Studies on the role of the pituitary in the control of atrial natriuretic factor secretion and sodium excretion.
Recent work suggests that hypophysectomized (HYPOX) rats show low levels of atrial natriuretic factor (ANF) and an attenuated diuresis and natriuresis to blood volume expansion. The purpose of this was (i) to examine the effect of various hormone replacements on ANF and renal excretion in HYPOX rats and (ii) to compare the renal responses to exogenous ANF in intact and HYPOX rats. Groups of rats received subcutaneous pellet implant of either dexamethasone (DEX), thyroxine (T4), or a placebo. Approximately 1 week later, they were anesthetized and subjected to a 20% blood volume expansion. DEX rats had a higher mean arterial pressure than placebo-treated rats while both MAP and heart rate were higher in T4 rats. Only the DEX rat showed augmented renal responses to volume expansion while no group showed significant changes in plasma ANF concentration during volume expansion. In a second series, groups of HYPOX rats received renal capsular transplants of either six hemi-pituitaries or six pieces of muscle which markedly raised serum prolactin levels in the hemi-pituitary group. The hemi-pituitary rats showed a greater diuresis and natriuresis during volume expansion than the muscle group and also showed a transient increase in plasma ANF. In addition, groups of either intact or HYPOX rats were anesthetized and received intravenous bolus injections of ANF. Both intact and HYPOX rats showed a very similar diuresis and natriuresis to exogenous ANF. However, potassium excretion was markedly reduced in HYPOX rats. The results show that DEX augments the renal responses to volume expansion by some mechanism which does not involve changes in plasma ANF. Thyroxine increases mean arterial pressure and heart rate in HYPOX rats but does not augment the renal or ANF responses to volume expansion. Chronic elevations in prolactin increase the renal response to volume expansion. Finally, the kidneys of HYPOX rats are capable of increasing sodium and water output in response to large doses of exogenous ANF.
Dietz
J R
JR
Department of Physiology and Biophysics, University of South Florida, College of Medicine, Tampa 33612.
Nazian
S J
SJ
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D001794:Blood Pressure / Q000187:drug effects; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology; D004343:Drug Implants; D006339:Heart Rate / Q000187:drug effects; D007016:Hypophysectomy; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology*; D011188:Potassium / Q000652:urine; D011388:Prolactin / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000652:urine*; D013974:Thyroxine / Q000008:administration & dosage / Q000494:pharmacology
D004343:Drug Implants; D003907:Dexamethasone; D009320:Atrial Natriuretic Factor; D011388:Prolactin; D012964:Sodium; D013974:Thyroxine; D011188:Potassium