CHANGES IN THE PLASMA-LEVELS OF VASOACTIVE HORMONES DURING APNEA IN SEALS

Prolonged and repetitive breath-hold periods (apnea) during diving and sleep are a routine component in the ecological physiology of marine mammals. Seals are among the few mammals in which control of heart rat e (HR) can be studied independent oi respiration, without pharmacochem ical manipulation. We hypothesized that the vasoactive hormones angiot ensin II (Ang II), arginine vasopressin (AVP), and atrial natriuretic peptide (ANP) were involved in the control of cardiovascular function in seals, and that the relationship was dependent upon input from the respiratory system. Venous plasma samples were collected and electroca rdiograms were recorded from Northern elephant seal (Mirounga angustir ostris) and Weddell seal (Leptonychotes weddellii) pups during both sp ontaneous breathing (eupnea) and apnea. Instantaneous HR and simultane ous plasma levels of ANP, AVP, and Ang II from periods of eupnea and a pnea were compared. In these seal pups, apnea was associated with brad ycardia, increased ANP, and decreased AVP and Ang II. The results supp ort the hypothesis of a complex involvement between the vasoactive hor mones and the control of cardiovascular function, and provide evidence for differential levels of control during periods of eupnea and apnea . (C) 1998 Elsevier Science Inc.