium excretion between 12-hour active and inactive periods, indicating a lack of diurnal control independent of maintained mean arterial pressure rhythms. Female Bmal1-/- rats, however, had significantly greater sodium excretion during the active versus inactive period similar to controls. Thus, we observed a clear dissociation between circadian blood pressure and control of sodium excretion that is sex dependent. These findings are consistent with a more robust ability of females to maintain control of sodium excretion, and furthermore, demonstrate a novel role for Bmal1 in control of diurnal blood pressure independent of sodium excretion.

Differences in renal BMAL1 contribution to Na+ homeostasis and blood pressure control in male and female mice

The renal circadian clock has a major influence on the function of the kidney. Aryl hydrocarbon receptor nuclear translocator-like protein 1 [ARNTL; also known as brain and muscle ARNT-like 1 (BMAL1)] is a core clock protein and transcription factor that regulates the expression of nearly half of all genes. Using male and female kidney-specific cadherin BMAL1 knockout (KS-BMAL1 KO) mice, we examined the role of renal distal segment BMAL1 in blood pressure control and solute handling. We confirmed that this mouse model does not express BMAL1 in thick ascending limb, distal convoluted tubule, and collecting duct cells, which are the final locations for solute and fluid regulation. Male KS-BMAL1 KO mice displayed a substantially lower basal systolic blood pressure compared with littermate control mice, yet their circadian rhythm in pressure remained unchanged [male control mice: 127 ± 0.7 mmHg (n = 4) vs. male KS-BMAL KO mice: 119 ± 2.3 mmHg (n = 5), P < 0.05]. Female mice, however, did not display a genotype difference in basal systolic blood pressure [female control mice: 120 ± 1.6 mmHg (n = 5) vs. female KS-BMAL1 KO mice: 119 ± 1.5 mmHg (n = 7), P = 0.4]. In addition, male KS-BMAL1 KO mice had less Na+ retention compared with control mice in response to a K+-restricted diet (15% less following 5 days of treatment). However, there was no genotype difference in Na+ handling after a K+-restricted diet in female mice. Furthermore, there was evidence indicating a sex-specific response to K+ restriction where female mice reabsorbed less Na+ in response to this dietary challenge compared with male mice. We propose that BMAL1 in the distal nephron and collecting duct contributes to blood pressure regulation and Na+ handling in a sex-specific manner.

Loss of endothelin type B receptor function improves insulin sensitivity in rats

High salt intake (HS) is associated with obesity and insulin resistance. ET-1, a peptide released in response to HS, inhibits the actions of insulin on cultured adipocytes through ET-1 type B (ETB) receptors; however, the in vivo implications of ETB receptor activation on lipid metabolism and insulin resistance is unknown. We hypothesized that activation of ETB receptors in response to HS intake promotes dyslipidemia and insulin resistance. In normal salt (NS) fed rats, no significant difference in body mass or epididymal fat mass was observed between control and ETB deficient rats. After 2 weeks of HS, ETB-deficient rats had significantly lower body mass and epididymal fat mass compared to controls. Nonfasting plasma glucose was not different between genotypes; however, plasma insulin concentration was significantly lower in ETB-deficient rats compared to controls, suggesting improved insulin sensitivity. In addition, ETB-deficient rats had higher circulating free fatty acids in both NS and HS groups, with no difference in plasma triglycerides between genotypes. In a separate experiment, ETB-deficient rats had significantly lower fasting blood glucose and improved glucose and insulin tolerance compared to controls. These data suggest that ET-1 promotes adipose deposition and insulin resistance via the ETB receptor.

Greater natriuretic response to ENaC inhibition in male versus female Sprague-Dawley rats

