A Comparison of Pharmacokinetic Methods for In Vivo Studies of Nonmediated Glucose Absorption

Napier, Kathryn R.; McWhorter, Todd J.; Fleming, Patricia A.

doi:10.1086/664669

Cited by 5 publications

(7 citation statements)

References 30 publications

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“…accommodates small birds that are sensitive to repeated blood sampling, and allows for measurements in non-restrained birds, which are therefore able to continue feeding (Napier et al, 2012). ) in the blood sample taken ~2h after injection; t is the actual time the blood sample was collected (h); and K ) as predicted by K 14 C from a blood sample taken ~2h after injection.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Not all birds commenced feeding immediately after they were returned to the cage after injection of the radioisotopes. We previously have shown that the pharmacokinetic calculations are extremely sensitive to this assumption of steady-state feeding, and any time that the animal is not feeding needs to be taken into account in the calculations, especially for intake rates (Napier et al, 2012). To do this, the intake rates were adjusted for actual time spent feeding; this was done by re-setting t=0 to the point when the birds started to defecate regularly (and were thus feeding regularly).…”

Section: Total Evaporative Water Lossmentioning

confidence: 99%

“…Data editing is an important but also very unreliable aspect of handling pharmacokinetic data (Napier et al, 2012). The first excreta samples are likely to have a low concentration of 3 H and 14 C, because these samples may reflect CF produced before the i.m.…”

Section: Total Evaporative Water Lossmentioning

confidence: 99%

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Gastrointestinal and renal responses to variable water intake in whitebellied sunbirds and New Holland honeyeaters

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Napier

Nicolson

et al. 2013

Journal of Experimental Biology

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SUMMARYNectarivores face a constant challenge in terms of water balance, experiencing water loading or dehydration when switching between food plants or between feeding and fasting. To understand how whitebellied sunbirds and New Holland honeyeaters meet the challenges of varying preformed water load, we used the elimination of intramuscular-injected [ 14 C]-L-glucose and 3 H 2 O to quantify intestinal and renal water handling on diets varying in sugar concentration. Both sunbirds and honeyeaters showed significant modulation of intestinal water absorption, allowing excess water to be shunted through the intestine when on dilute diets. Despite reducing their fractional water absorption, both species showed linear increases in water flux and fractional body water turnover as water intake increased (both afternoon and morning), suggesting that the modulation of fractional water absorption was not sufficient to completely offset dietary water loads. In both species, glomerular filtration rate was independent of water gain (but was higher for the afternoon), as was renal fractional water reabsorption (measured in the afternoon). During the natural overnight fast, both sunbirds and honeyeaters arrested whole kidney function. Evaporative water loss in sunbirds was variable but correlated with water gain. Both sunbirds and honeyeaters appear to modulate intestinal water absorption as an important component of water regulation to help deal with massive preformed water loads. Shutting down glomerular filtration rate during the overnight fast is another way of saving energy for osmoregulatory function. Birds maintain osmotic balance on diets varying markedly in preformed water load by varying both intestinal water absorption and excretion through the intestine and kidneys.Supplementary material available online at

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Total Evaporative Water Lossmentioning

confidence: 99%

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Gastrointestinal and renal responses to variable water intake in whitebellied sunbirds and New Holland honeyeaters

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Napier

Nicolson

et al. 2013

Journal of Experimental Biology

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“…The possible occurrence of such modulation of intestinal water absorption has been tested experimentally by means of pharmacokinetic techniques, using the model developed by McWhorter and Martínez del Rio (McWhorter and Martínez del Rio, 1999). Assumptions and limitations of the steady-state pharmacokinetic method have recently been explored in detail (Purchase et al, 2013b;Napier et al, 2012). Data collected to date suggest that there is no modulation of intestinal water absorption in two hummingbird species [green-backed firecrowns, Sephanoides sephaniodes (Fig.…”

Section: Regulation Of Intestinal Water Absorptionmentioning

confidence: 99%

“…Variations in patterns of excretion suggest subtle differences in how sunbirds and honeyeaters deal with short-term disturbances. When birds are captured and handled for an intramuscular injection as part of a pharmacokinetic technique (Napier et al, 2012;Purchase et al, 2013b), they may take different lengths of time to return to feed, thereby experiencing a short-term fast. Variations in patterns of excretion following this disturbance suggest that whitebellied sunbirds probably reduce GFR in response to disturbance, but New Holland honeyeaters reduce the frequency of excretion (i.e.…”

Section: How Do Nectarivorous Birds Deal With Fasting?mentioning

confidence: 99%

Drinking problems on a ‘simple’ diet: physiological convergence in nectar-feeding birds

Nicolson

Fleming

2014

Journal of Experimental Biology

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Regulation of energy and water are by necessity closely linked in avian nectarivores, because the easily available sugars in nectar are accompanied by an excess of water but few electrolytes. In general, there is convergence in morphology and physiology between three main lineages of avian nectarivores that have evolved on different continents -the hummingbirds, sunbirds and honeyeaters. These birds show similar dependence of sugar preferences on nectar concentration, high intestinal sucrase activity and rapid absorption of hexoses via mediated and paracellular routes. There are differences, however, in how these lineages deal with energy challenges, as well as processing the large volumes of preformed water ingested in nectar. While hummingbirds rely on varying renal water reabsorption, the passerine nectarivores modulate intestinal water absorption during water loading, thus reducing the impact on the kidneys. Hummingbirds do not generally cope with salt loading, and have renal morphology consistent with their ability to produce copious dilute urine; by contrast, as well as being able to deal with dilute diets, honeyeaters and sunbirds are more than capable of dealing with moderately high levels of added electrolytes. And finally, in response to energy challenge, hummingbirds readily resort to torpor, while the passerines show renal and digestive responses that allow them to deal with short-term fasts and rapidly restore energy balance without using torpor. In conclusion, sunbirds and honeyeaters demonstrate a degree of physiological plasticity in dealing with digestive and renal challenges of their nectar diet, while hummingbirds appear to be more constrained by this diet.

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Effect of macronutrient and micronutrient manipulation on avian blood glucose concentration: A systematic review

Basile

Singh²,

Watson³

et al. 2022

Comparative Biochemistry and Physiology Part A: Molecular &

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A Comparison of Pharmacokinetic Methods for In Vivo Studies of Nonmediated Glucose Absorption

Cited by 5 publications

References 30 publications

Gastrointestinal and renal responses to variable water intake in whitebellied sunbirds and New Holland honeyeaters

Gastrointestinal and renal responses to variable water intake in whitebellied sunbirds and New Holland honeyeaters

Drinking problems on a ‘simple’ diet: physiological convergence in nectar-feeding birds

Effect of macronutrient and micronutrient manipulation on avian blood glucose concentration: A systematic review

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