Unexpected changes in the catecholamine content of platelets and plasma during exercise

Catecholamines are retained within platelets for several hours after plasma catecholamine concentrations have returned to baseline. To determine whether platelet catecholamine concentrations may provide an index of short-term elevations in plasma adrenaline (A) and noradrenaline (NA), the response of plasma and platelet catecholamines to an interval supramaximal, Max (107% VO(2) Max), and submaximal, Submax (37% VO(2) Max), cycling protocol was examined in seven healthy male volunteers, 22-34 years. Despite large rises in plasma NA and A in the Max study (12- and 8-fold increases above baseline, respectively) and smaller rises in the Submax study, the baseline platelet concentrations of A and NA fell significantly in the first 15 min of exercise in both groups. This fall was greater in the SubMax protocol. Catecholamine concentrations then increased slowly in the second half of exercise, but never returned to baseline. The circulating platelet count almost doubled during the exercise period, increasing from 308 to 569 X 10(3) platelets/ml plasma in both studies, returning close to baseline in recovery. These results indicate that at the beginning of exercise there is large rise in plasma catecholamines and the circulating platelet count, with a fall in the platelet catecholamine concentrations. This suggests that a sequestered platelet population, free of catecholamines, is released at the beginning of exercise. This release most probably occurs from the spleen. If this is the case, the reason for a propagation of platelets in the spleen, free of catecholamines, requires further investigation.

The measurement of plasma catecholamine and lactate thresholds: a comparison of methods

Plasma lactate and catecholamine thresholds were calculated using three different variations of linear regression, an algorithmic linear regression method, a log-log transformation method and a semi-log method. A group of 18 male sports science students undertook an incremental test to exhaustion on a cycle ergometer. A 5-ml blood sample was drawn at rest, after 4 min of exercise and every 2 min thereafter until the cessation of the test. Lactate, adrenaline and noradrenaline concentrations were measured. Lactate threshold (Th1a), adrenaline threshold (ThA) and noradrenaline threshold (ThNA) were calculated using each of the three methods. The best fits of the methods were examined by comparing their standard error of estimates (SEEs). The algorithmic method demonstrated a higher SEE than the other two methods, but only for Th1a and ThNA. The power output for which each method calculated the thresholds demonstrated a main effect for method. Tukey post hoc tests showed that the algorithmic method produced significantly higher outputs than the other two methods, which did not differ significantly from one another. Comparison of these power outputs showed that Th1a and ThA differed significantly, regardless of method, there were no other significant differences. Plasma concentrations of lactate, adrenaline and noradrenaline showed that the values of Th1a and ThNA calculated by the algorithmic method were significantly higher than those calculated using the other two methods, which did not differ significantly from one another. The only significant difference for ThA was between the algorithmic and semi-log methods. Correlations between the power outputs at which each method calculated the thresholds varied greatly between methods, and were at best only moderate (r = 0.63). It was concluded that the algorithmic method was less powerful than the other two methods, and that Th1a, ThA and ThNA are not highly correlated.

The assay of the catecholamine content of small volumes of human plasma

Plasma catecholamines are routinely measured using high-performance liquid chromatography (HPLC) with electrochemical detection. Most of the present assays require sample volumes of at least 500 microL and are complex and labour-intensive procedures, or require large capital investment to reduce the sample size. This paper describes a liquid/liquid plasma catecholamine extraction procedure, HPLC separation and electrochemical detection method which is simple, sensitive and reproducible. The resting catecholamine concentration of 50 microL adult human plasma can be assayed using standard electrochemical detection. The limits of detection were 0.1 fmol injected onto the column for each catecholamine. This method allows the routine assay of plasma catecholamine concentrations within the normal adult ranges in both 500 and 50 microL samples. The within assay coefficient of variation (CV) for noradrenaline (NA) was 1.2% in 500 microL plasma and 1.9% for 50 microL plasma, corresponding values for adrenaline (A) were 8.5 and 6.6%. The between assay CVs were 3.9 and 7.8% for NA, and 9.9 and 5.7% for A.

Developmental changes in neurotensin and its metabolites in the neonatal rat

Neurotensin-like immunoreactivity (NT-LI) was measured in the di-, tel- and mesencephalon of rats from embryonic day 15 (E15) through birth ( approximately E22) until postnatal day 5 (P5) using radioimmunoassay (RIA) and an N-terminal directed polyclonal antibody. NT-LI and NT metabolite-like immunoreactivities (NT 1-8, NT 1-10, NT 1-11 and NT 1-12-LI) were also similarly determined using high performance liquid chromatography (HPLC) coupled with RIA. NT-LI was low at E15 but increased to peak levels at around E20 or birth in the di- and telencephalon, after which the levels declined. Similar, but lower, changes were observed with NT 1-10-LI but not other metabolites while much lower NT-LI and metabolites were observed in the mesencephalon where no transitory changes occurred. The changes in neonatal rat brain NT and metabolites are discussed with respect to the possible neonatal trophic roles of these peptides.

