FACTORS ASSOCIATED WITH VASOPRESSIN RELEASE IN EXERCISING SWINE

This study examined the effect of dynamic exercise on vasopressin rele ase in the miniswine and factors that may elicit this response (n = 15 ). Thus lysine vasopressin (LVP), the catecholamines epinephrine and n orepinephrine (EPI and NE), plasma renin activity (PRA), and plasma vo lume, Na+, and osmolality were measured before and during treadmill ru nning at work intensities of 60, 80, and 100% of each swine's maximal heart rate reserve (HRR). LVP increased in a progressive manner simila r to that of humans, ranging from 5.9 +/- 0.4 pg/ml before exercise to 30.1 +/- 4.5 pg/ml during maximal exercise. EPI, NE, and PPA [an inde x of angiotensin II (ANG II) activity] demonstrated a pattern of respo nse comparable to LVP. Although these hormones can influence the relea se of LVP, only PRA displayed a strong correlation with LVP (r = 0.84) . When ANG II synthesis was blocked (captopril, 1-3 mg/kg, intra-atria l injection) during exercise (80% HRR), plasma LVP was reduced from 9. 9 +/- 0.6 to 7.5 +/- 0.6 pg/ml (P < 0.05). In addition, moderate-to-st rong correlations were found between plasma concentrations of LVP and plasma osmolality (r = 0.79) and body temperature (r = 0.78). Plasma L VP also correlated with decreases in plasma volume (r = 0.84). These d ata suggest that the miniswine model is a good one for studying vasopr essin effects during exercise and that ANG II appears to be a particul arly strong stimulus for the release of this hormone.