Genes for the epithelial sodium channel (ENaC) subunits are expressed in a circadian manner, but whether this results in time-of-day differences in activity is not known. Recent data show that protein expression of ENaC subunits is higher in kidneys from female rats, yet females are more efficient in excreting an acute salt load. Thus, our in vivo study determined whether there is a time-of-day difference as well as a sex difference in the response to ENaC inhibition by benzamil. Our results showed that the natriuretic and diuretic responses to a single dose of benzamil were significantly greater in male compared with female rats whether given at the beginning of the inactive period [Zeitgeber time 0 (ZT0), 7 AM] or active period (ZT12, 7 PM). However, the response to benzamil was not significantly different between ZT0 and ZT12 dosing in either male or female rats. There was no difference in renal cortical α-ENaC protein abundance between ZT0 and ZT12 or males and females. Given previous reports of flow-induced stimulation of endothelin-1 (ET-1) production and sex differences in the renal endothelin system, we measured urinary ET-1 excretion to assess the effects of increased urine flow on intrarenal ET-1. ET-1 excretion was significantly increased following benzamil administration in both sexes, but this increase was significantly greater in females. These results support the hypothesis that ENaC activity is less prominent in maintaining Na⁺ balance in females independent of renal ET-1. Because ENaC subunit genes and protein expression vary by time of day and are greater in female rat kidneys, this suggests a clear disconnect between ENaC expression and channel activity.

Abstract P173: Sex Differences in the Diurnal Natriuretic Response to Benzamil in Sprague Dawley Rats

Epithelial sodium channel (ENaC) expression follows a circadian pattern, but how this impacts activity is not known. In addition to the well-established sex differences in renal Na handling, recent data show that ENaC expression is higher (Western blot) in female rats. Further, we do not know if there are time of day differences or sex differences in ENaC activity. Therefore, the aim of this study was to determine if the diuretic response to ENaC inhibition (benzamil) is different between sexes at different times of day. SD rats (12-16 wk old) were placed in metabolic cages, where 12-hour urine collections were obtained to measure baseline urine volume and Na excretion as well as water and food intake. On day 3, benzamil was given at a dose of 1mg/kg (i.p.) either at the beginning of their inactive period/lights on (Zeitgeber Time 0, ZT0) or their active period/lights off (ZT12). The natriuretic response to benzamil was significantly greater in male compared to female rats (909 ± 302 vs 523 ± 83 μEq/kg/hr n=8) at ZT0 and (934 ± 94 vs 714 ± 151 μEq/kg/hr n=8) at ZT12. The diuretic response followed natriuresis being more prominent in male than female rats regardless of time of day (4.2 ± 0.7 vs 3.3 ± 0.5 ml/kg/hr n=8) at ZT0 and (3.6 ± 0.6 vs 2.5 ± 0.3 ml/kg/hr n=8) at ZT12. However, the larger response to benzamil given at the beginning of the inactive period (ZT0) compared to active period (ZT12) was not statistically significant (311 ± 98 vs 354 ± 30 μEq/hr and 120 ± 17.75 vs 174 ± 37 μEq/hr n=8) in male and female rats respectively. Given that endothelin-1 (ET-1) is an upstream inhibitor of ENaC, we measured urinary ET-1 levels to assess intrarenal production. ET-1 excretion significantly increased following benzamil administration in both sexes but was significantly greater in females. ET-1 excretion increased from 0.06 ± 0.01 to 0.29 ± 0.05 pg/hr in males (n=8) and from 0.10 ± 0.01 to 0.57 ± 0.28 pg/hr in females (n=8) at ZT0. At ZT12, ET-1 increased from 0.09 ± 0.02 to 0.23 ± 0.06 pg/hr in males (n=8) and from 0.14 ± 0.05 to 0.34 ± 0.06 pg/hr in females (n=8). These results demonstrate that the response to ENaC inhibition is less prominent in females independent of renal ET-1. This suggests less ENaC activity independent of expression in females or differences in non-ENaC related effects of benzamil.

Circadian regulation of renal function

The kidneys regulate many vital functions that require precise control throughout the day. These functions, such as maintaining sodium balance or regulating arterial pressure, rely on an intrinsic clock mechanism that was commonly believed to be controlled by the central nervous system. Mounting evidence in recent years has unveiled previously underappreciated depth of influence by circadian rhythms and clock genes on renal function, at the molecular and physiological level, independent of other external factors. The impact of circadian rhythms in the kidney also affects individuals from a clinical standpoint, as the loss of rhythmic activity or clock gene expression have been documented in various cardiovascular diseases. Fortunately, the prognostic value of examining circadian rhythms may prove useful in determining the progression of a kidney-related disease, and chronotherapy is a clinical intervention that requires consideration of circadian and diurnal rhythms in the kidney. In this review, we discuss evidence of circadian regulation in the kidney from basic and clinical research in order to provide a foundation on which a great deal of future research is needed to expand our understanding of circadian relevant biology.

