Archive for the 'EB2016' category

Cures and Consequences #expbio

Apr 06 2016 Published by under EB2016

Pulmonary and Systemic Vascular Responses in Rats Exposed to Perinatal Hyperoxia

Greiner T, et al.

Ventilated premie

Ventilated premie

Premature infants used to die of lung immaturity. With surfactant treatment and ventilation, they have a much better survival rate. However, these interventions come with a cost. High oxygen causes retinopathy of prematurity which can lead to blindness. It may also have long-term effects on the cardiovascular system. In humans, teasing out the effects of the oxygen and the barotrauma (the pressure pushing the oxygen into the lungs) can be tricky.

The humble Sprague-Dawley rat is born at a stage of organ development similar to a premature infant. The lungs are saccular; the terminal ventilatory sacs have formed, but have not yet matured into alveoli. Exposing rat pups to high oxygen at birth can allow study of just the oxygen toxicity on the vascular function.

At birth, rats and mothers were housed in room air (21% oxygen) or 80% oxygen for two weeks.  Three to six months later they were exposed to a hypoxic challenge (12% oxygen) and systemic and vascular responses were studied.

Hypoxia resulted in an increase in pulmonary vascular pressure; however, this observation was not primarily due to an increase in pulmonary resistance. Most was due to an increase in flow from an elevated stroke volume.

This model offers promise for understanding oxygen toxicity in the neonatal lung. Clinicians have assumed that barotrauma is responsible for much of the chronic lung and reactive airway disease seen in ex-premies. Challenging these rats with bronchoconstrictors could let us determine what role hyperoxia may play in these conditions.

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Androgens and Angiotensin #expbio

Apr 06 2016 Published by under EB2016

Chronic Flutamide Treatment Alters Intrarenal Renin Angiotensin System Expression in Intrauterine Growth Restricted Female Rats

Designer JH, et al.

For many years, a relationship has been demonstrated between low birth weight and later development of cardiovascular and kidney disease in humans and in animal models. One model involves tying off uterine arteries late in rat pregnancy, effectively starving the pups. Female animals in this model develop hypertension as they age, as well as elevated testosterone levels and premature cessation of estrus cycling.

Mr. T, aka Testosterone

Mr. T, aka Testosterone

Post-cycling female IUGR rats underwent treatment for 2 weeks with vehicle or flutamide, an androgen receptor antagonist. This treatment blocked the development of hypertension in this model, as does renin-angiotensin blockade. The intrarenal renin-angiotensin system (RAS) was examined in these animals. Hypertensive  females had elevated angiotensin receptors in the kidney. Flutamide treatment prevented this rise in receptors, suggesting that androgen-induced activation of the intrarenal RAS is the mechanism of hypertension in this model.

One criticism of this model is its severity; certainly further translational work is needed before we start treating postmenopausal women with flutamide for hypertension.

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Kidney Function for the Birds #expbio

Apr 05 2016 Published by under EB2016

The Integration of Gastrointestinal and Renal Function in Nectar-Feeding Birds

McWhorter TJ.

King of the Feeder

King of the Feeder

Regular Whizbangers know that I love hummingbirds. I spent hours watching these tiny feathered warriors at our feeder last summer. When I came across an abstract about their kidney function, it had to be blogged.

Most birds we encounter have very little fluid in their diets. They primarily ingest seeds and bugs, and they maximally retain water from their food. Nectar-feeding birds have an all-liquid diet. Hummingbirds, sunbirds, and honeyeaters must deal with high water loads during their daylight hours. For example, a hummingbird requires the calories in an amount of nectar 1.6 times the bird’s body weight during ideal environmental conditions to meet minimum metabolic needs. With cool temperatures or other stresses, intake may go as high as 3.3 times its body mass. Imagine the mythical 70 kg male drinking more than 200 liters of fluid each day! My kidney stone patients freak out about 2.5 to 3 liters daily!

Birds have much different anatomy than mammals as well (see diagram below). Food enters the crop where digestion begins, then moves into the proventiculus or stomach. After a pass through the gizzard, it hits the intestine where absorption occurs. The remaining material passes into the cloaca from where it leaves the body. Water absorbed from the intestine can be filtered by the kidney. Urine passes into the cloaca. From there it can be directed into the lower intestine for more processing or pass directly out of the body.

From Beuchat 1990 Physiological Zoology 63:1059

From Beuchat 1990 Physiological Zoology 63:1059

These birds have different renal structures from mammals as well. Two types of nephrons occur in birds, looped or mammalian nephrons which reach into medullary pyramids and produce a countercurrent multiplier system for concentrating urine, and reptilian nephrons without loops. Hummingbird kidneys consist primary of unlooped nephrons, so their kidneys are built for maximal urine dilution.

