1 Department of Clinical Medicine, Department of Clinical Medicine, Faculty of Health and Medical Sciences, Københavns Universitet2 Institut for Klinisk Medicin - Billeddiagnostisk afd., SKS3 Center for Klinisk Forskning4 Institut for Biomedicin - Forskning og uddannelse, Vest5 Institut for Biomedicin - Fysiologi6 Zoofysiologi, Biologisk Institut7 University of British Columbia8 Veterinary Clinical Microbiology, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, Københavns Universitet9 Copenhagen Zoo10 Hjerte-Lunge-Karkirurgisk Afd. T, SKS11 AU Forskning og Talent - AU Forskning og Talent12 Århus Universitets Hospital13 Institut for Bioscience - Zoofysiologi14 Department of Pathology, Vendsyssel Hospital and Center for Clinical Research, Aalborg University15 Education & Student Services, Faculty Service, Faculty of Health and Medical Sciences, Københavns Universitet16 University of British Columbia17 Veterinary Clinical Microbiology, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, Københavns Universitet18 Department of Clinical Medicine, Department of Clinical Medicine, Faculty of Health and Medical Sciences, Københavns Universitet19 Education & Student Services, Faculty Service, Faculty of Health and Medical Sciences, Københavns Universitet
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.
American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 2013, Vol 305, Issue 9
Resistance artery structure; Smooth muscle; Sphincter; Sympathetic innervation; Ultrasound; Journal Article; Research Support, Non-U.S. Gov't; Video-Audio Media