Small Bowel Obstruction: A Review of 456 Cases in a West of Ireland Region

A retrospective study was carried out of 456 patients with small bowel obstruction (SBO). The operative findings of all patients who presented with SBO between 1977 and 1982 were compared and contrasted with those who presented during equivalent periods in the previous three decades. Obstructed hernias still account for the highest percentage of cases. Surprisingly, adhesions as a causative factor are not significantly more common than they were three decades ago, despite the enormous increase in the frequency with which abdominal surgery is now being carried out. The postoperative mortality rate for the period 1977–82 was 14%.

High dietary sodium causes dyssynchrony of the renal molecular clock in rats

Speed JS, Hyndman KA, Roth K, Heimlich JB, Kasztan M, Fox BM, Johnston JG, Becker BK, Jin C, Gamble KL, Young ME, Pollock JS, Pollock DM. High dietary sodium causes dyssynchrony of the renal molecular clock in rats. Am J Physiol Renal Physiol 314: F89-F98, 2018. First published September 27, 2017; doi:10.1152/ajprenal.00028.2017.-Dyssynchrony of circadian rhythms is associated with various disorders, including cardiovascular and metabolic diseases. The cell autonomous molecular clock maintains circadian control; however, environmental factors that may cause circadian dyssynchrony either within or between organ systems are poorly understood. Our laboratory recently reported that the endothelin (ET-1) B (ETB) receptor functions to facilitate Na+ excretion in a time of day-dependent manner. Therefore, the present study was designed to determine whether high salt (HS) intake leads to circadian dyssynchrony within the kidney and whether the renal endothelin system contributes to control of the renal molecular clock. We observed that HS feeding led to region-specific alterations in circadian clock components within the kidney. For instance, HS caused a significant 5.5-h phase delay in the peak expression of Bmal1 and suppressed Cry1 and Per2 expression in the renal inner medulla, but not the renal cortex, of control rats. The phase delay in Bmal1 expression appears to be mediated by ET-1 because this phenomenon was not observed in the ETB-deficient rat. In cultured inner medullary collecting duct cells, ET-1 suppressed Bmal1 mRNA expression. Furthermore, Bmal1 knockdown in these cells reduced epithelial Na+ channel expression. These data reveal that HS feeding leads to intrarenal circadian dyssynchrony mediated, in part, through activation of ETB receptors within the renal inner medulla.

Diurnal pattern in skin Na+ and water content is associated with salt-sensitive hypertension in ETB receptor-deficient rats

Impairment in the ability of the skin to properly store Na⁺ nonosmotically (without water) has recently been hypothesized as contributing to salt-sensitive hypertension. Our laboratory has shown that endothelial production of endothelin-1 (ET-1) is crucial to skin Na⁺ handling. Furthermore, it is well established that loss of endothelin type B receptor (ET_B) receptor function impairs Na⁺ excretion by the kidney. Thus we hypothesized that rats lacking functional ET_B receptors (ET_B-def) will have a reduced capacity of the skin to store Na⁺ during chronic high-salt (HS) intake. We observed that ET_B-def rats exhibited salt-sensitive hypertension with an approximate doubling in the diurnal amplitude of mean arterial pressure compared with genetic control rats on a HS diet. Two weeks of HS diet significantly increased skin Na⁺ content relative to water; however, there was no significant difference between control and ET_B-def rats. Interestingly, HS intake led to a 19% increase in skin Na⁺ and 16% increase in water content (relative to dry wt.) during the active phase (zeitgeber time 16) versus inactive phase (zeitgeber time 4, P < 0.05) in ET_B-def rats. There was no significant circadian variation in total skin Na⁺ or water content of control rats fed normal or HS. These data indicate that ET_B receptors have little influence on the ability to store Na⁺ nonosmotically in the skin during long-term HS intake but, rather, appear to regulate diurnal rhythms in skin Na⁺ content and circadian blood pressure rhythms associated with a HS diet.

