Comparison of beta-adrenoceptors mediating vasodilatation in canine subcutaneous adipose tissue and skeletal muscle.

Blood flow changes in response to various drugs in simulataneously autoperfused canine subcutaneous adipose tissue and gracilis muscle were compared to study the vascular beta-adrenoceptors. Compared to isoprenaline the beta 2-selective agonist salbutamol was 4--6 times more potent as a vasodilator in the muscle than in adipose tissue. Furthermore two beta 1-selective agonists (Tazolol and H80/62) caused vasodilatation in adipose tissue but not in the gracilis muscle. When given by close i.a. injection after beta-adrenoceptor blockade, adrenaline was a more potent vasoconstrictor than noradrenaline in both tissues. Before beta-blockade, however, noradrenaline was the more potent vasoconstrictor in the gracilis muscle whereas adrenaline was more potent in adipose tissue. Intravenous infusion of adrenaline in doses causing vasodilatation in the muscle caused vasoconstriction in adipose tissue whereas intravenous infusion of noradrenaline caused vasoconstriction in both tissues. The present findings suggest that the beta-adrenoceptors mediating vasodilatation in skeletal muscle are mainly ose tissue. Since adrenaline is a much more potent beta2- than beta1-agonist, these differences point to different roles of intravascular adrenaline in the two sites. In skeletal muscle circulating adrenaline is mainly a vasodilator whereas in subcutaneous adipose tissue it mainly acts as a vasoconstrictor.     

Engineered adipose tissue supplied by functional microvessels

A volume-persistent culture of adipose tissue under in vivo conditions can be achieved only by early vascularization after cell transplantation. Cotransplantation of autologous preadipocytes with endothelial cells may enable the early formation of a capillary network. Investigations were performed in vivo in a specially adapted chorioallantoic membrane (CAM) model. Fertilized White Leghorn eggs were incubated and opened on day 3 of incubation and human dermal microvascular endothelial cell (HDMVEC) spheroids and preadipocytes were transferred in a fibrin matrix to the CAM. On day 7 after incubation the composites were explanted and immunohistologically investigated. Numerous vessels consisting of HDMVECs could be detected and the lumena of these vessels were perfused by chick erythrocytes. These results show the formation of a capillary network consisting of transplanted HDMVECs. The microcirculation of chick erythrocytes in vessels consisting of human endothelial cells proves the continuity of a newly formed capillary system to the host vessel system. The experiments demonstrate the first patent connection of tissue-engineered microvessels in adipose tissue to a host vessel system without applying exogenous angiogenic growth factors or transient transfection. The cotransplantation of endothelial cell spheroids with angiogenic mesenchymal cells may lead to the engineering of complex three-dimensional implants.     

Thyroid hormone-sensitive brown adipose tissue respiration in the newborn rabbit

The effects of thyroid hormone treatment on brown adipose tissue (BAT) and liver metabolism were assessed by measuring oxygen consumption, sodium-potassium adenosine triphosphatase (Na-K-ATPase), and mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) activities in tissues from triiodothyronine- (T3) and vehicle-injected (for 3 days) newborn and adult rabbits. In the newborns, basal BAT cellular respiration was increased [mean (%/- SE) = 119 +/- 18 vs. 65 +/- 4 microliter O2/10(6) cells-1 . h in controls (P less than 0.005)], whereas hepatic respiration was unchanged. Ouabain had no effect on basal BAT cellular respiration, but suppressed hepatic respiration by 30% in both newborn groups. T3 treatment had no effect on NE- (10(-6) M) stimulated BAT respiration, whereas adult hepatic respiration was increased almost twofold. alpha-GPD activities were increased in both newborn BAT and adult liver but not in newborn liver. Na-K-ATPase activity was significantly increased only in newborn liver. In conclusion, 1) both BAT and liver are thyroid-hormone sensitive in the newborn rabbit, but the responses to T3 treatment are different in the two tissues; 2) the failure to stimulate both hepatic alpha-GPD and respiration in the newborn appears to be a developmental phenomenon characteristic of the rabbit; 3) thyroid hormones have little effect on sodium transport-dependent respiration in either BAT of liver in the newborn rabbit.     

The blood flow and oxygen consumption of brown adipose tissue in the new-born rabbit

1. A direct method for measuring venous outflow from brown adipose tissue in anaesthetized new-born rabbits is described.

