Osmoregulation and body fluid compartmentalization in dehydrated heat-exposed pigeons

Abstract

Osmoregulatory and volume-regulatory responses of heat-acclimated pigeons (Columba livia) were studied during normal hydration and dehydration combined with heat exposure. Dehydrated heat-exposed pigeons (exposure to 50 degrees C following 48 h of water deprivation; 16-18% mass loss) could recover 97% of their initial body mass within 30 min of free drinking at the end of heat exposure. At the end of heat exposure, body temperature increased by 3 degrees C and hematocrit increased by 12.5%. Serum electrolyte and protein concentrations increased by 33-53% (P less than 0.001). Serum osmolality reached an outstanding mean value of 436.7 +/- 28.5 mosmol/kg (n = 11), 30.5% higher than the normal mean value. Serum glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase concentrations did not change during dehydration, suggesting no impairment in circulatory function. Blood urea nitrogen increased sixfold, indicating a total shutdown of the kidney. Relative plasma volume was maintained during dehydration at the expense of extravascular spaces and with a decreased vascular permeability as indicated by the increase in Evans blue-labeled albumin half-life (control, 104 +/- 53 min; dehydration, approaching infinity). Altogether, extracellular fluid volume and intracellular fluid volume contributed 53 and 47% of the evaporative water loss, respectively. It is concluded that plasma volume regulation may play an important role in the effective thermoregulatory responses of heat-exposed dehydrated pigeons. This regulation is achieved by preferential shifts of body water reserves among the various body water compartments coinciding with a remarkable tolerance to high osmotic pressures.

Combined Effect of Short-Term Dehydration and Sublethal Acute Oral Dicrotophos Exposure Confounds the Diagnosis of Anticholinesterase Exposure in Common Quail (Coturnix Coturnix) Using Plasma Cholinesterase Activity

“…Increases in these plasma parameters have been observed in birds in response to water deprivation, although not always concurrently. Significant increases in P osm have resulted from short-term water deprivation in chickens (Gallus domesticus; Arad et al, 1985), Rock Pigeons (Columba livia; Arad et al, 1989;Carmi et al, 1994), European Starlings (Sturnus vulgaris; Roberts and Dantzler, 1989), and Japanese Quail (Coturnix japonica; Takei et al, 1988). However, among these studies, only the work with Japanese Quail found a significant increase in hematocrit associated with water deprivation (Takei et al, 1988).…”

“…However, among these studies, only the work with Japanese Quail found a significant increase in hematocrit associated with water deprivation (Takei et al, 1988). Arad et al (1985) examined the response of chickens subjected to 48 hr of water deprivation and observed significant increases in P osm . However, their work focused on the relation between osmoregulation and hormones, and no inferences were made regarding ECV and PV (Arad et al, 1985).…”

“…Arad et al (1985) examined the response of chickens subjected to 48 hr of water deprivation and observed significant increases in P osm . However, their work focused on the relation between osmoregulation and hormones, and no inferences were made regarding ECV and PV (Arad et al, 1985). Arad et al (1989) later conducted similar work with Rock Pigeons and measured both P osm and Hct.…”

“…Responses to dehydration have been monitored using measures of plasma osmolality (P osm ; Arad et al, 1989) and hematocrit (Hct; Takei et al, 1988). Increase in P osm was associated with loss of extracellular fluid volume (ECV; Arad et al, 1989), while increase in Hct was associated with loss of plasma volume (PV; Takei et al, 1988).…”

“…Increase in P osm was associated with loss of extracellular fluid volume (ECV; Arad et al, 1989), while increase in Hct was associated with loss of plasma volume (PV; Takei et al, 1988). No data are available on the effect of hydration state on ChE activity in plasma.…”