Partitioning of body fluids and cardiovascular responses to circulatory hypovolaemia in the turtle, Pseudemys scripta elegans

Investigations were conducted (1) to measure the steady state compartmentation of body fluids and (2) to assess the efficacy of blood volume and pressure maintenance during haemorrhage-induced hypovolaemia in the pond turtle, Pseudemys scripta elegans. The pre-haemorrhage blood volume, as determined by tracer dilution of ⁵¹Cr-labelled erythrocytes, averaged 6.89 ± 0.33% of the body mass, and was part of comparatively large extracellular (40.2 ± 0.70%) and total body fluid volumes (75.25 ± 1.48%). Turtles exhibited progressive reductions in systemic arterial pressure throughout a cumulative haemorrhage of -48% of their original blood volume, despite dramatic increases in heart rate and comparatively large magnitudes of transcapillary fluid transfer from interstitial to intravascular spaces. Arterial blood pressure returned to pre-haemorrhage values 2 h after experimental haemorrhage ceased, comcomitant with the restoration of the original blood volume. Our results support arguments made in previous studies that the resistance to fluid movement between vascular and extravascular locations in reptiles is comparatively low. Furthermore, the haemodynamic responses of turtles to experimental hypovolaemia suggest that barostasis through adjustments in vascular tone is less effective than that observed in other reptiles.