title: Protection against high intravascular pressure in giraffe legs.
abstract: The high blood pressure in giraffe leg arteries renders giraffes vulnerable to edema. We investigated in 11 giraffes whether large and small arteries in the legs and the tight fascia protect leg capillaries. Ultrasound imaging of foreleg arteries in anesthetized giraffes and ex vivo examination revealed abrupt thickening of the arterial wall and a reduction of its internal diameter just below the elbow. At and distal to this narrowing, the artery constricted spontaneously and in response to norepinephrine and intravascular pressure recordings revealed a dynamic, viscous pressure drop along the artery. Histology of the isolated median artery confirmed dense sympathetic innervation at the narrowing. Structure and contractility of small arteries from muscular beds in the leg and neck were compared. The arteries from the legs demonstrated an increased media thickness-to-lumen diameter ratio, increased media volume, and increased numbers of smooth muscle cells per segment length and furthermore, they contracted more strongly than arteries from the neck (500 ± 49 vs. 318 ± 43 mmHg; n = 6 legs and neck, respectively). Finally, the transient increase in interstitial fluid pressure following injection of saline was 5.5 ± 1.7 times larger (n = 8) in the leg than in the neck. We conclude that 1) tissue compliance in the legs is low; 2) large arteries of the legs function as resistance arteries; and 3) structural adaptation of small muscle arteries allows them to develop an extraordinary tension. All three findings can contribute to protection of the capillaries in giraffe legs from a high arterial pressure.
authors.affiliation: Department of Radiology, Aarhus University Hospital, Skejby, Denmark;
authors.forename: Karin K
authors.initials: KK
authors.lastname: Petersen
authors.forename: Arne
authors.initials: A
authors.lastname: Hørlyck
authors.forename: Kristine H
authors.initials: KH
authors.lastname: Ostergaard
authors.forename: Joergen
authors.initials: J
authors.lastname: Andresen
authors.forename: Torbjoern
authors.initials: T
authors.lastname: Broegger
authors.forename: Nini
authors.initials: N
authors.lastname: Skovgaard
authors.forename: Niklas
authors.initials: N
authors.lastname: Telinius
authors.forename: Ismael
authors.initials: I
authors.lastname: Laher
authors.forename: Mads F
authors.initials: MF
authors.lastname: Bertelsen
authors.forename: Carsten
authors.initials: C
authors.lastname: Grøndahl
authors.forename: Morten
authors.initials: M
authors.lastname: Smerup
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.forename: Emil
authors.initials: E
authors.lastname: Brøndum
authors.forename: John M
authors.initials: JM
authors.lastname: Hasenkam
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
authors.forename: Ulrik
authors.initials: U
authors.lastname: Baandrup
authors.forename: Christian
authors.initials: C
authors.lastname: Aalkjaer
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D062186:Arterial Pressure; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D002196:Capillaries / Q000503:physiopathology*; D002199:Capillary Permeability; D004487:Edema / Q000503:physiopathology / Q000517:prevention & control*; D006874:Hydrostatic Pressure; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D012418:Ruminants; D016909:Tibial Arteries / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors; D014463:Ultrasonography; D014655:Vascular Resistance; D014661:Vasoconstriction
keywords: resistance artery structure; smooth muscle; sphincter; sympathetic innervation; ultrasound