2. During noradrenaline infusion the mean blood flow through brown adipose tissue increased from 87 to 360 ml./100 g tissue (wet wt.).min, and the mean rate of oxygen consumption of brown adipose tissue rose from 9·3 to 60 ml. O₂/100 g tissue.min.

3. During cold exposure the mean blood flow through brown adipose tissue increased from 90 to 304 ml./100 g tissue.min.

4. The mean cardiac output was 266 ml./kg body weight.min; during noradrenaline infusion it was 405 ml./kg body weight.min. At rest about one tenth, and during noradrenaline infusion about one quarter of the cardiac output went to brown adipose tissue.

5. It was calculated that most of the extra oxygen consumed during the metabolic response of the anaesthetized new-born rabbit to noradrenaline infusion or cold exposure was consumed by brown adipose tissue.

6. Hypoxia (breathing 10% O₂ in N₂) greatly reduced the increase in oxygen consumption but not the increase in blood flow in brown adipose tissue caused by noradrenaline infusion.

     

Experimental study of ectopic-free tissue transfer of rabbit epigastric flap using small-caliber vascular grafts.

Ectopic intraperitoneal free-tissue grafting using small-caliber artificial vascular grafts is reported. The vascular grafts were polyurethane tubes (inner diameter 1.4 mm; outer diameter 1.9 mm; length 15 mm) with a coating of the antithrombotic agents argatroban and 2-hydroxyethylmethacrylate-styrene block copolymer (HS)on the inner surface. The patency of the artificial vessels was investigated in an ectopic-free rabbit epigastric flap in which grafts were used for anastomosis between the femoral and renal vessels. The mean patent duration of uncoated controls (n = 10) was 128 +/- 37 min. Flap viability after one week (n = 17) and the patency of the coated grafts were investigated histologically. The flap take rate was 65%, the arterial graft patency rate 41%, and the venous graft patency rate 24%. The HS-treated surface combined with the argatroban slow-release system exhibited improvement of flap survival in an intraperitoneal ectopic -free grafting model.     

Comparison of β-adrenoceptors mediating vasodilatation in canine subcutaneous adipose tissue and skeletal muscle

Blood flow changes in response to various drugs in simultaneously autoperfused canine subcutaneous adipose tissue and gracilis muscle were compared to study the vascular β-adrenoceptors. Compared to isoprenaline the β₂-selective agonist salbutamol was 4–6 times more potent as a vasodilator in the muscle than in adipose tissue. Furthermore two β₁-selective agonists (Tazolol and H80/62) caused vasodilatation in adipose tissue but not in the gracilis muscle. When given by close i.a. injection after β-adrenoceptor blockade, adrenaline was a more potent vasoconstrictor than noradrenaline in both tissues. Before β-blockade, however, noradrenaline was the more potent vasoconstrictor in the gracilis muscle whereas adrenaline was more potent in adipose tissue. Intravenous infusion of adrenaline in doses causing vasodilatation in the muscle caused vasoconstriction in adipose tissue whereas intravenous infusion of noradrenaline caused vasoconstriction in both tissues. The present findings suggest that the β-adrenoceptors mediating vasodilatation in skeletal muscle are mainly of the β₂-type, whereas β₁-adrenoceptors seem to predominate in subcutaneous adipose tissue. Since adrenaline is a much more potent β₂- than β₁-agonist, these differences point to different roles of intravascular adrenaline in the two sites. In skeletal muscle circulating adrenaline is mainly a vasodilator whereas in subcutaneous adipose tissue it mainly acts as a vasoconstrictor.     

The role of plasma kinin in functional vasodilatation in the pancreas

1. Freshly collected pancreatic juice of the cat contained active kinin-forming enzyme (kallikrein) and, in addition, an active kininase.2. In response to successive doses of secretin, the kinin-forming activity of pancreatic juice fell off considerably. It was restored by pancreozymin.3. Stimulation of the dorsal vagus nerve caused an increase in venous outflow from the pancreas which was greater and more consistently seen when the splanchnic nerves had been sectioned.4. Intravenous injection of highly purified secretin usually had no effect on the outflow, whereas pancreozymin increased it up to 5 times.5. When the pancreas was perfused with oxygenated Locke solution, the effluent contained some kinin-forming enzyme when the gland was at rest. The enzyme activity did not increase when secretin was added to the perfusing fluid, but when acetylcholine or pancreozymin was added, the activity rose about fourfold.6. These results are discussed in relation to the theory that plasma kinins play a prominent role in the functional vasodilatation of glandular tissues.