Effect of Beta-Adrenoceptor Blockade and Calcium Antagonism, Alone and in Combination, on Thermoregulation During Prolonged Exercise*

Abstract

The effect of clinically used doses of propranolol, atenolol, nifedipine, propranolol plus nifedipine, and atenolol plus nifedipine on thermoregulatory responses of 11 healthy men was studied during 2-h block-stepping in heat. Drug intervention did not alter ventilation during exercise. In contrast, propranolol and atenolol produced equivalent reductions in exercise tachycardia, implying a similar level of beta 1-adrenoceptor blockade. The heart rate response to exercise was unaffected by nifedipine and during dual beta-adrenoceptor blockade and calcium antagonism was equivalent to that with beta-adrenoceptor blockade alone. While rectal temperature rises were not modified by drug ingestion, propranolol and, to a lesser degree, atenolol and combination therapy, but not nifedipine alone, attenuated skin temperature rises. Moreover, although atenolol, nifedipine, and their combination did not alter sweating, propranolol and its combination with nifedipine enhanced sweating during the 1st and 2nd h of exercise. This study concludes that nifedipine does not modify thermoregulation during exercise and allows for greater confidence of its use during cardiac rehabilitation. Furthermore, the present data confirm that propranolol does enhance sweating during exercise and demonstrate that this effect is not mediated simply by an earlier onset of rapid sweating nor abolished by concomitant calcium antagonism.

Iontophoretic β‐adrenergic stimulation of human sweat glands: possible assay for cystic fibrosis transmembrane conductance regulator activity in vivo

“…Normal thermoregulatory sweating is mediated via autonomic cholinergic receptors (Cummings, 1960; Nakazato et al 2005; Shibasaki et al 2006). There is no known function of the β‐adrenergically stimulated component (Gordon et al 1987), but it is recognized that stimulating with a β‐agonist alone induces cross‐over cholinergic stimulation. Previously, in order to reliably obtain β‐adrenergic sweating in vivo , investigators stimulated local sweating with a cocktail of isoprenaline, theophylline and atropine injected subcutaneously (Sato & Sato, 1984; Behm et al 1987).…”

Nifedipine inhibits picrotoxin‐induced seizure activity: further evidence on the involvement of L‐type calcium channel blockers in epilepsy

“…Moreover, the hemodynamic changes induced by the drug such as hypotension and hypothermia may act as indirect effects to explain nifedipine antiepileptic activity. However, the fact that some experimental and clinical studies showed that the hypotensive action of nifedipine is mainly selective to hypertensive and not to normotensive situations [20,21] and the disparity in the thermoregulatory effect of the drug [22–24] may require more studies to confirm this mechanism.…”