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Cutaneous blood flow in the pigeon Columba livia: its possible relevance to cutaneous water evaporation

E. Ophir^1,2, Y. Arieli^1,2,*, J. Marder^1, and M. Horowitz²

¹ Department of Cell and Animal Biology, Institute of Life Sciences, Hadassah School of Dental Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
² Division of Physiology, Hadassah School of Dental Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
Deceased (8 March, 2000).

View larger version (30K): [in a new window]   Fig. 1. Representative recordings of skin blood flow measured by the ultrasonic flowmetry method from individual heat-acclimated and non-acclimated pigeons treated with propranolol (1.3 mg kg-1) or clonidine (80 µg kg-1). The control recordings are pretreatment values.

View larger version (26K): [in a new window]   Fig. 2. The effect of heat exposure on CWE, Ts and Tb of heat-acclimated (HAc; filled bars and symbols) and non-acclimated (NAc; open bars and symbols) pigeons. The birds were exposed to different ambient temperatures (30-60°C Ta) for 90 min prior to each measurement. (A) Cutaneous water evaporation (CWE) increased continuously with increased Ta in both NAc (N=8) and HAc (N=12) pigeons. However, this trend was much stronger in the HAc birds, reaching a CWE mean value of 10.6 mg cm-2h-1 at 50°C Ta and a maximum mean value of 18.9 mg cm-2h-1 at 60°C Ta, compared with 3.3 mg cm-2h-1 at 50°C Ta in NAc pigeons. (B) The different effect of Ta on Ts (triangles) and Tb (circles) in the NAc (N=7) and HAc (N=8) birds. While Ts and Tb at 30-55°C Ta in the NAc birds was 2.0 and 1.4°C, respectively (P<0.005), the corresponding values in the HAc birds were 0.5 and 0.6°C, respectively (not significant). Values are the means ± S.E.M. Dunnett's analysis was used to determine the significance of difference from control (values at Ta 30°C); *P<0.05, **P<0.005.

View larger version (31K): [in a new window]   Fig. 3. The effect of propranolol and clonidine on body temperature Tb (A) and cutaneous water evaporation (CWE) (B) in heat-acclimated (HAc; N=8) and non-acclimated (NAc; N=8) pigeons. The decrease in Tb from control values in birds injected with saline (grey bars) following the administration of clonidine (80 µg kg-1, i.m.; black bars) was stronger than that following propranolol (1.2 mg kg-1, i.m.; hatched bars), reaching a maximum in HAc animals. The elevation in CWE values 40min after drug administration was much greater in HAc pigeons than in NAc birds. Values are means ± S.E.M. Asterisks denote values significantly different from the control group: *P<0.05, **P<0.005; daggers denote values significantly different between the HAc and NAc groups: P<0.005.

View larger version (20K): [in a new window]   Fig. 4. Cutaneous water evaporation (CWE), skin temperature Ts and body temperature Tb in anesthetized pigeons, 0, 20 and 50min after propranolol (filled circles) and clonidine (open circles) administration. Both drugs induced intense CWE, concomitant with a decrease in Ts and Tb in the heat-acclimated HAc (solid lines; N=7), but not in the non-acclimated NAc (broken lines; N=8) pigeons. Mild hypothermia was also observed in the clonidine-treated pigeons. Values are means ± S.E.M. Asterisks denote values significantly different from control values (at time 0) *P<0.05, **P<0.005.

View larger version (20K): [in a new window]   Fig. 5. Changes in skin blood flow (A—C) and cutaneous water evaporation (CWE) (D—F) in non-acclimated (NAc; open bars) and heat-acclimated (HAc; black bars) pigeons following heat exposure (Ta=50°C) or pharmacological manipulation with propranolol or clonidine. Both skin blood flow and CWE increased in response to heat exposure in the NAc and HAc groups (A and D, respectively), and both were significantly greater in HAc pigeons. The effect of propranolol on skin blood flow (B) was dichotomous: it increased in the HAc pigeons and decreased in NAc pigeons. However, as can be seen in the HAc pigeons, clonidine dissociated skin blood flow (C) from CWE (F), reducing the former while inducing considerable CWE. Values are means ± S.E.M. *P<0.05, **P<0.005. The asterisks in parentheses indicate a significant difference between the HAc and NAc groups.

View larger version (25K): [in a new window]   Fig. 6. The effect of propranolol (A,B) and clonidine (C,D) on arterial (Qa) and venous (Qv) blood flow to the abdominal skin in non-acclimated (NAc; A,C) and heat-acclimated (HAc; B,D) pigeons at room temperature. HAc pigeons responded to both treatments by an increase in Qa and a decrease in Qv (P<0.005). No difference in Qa—v blood flow was observed in the NAc pigeons (P>0.05). Values are means ± S.E.M. of 7 birds. *P<0.05, **P<0.005. The asterisks in parentheses indicate a significant difference between Qa and Qv values.

View larger version (42K): [in a new window]   Fig. 7. Diagram of a possible mechanism for vasomotor control in the pigeon skin vasculature. We suggest that activation of ß-adrenergic receptors (ß-AR) constricts arterial vessels (A), while activation of 2-ARs constricts vessels somewhere along the venous side (B). These effects can be direct or indirect. Thus propranolol (ß-AR) and clonidine (2-AR) act jointly to raise capillary hydrostatic pressure by decreasing arterial resistance and inducing greater resistance at the venous side. The rise in pressure may induce water outflow from the capillary, thereby increasing cutaneous water evaporation.

View larger version (26K): [in a new window]   Fig. 8. Diagram of the hypothetical route of blood flow (BF; coloured arrows) in the cutaneous microvasculature accounting for the prominent Qa-v following chemically induced cutaneous water evaporation. As intensive extravasation occurs in the capillary bed, extensive lymphatic vasculature is responsible for the reabsorption of any excess fluid volume (black arrows).