This paper shows that the two classes of nectar feeding birds have different strategies for dealing with massive water intake. Both groups of birds drop their filtration rate to zero overnight when they do not feed. It then increases again during the day as they drink. Hummingbirds primarily absorb water and filter it out via their kidneys, while Passeriformes (those sunbirds and honeyeaters) reduce gastrointestinal water absorption. Imagine instrumenting tiny 4.5 g birds to see how much fluid remains in the intestine as they eat more. Yup, this group did it! The hummingbirds had stable intestinal water excretion across all levels of intake, while water absorption decreased dramatically with higher intake in the Passeriformes, allowing them to send it straight on through the intestine.

These birds have evolved different strategies to handle the same problem, namely high water intake. There are interesting physiological lessons here. And besides, birds are fun! And bird kidneys? Well, what more could you want in a blog post...?

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Damage Control in the Cortical Collecting Duct #expbio

Apr 04 2016 Published by under EB2016, Uncategorized

Vasopressin-Escape Does Not Involve marked Changes in the Ratio of Intercalated-to-Principal Cells in the Cortical Collecting Duct

Chou C-L, et al.

Vasopressin, also known as anti-diuretic hormone (ADH), promotes absorption of water from the kidney’s cortical collecting duct. Under certain conditions, ADH can be inappropriately secreted, resulting in excess water retention and lowering of the body’s osmolality. Changes in osmolality can be quite dangerous, especially for the brain, so it is not surprising that the collecting duct can “escape” the effect of ADH to limit low plasma sodium and osmolality. This group previously showed that such vasopressin-escape occurs in association with lowered levels of expression for aquaporin 2 (AQP2), a water channel that allows ADH to do its job.

Autocrine and paracrine regulation of collecting duct principal cell ENaC and AQP2. Much commonality exists in regulation of ENaC (left) and AQP2 (right). Flow stimulates ATP, PGE2, and ET-1, which act on their cognate receptors to inhibit Na and water reabsorption. Similarly, bradykinin, adenosine, and NE act on their receptors to inhibit ENaC and AQP2. Flow-stimulated EET uniquely inhibits Na, but not water, transport. Compared with the wide variety of inhibitors, relatively few autocrine or paracrine factors stimulate ENaC and/or AQP2 activity. Renin, ultimately via AngII, as well as PGE2 binding to EP4 receptors, are potentially capable of augmenting principal cell Na and water transport. TZDs (via PPARγ) and kallikrein (via cleavage of an autoinhibitory domain in ENaC) may increase Na reabsorption. See the text for more detailed descriptions of each regulatory factor. ACE, angiotensin-converting enzyme; AGT, angiotensinogen; Ang, angiotensin; AQP, aquaporin; EET, eicosataetranoic acid; EP, PGE receptor; ET, endothelin; NE, norepinephrine; NO, nitric oxide; PPARγ, peroxisome proliferator–activated receptor-γ; TZD, thiazolidinedione.

Autocrine and paracrine regulation of collecting duct principal cell ENaC and AQP2. Much commonality exists in regulation of ENaC (left) and AQP2 (right). Flow stimulates ATP, PGE2, and ET-1, which act on their cognate receptors to inhibit Na and water reabsorption. Similarly, bradykinin, adenosine, and NE act on their receptors to inhibit ENaC and AQP2. Flow-stimulated EET uniquely inhibits Na, but not water, transport. Compared with the wide variety of inhibitors, relatively few autocrine or paracrine factors stimulate ENaC and/or AQP2 activity. Renin, ultimately via AngII, as well as PGE2 binding to EP4 receptors, are potentially capable of augmenting principal cell Na and water transport. TZDs (via PPARγ) and kallikrein (via cleavage of an autoinhibitory domain in ENaC) may increase Na reabsorption. See the text for more detailed descriptions of each regulatory factor. ACE, angiotensin-converting enzyme; AGT, angiotensinogen; Ang, angiotensin; AQP, aquaporin; EET, eicosataetranoic acid; EP, PGE receptor; ET, endothelin; NE, norepinephrine; NO, nitric oxide; PPARγ, peroxisome proliferator–activated receptor-γ; TZD, thiazolidinedione. Click image to access full review article.

Their current question centers on how AQP2 gets down regulated. It could be an intracellular mechanism or remodeling of the collecting duct, with a change in the ratio of principal and intercalated cells in that structure. Principal cells regulate sodium, potassium, and water reabsorption in the collecting duct, while intercalated cells influence acid-base balance. Decreasing the number of principal cells could decrease the effect of ADH. A full review of principal function can be found here; the image above comes from this paper.

After micro dissecting cortical collecting duct segments from animals in the early phases of vasopressin escape, the investigators probed them with a marker for all cells; an antibody to H+-ATPase, a marker of alpha intercalated cells; and an antibody to pendrin, found in in beta intercalated cells. They could then calculate the number of principal cells and intercalated cells to see if the principal cells decreased to explain the diminished AQP2 expression.

