2007, Piran, Slovenia

Cold water immersion
RESULTS
Experiments revealed that infusions of the optimal dose of the β1 agonist (Dobutamine)
increased metabolic rate of humans resting at thermoneutal conditions by 39 %, while
infusions of the β2 agonist (Bricanyl) increased metabolic rate by 20%, in absolute terms the
increase being 77 ml O2. kg -1 .hr -1 , or 57 ml O2. kg -1 .hr -1 , respectively (Fig. 1, 2). This
indicates greater role of β1 adrenoceptors in mediating metabolic response. In winter
swimmers administrations of both adrenomimetics were without effect, indicating
downregulation of adrenergic receptors (Fig. 1, 2).
Metabolic rate (mlO 2.kg -1 .hr -1 )
390
370
350
330
310
290
270
250
230
210
β1 adrenergic agonist
-0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
Infusion rate (µg.kg -1 .min -1 )
Figure 1. Effect of increasing concentrations of the β1 agonist on metabolic rate in controls
(white points, interrupted line) and winter swimmers (black points, solid line).
Metabolic rate (ml O 2.kg -1 .hr -1 )
390
370
350
330
310
290
270
250
230
210
β2 adrenergic agonist
-0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45
Infusion rate (µg.kg -1 .min -1 )
Figure 2. Effect of increasing concentrations of the β2 agonist on metabolic rate in controls
(white points, interrupted line) and winter swimmers (black points, solid line).
In contrast to the effect on metabolic rate, the actions of the β1 and of the β2 agonist on heart
rate were different. The β1 agonist was without effect, while the β2 agonist increased heart
rate by about 100%, indicating dominant role of β2 adrenoceptors in controlling heart rate
(Fig. 3, 4). In winter swimmers the effect of the β2 agonist was supressed by about a half
(Fig. 3, 4).
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