Abstract P207: High Salt Intake desynchronizes the Molecular Clock in Rats

Circadian rhythms in physiologic functions are driven, at the molecular level, by a group of transcription factors that oscillate over a 24 hour period, collectively termed the molecular clock. Within the kidney, it has been shown that the molecular clock directly influences transcription of Na + transporters and channels, including ENaC. ENaC is regulated by endothelin-1 (ET-1), via ET B receptor activation, in response to high salt intake. Thus, we hypothesized that increases in dietary sodium regulate the renal molecular clock (which in turn would facilitate Na+ homeostasis) through an ET B dependent mechanism. To address this question, we examined the effect of high salt (HS) intake on renal clock gene ( Bmal1, Cry1, Per1, Per2 ) expression. Control and ET B receptor deficient (ET B def) rats (a model of elevated renal ENaC) were placed on either HS or normal salt (NS) for two weeks and euthanized every 4 hours beginning at Zeitgeber Time 0 (Lights on). In the inner medulla, HS causes a phase delay in Bmal1 (Fig 1A) expression in control but not ET B def rats (Fig 1B). In addition, HS suppressed the expression of Cry1 , and Per2 during the respective acrophase in both control and ET B def rats (Fig 1C-1F) with no significant effect on Per1 . In contrast, no significant difference in the expression of Bmal1, Cry1, Per2, or Per1 (Fig 1I-1P) was found in response to HS in the renal cortex of either control or ET B def. These data indicate that HS feeding desynchronizes the molecular clock within the kidney and provides evidence that peripheral clocks are regulated in a cell type specific manner, even within the same organ.

Loss of endothelin B receptor function impairs sodium excretion in a time- and sex-dependent manner

Recent studies suggested a direct link between circadian rhythms and regulation of sodium excretion. Endothelin-1 (ET-1) regulates sodium balance by promoting natriuresis through the endothelin B receptor (ET_B) in response to increased salt in the diet, but the effect that the time of day has on this natriuretic response is not known. Therefore, this study was designed to test the hypothesis that ET_B receptor activation contributes to the diurnal control of sodium excretion and that sex differences contribute to this control as well. Twelve-hour urine collections were used to measure sodium excretion. On day 3 of the experiment, a NaCl load (900 μeq) was given by oral gavage either at Zeitgeber time [ZT] 0 (inactive period) or ZT12 (active period) to examine the natriuretic response to the acute salt load. Male and female ET_B-deficient (ET_B def) rats showed an impaired natriuretic response to a salt load at ZT0 compared with their respective transgenic controls (Tg cont). Male ET_B def rats showed a delayed natriuretic response to a salt load given at ZT12 compared with male Tg cont, a contrast to the prompt response shown by female ET_B def rats. Treatment with ABT-627, an ET_A receptor antagonist, improved the natriuretic response seen within the first 12 h of a ZT0 salt load in both sexes. These findings demonstrate that diurnal excretion of an acute salt load 1) requires ET-1 and the ET_B receptor, 2) is more evident in male vs. female rats, and 3) is opposed by the ET_A receptor.

Endothelin and renal ion and water transport

The renal tubular epithelial cells produce more endothelin-1 (ET-1) than any other cell type in the body. Moving down the nephron, the amount of ET-1 produced appears fairly consistent until reaching the inner medullary collecting duct, which produces at least 10 times more ET-1 than any other segment. ET-1 inhibits Na(+) transport in all parts of the nephron through activation of the ETB receptor, and, to a minor extent, the ETA receptor. These effects are most prominent in the collecting duct where ETB-receptor activation inhibits activity of the epithelial Na(+) channel. Effects in other parts of the nephron include inhibition of Na(+)/H(+) exchange in the proximal tubule and the Na(+), K(+), 2Cl(-) co-transporter in the thick ascending limb. In general, the renal epithelial ET-1 system is an integral part of the body's response to a high salt intake to maintain homeostasis and normal blood pressure. Loss of ETB-receptor function results in salt-sensitive hypertension. The role of renal ET-1 and how it affects Na(+) and water transport throughout the nephron is reviewed.

