Role of adrenal catecholamines during forced submergence in ducks.

Maximum underwater tolerance (UTmax) of chronically adrenalectomized ducks (ADX, 5.3 +/- 0.3 min) and chronically adrenal-denervated ducks (DNX, 7.2 +/- 0.2 min) was significantly lower than sham-operated controls (SH-ADX, 10 +/- 0.8 min; SH-DNX, 12.2 +/- 0.5 min). After 4 min forced submergence, heart rates of ADX (62 +/- 16 beats/min) and DNX (31 +/- 2 beats/min) ducks were significantly higher than in their respective sham-operated controls (23 +/- 3 and 17 +/- 2 beats/min), although their blood pressure was significantly lower. Arterial partial pressure of O2, arterial O2 content, arterial pH, and lactate levels in DNX ducks (42 +/- 2 mmHg, 4.5 +/- 0.8 ml O2/100 ml blood, 7.233 +/- 0.016, 3.1 +/- 0.3 mM, respectively) were significantly lower than in SH-DNX ducks after 5 min forced submergence (53 +/- 1 mmHg, 6.8 +/- 0.4 ml O2/100 ml blood, 7.301 +/- 0.007, 4.8 +/- 0.4 mM, respectively). Venous infusion of catecholamines in ADX and DNX ducks during forced submergence significantly increased UTmax. It is suggested that adrenal catecholamines increase tolerance to underwater submersion by enhancing peripheral vasoconstriction, thus preserving the O2 stores for the heart and brain. Other adrenal products could also be involved.