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Physiological role of the secondary circulatory system in fish
s40 S27-2
s27-4
Physiology of perfusion of the secondary circulatory system
in fish.
Steffensen. J. F.
Marine Biological Laboratory, University of Copenhagen, DK-3000 Helsingar, Denmark. Teleosts were believed to possess a lymphatic system similar to that of mammalians until Vogel & Claviez (1981) via corrosion casts showed connections between segmental arteries and the hitherto considered lymphatic
system. Since this system did not have any terminal vessels it was termed the secondary vascular system, and the connections between this system and the traditionally (primary) vascular system accordingly inter-arterial anastomoses. In an in vivo morphological study the secondary system in glass catfish (Cryptopferus bicirrhus) was described by Steffensen & Lomholt (1986). Plasma skimming was observed to take place in the anastomoses and the blood in the secondary system had a significantly lower haematocrit than in the primary system. This has later been confirmed for a number of other species. Later Steffensen & Lomholt (1992) suggested that the volume of the secondary system was approximately 50 % larger than the primary system. The physiological significance of the secondary system is still not clear, but will be discussed. Among others it may play an important role in distributing white blood cells to the skin in case of infections, it may be involved in transporting lipids via the primary system from the intestine, or it may even functionally work as a lymphatic system. References: Steffensen, J. F., Lomholt, J. P. and Vogel, W. 0. P. (1986). In vivo observations on a specialized microvasculature, the primary and secondary vessels in fishes. Acta Zool. 67; 193-200. Steffensen, J. F. & Lomholt, J. P. (1992). The secondary vascular system. In “Fish Physiology”. Eds.: Randall, D. J. & Farrell, A. P. Academic Press. Vogel, W. 0. P. & Claviez, M. (1981). Vascular specialization in fish, but no evidence for lymphatics. Z. Naturforsch. 36C; 490-492.
The role of pseudohranch and choroid rete for ocular oxygen supply Waser. W.P. & Heisler, N. Dept. Animal Physiology, Humboldt Universitgt Berlin, Germany Mechanisms
for ocular oxygen
concentration,
elevating
PO> in the eye above arterial levels, are found in many teleost
fish species. These mechanisms are considered crucial for sufficient oxygen supply of non-vascularized retinae providing unusually large diffusion distances. Liberation of oxygen in the choroid rete mirabile, the ocular counter-current capillary exchange system, is considered to be performed similar to the rete mirabife of the swimbladder. In contrast to the swimbladder, however, the choroid rete mirabile is supplied with blood only in series with the pseudobranch, a reduced mandibular gill arch. This close association led Miiller in 1839 to suggest that the pseudobranch may have a role related to vision. This allusion was followed up by separating functions of pseudobranch and choroid rete in isolated preparations. For this purpose perfusion rate of the system was determined in vivo by application of a special pulsed Doppler technique to the pseudobranchial artery and direct calibration of the velocity signal to flow in situ (745 c 282 ~1 min“ kg-‘). Applying the obtained blood flow rates to isolated eye preparations, intraocular I’01 profiles were determined by use of oxygen microelectrodes. Changes in ocular PO* were related to electroretinograms as the expression of varied retinal metabolic activity, and pseudobranch function was simulated by changes of the perfusing blood. The obtained data support the notion that the pseudobranch may play a role in preconditioning the perfusate for liberation of oxygen in the eye.
S27-3 Physiological
role of the secondary circulatory system in fish
Heisler, N.‘, Ishimatsu, A.2 and Iwama, G.K.3 ’Animal Physiology, Humboldt Universitit zu Berlin, Germany; ‘Univ. of Nagasaki, Japan; ’ Univ. of BC, Vancouver/Canada Vessels of the secondary circulatory system (SCS) of fish originate from primary arteries through capillary-sized anastomoses. They are mainly located close to the body surfaces, often in juxtaposition to mitochondria-rich cells. Accordingly, they have been suggested as sites for ionic and acid-base regulation, a proposition supported by recent studies on fluid composition and flow rate in SCS-vessels. In rainbow trout exposed to environmental hypercapnia, [HCO;] in the erythrocyte-poor fluid of the lateral cutaneous SCS vessel (LCV) is elevated above the level of dorsal aortic (DA) plasma by 2.2 mM as compared to control conditions, with the increase being balanced by a reduction in [Cl-]. However, LCV flow rate has been estimated to be only about 0.3 % of cardiac output, so that even substantial elevations in LCV-[HCO; ] probably cannot contribute significantly to the overall compensation. The contribution of the branchial SCS is considerable on the basis of a much larger flow rate. As estimated by indicatordistribution, flow through the branchial vein (BV) as the collecting SCS vessel of this area is about 7 % of cardiac output. With the [HCO;] difference between DA and BV rising during hypercapnia to about the same value as in the LCV, net transfer of bicarbonate equivalents from the environment amounts to 3 mmol.kg” body weight during 8 h of hypercapnia. These data indicate that more than 90% of bicarbonate-equivalents gained from the environment are transported through the secondary circulatory system. In contrast to the LCV, the [HCO;] difference between DA and BV is not balanced by any other ionic concentration change. These data suggest an electrogenic hydrogen ion pump as the underlying mechanism, with electroneutrality maintained by passive diffusion through the epithelial integument related to the primary circulation.