Abstract P639: Attenuation of Renal Inner Medullary Circadian Clock Gene Expression in Response to High Salt Intake is Dependent on the Endothelin B Receptor

Our lab has recently shown that ETB deficient (ETB def) rats have a time of day dependent impairment in their ability to excrete a Na+ load. These observations suggest an interaction between renal ETB receptors and circadian mechanisms that regulate renal tubular Na+ transport and excretion. Given that knockout of the circadian clock gene Bmal1 reduces blood pressure in mice, we hypothesized that a high salt intake impairs the clock mechanism in the renal inner medulla in an ETB dependent manner. Transgenic control (Tg con) or ETB def rats were fed normal (NS, 0.8% NaCl) or high (HS, 4% NaCl) salt for two weeks. In one group, rats were euthanized every 4 hours beginning at zeitgeber time 0 (lights on) for tissue collection (and subsequent assessment of circadian clock genes), while in a second group of rats urine was collected in 12-hour intervals (active vs. inactive). Consistent with our hypothesis, we observed that HS abolished the normal oscillation in Bmal1 expression in the renal inner medulla of Tg con rats, and effect not observed in ETB def rats. Interestingly, renal production of ET-1, was significantly higher during the active period vs. inactive period in both NS (3.6±1.1 vs. 0.8±0.2 pg/12hr respectively) and HS (9.2±4.1 vs. 1.6±0.3 pg/12hr respectively) fed Tg con rats. There was no time-of-day-dependent difference in ET-1 excretion in ETB def rats on NS (6.6±2.2 vs. 4.6±1.7 pg/12hr respectively), although this pattern was restored in ETB def rats fed HS (2.2±1.0 vs. 9.2±2.5 pg/12hr inactive vs. active). Taken together, these data indicate that an increase in renal ET-1/ETB activation in response to HS modulates inner medullary clock gene expression to promote renal Na+ excretion.

The mouse mutation reeler causes increased adhesion within a subpopulation of early postmitotic cortical neurons

Early postmitotic cortical neurons are mostly corticofugal projection neurons that take up positions in deep cortical laminae. Later postmitotic neurons are preferentially localized to superficial cortical laminae. In reeler mutant mice it appears that cortical laminar positions with respect to birthdate are reversed (Caviness, 1982). In a reanalysis of reeler lamination we found that early postmitotic cortical neurons labeled by embryonic day (E) 11-13 injections of a birthdate marker, or by early postnatal day (PND) 2 retrograde labeling through their output projections, appear to take up positions both in the superficial and deep cortex. Neurons born on E11 and E12 are more likely to be situated superficially in the reeler cortex and neurons born on E13 are more likely to be situated in the deep reeler cortex. Many corticofugal projection neurons in the deep (but not superficial) reeler cortex either die or retract their axons before PND 21. We hypothesize that the earliest postmitotic (E11-E12) of the early postmitotic reeler cortical neurons are overly adhesive and act as a barrier to later postmitotic migrating neurons. In vitro cortical aggregation cultures confirmed that early postmitotic (E12) reeler neurons are more adhesive than early postmitotic (E12) wild-type neurons or late postmitotic (E16) reeler or wild-type cortical neurons. We suggest that the moderate wild-type preferential adhesion of early postmitotic cortical neurons to each other helps deep and superficially fated lineages to form cortical laminae.

The inhibition of liver ornithine decarboxylase expression in neonatal rats by maternal separation or CNS beta-endorphin is independent of the pituitary

Previously we have shown, in rat pups, that either short-term maternal separation (MS) or central (but not peripheral) administration of beta-endorphin (BE) markedly decreases basal levels of ornithine decarboxylase (ODC) activity throughout the body and suppresses liver ODC responsiveness to injected growth hormone (GH). In this study, hypophysectomized (hypox) pups were used to determine whether the pituitary mediates these effects. Hypophysectomy clearly did not prevent the inhibitory actions of MS or intracisternal (i.c.) BE on liver ODC gene expression. The inability of GH to stimulate ODC activity in hypox animals exposed to MS or given BE i.c. is not due to nutritional deprivation, as glucose supplementation did not reverse the response. The results from these studies demonstrate that the pituitary is not the conduit by which either MS or centrally-administered BE regulates liver ODC activity. Also, they support the hypothesis that BE or an analogous opioid neuropeptide is a prime organizer within the CNS of the adaptive physiological response of neonatal rats to short-term MS. As we have previously shown that autonomic neuronal pathways are not involved in the effects of MS on peripheral tissues, the data obtained suggest that increased activity of this CNS opioid system during MS triggers the release of "neurochemicals" into the bloodstream capable of suppressing growth in the mammalian neonate.

