The interplay of cutaneous water loss, gas exchange and blood flow in the toad,<i>Bufo woodhousei:</i>adaptations in a terrestrially adapted amphibian
Bibliographic record
Abstract
Toads experiencing dehydrating conditions exhibit complex physiological and behavioral responses, some of which can potentially impact cutaneous gas exchange, an important component of total gas exchange. We measured the effect of dehydration on cutaneous gas exchange in the xeric-adapted toad Bufo woodhousei. First, two pharmacological agents were used to stimulate cutaneous blood flow--phentolamine (an alpha-blocker) and isoproterenol, a beta-stimulant and powerful cardio-accelerator--to determine a relationship between cutaneous blood flow and water loss. Both drugs increased heart rate and blood pressure, and caused visually evident extensive vasodilation of the skin. Untreated toads in a dry air stream took an average of 10.1+/-0.7 h to dehydrate to 80% body mass, while animals treated with isoproterenol and phentolamine requires only 7.2+/-0.8 h and 7.4+/-0.9 h, respectively. Rehydration, which was more rapid than dehydration, was similarly accelerated in pharmacologically treated toads. Cutaneous gas exchange (M(O2), M(CO2)) and C18O diffusing capacity (D(Skin)C18O) were then examined in unanesthetized toads under different states of body hydration. Blood gases and hematocrit were measured separately but under identical conditions. In fully hydrated toads at 23-25 degrees C, cutaneous gas exchange values were: M(O2) = 1.43+/-0.47 micromol g(-1) h(-1), M(CO2) = 1.75+/-0.85 micromol g(-1) h(-1), and the respiratory exchange ratio R = 1.36+/-0.56 (N=6, mean + 1 S.D.). D(Skin)C18O was 0.48+/-0.03 micromol g body mass(-1) h(-1) kPa. Following an enforced 20-25% loss of body water, D(Skin)C18O fell by nearly 50% to 0.28+/-0.09 micromol g(-1) h(-1) kPa. However, cutaneous M(O2), M(CO2) and R were unchanged at 1.48+/-0.15 micromol g(-1) h(-1), 1.72+/-0.29 micromol g(-1) h(-1) and 1.13+/-0.08 micromol g(-1) h(-1), respectively. Partial pressure of arterial (sciatic) oxygen, Pa(O2), normally about 12-13 kPa, remained unchanged by dehydration, but Pa(CO2) increased about 250% from 0.93+/-0.27 up to 2.27+/-0.93 kPa. The fall in D(Skin)C18O during dehydration presumably results at least in part from decreased cutaneous blood flow, possibly in an attempt to reduce the transcutaneous water loss that would otherwise result during dehydrating conditions. Concurrently, cutaneous M(CO2) is maintained under dehyrdating conditions by a greatly increased Pa(CO2) diffusion gradient across the skin. Thus, Bufo woodhousei appears able to restrict cutaneous blood flow without compromising vital cutaneous CO2 loss.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".