Adrenal contribution to cardiac responses elicited by acute hypoxia in piglets

Abstract

The adrenal contribution to cardiac responses elicited by acute hypoxia was assessed in 16 piglets, 1-12 wk old, anesthetized with pentobarbital (30 mg/kg). External cardiac work was held constant and parasympathetic blockade was produced in each animal with atropine (1 mg). Hypoxia was produced by addition of N2 to the respirator. In a sham-adrenalectomy group (n = 6) left ventricular (LV) dP/dtmax [rate of change in pressure] increased significantly during hypoxia (PaO2 [arterial partial pressure of O2] .apprx. 30 mmHg) to 3680 .+-. 414 mmHg/s from control values of 2686 .+-. 317 mmHg/s (P < 0.01). Heart rate rose from 171 .+-. 6 to 186 .+-. 7 beats/min (P < 0.02). These responses were not significantly altered by ganglionic blockade with trimethaphan camsylate (0.5 mg .cntdot. kg-1 .cntdot. min-1). Equally large increases of LV dP/dtmax appeared when heart rate was held constant by pacing, .beta.-Adrenoreceptor blockade with practolol (4 mg/kg) sharply reduced but did not eliminate the response. In contrast, no changes in LV dP/dtmax or heart rate were observed during hypoxia in adrenalectomized piglets (n = 6). The increased cardiac contractility during acute hypoxia in piglets apparently is dependent on the integrity of the adrenal glands, there is minimal contribution from cardiac sympathetic nerves.