Spatially localized neuronal cell lineages in the developing mammalian forebrain

The role of cell lineage in the organization of the cerebral cortex and striatum of the developing rat forebrain was analysed using retroviral-mediated gene transfer to mark the progeny of individual progenitors. Injections around the onset of neurogenesis (embryonic day 14) produced neuronal- and glial-specific clones in the striatum and cortex. The majority of the neuronal clones were restricted to either the deep or superficial layers of the cortex and to either the striatal patch or matrix compartments of the striatum. Moreover, modeling the distributions of the neuronal clones in various ways revealed that grouping the clones into deep vs superficial cortical compartments and patch vs matrix striatal compartments best accounted for the clone distributions. These results suggest that at the onset of neurogenesis there is a heterogeneity of neuronal progenitors within the proliferative ventricular zone.

Ten-year Review of Treatment of the Undescended Testis in the West of Ireland

Advances continue to be made in the treatment of the undescended testis, and treatment recommendations are continually changing. We reviewed 543 patients admitted for treatment of undescended testes in the 10-year period 1977 to 1986. The side and position of the testis were recorded, the patient's age at operation and the procedure carried out. The presence of an associated inguinal hernia was noted. The necessity for reoperation was recorded and predisposing factors sought. We found the mean age at operation to be 9.5 years and this decreased significantly over the study period. Dartos pouch orchiopexy was the commonest operation (69%). No significant link was found between the procedure performed or the presence of a hernia and the need for further procedures; 2.7% of patients required such further procedures. A coherent classification of position is lacking for abnormally descended testes. We report a classification which we used to tackle this situation.

Contrasting enrollment trends for BSN students in the United States and in New York State: an assessment and analysis

The paper provides a description, assessment, and analysis of enrollment trends for generic and registered nurse students in baccalaureate programs in both the United States and New York state over the past 30 years. The analysis focuses on the reasons for the recent declining enrollment of both types of BSN students in New York state. Primary data sources were the National League for Nursing's annual student census statistics, policy statements and reports of the NLN and the American Nurses Association (ANA), and statements on the recruitment and retention of nurses.

Mechanisms of striatal pattern formation: conservation of mammalian compartmentalization

The striatum is composed of two neuroanatomically and neurochemically defined compartments, termed the patches and matrix. We compared this compartmentalization of the striatum in sections from the rat, rhesus monkey and human, in terms of (1) total striatal area, (2) the ratio of patch to matrix areas, (3) the number of patches and (4) the cross-sectional area of individual patches. Dense mu-opiate receptor binding and immunohistochemical staining for enkephalin were used as histochemical markers for the patch compartment and heavy immunostaining for calcium binding protein was used as a matrix marker. Analysis of coronal sections revealed that a relatively constant ratio of 15% patch to 85% matrix area is maintained in each species. The numbers of patches also remain relatively constant across species, despite a 19-fold increase in total striatal area from rat to human. The constant ratio of patch to matrix areas is maintained by an increase in the size of the individual patches. We hypothesize that the maintenance of a 15% patch to 85% matrix ratio in the striata of different mammalian species occurs through proportionate changes in the length of striatal neurogenesis and the numbers of striatal precursors in the ventricular zone, whereas the maintenance of average patch number is proposed to be a function of reciprocal connections with the substantia nigra and adhesive factors that are specific to patch cells.

Protooncogene expression identifies a transient columnar organization of the forebrain within the late embryonic ventricular zone

Immunocytochemical studies using monoclonal antibodies directed against oncogenic peptides revealed a heterogeneous distribution of the peptides within the ventricular zone of the embryonic day 18 rat forebrain. The sis-, src-, ras-, and myc-encoded peptides were concentrated in the same isolated clusters of 5-25 radial glial cells (also identified by vimentin staining), providing a transient columnar compartmentalization to the ventricular zone. An increased number of [3H]thymidine-labeled ventricular zone cells were observed within the protooncogene stained radial glial cell columns as compared to noncolumn areas. The columnar heterogeneity of radial glial cells reveals the mosaicism of the embryonic ventricular zone and the differential proliferation of its cells.

