HYPOXIA-INDUCED AND NORMOXIA-INDUCED REVERSIBILITY OF AUTONOMIC CONTROL IN ANDEAN GUINEA-PIG HEART

We herein describe the regulation of cardiac receptors in a typical hi gh-altitude native animal. Heart rate response to isoproterenol (HR(Is o)) (beats . min(-1). mg Iso . kg(-1)) and atropine, the density of be ta-adrenergic (beta(AR)) and muscarinic (M(2)) receptors, and the vent ricular content of norepinephrine (NE) and dopamine (DA) were studied in guinea pigs (Cavia porcellus). Animals native to Lima, Peru(150 m) were studied at sea level (SL) and after 5 wk at 4,300-m altitude (SL- HA). Animals native to Rancas [Pasco, Peru (4,300 m)] were studied at high altitude (HA) and after 5 wk at SL (HA-SL). HA animals had a lowe r HR(Iso), maximum number of beta(AR) binding sites (B-max), beta(AR) dissociation constant (K-d), NE, and DA (P < 0.05) and a higher M(2) B -max (P < 0.001) when compared with the SL group. HA-SL showed an incr ease of the HR(Iso), beta(AR) K-d, and NE (P < 0.05) and a decrease of the M(2) B-max and K-d (P < 0.0001) when compared with the HA group. The present study demonstrates the differential regulation and reversi bility of the autonomic control in the guinea pig heart.