Rete Mirabile Research Articles

Limits of gas secretion by the salting-out effect in the fish swimbladder rete

The high dissolved gas tensions required for the secretion of gases into deep-sea fish swimbladders are thought to be produced in the rete mirabile by a countercurrent multiplication mechanism, the capacity of which is theoretically limited by the physical characteristics of the rete and by the magnitudes of minute gas solubility changes in the blood plasma. These gas solubility changes are presumably induced through the salting-out effect following the addition of lactic acid to rete venous blood as it circulates through the gas gland. In order to estimate the maximum swimbladder gas pressures attainable by this mechanism, the effects of lactic acid on N2 and Ar solubilities in water were determined at 5 and 25°C with a new volumetric method. The results show that the salting-out effect with lactic acid is much smaller than with NaCl, and that the agreement between predicted and observed swimbladder gas pressures is more critically dependent on the physical properties of the rete vasculature than indicated by previous theoretical treatments. When augmented by the release of hemoglobin-bound O2, the salting-out effect with lactic acid appears large enough to account for the production of even the highest swimbladder O2 pressures, provided the rete characteristics lie within certain reasonable limits. However, successful theoretical explanation of observed swimbladder N2 pressures in some deep-sea species will require rigorous attention to such theoretically neglected factors as dissolved gas backdiffusion along the rete and the unequal size and number of the rete arterial and venous capillaries.

The rete mirabile of the maxillary artery in the cat.

The rete mirabile of the maxillary artery in the cat.

Superoxide dismutase, catalase, and glutathione peroxidase in the swim bladder of the physoclistous fish, Opsanus tau L.

The antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase were measured in the rete mirabile and gas gland epithelium area of the swim bladder of the toadfish Opsanus tau. When the concentration of enzyme in the swim bladder was compared with the concentration in other organs (kidney, heart, gills) of the same fish, the swim bladder was found to have the highest concentration of superoxide dismutase but relatively low levels of glutathione peroxidase and catalase. Cytochemical assay for the peroxidatic activity of catalase confirmed that virtually no catalase is present in epithelial cells of the gas gland. A similar assay for peroxidase revealed a cyanide-sensitive peroxidase in the multilamellar bodies of these cells. Most of the catalase and peroxidase in the rete mirabile appears to be confined to the granules of neutrophils and the cytoplasm of erythrocytes. Enzyme activity in the neutrophils is not inhibited by 10(-1) M KCN. Cyanide does not appear to inhibit the peroxidase activity in erythrocytes but has little effect on catalase in these cells.

The effect of hyperosmolality on the permeability and structure of the capillaries of the isolated rete mirabile of the eel.

