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This Article Full Text Full Text (PDF) All Versions of this Article: 295/6/F1855    most recent 90349.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hartman Bakken, B. Articles by Martínez del Rio, C. Search for Related Content PubMed PubMed Citation Articles by Hartman Bakken, B. Articles by Martínez del Rio, C.

A nectar-feeding mammal avoids body fluid disturbances by varying renal function

¹Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming; ²Instituto de Biología, Estación de Biología Chamela, Universidad Nacional Autónoma de México, San Patricio, Jalisco; and ³Centro de Investigaciones en Ecosistemas, Universidad Nacional Autónoma de México, Campus Morelia, Michoacán, México

Submitted 6 June 2008 ; accepted in final form 14 October 2008

To maintain water and electrolyte balance, nectar-feeding vertebrates oscillate between two extremes: avoiding overhydration when feeding and preventing dehydration during fasts. Several studies have examined how birds resolve this osmoregulatory dilemma, but no data are available for nectar-feeding mammals. In this article, we 1) estimated the ability of Pallas's long-tongued bats (Glossophaga soricina; Phyllostomidae) to dilute and concentrate urine and 2) examined how water intake affected the processes that these bats use to maintain water balance. Total urine osmolality in water- and salt-loaded bats ranged between 31 ± 37 mosmol/kgH₂O (n = 6) and 578 ± 56 mosmol/kgH₂O (n = 2), respectively. Fractional water absorption in the gastrointestinal tract was not affected by water intake rate. As a result, water flux, body water turnover, and renal water load all increased with increasing water intake. Despite these relationships, glomerular filtration rate (GFR) was not responsive to water loading. To eliminate excess water, Pallas's long-tongued bats increased water excretion rate by reducing fractional renal water reabsorption. We also found that rates of total evaporative water loss increased with increasing water intake. During their natural daytime fast, mean GFR in Pallas's long-tongued bats was 0.37 ml/h (n = 10). This is 90% lower than the GFR we measured in fed bats. Our findings 1) suggest that Pallas's long-tongued bats do not have an exceptional urine-diluting or -concentrating ability and 2) demonstrate that the bats eliminate excess ingested water by reducing renal water reabsorption and limit urinary water loss during fasting periods by reducing GFR.

glomerular filtration rate; Glossophaga soricina; urine dilution; water balance; water flux