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Golland, L. C., Evans, D. L., McGowan, C. M., Hodgson, D. R., & Rose, R. J. (2003). The effects of overtraining on blood volumes in standardbred racehorses. Vet J, 165(3), 228–233.
Abstract: Red blood cell hypervolaemia has been used for diagnosis of overtraining in racehorses, and has been suggested as a mechanism of this cause of loss of racing performance. The effects of overload training (OLT) on the plasma, blood and red cell volumes were investigated in a prospective study in 12 Standardbred horses. Measurements of blood volumes were made after eight and 32 weeks of an exercise training study. Horses were randomly allocated to OLT and control groups (n=6) after 16 weeks of training. Training duration and intensity were increased more rapidly for the OLT group from week 16, until overtraining was diagnosed in week 32.There were no significant effects of OLT on plasma, blood or total red cell volumes between weeks eight and 32. These volumes significantly decreased with time. Maximal haematocrit after exercise was lower (P<0.05) in the OT group in week 32 (0.57+/-0.003% L/L) than in week eight (0.59+/-0.004 L/L). It was concluded that red cell hypervolaemia was not a mechanism for the decrease in capacity for exercise that occurs with overtraining.
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Houpt, K. A., Northrup, N., Wheatley, T., & Houpt, T. R. (1991). Thirst and salt appetite in horses treated with furosemide. J Appl Physiol, 71(6), 2380–2386.
Abstract: When a preliminary experiment in sodium-replete ponies revealed an increase, but not a significant increase, in salt consumption after furosemide treatment, the experiment was repeated using sodium-deficient horses in which aldosterone levels might be expected to be elevated to test the hypothesis that a background of aldosterone is necessary for salt appetite. Ten Standardbred mares were injected intravenously with furosemide or an equivalent volume of 0.9% sodium chloride as a control to test the effect of furosemide on their salt appetite and blood constituents. Sodium intake and sodium loss in urine, as well as water intake and urine output, were measured and compared to determine accuracy of compensation for natriuresis and diuresis. Plasma protein and packed cell volume showed significant increases in response to furosemide treatment (F = 29.31, P less than 0.001 and F = 11.20, P less than 0.001, respectively). There were no significant changes in plasma sodium concentration or osmolality in response to the treatment (P greater than 0.05). The furosemide-treated horses consumed 126 +/- 14.8 g salt, significantly more than when they were given the control injection (94.5 +/- 9.8 g; t = 2.22, P = 0.05). In response to furosemide, horses lost 962 +/- 79.7 and consumed 2,170 +/- 5 meq sodium; however, compared with control, they lost 955 meq more sodium and ingested only 570 meq more sodium, so they were undercompensating for natriuresis. The furosemide-treated horses drank 9.6 +/- 0.8 kg of water, significantly more than when they received the control injection (6.4 +/- 0.8 kg; t = 6.9, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
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Youket, R. J., Carnevale, J. M., Houpt, K. A., & Houpt, T. R. (1985). Humoral, hormonal and behavioral correlates of feeding in ponies: the effects of meal frequency. J. Anim Sci., 61(5), 1103–1110.
Abstract: The effect of meal frequency on body fluid, glucose, triiodothyronine (T3), heart rate and behavior was measured in 10 ponies. A simple reversal design was used in which each pony received one meal/day (1X) for 2 wk and six meals/day (6X) for 2 wk. The total intake/day was held constant. Feeding was followed by a rise in plasma levels of glucose, T3, protein and osmolality. One large meal was followed by significantly greater changes in all of the variables than was a meal one-sixth the size. Plasma T3 rose from 41 +/- 5 (SE) ng/liter before feeding to 43 +/- 5 ng/liter following a small meal, but rose significantly higher, from 39 +/- 4 to 60 +/- 10 ng/liter, following a large meal. Glucose rose from 84 +/- 3 to 109 +/- 7 mg/dl following a small meal and rose significantly higher, from 83 +/- 3 to 154 +/- 11 mg/dl, after a large meal. Plasma protein rose from 6.55 +/- .14 to 6.62 +/- .16 g/dl following a small meal and from 6.45 +/- .14 to 6.99 +/- .11 g/dl following a large meal. Osmolality rose from 227 +/- 1 mosmol/liter before to 279 +/- 1 mosmol/liter following a small meal and significantly higher from 278 +/- 2 to 285 +/- 1 mosnol/liter following a large meal. Heart rate rose from 42 beats/min in the absence of feed to 50 beats/min when food was visible to the ponies and did not rise higher when eating began. There were no significant differences in the cardiac response to one large meal and that to a small meal.(ABSTRACT TRUNCATED AT 250 WORDS)
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Ziegler, W. H. (1976). [Endocrinological studies in arterial hypertension. Search for phaeochromocytoma]. Schweiz Med Wochenschr, 106(34), 1148–1150.
Abstract: Elevated urinary catecholamines and their metabolites are the only findings which confirm the presence of pheochromocytoma. This examination is of particular interest if carried out in urine produced after spontaneous hypertensive episodes. Pharmacologic tests when carried out under standard conditions have proven to be a reliable aid in cases of suspected pheochromocytoma. Roentgenographic studies, determination of local plasma catecholamine concentrations and blood volume control should be undertaken in these patients before surgical procedure.
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