HomeCirculation ResearchVol. 49, No. 3The effect of hyperosmolality on the permeability and structure of the capillaries of the isolated rete mirabile of the eel. Free AccessAbstractPDF/EPUBAboutView PDFSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyRedditDiggEmail Jump toFree AccessAbstractPDF/EPUBThe effect of hyperosmolality on the permeability and structure of the capillaries of the isolated rete mirabile of the eel. E A Rasio, M Bendayan and C A Goresky E A RasioE A Rasio Search for more papers by this author , M BendayanM Bendayan Search for more papers by this author and C A GoreskyC A Goresky Search for more papers by this author Originally published1 Sep 1981https://doi.org/10.1161/01.RES.49.3.661Circulation Research. 1981;49:661–676 Previous Back to top Next FiguresReferencesRelatedDetailsCited By Tanaka N, Kawasaki K, Kubota Y, Nakamura K, Hashimoto M, Kunitomo M and Shinozuka K (2003) P2Y-receptor regulates size of endothelial cells in an intracellular Ca2+ dependent manner, Life Sciences, 10.1016/S0024-3205(02)02416-5, 72:13, (1445-1453), Online publication date: 1-Feb-2003. Rasio E and Bendayan M (2002) Sequential morphological and permeability changes in the rete capillaries during hyperglycaemia, Microscopy Research and Technique, 10.1002/jemt.10093, 57:5, (408-417), Online publication date: 1-Jun-2002. Rasio E, Bendayan M and Goresky C (1998) Study of Blood Capillary Permeability with the Rete Mirabile Whole Organ Approaches to Cellular Metabolism, 10.1007/978-1-4612-2184-5_3, (71-90), . Kajimura M, O'Donnell M and Curry F (2004) Effect of Cell Shrinkage on Permeability of Cultured Bovine Aortic Endothelia and Frog Mesenteric Capillaries, The Journal of Physiology, 10.1111/j.1469-7793.1997.413bh.x, 503:2, (413-425), Online publication date: 1-Sep-1997. Bendayan M and Rasio E (1996) Transport of insulin and albumin by the microvascular endothelium of the rete mirabile, Journal of Cell Science, 10.1242/jcs.109.7.1857, 109:7, (1857-1864), Online publication date: 1-Jul-1996. O'Donnell M, Brandt J and Curry F (1995) Na-K-Cl cotransport regulates intracellular volume and monolayer permeability of trabecular meshwork cells, American Journal of Physiology-Cell Physiology, 10.1152/ajpcell.1995.268.4.C1067, 268:4, (C1067-C1074), Online publication date: 1-Apr-1995. Bendayan M (1995) Colloidal Gold Post-Embedding Immunocytochemistry, Progress in Histochemistry and Cytochemistry, 10.1016/S0079-6336(11)80027-6, 29:4, (III-159), Online publication date: 1-Jan-1995. RASIO E, BENDAYAN M and GORESKY C (1994) The isolated rete Analytical Techniques, 10.1016/B978-0-444-82033-4.50023-4, (191-203), . Satchell G (1992) The Venous System The Cardiovascular System, 10.1016/S1546-5098(08)60333-7, (141-183), . Rasio E, Bendayan M and Goresky C (1992) Effect of temperature change on the permeability of eel rete capillaries., Circulation Research, 70:2, (272-284), Online publication date: 1-Feb-1992. Buchanan R and Wagner R (1990) Associations between pericytes and capillary endothelium in the eel rete mirabile, Microvascular Research, 10.1016/0026-2862(90)90059-Z, 39:1, (60-76), Online publication date: 1-Jan-1990. BENDAYAN M (1989) Protein A–Gold and Protein G–Gold Postembedding Immunoelectron Microscopy Colloidal Gold, 10.1016/B978-0-12-333927-0.50008-8, (33-94), . Londoño I and Bendayan M (2005) Distribution of endogenous albumin across the rat aortic wall as revealed by quantitative immunocytochemistry, American Journal of Anatomy, 10.1002/aja.1001860410, 186:4, (407-416), Online publication date: 1-Dec-1989. Rasio E, Bendayan M and Goresky C (1989) Effect of reduced energy metabolism and reperfusion on the permeability and morphology of the capillaries of an isolated rete mirabile., Circulation Research, 64:2, (243-254), Online publication date: 1-Feb-1989. Burns M, Bellhorn R, Korte G and Heriot W (1986) Chapter 10 Plasticity of the retinal vasculature, Progress in Retinal Research, 10.1016/0278-4327(86)90013-1, 5, (253-307), Online publication date: 1-Jan-1986. Rasio E and Goresky C (1985) Passage of ions and dextran molecules across the rete mirabile of the eel. The effects of charge., Circulation Research, 57:1, (74-83), Online publication date: 1-Jul-1985. Bendayan M (1984) Protein A-gold electron microscopic immunocytochemistry: Methods, applications, and limitations, Journal of Electron Microscopy Technique, 10.1002/jemt.1060010304, 1:3, (243-270), . Granger D and Perry M (1983) Permeability Characteristics of the Mircocirculation The Physiology and Pharmacology of the Microcirculation, 10.1016/B978-0-12-508301-0.50012-0, (157-208), . Wagner R and Robinson C (1982) Tannic acid tracer analysis of permeability pathways in the capillaries of the rete mirabile: demonstration of the discreteness of endothelial vesicles, Journal of Ultrastructure Research, 10.1016/S0022-5320(82)90039-9, 81:1, (37-46), Online publication date: 1-Oct-1982. September 1, 1981Vol 49, Issue 3Article InformationMetrics Copyright © 1981 by American Heart Associationhttps://doi.org/10.1161/01.RES.49.3.661 Originally publishedSeptember 1, 1981 PDF download Advertisement

Micromorphology of the epidural rostral rete mirabile and the sinus cavernosus of sheep (Ovis aries)

AbstractThe thin walled vessels of the Rete mirabile epidurale rostrale are invaginated into the Sinus cavernosus. Because of that most of Rete vessels are not surrounded by connective or supporting tissues of organs, but only by blood. The fluid surroundings influence the structure of the vessel wall. As a result of its specific construction and its special location the arterial Rete mirabile epidurale rostrale is functionally associated with the venous Sinus cavernosus.

