Beta-adrenoreceptor blockade attenuates heat-induced tachycardia,but not the tolerance to the stress.
Ten healthy males (age 34 +/- 3 yr 9 SE) underwent 40 min of heat exposure (WD 39.7.C) after 2 hours of ingesting 120 mg of Propranolol (Inderal; ICI), or a placebo, in a random manner, the exposures being about a week apart. That there was no placebo effect was ensured by giving a control run (no medication). In the placebo trials, the end-experiment heart rate had increased by 52%, while after propranolol the increase was only 43%. Regression analysis showed that with the placebo, the HR increased by 22 beats/min/o rise in core (aural) temperature, while with propranolol, the rise (14 beats/min) was significantly lower (P < 0.02). The various heat strain indices viz the Craig's Index, the Body heat storage (Kilocals/m2/hr), and the effective heat storage were also similar for both the treatments. We conclude that beta-adrenoreceptor activity plays a significant role in producing tachycardia of heat exposure in humans, but blocking this activity with propranolol does not affect tolerance to heat stress.
Apte
C V
CV
Department of Physiology, Armed Forces Medical College, Pune.
Dikshit
M B
MB
Prasad
B A
BA
D000284:Administration, Oral; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D011433:Propranolol / Q000008:administration & dosage / Q000494:pharmacology*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects; D013312:Stress, Physiological / Q000503:physiopathology*; D013610:Tachycardia / Q000209:etiology / Q000517:prevention & control*
D011943:Receptors, Adrenergic, beta; D011433:Propranolol