Category Archives: vasopressin

Circadian phase delays and metabolism

Remember the “jet lag-resistant” mice?  Guess what: screw with circadian biology and metabolism pays the price.

In brief, vasopressin was classically thought of as an anti-hypotensive hormone.  The vasopressin analog Desmopressin is used to treat bed-wetting.  But vasopressin biology is much more interesting than that: mice lacking both vasopressin receptors require very little time adapting to large circadian phase changes.  And as with many fundamental concepts in chronobiology, this is intimately linked with metabolism.

People with certain polymorphisms of the vasopressin receptor, V1A, exhibit elevated blood glucose levels and are at greater risk for diabetes (Enhorning et al., 2009):

genotype

This risk is strongest in men in the highest quartile of fat intake, and is statistically more significant after adjusting for age and physical activity:

Fat consumption

This study wasn’t designed to be a very powerful indicator of diet-disease relationships, but a little speculation: some think higher fat [and lower carb] intake should be protective against diabetes… which may be true, for people who can tell time.  Alter one nucleotide in the vasopressin 1A receptor gene and the game changes.

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Angiotensin: more than just blood pressure.

Pathologically low blood pressure can lead to shock & death.  Angiotensin II is there to prevent that, but it does much more.  A bit non-sequiter, perhaps.

This is what I call teamwork: low blood pressure detected by kidneys –> secretes renin.  Angiotensinogen (liver) is cleaved by renin to Angiotensin I.  Angiotensin Converting Enzyme (lungs [among other tissues]) cleaves angiotensin I into angiotensin II.

RAAS

Angiotensin II increases blood volume and restores blood pressure.  Good if you’ve lost a ton of blood fighting a wild beast; not good if you’re an overweight pen pusher on potato chips.  ACE inhibitors reduce angiotensin II, lowering blood pressure.  ACE is present in lungs probably because it deactivates bradykinin.  ACE inhibitors prevent this which might contribute to one of their side effects, a persistent dry cough which makes these drugs intolerable for many.  One alternative is angiotensin II receptor 1 blockers, or “ARBs.”


If anyone in pharma reads my blog (doubtful, unless they are monitoring for people to polonium-laced blow-dart), this will be their favorite post because I think ARBs are an interesting class of drugs.

If diet and weight loss are inadequate, telmisartan might be the next best thing to manage hypertension in diabetics:  Telmisartan for the reduction of cardiovascular morbidity and mortality (Verdecchia et al., 2011) –> effective at reducing mortality in patients with diabetes.

Efficacy of RAS blockers on cardiovascular and renal outcomes in NIDDM (Cae & Cooper 2012)  –> reduces morbidity and slows progression of renal disease (both hypertension and diabetes contribute to [irreversible] kidney damage, and frequently occur together, which makes this endpoint particularly relevant).  Hyperglycemia should be managed via diet, of course, and ARBs would need to be tested in people following something other than a Western diet (although said people may not even need treatment in the first place) (just thinking out loud here.  Or typing/whatever.)

But enough about blood pressure (<– boring); on to the more interesting stuff:

It started here: Chronic perfusion of angiotensin II causes cognitive dysfunctions and anxiety in mice (Duchemin et al., 2013)

Then: Candesartan prevents impairment of recall caused by repeated stress in rats (Braszko et al., 2012)

And: Anti-stress and anxiolytic effects of [candesartan] (Saavedra et al., 2005)

[Candesartan] prevents the isolation stress-induced decrease in cortical CRF1 receptor and benzodiazepine binding (Saavedra et al., 2006)

[Candesartan] ameliorates brain inflammation (Benicky et al., 2011)   brain inflammation induced by chronic exposure to artificial lights causes depression-like symptoms (in mice) (probably humans, too)

Finally, a human study: Candesartan and cognitive decline in older patients with hypertension (Saxby et al., 2008)

And then there’s this: Angiotensin receptor blockers for bipolar disorder (de Gois et al., 2013)


No mechanistic stuff because, well, I have no idea how it works.  On one hand, it might seem obvious that stress & anxiety can raise blood pressure, so something that lowers stress & anxiety could lower blood pressure.  Candesartan appears to do both (cause <–> effect?).  There are two unique properties of candesartan to note: 1) it gets into the brain; and 2) it leads to increased levels of angiotensin II (which presumably can’t do much because candesartan blocks the receptor for angiotensin II).  Perhaps angiotensin II targets a different receptor?  ARBs might blunt angiotensin II-induced CRH secretion, leading to anxiolysis, stress-tolerance, and pro-cognitive effects (that speculation was made possible by a thread on Avant Labs’ Forum and a few posts by Jane Plain on CRH [eg, here & here]).

Oh yeah, ARBs also prevent cafeteria diet-induced weight gain, insulin resistance, and ovulatory dysfunction [in rats] (Sagae et al., 2013).  And are sympatholytic like bromocriptine (Kishi & Hirooka 2013).

“The Angiotensin-melatonin axis” (Campos et al., 2013).

just sayin’

calories proper

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Circadian disruptions impact behavior and metabolism in a tissue-specific manner.

The control of circadian gene expression is complex, with layer upon layer of suppressors and enhancers, numerous transcription factors, and a lot of interactions.  A gross oversimplification: Clock and Bmal1 are positive regulators of circadian gene expression; Per and Cry are negative (you don’t really need to know any of this).

 

Some pretty cool progress has been made in examining the effects of global and tissue-specific deletion of circadian rhythm-related transcription factors.  Bear with me :)

For example, global Bmal1 knockout mice (ie, mice that don’t express Bmal1 anywhere in their whole body.  Zero Bmal1.  Nil.) (Lamia et al., 2008).  These mice are obese, and exhibit impaired glucose tolerance yet improved insulin sensitivity.

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Circadian biology: jet lag, mood, & potential role of BP regulatory peptides

There are enough connections here to suggest it’s an interesting rabbit hole.  Besides the effects of ARBs & desmopressin on mood and cognition, blood pressure regulation is not interesting <– fact.  But if it ties into fertility, circadian biology, and seasonal changes in how we should be doing things…

Way back in 1998 when I was graduating high school, Murphy and colleagues were screwing with “light-entrainable” and “food-entrainable” oscillators of circadian rhythmicity (1998).  They did this in two lines of rats, one with intact vasopressin signaling and one without.  With little mechanistic work, they showed vasopressin mediates circadian effects driven by light; and rats without vasopressin were more entrainable by meal timing.  N.B. in addition to the posterior pituitary, vasopressin is also found in the famous circadian light-regulated SCN neurons (Rosving 2010).

While it is speculated to play a role in social behaviors and sexual motivation, vasopressin is primarily known for its anti-hypotensive effects.  When plasma volume drops, vasopressin is secreted to decrease urinary water loss and increase blood pressure.  This is antagonized by alcohol, which is thought to be one reason why alcohol can dehydrate you.

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