摘要:

This work was undertaken to determine if the thermogenic activity of brown fat decreased with age in young rabbits despite the morphological evidence indicating persistence of the brown adipocytes at 4 weeks of age. Data obtained by infusing five doses of noradrenaline and measuring oxygen consumption were used to construct cumulative dose–response curves for five age groups between 3 and 32 days of age. Blood flow to brown fat and other tissues was measured by the microsphere method at 1 and 3 weeks of age. The noradrenaline-induced increase in oxygen consumption when expressed as a percentage of resting oxygen consumption in millilitres per 100 g of body weight decreased (p < 0.05) with age. However, the absolute noradrenaline-induced increase in metabolic rate (millilitres per minute) increased with age. Total blood flow to brown fat (millilitres per minute) during noradrenaline infusion was unchanged between 1 and 3 weeks of age, but when the blood flow was expressed in millilitres per minute per gram of tissue flow decreased significantly (p < 0.05) probably because of infiltration of brown fat with white fat. These data suggest that the amount of brown fat and its thermogenic capacity remain relatively constant between 1 and 3 weeks of age, but as a thermogenic organ, brown fat becomes proportionally less effective with age because of the large increase in body mass.

ISSN:0008-4212    

DOI:10.1139/y85-201

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effects of agonists and antagonists, specific for the different adrenoceptor subtypes on the automaticity of cultured ventricular cells from postnatal rat, were studied. Chronotropic responses were assessed by recording monophasic action potentials using intracellular microelectrodes. Contraction was assessed by an electro-optical procedure. (−)-Isoproterenol, salbutamol, (−)-phenylephrine, and methoxamine increased the spontaneous rate in a dose-dependent manner, but the stimulatory potencies of α-adrenoceptor agonists were weaker than those of the β-alternates. The frequency response to (−)-isoproterenol was inhibited by atenolol but not by butoxamine. Atenolol was also more effective than butoxamine in antagonizing the rate acceleration by salbutamol. The chronotropic effects of phenylephrine and methoxamine were inhibited by prazosin. In contrast, neither clonidine nor yohimbine displayed any chronotropic action. These findings suggest that the postjunctional adrenoceptors present in the sarcolemma of the isolated cardiac muscle cells, which mediate automaticity responses to catecholamines, are of β1, β2, and α1types, the physiological contribution of the β1-adrenoceptors being predominant. Applicability of these conclusions to thein situmyocardiocytes is discussed with respect to the level of functional differentiation achieved by the rat myocardial cells in culture.

ISSN:0008-4212    

DOI:10.1139/y85-202

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Intracellular and patch clamp recordings were made from embryonic mouse spinal cord neurons growing in primary cell culture. Outside-out membrane patches obtained from these cells usually showed spontaneous single channel currents when studied at the resting potential (−56 ± 1.5 mV). In 18 out of 30 patches tested, spontaneous single channel activity was abolished by making Tris+the major cation on both sides of the membrane. The remaining patches continued to display spontaneous single channel currents under these conditions. These events reversed polarity at a patch potential of 0 mV and displayed a mean single channel conductance of 24 ± 1.2 pS. Application of the putative inhibitory transmitter γ-aminobutyric acid (0.5–10 μM) to outside-out patches of spinal cord cell membrane induced single channel currents in 10 out of 15 patches tested. These channels had a primary conductance of 29 ± 2.8 pS in symmetrical 145 mMCl solutions. Frequency distributions for the open times of these channels were well fit by the sum of a fast exponential term ("of") with a time constant τof = 4 ± 1.3 ms and a slow exponential term ("os") with a time constant τos = 24 ± 8.1 ms. Frequency distributions for channel closed times were also well fit by a double exponential equation, with time constants τcf = 2 ± 0.2 ms and τcs = 62 ± 20.9 ms.

