Lung surfactant function and composition in neonatal foals and adult horses

BACKGROUND: Lung surfactant function and composition are varied and adapted to the specific respiratory physiology of all mammalian species. HYPOTHESIS: Lung surfactant function and composition are different in neonatal foals as compared to adult horses. ANIMALS: Six adult horses, 7 term foals (<24 hours old), and 4 premature foals were used. Animals were part of the Auburn University teaching herd except for 3 client-owned premature foals. METHODS: Bronchoalveolar lavage fluid (BALF) was obtained from all animals. Ultracentrifugation of cell-free BALF separated surfactant into crude surfactant pellets (CSP) and supernatant. Both fractions were analyzed for phospholipid and protein content with the Bartlett and bicinchoninic acid method, respectively. Phospholipid composition of the CSP was determined by using high-performance liquid chromatography with an evaporative light scatter detector. Surface tension of the CSP was measured with a pulsating bubble surfactometer. Results from term foals (<24 hours old) were compared statistically to those from adult horses. Values of P < .05 were considered significant. RESULTS: BALF phospholipid content was similar between adult horses and term foals, but BALF protein content was significantly decreased in term foals. Phosphatidylglycerol was significantly decreased, phosphatidylinositol was significantly increased, and the minimum surface tension was significantly increased in the CSP from term foals compared to adult horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Surface tension and phospholipid composition of surfactant in neonatal foals are significantly different compared to adult horses. These changes may influence biophysical and immunologic functions of surfactant.     

Pulmonary driving pressure as a pulmonary function test in horses

Pulmonary Driving Pressure (PDP) is defined as the difference between the pulmonary artery pressure and the pulmonary capillary wedge pressure. Pulmonary driving pressure is a measure of alveolar ventilation. This parameter was determined in 20 normal horses. The mean value was 10.0 +/−2.37 mm Hg. The PaO2 in these horses varied between 98 and 110 mm Hg. In two of these 20 horses, pulmonary driving pressure was determined 10 timesconsecutively. The obtained values were within very narrow limits for the respective horses indicating the reproducibility of the technique.     

Calcium-stimulation test for the assessment of beta-cell function in cats

To assess the potential of an intravenous calcium-stimulation test (CST) as an indicator of insulin secretion in cats, indices calculated from CST results were compared with indices of insulin secretion derived from an intravenous glucose tolerance test (ivGTT) and hyperglycaemic glucose clamp (HGC) in 11 healthy, normal glucose tolerant, conscious cats. Intravenous administration of 2.5mg/kg Ca(2+) resulted in a significant increase in plasma free Ca(2+) (P<0.001) and plasma insulin (P=0.047) concentrations but did not affect the plasma glucose concentration. The indices of insulin secretion based on the CST did not correlate significantly with corresponding indices based on the ivGTT and HGC. In conclusion, the CST is not a useful test for assessing insulin secretion in cats. Other indices of insulin secretion, such as fasting insulin concentrations and the homeostasis model assessment of beta-cell function (HOMA-B), are easier to obtain and correlate better with indices of insulin secretion derived from the HGC, the gold standard technique for assessing insulin secretion.     

Equine thyroid function assessment with the thyrotropin-releasing hormone response test

The effect of thyrotropin-releasing hormone (TRH) on equine thyroid function was determined by quantifying serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) before and after TRH administration. Thyrotropin-releasing hormone was administered IV to adult horses (n = 5) and ponies (n = 6) at a dose of 1 mg or 0.5 mg, respectively. Serum T4 and T3 concentrations were determined before and 0.25, 0.5, 1, 2, 4, 6, 8, 12, and 24 hours after TRH administration. Serum T4 increased from a basal concentration of 24.4 +/- 8.7 ng/ml (mean +/- SD) to a maximum value of 48.2 +/- 10.2 by 4 hours after TRH administration. Serum T3 increased from a basal concentration of 0.44 +/- 0.18 ng/ml to a maximum value of 1.31 +/- 0.37 ng/ml by 2 hours after TRH administration. Seemingly, TRH increases serum concentrations of T4 and T3 and may be useful as a test of equine hypophysis-thyroid function.     