The Visceral Temperatures of Mackerel Sharks (Lamnidae)

The viscera of mako Isurus oxyrinchus and porbeagle Lamna nasus sharks are significantly warmer than the water. The large suprahepatic rete mirabile in these fish is identified as a heat exchanger which retains metabolic heat to warm the visceral organs. An argument is presented that the efficiency of heat exchange in the rete must be greater than 97% to maintain the observed tissue temperatures and that this requirement explains the large size of the rete. A venous passage with a muscular wall which runs through the suprahepatic rete could allow blood to bypass the heat exchanger, and its presence suggests a simple mechanism for controlling temperature. However, measurements of temperature by acoustic telemetry from freeswimming sharks over a 4.5-day period do not give a convincing indication that stomach temperature is altered in a manner independent of the environment.

Brain temperatures in running quail.

Hypothalamic (Tb) and colonic (Tc) temperatures of adult bobwhite (colinus virginianus) were measured simultaneously while the birds were resting and running on a motor-driven treadmill at fixed belt speeds ranging from 0.42 to 0.75 m.s-1 at two air temperatures, room and 30 degrees C. For comparison, Tb and Tc were also recorded simultaneously in resting bobwhite exposed to air temperatures of 30 to 45 degrees C. Hypothalamic temperatures of both environmentally heat-stressed and running bobwhite were consistently below colonic temperatures. The mean magnitude of this body-to-brain temperature difference in birds running at the highest speeds (i.e., with the greatest exercise heat loads) and at a high air temperature (30 degrees C) was similar to that of extremely heat-stressed resting birds [ambient temperature (Ta) = 45 degrees C]. Furthermore, the body-to-brain temperature difference in quail running at 30 degrees C increases with running speed. That these birds running at maximum speeds can maintain their Tb nearly constant while Tc increases suggests enhanced heat transfer in the rete mirabile ophthalmicum, an extracranial site of arteriovenous heat exchange.

Hyperglycemia and microangiopathy in the eel.

When female eels, fasting and sexually mature, were progressively adapted to cold water (2-4 degrees C), their blood sugar concentration rose to values averaging 600 mg/dl. Control eels, kept in warm water (18-20 degrees C), had a mean blood sugar concentration of 100 mg/dl. After a period of 5-6 mo, the blood capillaries of the rete mirabile in the swimbladder were examined in both control, low blood sugar eels, and in cold-adapted, high blood sugar eels. In the latter, the basal laminae of the capillaries were thickened; their amino acids composition was altered and the in vitro glucose carbon incorporation into basal laminae glycoproteins was increased over a wide range of medium glucose concentrations. Furthermore, the diffusion capacity of the rete, as measured with tracer molecules during steady-state conditions in a countercurrent perfusion system, was increased in the hyperglycemic eel. It is concluded that chronic hyperglycemia in the cold-adapted eel is associated with a microangiopathy characterized by morphologic, biochemical, and functional alterations.

An ultrastructural and fluorescence histochemical investigation of the innervation of retial arteries in Monodon monoceros.

In this study, the innervation of cerebrally related retial arteries in the narwhal Monodon monoceros was examined. Vessels were processed for the demonstration of adrenergic nerve endings by fluorescence histochemistry, and the results were confirmed by electron microscopy. Innervation of cerebrally related retial arteries was compared to that of a system situated in the haemal canal and supplying the tail. The retial arteries were poorly innervated. Adrenergic nerve endings, as indicated by fluorescence, occurred only in caudal portions of the spinal rete. Ultrastructurally, nerves were found in most retial vessels examined. However, except for arteries from caudal portions of the spinal rete, nerve numbers were few and because they occurred in outer layers of the adventitia were probably not functionally significant. In contrast, vessels in the haemal canal were well innervated. Nerve endings possessing neurotransmitter vesicles were adjacent to the smooth muscle cells. The cetacean rete mirabile, a system which supplies blood to the entire central nervous system, is apparently not under extensive nervous control, even though most reports suggest there is a relationship, possibly based on the presence of adjacent nerve trunks. Any vasomotor activity that does occur, possibly does so in response to catecholamines or other vasoactive agents circulating in the blood.