s27-5 Acid-base relevant metabolism of the pseudobranch Berenbrink M Dept. Animal Physiology, Humboldt UniversitLt zu Berlin, Germany An isolated saline-perfused preparation of the pseudobranch from rainbow trout (Uncorb~nchus mykiss) was utilized in order to investigate its biochemical characteristics and physiological functions. The experimental arrangement allowed for determination of glucose and oxygen consumption, as well as of lactic acid and carbon dioxide production as a function of perfusate pH. Changes in perfusate pH, induced by variations in Pco,, provoked significant changes in the rates of carbon dioxide and lactic acid production. As a consequence, shifts in pH of the perfusate entering the pseudobranch were not directly conducted to the perfusate leaving the pseudobranch. Additional data obtained on the blood-perfused pseudobranch confirm the notion that metabolic carbon dioxide production is an important factor in determining the acid-base status of blood leaving the pseudobranch. Accordingly, this tissue may have a pH-regulatory function, effectively uncoupling the post-pseudobranchial circulation from extensive pH-changes frequently encountered in the pre-pseudobranchial, arterial circulation. Since blood leaving the pseudobranch is the exclusive blood supply to the choroid rete ruirahik of the fish eye, this mechanism may have a protective role for the sensitive pH-dependent counter-current oxygen concentrating mechanism associated with the choroid rev mirrrhilr.
s27-4
Physiology of perfusion of the secondary circulatory system
in fish.
Steffensen. J. F.
Marine Biological Laboratory, University of Copenhagen, DK-3000 Helsingar, Denmark. Teleosts were believed to possess a lymphatic system similar to that of mammalians until Vogel & Claviez (1981) via corrosion casts showed connections between segmental arteries and the hitherto considered lymphatic
system. Since this system did not have any terminal vessels it was termed the secondary vascular system, and the connections between this system and the traditionally (primary) vascular system accordingly inter-arterial anastomoses. In an in vivo morphological study the secondary system in glass catfish (Cryptopferus bicirrhus) was described by Steffensen & Lomholt (1986). Plasma skimming was observed to take place in the anastomoses and the blood in the secondary system had a significantly lower haematocrit than in the primary system. This has later been confirmed for a number of other species. Later Steffensen & Lomholt (1992) suggested that the volume of the secondary system was approximately 50 % larger than the primary system. The physiological significance of the secondary system is still not clear, but will be discussed. Among others it may play an important role in distributing white blood cells to the skin in case of infections, it may be involved in transporting lipids via the primary system from the intestine, or it may even functionally work as a lymphatic system. References: Steffensen, J. F., Lomholt, J. P. and Vogel, W. 0. P. (1986). In vivo observations on a specialized microvasculature, the primary and secondary vessels in fishes. Acta Zool. 67; 193-200. Steffensen, J. F. & Lomholt, J. P. (1992). The secondary vascular system. In “Fish Physiology”. Eds.: Randall, D. J. & Farrell, A. P. Academic Press. Vogel, W. 0. P. & Claviez, M. (1981). Vascular specialization in fish, but no evidence for lymphatics. Z. Naturforsch. 36C; 490-492.
