title: Venous hydrostatic indifference point as a marker of postnatal adaptation to orthostasis in swine.
abstract: The postulate that venous adaptation assists postural baroreflex regulation by shifting the hydrostatic indifference point (HIP) toward the heart was investigated in eight midazolam-sedated newborn piglets. Whole body head-up (+15, +30, and +45 degrees ) and head-down (-15 and -30 degrees ) tilt provided a physiological range of orthostatic strain. HIP for all positive tilts shifted toward the heart (P < 0.05), +45 degrees HIP shifted most [6.7 +/- 0.3, 5.9 +/- 0.5, and 3.6 +/- 0.3 (SE) cm caudal to right atrium on days 1, 3, and 6, respectively]. HIP for negative tilts (3.0 +/- 0.2 cm caudal to right atrium) did not shift with postnatal age. Euthanasia on day 6 caused 2.1 +/- 0.3-cm caudal displacement of HIP for positive and negative tilts (P < 0.05). HIP proximity to right atrium was not altered by alpha-, beta-adrenoceptor and cholinoceptor blockade on day 5. It is concluded that early HIP migration reflects enhancement of venous pressure control to head-up orthostatic strain. The effect is independent of baroreflex-mediated adrenoceptor and cholinoceptor mechanisms.
authors.affiliation: Discipline of Human Physiology and Neuroscience Group, Faculty of Medicine and Health Sciences, University of Newcastle, Callaghan, New South Wales 2308, Australia.
authors.forename: P S
authors.initials: PS
authors.lastname: Buckner
authors.forename: A W
authors.initials: AW
authors.lastname: Quail
authors.forename: D B
authors.initials: DB
authors.lastname: Cottee
authors.forename: S W
authors.initials: SW
authors.lastname: White
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology*; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D015415:Biomarkers; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002496:Central Venous Pressure / Q000187:drug effects / Q000502:physiology*; D018680:Cholinergic Antagonists / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006874:Hydrostatic Pressure; D008297:Male; D011187:Posture / Q000502:physiology*; D013552:Swine; D018667:Tilt-Table Test
chemical_list: D018674:Adrenergic Antagonists; D015415:Biomarkers; D018680:Cholinergic Antagonists