Thyroid function in the cat: assessment by the TRH response test and the thyrotrophin stimulation test

Changes in total thyroxine (T4), free T4 and total tri-iodothyronine (T3) were measured in 13 cats after the intravenous injection of varying doses of thyrotrophin stimulating hormone (TSH) (0–5 U/cat n = 6; 1 U/cat n = 8; 1 U/kg bodyweight, n = 7) or thyrotrophin releasing hormone (TRH) (100 ug/cat, n = 10). All three doses of TSH resulted in a significant (P < 0–05) rise in T4, free T4 and T3 levels, with the mean peak in hormone concentrations occurring six to eight hours after injection. The three doses of TSH all appeared to produce maximal stimulation of thyroid hormone secretion. The mean percentage increase in hormone concentrations at seven hours following the three doses of TSH ranged from 167 to 198 per cent for T4, 240 to 365 per cent for free T4, and 73 to 116 per cent for T3. Following administration of TRH there was also a significant (P < 0–05) rise in T4, and free T4. The mean peak in T4 and free T4 levels occurred at four hours, and mean increases in hormone levels at this time were 92 per cent for T4, and 198 per cent for free T4. The administration of TRH produced little change in T3 levels. TSH administration resulted in a significantly higher (P < 0–05) percentage peak increase in T4, free T4 and T3 levels at all three dosages than did TRH.     

Propionate loading test for liver function in spontaneously ketotic dairy cows

Propionate utilisation by the liver in spontaneously ketotic dairy cows was investigated by determining blood glucose levels after an intravenous sodium propionate load (2.5 mmol kg-1). In addition, blood ketone body concentrations were measured after propionate loading. Cows were divided into three groups (control, mildly ketotic and severely ketotic) by their blood acetoacetate concentrations. Plasma glucose concentrations increased significantly after sodium propionate injection in all three groups (P less than 0.05). The maximum glucose concentration occurred earlier in the control group than in the ketotic groups. Changes in glucose concentrations following propionate loading of control and ketotic cows differed significantly at 20 minutes and beyond. Differences in the change in glucose concentration between mildly ketotic and severely ketotic cows were not significant. Acetoacetate concentration was significantly decreased at five minutes and beyond after the injection in ketotic cows, whereas beta-hydroxybutyrate concentration decreased more slowly. A decrease in beta-hydroxybutyrate concentration was significant at 40 minutes and beyond in the severely ketotic group and at 10 minutes and beyond in the mildly ketotic group after loading.     

Thyrotropin stimulation test for evaluation of thyroid function in psittacine birds

Serum thyroid hormone concentrations were determined before and after thyrotropin (thyroid stimulating hormone [TSH]) stimulation in caged psittacine birds to determine whether the TSH stimulation test could be used to evaluate thyroid function in this class of birds. The mean (+/- SD) resting thyroxine concentrations (ng/ml) for the species studied were: cockatoos, 13.63 +/- 6.53 (n = 6); Amazon parrots, 8.19 +/- 6.90 (n = 8); scarlet macaws, 1.34 +/- 0.51 (n = 9); blue and gold macaws, 3.41 +/- 1.78 (n = 8); African gray parrots, 1.42 +/- 0.44 (n = 6); conures, 1.76 +/- 0.77 (n = 5); and cockatiels, 11.83 +/- 6.76 (n = 3). The mean (+/- SD) thyroxine concentrations (ng/ml) 4 to 6 hours after TSH stimulation were 35.10 +/- 13.16, 27.40 +/- 15.93, 6.46 +/- 3.10, 12.36 +/- 6.34, 9.30 +/- 2.90, 13.50 +/- 7.71, and 39.0 +/- 5.66, respectively. Serum tri-iodothyronine concentration did not increase significantly after TSH stimulation. The results demonstrated that the TSH stimulation test can be used to evaluate thyroid function in caged psittacine birds.     

Plasma disappearance of creatinine as a renal function test in the dog

The serum concentration of creatinine at 120 minutes (SC120) after intravenous injection of 88 mg kg-1 of creatinine, the plasma half-life (t1/2) and the plasma clearance of creatinine (PCC) were evaluated as renal function tests in 30 healthy adult dogs and six adult dogs with known or suspected renal disease. The mean SC120 in the normal dog was 0.31 +/- 0.08 mmol litre-1 and in the clinical cases 0.71 +/- 0.19 mmol litre-1. The correlation coefficients between SC120 and renal creatinine clearance (RCC) for the normal dogs and the clinical cases were -0.76 and -0.69, respectively. At 120 minutes after injection, 95 per cent of normal dogs would be predicted to have a serum creatinine concentration below 0.46 mmol litre-1. The mean plasma t1/2 of creatinine for the normal dogs was 107.7 +/- 17.96 minutes, while the clinical cases had a wide range of values (148.8 to 620.1 minutes). Plasma t1/2 of creatinine was correlated with RCC for both the normal dogs and the clinical cases (r = -0.55, r = -0.91, respectively). The mean PCC for the normal dogs was 7.42 +/- 2.22 ml min-1 kg-1 (range 4.95 to 13.28 ml min-1 kg-1). There was a good correlation between RCC and PCC (r = 0.7). The PCC for the clinical cases ranged from 0.76 to 3.37 ml min-1 kg-1. The correlation between RCC and PCC was significant (r = 0.91). Thus SC120, t1/2 and PCC may be useful methods of assessing renal function in dogs with renal impairment insufficient to cause azotaemia.     