The role of pseudohranch and choroid rete for ocular oxygen supply Waser. W.P. & Heisler, N. Dept. Animal Physiology, Humboldt Universitgt Berlin, Germany Mechanisms
for ocular oxygen
concentration,
elevating
PO> in the eye above arterial levels, are found in many teleost
fish species. These mechanisms are considered crucial for sufficient oxygen supply of non-vascularized retinae providing unusually large diffusion distances. Liberation of oxygen in the choroid rete mirabile, the ocular counter-current capillary exchange system, is considered to be performed similar to the rete mirabife of the swimbladder. In contrast to the swimbladder, however, the choroid rete mirabile is supplied with blood only in series with the pseudobranch, a reduced mandibular gill arch. This close association led Miiller in 1839 to suggest that the pseudobranch may have a role related to vision. This allusion was followed up by separating functions of pseudobranch and choroid rete in isolated preparations. For this purpose perfusion rate of the system was determined in vivo by application of a special pulsed Doppler technique to the pseudobranchial artery and direct calibration of the velocity signal to flow in situ (745 c 282 ~1 min“ kg-‘). Applying the obtained blood flow rates to isolated eye preparations, intraocular I’01 profiles were determined by use of oxygen microelectrodes. Changes in ocular PO* were related to electroretinograms as the expression of varied retinal metabolic activity, and pseudobranch function was simulated by changes of the perfusing blood. The obtained data support the notion that the pseudobranch may play a role in preconditioning the perfusate for liberation of oxygen in the eye.
S27-3 Physiological
role of the secondary circulatory system in fish
Heisler, N.‘, Ishimatsu, A.2 and Iwama, G.K.3 ’Animal Physiology, Humboldt Universitit zu Berlin, Germany; ‘Univ. of Nagasaki, Japan; ’ Univ. of BC, Vancouver/Canada Vessels of the secondary circulatory system (SCS) of fish originate from primary arteries through capillary-sized anastomoses. They are mainly located close to the body surfaces, often in juxtaposition to mitochondria-rich cells. Accordingly, they have been suggested as sites for ionic and acid-base regulation, a proposition supported by recent studies on fluid composition and flow rate in SCS-vessels. In rainbow trout exposed to environmental hypercapnia, [HCO;] in the erythrocyte-poor fluid of the lateral cutaneous SCS vessel (LCV) is elevated above the level of dorsal aortic (DA) plasma by 2.2 mM as compared to control conditions, with the increase being balanced by a reduction in [Cl-]. However, LCV flow rate has been estimated to be only about 0.3 % of cardiac output, so that even substantial elevations in LCV-[HCO; ] probably cannot contribute significantly to the overall compensation. The contribution of the branchial SCS is considerable on the basis of a much larger flow rate. As estimated by indicatordistribution, flow through the branchial vein (BV) as the collecting SCS vessel of this area is about 7 % of cardiac output. With the [HCO;] difference between DA and BV rising during hypercapnia to about the same value as in the LCV, net transfer of bicarbonate equivalents from the environment amounts to 3 mmol.kg” body weight during 8 h of hypercapnia. These data indicate that more than 90% of bicarbonate-equivalents gained from the environment are transported through the secondary circulatory system. In contrast to the LCV, the [HCO;] difference between DA and BV is not balanced by any other ionic concentration change. These data suggest an electrogenic hydrogen ion pump as the underlying mechanism, with electroneutrality maintained by passive diffusion through the epithelial integument related to the primary circulation.
s27-5 Acid-base relevant metabolism of the pseudobranch Berenbrink M Dept. Animal Physiology, Humboldt UniversitLt zu Berlin, Germany An isolated saline-perfused preparation of the pseudobranch from rainbow trout (Uncorb~nchus mykiss) was utilized in order to investigate its biochemical characteristics and physiological functions. The experimental arrangement allowed for determination of glucose and oxygen consumption, as well as of lactic acid and carbon dioxide production as a function of perfusate pH. Changes in perfusate pH, induced by variations in Pco,, provoked significant changes in the rates of carbon dioxide and lactic acid production. As a consequence, shifts in pH of the perfusate entering the pseudobranch were not directly conducted to the perfusate leaving the pseudobranch. Additional data obtained on the blood-perfused pseudobranch confirm the notion that metabolic carbon dioxide production is an important factor in determining the acid-base status of blood leaving the pseudobranch. Accordingly, this tissue may have a pH-regulatory function, effectively uncoupling the post-pseudobranchial circulation from extensive pH-changes frequently encountered in the pre-pseudobranchial, arterial circulation. Since blood leaving the pseudobranch is the exclusive blood supply to the choroid rete ruirahik of the fish eye, this mechanism may have a protective role for the sensitive pH-dependent counter-current oxygen concentrating mechanism associated with the choroid rev mirrrhilr.