The purpose of these studies was to examine the effect of hypophysectomy (HYPOX) on the secretion of atrial natriuretic factor (ANF) and related changes in renal function. Pentobarbital sodium-anesthetized rats received a 20% intravenous blood volume expansion. In intact rats (n = 7), plasma ANF was 39 +/- 3 pg/ml before volume expansion and increased to 71 +/- 10 and 77 +/- 7 pg/ml after volume expansion (P less than 0.01). Volume expansion in HYPOX rats (n = 8) also resulted in an increase in plasma ANF concentration that was significantly less than in the intact group. With volume expansion, sodium excretion rate increased from 0.19 +/- 0.06 to 1.43 +/- 0.43 microM. min-1.100 g body wt-1 (P less than 0.01) in intact rats and from 0.24 +/- 0.08 to 0.74 +/- 0.14 microM.min-1.100 g body wt-1 (P less than 0.05) in HYPOX rats (HYPOX less than intact; P less than 0.05). In an isolated heart-lung preparation, HYPOX rats secreted significantly less ANF than intact rats during two 30-min perfusion periods (P less than 0.02). Atrial ANF concentration was also significantly less in HYPOX rats (P less than 0.05). These results show that hypophysectomy leads to an attenuation of the ANF response to atrial distention and attenuated natriuretic response to blood volume expansion and suggest that the pituitary is required to maintain normal cardiac endocrine function.
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