ISSN:0008-4212    

DOI:10.1139/y85-203

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Branched-chain-amino-acid:α-ketoglutarate transaminase and branched-chain α-ketoacid dehydrogenase have been assayed in brains of control and of streptozotocin-induced diabetic rats. Enzyme activities were measured in five distinct regions of the brain: cerebellum, pons + medulla, midbrain, thalamus + hypothalamus, and telencephalon. Subcellular distribution of these enzymes in whole brain was assessed by fractionating brain homogenate into cytoplasm, free mitochondria, and synaptosomes. The following enzymes were used as markers: lactate dehydrogenase for cytoplasm, glutamate dehydrogenase for mitochondria, and glutamate decarboxylase for synaptosomes. The activity of the branched-chain amino acid transaminase in all brain regions was considerably higher than that of the branched-chain α-ketoacid dehydrogenase. While the highest activity of the transaminase occurred in brain-stem regions, the highest activity of the dehydrogenase was present in cerebellum and telencephalon. Diabetes did not affect the activity of the transaminase, but it caused a decrease in the total activity of the dehydrogenase in midbrain and in thalamus + hypothalamus. The transaminase was localized in the cytoplasmic fraction of whole brain, while the dehydrogenase was enriched in the free mitochondria.

ISSN:0008-4212    

DOI:10.1139/y85-204

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

High affinity [3H]imipramine binding, endogenous levels of serotonin and noradrenaline, and serotonin uptake were determined in brain regions of rats with selective destruction of serotonergic neurons by 5,7-dihydroxytryptamine (5,7-DHT), of adrenergic neurons by 6-hydroxydopamine (6-OHDA), and of rats treated with reserpine. Neonatal treatment with 5,7-DHT resulted in a significant decrease of both serotonin levels and density (Bmax) of high affinity [3H]imipramine binding sites in the hippocampus. In contrast, an elevation of serotonin levels and an increase inBmaxof [3H]imipramine binding were noted in the pons–medulla region. No changes were observed in the noradrenaline content in either of these regions. Intracerebral 6-OHDA lesion produced a drastic suppression of noradrenaline levels in cerebral cortex but failed to alter the binding affinity (KD) or density (Brnax) of [3H]imipramine recognition sites. A single injection of reserpine (2.5 mg/kg) resulted in marked depletion of both serotonin (by 57%) and noradrenaline (by 86%) content and serotonin uptake (by 87%) in the cerebral cortex but had no significant influence of the parameters of high affinity [3H]imipramine binding in this brain region. The results suggest that high affinity [3H]imipramine binding in the brain is directly related to the integrity of serotonergic neurons but not to the magnitude of the uptake or the endogenous levels of the transmitter, and is not affected by damage to noradrenergic neurons or by low levels of noradrenaline.

ISSN:0008-4212    

DOI:10.1139/y85-205

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

To define the role of inorganic electrolyte secretion in hepatic bile formation, the effects of secretin, glucagon, and differently structured bile acids on bile flow and composition were studied in the dog, guinea pig, and rat. In the dog and guinea pig, secretin (2.5–10 clinical units∙kg−1∙30 min−1) increased bile flow and bicarbonate concentration in bile, a finding consistent with the hypothesis that the hormone stimulates a bicarbonate-dependent secretion possibly at the level of the bile ductule–duct. In the rat, secretin (5–15 CU∙kg−1∙30 min−1) failed to increase bile secretion. Glucagon (1.25–300 μg∙kg−1∙30 min−1) increased bile flow in all the three species, and produced no changes in biliary bicarbonate concentrations in the dog and rat. In the guinea pig, however, glucagon choleresis was associated with an increase in bicarbonate concentration in bile, similar to that observed with secretin. The choleretic activities of various bile acids (taurocholate, chenodeoxycholate, glycochenodeoxycholate, tauroursodeoxycholate, and ursodeoxycholic acid, infused at 30–360 μmol∙kg−1∙30 min−1) were similar in the rat (6.9–7.2 μL/μmol), but different in the guinea pig (11–31 μL/μmol). In the latter species, the more hydrophobic the bile acid, the greater was its choleretic activity. In all instances, bile acid choleresis was associated with a decline in the biliary concentrations of chloride, but with no major change in bicarbonate levels. The prominent finding of these studies is that, regardless of whether bile flow was stimulated by hormones or different bile acids, bicarbonate concentrations in bile were always similar to or higher than those in plasma. This is construed to support the view that bicarbonate is transported into bile, possibly at multiple sites within the biliary tree. Its excretion most likely provides the driving force for hormone-induced choleresis, and may in part account for the flow of bile associated with bile