Evoked otoacoustic emissions: An alternative test of auditory function in horses

Reasons for performing study: Deafness has been reported in horses due to a variety of causes and objective auditory assessment has been performed with brainstem auditory evoked potential testing. Evoked otoacoustic emission (OAE) tests are widely used in human patients for hearing screening, detecting partial hearing loss (including frequency‐specific hearing loss) and monitoring cochlear outer hair cell function over time. OAE tests are noninvasive, quick and affordable. Two types of OAE are commonly used clinically: transient evoked OAEs (TEOAEs) and distortion product OAEs (DPOAEs). Detection of OAEs has not been reported and OAE testing has not been evaluated for auditory assessment in horses. Objectives: To investigate whether TEOAEs and DPOAEs can be recorded in horses, and to evaluate the use of human OAE screening protocols in horses with apparently normal hearing. Methods: Sixteen systemically healthy horses with normal behavioural responses to sound were included. OAE testing was performed during general anaesthesia using commercially available equipment and the final outcome for each ear for the TEOAE test (after a maximum of 3 runs) and the DPOAE test (after one run) were compared. Results: TEOAEs and DPOAEs can be recorded in horses. Using the chosen TEOAE protocol, 96% of ears achieved a pass. Seventy percent of ears passed DPOAE testing, despite all of these ears passing TEOAE testing. Conclusions: Using the chosen stimulus and analysis protocols, TEOAEs were recorded from most ears; however, a smaller proportion of ears passed the DPOAE protocol, suggesting that this may be overly stringent and require further optimisation in horses. Potential relevance: OAE testing is rapid and easily performed in anaesthetised horses. It provides frequency‐specific information about outer hair cell function, and is a promising tool for audiological assessment in the horse; however, it has not been assessed in conscious or sedated animals.     

Thyrotropin-releasing hormone stimulation test to assess thyroid function in severely sick cats

Basal serum thyroxine (T4) concentration and the thyrotropin-releasing hormone (TRH) stimulation test were used to assess thyroid function in 36 critically ill cats examined between July 1996 and October 1998. Of the 36 cats. hyperthyroidism (as underlying or complicating disease) was suspected in 22 based on clinical signs, palpable thyroid nodules, and abnormal thyroid gland histology (study group). Hyperthyroidism was not suspected in the remaining 14 cats, which served as the control group. Based on serum T4 concentrations, suppression of thyroid function was documented in 14 (64%) cats of the study group and in 10 (71%) cats of the control group. The TRH stimulation test revealed an increase in serum T4 of less than 50% of the baseline concentration in 18 (82%) cats of the study group, and in 6 (43%) cats of the control group. In conclusion, based on the results of serum T4 determinations and the TRH stimulation tests, it was not possible to differentiate between cats with clinical and histologic evidence of thyroid dysfunction (hyperthyroidism) and cats with severe nonthyroidal illnesses.     

Propionate loading test for liver function during experimental liver necrosis in sheep

The first objective of this work was to study the conversion of propionate to glucose by liver of the sheep during experimentally induced liver necrosis. An additional objective was to determine the most appropriate sampling time after a propionate load has been given to use glucose concentration as an aid in the diagnosis of disturbed liver function. Sodium propionate (3 mmol/kg) was injected IV into 6 healthy sheep before and after they were given carbon tetrachloride (20% CCl4 in mineral oil; 0.25 ml of CCl4/kg, orally). To differentiate the effects of liver necrosis from the effects of decrease in food intake after CCl4 administration, 5 sheep which were fasted for 2 days, but not given CCl4, were studied. Microscopically, liver necrosis was observed, as well as an increase of fatty infiltration in nonnecrotic liver tissue. After sheep were given CCl4, the plasma liver-specific enzyme activities (namely, those of iditol dehydrogenase and gamma-glutamyl-transferase) were elevated. Microscopic and enzymatic changes were not observed in fasted animals. Serum sulfobromophthalein (BSP) half-life (t1/2) was markedly increased in the sheep given CCl4 treatment (t1/2 = 22.8 +/- 11 minutes) when compared with the t1/2 before treatment (t1/2 = 2.5 +/- 0.2 minutes). The BSP t1/2 did not differ between fed and fasted sheep. The t1/2 of the IV propionate load increased significantly, from 6.9 +/- 0.4 minutes in the control sheep to 12.8 +/- 2 minutes in the CCl4-treated sheep, whereas an insignificant increase was seen after fasting (6.8 +/- 1 minutes to 8.3 +/- 1 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)