Effects of epinephrine infusion on adipose tissue: interactions between blood flow and lipid metabolism

Epinephrine has effects on both blood flow and metabolism in adipose tissue. To investigate how these effects might interact in vivo, epinephrine was infused into six healthy volunteers at a rate of 25 ng.kg-1.min-1. The rates of action of lipoprotein lipase and hormone-sensitive lipase in adipose tissue were calculated by measurement of arteriovenous differences across subcutaneous abdominal adipose tissue, and adipose tissue blood flow was measured. Epinephrine caused a significant rise in adipose tissue blood flow (P < 0.001), and the net efflux of nonesterified fatty acids (NEFA) from adipose tissue increased significantly (P < 0.05). Most of this efflux could be accounted for by hormone-sensitive lipase-derived NEFA efflux from cells (P < 0.05), but there was also a significant rise in the contribution of lipoprotein lipase-derived NEFA (P < 0.05). We conclude that adipose tissue blood flow plays an important role in the regulation of lipid metabolism, controlling substrate presentation for lipoprotein lipase and also preventing the local accumulation of fatty acids derived from both hormone-sensitive lipase and lipoprotein lipase.

Effects of adrenaline infusion on the interstitial environment of subcutaneous adipose tissue as studied by microdialysis

1. Adrenaline was infused at a rate of 25 ng min-1 kg-1 into seven healthy volunteers and its effects on adipose tissue were studied by microdialysis. 2. Adrenaline infusion led to a rapid rise in plasma adrenaline concentration from a basal value of 0.15 +/- 0.03 nmol/l to a peak value of 1.82 +/- 0.15 nmol/l within 30 min (analysis of variance: P < 0.001). Plasma noradrenaline levels increased from the basal value of 1.48 +/- 0.21 nmol/l to 1.78 +/- 0.20 nmol/l within 30 min of infusion (analysis of variance: P < 0.05). Once the infusion was stopped the plasma adrenaline and noradrenaline levels returned to basal values within 15 min. 3. The arterialized blood glycerol concentration increased from the basal value of 47 +/- 6 mumol/l to 101 +/- 8 mumol/l (analysis of variance: P < 0.001), and the interstitial glycerol concentration increased from 181 +/- 17 mumol/l to 350 +/- 47 mumol/l (analysis of variance: P < 0.001) within 30 min of adrenaline infusion. Thereafter the concentrations declined gradually towards basal values. When the infusion was discontinued the levels declined further, below the basal value. 4. Adrenaline infusion caused a significant increase in the plasma glucose and blood lactate concentration (analysis of variance: P < 0.001 and P < 0.001), but no such effect was observed in the interstitial concentrations. 5. The basal dialysate concentrations of adrenaline and noradrenaline were 43 +/- 37 pmol/l and 1170 +/- 430 pmol/l respectively. There were difficulties in estimating the absolute interstitial concentrations of adrenaline and noradrenaline which are discussed. The dialysate adrenaline concentration increased to a peak value of 112 +/- 48 pmol/l (analysis of variance: P < 0.05) within 30 min. The dialysate noradrenaline concentration increased to a peak value of 2830 +/- 1470 pmol/l, but the rise was not significant. 6. These results show that the interstitial concentrations of metabolites and hormones can be significantly different from those of blood and plasma and these differences reflect tissue specialization.

Effects of high-intensity exercise on plasma catecholamines in the thoroughbred horse

In Study 1, a single speed test of 6 to 12 m/sec was performed for 2 mins at an incline of 5 degrees on a high-speed treadmill (single-step test). Only one speed was performed per session and blood samples were taken before and after the test. In Study 2 horses cantered for 1 min at increasing speeds of 6 to 13 m/sec on an incline of 3 degrees (multiple-step test). Blood samples were taken before exercise, throughout the test and during recovery. In the single-step test plasma concentrations of adrenaline and noradrenaline both increased at speeds of 9 m/sec, as did blood lactate. Mean concentrations of adrenaline and noradrenaline at the end of the 12 m/sec test were 153 and 148 nmol/litre, respectively. Plasma concentrations were similar over all speeds although there was a tendency for the increase in noradrenaline to be greater than that of adrenaline at the lower speeds. The multiple-step test resulted in smaller increases in both adrenaline and noradrenaline. Although again closely correlated, increases in adrenaline were 20-30% greater than those for noradrenaline. In both exercise models, changes in plasma adrenaline and noradrenaline values with exercise showed an exponential relationship to plasma lactate. A plasma half-life of less than 30 secs was indicated during recovery from the multiple-step test. Changes in adrenaline and noradrenaline were much greater than previously recorded in man and emphasise the importance of catecholamines in mediating the physiological response of the horse to exercise.