ISSN:0008-4212    

DOI:10.1139/y85-206

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

It has been proposed that the adult castrated male rat may be used as a model of human postmenopausal osteoporosis. If such a model is valid then the total body calcium of castrated rats should progressively decrease compared with normal rats. To search for this age-related difference, it will be necessary to use a measurement technique with a precision which is small compared with the magnitude of the change to be detected. From measurements of total body calcium by neutron activation and by whole body ashing of eight dead rats, it has been shown that total body calcium can be measured with an accuracy and precision which should allow distinction between the expected lifetime changes in normal and castrated rats.

ISSN:0008-4212    

DOI:10.1139/y85-207

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Blood pressure responsiveness to iv noradrenaline and angiotensin II was studied in conscious, freely moving, age-matched spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats from 4 to 16 weeks of age. At 4 and 6 weeks the SHR showed small, but nonsignificant increases in responsiveness compared with WKY to both noradrenaline and angiotensin II. At 8 weeks they exhibited similar responses to the WKY. Subsequently, at 12 and 16 weeks decreased responsiveness to noradrenaline (nonsignificant) and angiotensin II (p < 0.05 at 12 and 16 weeks) was observed in SHR versus WKY. At 16 weeks of age, hexamethonium caused potentiation of the blood pressure response to noradrenaline and angiotensin II, but to the same degree in the two strains. Captopril at this age did not elicit potentiation to noradrenaline or angiotensin II in either strain. These results indicate that there is no rise in blood pressure responsiveness to circulating pressor agents, parallel to the development of hypertension in SHR. Increased receptor occupancy or more active attenuating reflexes in SHR versus WKY appear not to be involved in the absence of hyperresponsiveness in intact consious SHR at 16 weeks of age.

ISSN:0008-4212    

DOI:10.1139/y85-208

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

N-Glucosidation is a novel pathway of barbiturate metabolism, so far known to occur only in man. A search for an animal model, conducted throughin vitroscreening, revealed that amobarbital-N-glucoside was formed in liver preparations from the cat. The presence of amobarbital-N-glucoside was demonstrated in cat urine, following i.p. administration of amobarbital.

ISSN:0008-4212    

DOI:10.1139/y85-209

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Effects of a novel slow channel activator, Bay K-8644 (Bay K), were studied on slow action potential (APs) in young and old embryonic chick hearts, and on its antagonism of the effects of diacetyl monoxime (DAM). The slow APs of young hearts are mediated by slow Na+channels, whereas those of old hearts are mediated by slow Ca2+channels. In slow APs of old (13–18 days old) embryonic chick hearts superfused with a high (22 mM) K+solution, Bay K (10−6 M) gradually increased the amplitude, maximum rate of rise, and duration of the slow APs. The actions of Bay K persisted for a long time (>30 min) after washout of the drug. DAM (10 mM) depressed the, duration and amplitude of the slow APs. Some of the changes in slow AP parameters produced by DAM, e.g.,decrease, were antagonized by the addition of Bay K (10−6 M). In 3-day-old embryonic chick hearts, Bay K potentiated the slow APs and DAM depressed them; Bay K antagonized these effects of DAM. Thus, the actions of Bay K and DAM are likely to be produced, respectively, via the activation and depression of slow Ca2+channels in old embryonic chick hearts. In addition, the drugs seem to influence slow Na+channels found in young embyronic chick hearts.

ISSN:0008-4212    

DOI:10.1139/y85-210

出版商:NRC Research Press    

年代:1985

数据来源: NRC