There are very few pathways in physiology that do only one thing. Virtually all pathways evolved from something else, so they have multiple activities. That is one of the things that makes physiology so difficult to understand, there are so many things going on simultaneously.

Anemia also raises NO levels because hemoglobin is the sink for NO. That has been observed in isovolemic anemia (replacement of blood with plasma or other red blood cell free extenders) in rabbits where exhaled NO increases with anemia. Similarly isovolemic anemia causes vasodilatation and tachycardia, but with no hypoxia. The partial pressure of O2 in the venous return blood is not lower during isovolemic anemia even with ~50% reductions in blood hemoglobin.

NO prevents the formation of bacterial biofilms. I think that is the reason behind the very high NO levels of septic shock, to generate very high NO levels to prevent formation of a biofilm in the vasculature (which would very likely be fatal). Anemia may facilitate that, and may be why anemia during pregnancy occurs and why there are more adverse effects in pregnancies with high hemoglobin levels. Puerperal fever was a major cause of death before antibiotics. Evolution is going to â??optimizeâ? survival by trading off death due to anemia, puerperal fever, cephalopelvic disproportion and everything else.

That might be a good question or it might be a side trip for now. I would not say with confidence that nausea arose in any other species. Offhand I can’t think of any research on that at all. Puking, yes, bu nausea, I really don’t know.

According to William’s hypothesis on disease, nausea would play the role not in diverting or not food related to fighting the dissease, but rather, diverting food from the pathogen. As does (and this may be related functionaly) aenemea.

If that was shown, it would not eliminate Sherman’s hypothesis. I can’t think of too many adaptive systems that don’t relate to or piggy back on some other existing system. If there is rising progesterone (and there is) it is going to be the signal for any number of other systems that are adaptations related to pregnancy.

Then she pukes. Side effect.

So, this is an “adaptive explanation” in that it is an explanation that involves an adaptation, but not that the specific symptoms we identify as the syndrome are themselves adaptive.

What is the â??purposeâ? of nausea in the first place, among the non-pregnant? We know that nausea evolved, and that many organisms have states that seem to be nausea-like. Presumably nausea didnâ??t suddenly appear with humans.

Nausea does occur during sickness, and reduces food consumption during sickness. The bodyâ??s need for energy and nutrients is not reduced during sickness, however the bodyâ??s metabolic capacity is being diverted to sickness fighting, and perhaps nausea is the way to divert metabolic capacity away from food digestion to sickness fighting. If your body can successfully deal with the sickness, then you can regain what ever weight you lost. If it doesnâ??t, then you didnâ??t divert enough resources to fighting it.

During sickness, the body generates high nitric oxide levels through the expression of iNOS. That high NO level is what causes the vasodilation and hypotension of septic shock. NO normally blocks heme enzymes including the cytochrome P450 enzymes which are the major xenobiotic metabolizing enzymes. If the P450 enzyme activity is compromised by high NO, then avoiding consumption of xenobiotic chemicals would be advantageous. Similarly if those P450s are needed to metabolize toxins produced by pathogens, avoiding food might be advantageous.

Early fetal life is pretty hypoxic. Much of the energy is produced by glycolysis which produces far fewer free radicals than oxidative phosphorylation. Early pregnancy does not require additional energy. What is most important is that the fidelity of DNA replication is kept very high. NO is an excellent anti-oxidant, several orders of magnitude better than vitamin E.

What is needed in the first trimester is to expand the blood supply (requires NO to increase Epo), increase mitochondria number (requires NO to trigger mitochondria biogenesis), increase vascularization of the placenta (requires NO for angiogenesis). I suspect that the high NO of sepsis and the high NO of early pregnancy both trigger nausea. I think that trying to counter the nausea of pregnancy is not a good idea.

Sailor: No, I doubt that they do. Remember: Dog are always puking. To a dog, puking is just fun. They are obviously using pregnancy as an excuse to puke more…