The pathomorphology of malignant catarrhal fever. I. Generalized lymphoid vasculitis.

A histologic, ultrastructural and immunohistochemical study of the vasculitis in the rete mirabile of 18 calves with experimental and two calves with spontaneous malignant catarrhal fevel showed lesions similar to those reported in graft rejection and some other lymphocyte-associated vasculopathies. The calves were examined at early, mid and late stages of clinical disease. Vascular lesions in the carotid rete were representative of those in other tissues examined. The magnitude of the arterial wall mononuclear cell infiltrate and the degree of arterial wall necrosis and degeneration increased with progression of the clinical disease. The predominant site of mononuclear cell accumulation was the adventitia. There was less medial and intimal involvement. The mononuclear infiltrate was composed of lymphocytes and macrophages with neutrophils and plasma cells rarely present. Endothelial hyperplasia, fibrinoid change and thrombosis were uncommon. Many changes contrasted with those recognized in an active Arthus reaction where adventitial change was minimal and most inflammatory cells were neutrophils or plasma cells. IgG and C3 rarely were detected in vessel walls with fluorescent antibody techniques. Serum immunoglobulins as measured by radial immunodiffusion were not elevated. Viral structures were not seen in tissues examined ultrastructurally.

Capillary limitation of oxygen distribution in the isolated rete mirabile of the eel (Anguilla anguilla).

HomeCirculation ResearchVol. 44, No. 4Capillary limitation of oxygen distribution in the isolated rete mirabile of the eel (Anguilla anguilla). Free AccessAbstractPDF/EPUBAboutView PDFSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyRedditDiggEmail Jump toFree AccessAbstractPDF/EPUBCapillary limitation of oxygen distribution in the isolated rete mirabile of the eel (Anguilla anguilla). E A Rasio and C A Goresky E A RasioE A Rasio Search for more papers by this author and C A GoreskyC A Goresky Search for more papers by this author Originally published1 Apr 1979https://doi.org/10.1161/01.RES.44.4.498Circulation Research. 1979;44:498–503 Previous Back to top Next FiguresReferencesRelatedDetails April 1, 1979Vol 44, Issue 4Article InformationMetrics Copyright © 1979 by American Heart Associationhttps://doi.org/10.1161/01.RES.44.4.498 Originally publishedApril 1, 1979 PDF download Advertisement

Kollateralkreisläufe bei zerebralen arteriovenösen Mißbildungen kombiniert mit Verschlüssen kranialer Hauptgefäße

Arteriovenous malformations (AVM) of the brain are diagnosed mostly in the early adult life. With the come up of Computerized Tomography (CT) which often is done without the strong indications as postulated for the conventional neuroradiologic examinations, asymptomatic AVM in the elderly population may be found. Since May 1977 4 asymptomatic arteriovenous malformations were diagnosed in our institution using CT. 2 of these patients had severe degenerative changes of the great cerebral vessels and an unusual collateral circulation developed probably because of the steal-phenomenon in the vascular malformation. These 2 cases allow to study all possibilities of cerebral collateral circulation. Uncommon in one of the cases was a capillary anastomotic network through the thalami, in the other case an extensive dural rete mirabile developed. The problems of collateral circulation are discussed.

On the identity and pelagic occurrence of larval and juvenile stages of rattail fishes (family macrouridae) from 60°N, 20°W and 53°N, 20°W

Abstract A rare opportunity to study the early life history of some macrourid fishes arose from midwater discrete depth collections over soundings of 2700 to 2800 m during April and May, 1971. Seven juveniles, all caught at 60°N, were identified as Coryphaenoides (Coryphaenoides) rupestris (four from 700 to 900 m), C. (Coryphaenoides) guntheri (two from 800 to 1250 m) and C. (Lionurus) carapinus (one from 1500 to 2000 m). In addition, 60 larvae were collected, 28 C. (C.) rupestris (19 from 60°N, 25 to 800 m and nine from 53°N, 300 to 900 m and 32 specimens of C. (Lionurus) species, designated as sp. A (one from 60°N, 50 to 100 m and 24 from 53°N, 10 to 600 m) and sp. B (six from 53°N, 25 to 600 m) and one specimen of doubtful affinity (from 53°N, 600 to 700 m depth). The depth distribution of both juveniles and larvae is shown, with no indication of diurnal vertical migration. A positive correlation between living depth and size among the larvae is confirmed. An attempt to verify a similar correlation between living depth and the length of the retia mirabilia in the larval swimbladder suggested that retial growth conformed more closely to body growth than to living depth. Other developmental trends in the larvae are described. Food remains were absent from the juveniles, but selected larvae of all species examined were eating copepods only. The larvae were considered to be of local origin. While the juveniles of all species occupied similar levels to the adult peak depth range, those of C. (C.) rupestris were some 70 miles away from slopes of equivalent depth. The ecological implications of reproductive strategies similar to that of the macrourids among bottom-living deep-sea fishes are considered.