The cellular ratios did not differ between normal and vasopressin-escape animals.

So what intracellular process could be involved? Further exploration suggests a shift in cell cycle from G0 (resting) to mitosis. How this reduces AQP2 expression is not yet clear.

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Why I Am (Still) a Physiologist #expbio

Apr 04 2016 Published by under EB2016

A few years ago when my spouse took his current position, I decided to “gracefully” close down my laboratory. I enjoyed studying and writing about puberty, sex, and the kidney for twenty years, but lack of funding finally brought me down. I was lucky; being an MD, I had other skills to keep my faculty position.

I no longer play with new scientific gizmos in the lab. I do miss exploring questions of the how and why the kidneys do what they do. I still have some clinical studies going, but my days mostly consist of caring for children with kidney disease.

So why do I still belong to the American Physiological Society? Why do I work on their committees? And why do I attend Experimental Biology?

Because medicine is physiology.

Let’s take a common healthcare example. You go to your doctor because of seasonal allergies. Your symptoms of runny, itchy nose make you crazy, interfering with your sleep and work. Whatever your allergen, it triggers the release of histamine which induces itching and swelling in the nasal passage. These physiological changes can be ameliorated by blocking the histamine. Such drugs (Benadryl; Claritin; Zyrtec) form the first-line therapy. If they do not get the job done, other physiological systems of nasal inflammation can be blocked. Glucocorticoids (Flonase; Nasocort), the anti-inflammatory steroids, can be given as nasal sprays. Montelukast (Singular) blocks leukotriene receptors and prevents the allergic inflammatory response through another pathway. Now some individuals would say this example was immunology or pharmacology, but I would argue that understanding how the body responds to an allergen falls under the umbrella of physiology. We also have to know this physiology before we can design the pharmacology.

Perhaps my example has not convinced you. Who am I, after all? Just a random pediatric nephrologist who likes to write online. You want an opinion from recognized authority, damn it!

Remember, the Nobel Prize is for Physiology or Medicine. If the Nobel committee considers these fields so closely bonded, then who are we to question it?

That is why I am in San Diego, blogging a very basic science meeting. It’s not just for fun; it will make me a better physician.

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Starling 2016 at #ExpBio

Apr 04 2016 Published by under EB2016

David Pollock of University of Alabama - Birmingham gave the Starling Lecture for the APS Water and Electrolyte Homeostasis Section on Sunday, April 3. Live tweets of the event are summarized below.

 

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Exercise and the Damaged Kidney #expbio

Apr 04 2016 Published by under EB2016

Endothelial Dysfunction Predicts Systolic Blood Pressure Slope During Whole Body Maximal Exercise in Patients with Chronic Kidney Disease

Downey RM, et al

Exercise is good for almost anything that ails someone. Patients with chronic kidney disease (CKD) often find it difficult to exercise, even before their disease advances to requiring intervention. Little is known about the vascular response of CKD patients to exercise.

BpKidneysThis study looked at the vascular effects of high intensity exercise in patients with stage 3 CKD compared to age-matched control subjects. CKD3 patients are often asymptomatic, diagnosed only through an abnormal lab test. CKD3 is the level of kidney dysfunction that gets flagged as abnormal by most labs. CKD3 has a wide range of function, from 20 mL/min/1.73m^2 to  59 mL/min/1.73m^2. Patients above 40 mL/min/1.73m^2 are much less likely to have secondary complications of CKD than those in the lower half of the range.

They then subjected these participants to maximal treadmill exercise while monitoring blood pressure, heart rate, and peak oxygen uptake. Brachial artery flow-mediated dilation (FMD) was measured to assess endothelial dysfunction. This study occurred just before and 1 hour after the treadmill test.

CKD patients had similar maximal blood pressure to controls; however, the rate of rise to maximal blood pressure was much greater in CKD patients. Maximum heart rate was lower in CKD patients, but the rate of rise was higher than the age-matched controls. Finally, peak oxygen uptake was significantly lower in CKD patients than in control subjects. FMD did not change pre- and post-exercise in either group, but they were significantly lower in the CKD patients. Basal levels of FMD predicted the slope of rise of blood pressure with exercise in CKD patients. Those with lower FMD had accelerated blood pressure and heart rate response during exercise.

CKD encompasses a relatively wide range of estimated glomerular filtration rate. Some nephrologists have suggest splitting it into CKD3a (40-59 mL/min/1.73m^2) and CKD3b because of the different risk profiles for these groups. Did dividing the study patients this way predict lower FMD for CKD3b? Apparently not.

So what follows this translational study? The next step will be exercise training for CKD3 patients to see if their endothelial dysfunction can be improved, resulting in better exercise tolerance. After all, exercise is good for almost everything.