Compartmentalization of the embryonic striatum after intraocular transplantation

In order to assess the intrinsic potential of the isolated embryonic striatum to develop its adult patch and matrix compartments, embryonic day 16 striata were transplanted into the anterior eye chamber of adult host rats. After 2-12 weeks of survival the transplants showed heterogeneous and in the majority of cases complementary distributions of opiate receptor binding and acetylcholinesterase staining, which mark the patch and matrix compartments of the adult striatum, respectively. The complementarity of patch and matrix markers in the transplants shows that the transplants do compartmentalize. However, the density of the markers in the transplants did not reach the levels seen in the adult striatum. The results suggest that the commitment of cells to a striatal compartment is a very early event in the embryonic development of the forebrain.

Epidemic Venezuelan equine encephalitis in North America in 1971: vector studies

A major epidemic of Venezuelan equine encephalitis occurred in south Texas in the summer of 1971. More than 1500 equines died of VEE in Texas, and 110 human cases with no deaths were reported. Vector studies in south Texas and northern Tamaulipas revealed that the overall mosquito infection rates during the peak of the epidemic were about 1:100, one of the highest rates observed for a major epidemic. Mosquito infection rates of this magnitude could easily explain the intensity of VEE outbreaks in both equines and man. A total of 943 VEE virus isolations were made from mosquitoes. Eight of the 12 mosquito species found infected were implicated in the epidemic cycle of VEE for the first time. Sufficient laboratory and field evidence is available to prove that Psorophora confinnis was one of the primary vectors of VEE. The lack of laboratory evidence necessitates the use of the term "probable" primary vectors for other species apparently equally as involved on the basis of field infections; these include Aedes sollicitans, Aedes thelcter and Psorophora discolor. Eight other species from which less than 10 VEE virus isolations were made were considered auxiliary vectors. Mosquitoes of some species were tested individually; such tests showed 2-4% of the probable primary vectors to be infected. The first isolation of VEE virus of the epidemic was made from P. confinnis on June 28, 1971. Highest mosquito infection rates occurred during the week of July 5. Mosquito infection rates declined precipitously in the last 3 weeks of July 1971, signaling the end of the epidemic in the study area. One explanation for the decline was that equines, the principal epidemic hosts, were eliminated as a source of virus by death or by acquisition of natural or induced immunity. Mosquito control appeared to be effective in reducing the infected mosquito population while the immunization of equines with TC 83 VEE vaccine was accomplished. Quarantines appeared to be effective in restricting the VEE virus activity to south Texas. Undoubtedly all of the control measures contributed to stopping the epidemic. Continued VEE surveillance by various government and other agencies failed to reveal any further epidemic VEE activity in the US in 1972. Other arboviruses isolated during the VEE studies in south Texas included St. Louis encephalitis virus, and San Angelo subtype of the California Group. A virus of the Bunyamwera Group was also isolated from Palo Blanco, Tamaulipas.

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies. Am J Epidemiol 101:36-50, 1975.-In June 1971, epidemic Venezuelan equine encephalitis (VEE) invaded the lower Rio Grande Valley in south Texas. The Boca Chica area of Cameron County was selected as a study site to investigate vertebrate involvement in the natural cycle of epidemic VEE on the basis of considerable evidence of VEE virus activity there in equines, humans, and mosquito vectors. Only one VEE virus isolation was made from 4739 wild and domestic non-equine vertebrates, although numerous equine and human VEE virus isolations were made in concurrent studies. Serologic studies indicated that VEE virus activity was far greater in large domestic animals than in wild birds, wild mammals, or reptiles. Apparently epidemic VEE virus failed to establish itself in a wild vertebrate cycle in south Texas, since VEE antibody was found only in rabbits in 1972. Eventual cessation of VEE transmission in south Texas has been attributed 1) to the elimination of equines as a source of VEE virus by death, naturally acquired antibodies, or vaccination, 2) to quarantines, 3) to mosquito control, and 4) to the failure of epidemic VEE virus to become established in the wild vertebrate population. Equines emerge as the most important vertebrate host in the amplification and spread of virus during an epidemic of VEE.