Glucose-induced alterations of the metabolism of an isolated capillary preparation.

A preparation of blood capillaries was isolated from the rete mirabile of the eel swin bladder. The capillaries, incubated for two hours at 37 degrees C. in Krebs-Ringer bicarbonate buffer with 5 mM glucose, contained 29.3 +/- 4.6 nmoles of sorbitol per gram and released in the medium 725 +/- 60 nmoles of fructose per gram. When glucose in the medium was raised from 5 to 30 mM, capillary sorbitol and medium fructose rose by approximately 100 per cent. There were no accompanying changes in capillary water content as determined by the ratio of wet weight to dry weight and by the difference between water-3H space and inulin-14C space. Respiration of capillary tissue was lower at 30 mM glucose than at 5 mM glucose. The addition of 30 mM mannitol to a medium containing 30 mM glucose did not restore the oxygen uptake by capillary tissue to values obtained with a medium containing 5 mM glucose alone. It is concluded that the polyol pathway is operative in vertebrate blood capillaries. At high medium glucose concentration, the activity of the pathway is enhanced, respiration is depressed, and water content is unchanged

Swimbladder and skeletal deformations in hatchery bred Spams aurata

Among hatchery bred Sparus aurata, 5.4% of the offspring of a single parent pair showed severe skeletal deformations coupled with marked growth retardation and pathological changes in the swimbladder. This resulted from extreme proliferation, then hypertrophy, of the cuboidal epithelial cells of the gas gland and proliferation of the rete mirabile. This caused almost complete congestion of the swimbladder air space. The nature of the pathological changes in the swimbladder and the possibility of hereditary origin for both the skeletal and swimbladder deformations are discussed.

Diffusion permeability of an isolated rete mirabile.

The rete mirabile of the swimbladder of the eeel is a countercurrent exchange organ composed of alternately disposed and venous capillaries. A countercurrent perfusion of these was set up by isolating arterial input and outflow, and venous input and outflow, and perfusing each set of capillaries with oxygenated albumin-containing Krebs-Ringer bicarbonate buffer. Constant arterial infusions containing tracer albumin, inulin, 3-O-methylglucose, urea, and water were begun and tracer concentrations at the outlets of arterial and venous beds were determined. Capillary permeabilities were determined from the resulting steady state values. The method of calculation of permeability values from the data acquired in the rete involves no approximations and appears to yield unequivocal values. For the solutes, the values appear compatible with transcapillary passage by free diffusion. No evidence of increasing restriction (in comparison to the diffuse coefficients) was found over the range of molecular sizes explored. The permeability for labeled water, in relation to the solutes, was too high, and this augmentation was attributed to the larger surface available for its exchange. Despite this larger value, labeled water did not undergo flow-limited exchange. A significant barrier to its distribution is present in this capillary system.

Acute Hemiplegia and Cortical Blindness Due to Moya Moya Disease: Report of a Case in a Child With Down's Syndrome

We are reporting what we believe to be the first case of moya moya disease (hemiplegia associated with supraclinoid carotid stenosis and multiple cerebral telangiectasia) in a child with Down's syndrome. On cerebral angiography, multiple collateral vessels and rete mirabile (anastomosis of meningeal vessels with internal cerebral vessels) were noted, in addition to the supraclinoid carotid stenosis. Computerized tomography revealed nonobstructive hydrocephalus and findings consistent with multiple vascular insults or infarcts. It is not clear whether moya moya disease represents a true disease entity (congenital arterial dysplasia) or is a syndrome caused by nonspecific vascular reaction. Since abnormal vascular morphology has previously been described in children with trisomy 21, we suggest that the presence of these two disease entities may not be coincidental. It may represent a genetic predisposition in Down's syndrome toward vascular abnormalities, with variable expressivity which manifested itself in this case by abnormalities in the cerebral circulation.