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Why Should Kidneys Smell Fungus? #expbio

Apr 03 2016 Published by under EB2016

Renal Olfactory Receptor 90 (Olfr90) Responds to Fungal Metabolites

Halperin Kuhns RL, Pluznick JL

Receptors that help detect smells often have no known ligand, the molecule that turns them on, so to speak. That makes them orphan receptors. As these receptors are found well outside of the nose, we have to figure out what they react with to try and understand their function.

KidneySmellsFirst we need a bit of vocabulary to study the family tree. Olfactory receptors have families, even though they may not have parents. Structurally similar receptors often have overlap in their ligands, as may less similar receptors found in the same tissues. When ligands for an orphan receptor are identified, the receptor is “de-orphanized” (why don’t we say adopted and complete the damn metaphor, please?).

Olfr90 is an orphan olfactory receptor, found in the macula densa of the kidney. After expressing this molecule in a cell line with a reporter so cells would glow when the receptor got turned on, these investigators exposed these cells to a number of potential ligands. These included mixtures of odorant chemicals (after all, these are olfactory receptors), common ligands for “siblings” of the receptor, physiologically relevant ligands of “sibling” receptors, and physiologically relevant odorants. This strategy produced 9 ligands with little in common structurally; however, 4 of the 9 represented fungal metabolic products. When tested against other fungal-derived metabolites as well as conditioned media from various fungi, an additional 7 ligands occurred. Thus, 11 of 16 ligands for Olfr90 are of fungal origin.

So why does the kidney need to react to fungus? After all, this is an internal organ that should not regularly be exposed to yeasty-beasties, even though those wily single-cells run all over out skin and guts. Kidney and urinary tract infections with fungus do occur, but generally in immunosuppressed patients or those with instrumented urinary tracts. Making receptors has metabolic costs for cells, so should have a benefit beyond a relatively rare infection risk.

As noted last at the Cannon Lecture, microbes do not always have to enter the body to wreck havoc. Under certain circumstances the gut and other mucosa can become “leaky” and allow microbial metabolites into the circulation. These sensors may be waiting for the metabolites as a signal of these processes.

So what response does the kidney make to these ligands? Experiments are still in progress, but given the Olfr90 localization to the macula densa, changes in glomerular filtration rate could occur.

Study of olfactory receptors opens a world well beyond the nose. They do not mean the kidney smells, in any sense of the word!

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Speaking Up and Out for Science

Apr 03 2016 Published by under EB2016

The American Physiological Society Communications Committee sponsors a workshop at Experimental Biology every year to aid members on getting our messages out to the lay public. On Saturday, April 2, a panel discussed writing for local and national news outlets.

From the program:

Be a Champion for Science in the Media—The Communications Committee Symposium Will Show You How

We’ve all seen examples of science misrepresented in the media. Scientifically inaccurate news can quickly go viral, turning misunderstood concepts into widely accepted beliefs that can influence public support for and trust in research. The Communications Committee symposium “Setting the Record Straight for Science: How to Write to Local and National News Outlets” addresses the why, when and how of responding to scientific inaccuracies in the media. We’ll look at examples of scientific misinterpretation and discuss how researchers can be champions for science by crafting media-ready materials such as op-eds and letters to the editor. Join us on Saturday, April 2, from 3 to 5 p.m. in SDCC Room 25C.

The panel discussion started with Bill Yates, a professor otolaryngology and neuroscience at the University of Pittsburgh. He discussed his advocacy for Class B animal use in research over several years. His congressional representative, Mike Doyle, sponsored the legislation in question and wrote an inflammatory and inaccurate editorial for The Hill, a congressional news outlet. He wrote a piece demonstrating the inaccuracies that was published a week later. Over many subsequent contacts with Representative Doyle,Yates managed to delay the dissolution of class B animal dealers until an NIH approved alternative became available.

The following speaker, Bruce Lieberman, writes and edits science as a freelancer. He spoke to the contraction of the media in recent years, along with the demise of dedicated science writers and editors. Mario Aguilera is Interim Director of Communications at Scripps Institution of Oceanography. He provides the bridge between scientists and journalists for his institution. Both of these speakers emphasized the importance of knowing who you talk to in the press. Your biggest help will be your institutional communication and publicity office. They can tell you about local media outlets and who can help spread your story.

Things to remember, whether you are talking about your own science or something covered poorly:

  • What is your message? Should be short, sweet, and meaningful
  • What scientists consider significant may not be newsworthy for the general public
  • Provide contact information
  • Images and video can make or break a story, but make sure they are high resolution
  • Is there a “wow factor”?
  • Nothing is ever off the record - even if it happens in casual conversation before the "official" interview

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And So It Officially Begins: #expbio 2016

Apr 03 2016 Published by under EB2016

 

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