A mathematical model for counter-current multiplications in the swim-bladder.

1. A computer model for swim-bladder gas filling has been developed. Phenomenological descriptions of the Root effect (pH-dependent O2 capacity of fish haemoglobin), of the lactic acid production in the gas gland and of the geometry of the rete mirabile are incorporated in the general counter-current equations to give a comprehensive model of gas filling. 2. It is known that pH along the rete is not constant, as supposed in an earlier gas-filling model. It is also known that the Root shift reaction has a different half-time model. It is also known that the Root shift reaction has a different half-time depending on whether the haemoglobin absorbs or releases O2. These particular effects are accounted for in the present model. 3. The model gives gas filling rate and maximum swim-bladder pressure for CO2, O2 and N2. The partial pressure of these gases as well as the concentration of lactic acid and the pH along the rete are also calculated. 4. The model reproduces quite accurately experimental values for gas-filling rate in eel, together with lactic acid, CO2 and O2 concentrations measured at the rete end-points. There is also good correlation between maximum predicted stable swim-bladder pressure and maximum recorded depth for four fishes investigated (r=0-937; P=0-06). 5. The model predicts an enhancement of O2 filling rate and maximum swim-bladder pressure of at least 4 when the reaction rates of the Root shift in eel haemoglobin are 0-2 sec (Root-off) and 10 sec (Root-on), as compared to an instantaneous Root shift. 6. With a swim-bladder pressure of 1 atm and Root-shift reaction rates of equal magnitude, the po2-profile along the rete is nearly linear. When the reaction rates are such as found experimentally in eel haemoglobin, the po2 along the rete is non-linear, with a maximum of approximately 2 atm near the bladder pole of the rete. An experimental verification of this maximum will constitute a crucial test of the model. 7. The calculations show that blood flow through rete can regulate both gas-filling rate and stable swim-bladder pressure. At high pressure, the main factor limiting gas filling is loss of gas through back diffusion along the rete. 8. Maximum po2 in the swim-bladder is highly dependent upon the Root effect. If the Root effect persists up to about 100 atm, as seems to be the case blue hake, maximum po2 is more than 200 atm. When the Root effect is abolished at 10 atm, as is expected in eel, the maximum po2 drops to about 30 atm. 9. The pN2 in the bladder can reach 10-15 atm depending on blood flow, whereas PCO2 will not exceed 1 atm.

The effect of plasma proteins on the capillary permeability in the rete mirabile of the eel (Anguilla vulgaris L.).

Measurements of transcapillary exchange of high-molecular dextrans, K+ and THO in the rete mirabile of the eel (Anguilla vulgaris L.) have been made under steady-state conditions while varying the amounts of plasma proteins in the perfusates. When the perfusates contained 20% or less horse serum the permeabilities of D-75 000, K% and THO increased significantly. The effect on the K+ permeability was irreversible while that on D-75 000 and THO was not. The permeability was unaffected when the perfusate contained 30% serum or more. Adding 1.3 g/100 ml bovine albumin to the perfusate maintained the D-75 000 and THO permeabilities unchanged while that of K+ appeared to increase. At an albumin content of 0.33 g/100 ml the effect was similar to that produced by low serum perfusates. Our main conclusion is that lack of the albumin fraction of the plasma proteins reversibly increases the intercellular pore area and irreversibly changes the K+ permeability of the cell membrane.

Blood supply to the testis of a Brazilian marsupial (Didelphis azarae) and its abdominotesticular temperature gradient.

The testicular arteries of Didelphis azarae originate from the abdominal aorta either independently from each other or by way of a common trunk. Accessory testicular arteries may be found. At the spermatic cord they form a rete mirabile having 26.8 +/- 5.0 and 29.3 +/- 4.9 slender branches on the right and left sides, respectively. The arterial branches are intermingled with veins of similar caliber and number. Near the testis the branches of the rete reunite in a single vessel which then penetrates the parenchyma of the testis. Inside the testis the artery divides usually into two main branches that course toward the caudal pole. The rectal, scrotal and testicular temperatures were 32, 28.5 and 30.4 degrees C, respectively, appearing than an abdominotesticular gradient temperature exists in this animal. Whether this mechanism is thermoregulatory for the normal spermatogenesis cannot be inferred from the present work.