摘要:

The mammalian brain appears to be inherently feminine and the action of testicular hormones during development is necessary for the differentiation of the masculine brain both in terms of functional potential and actual structure. Experimental evidence for this statement is reviewed in this discussion. Recent discoveries of marked structural sex differences in the central nervous system, such as the sexually dimorphic nucleus of the preoptic area in the rat, offer model systems to investigate potential mechanisms by which gonadal hormones permanently modify neuronal differentiation. Although effects of these steroids on neurogenesis and neuronal migration and specification have not been conclusively eliminated, it is currently believed, but not proven, that the principle mechanism of steroid action is to maintain neuronal survival during a period of neuronal death. The structural models of the sexual differentiation of the central nervous system also provide the opportunity to identify sex differences in neurochemical distribution. Two examples in the rat brain are presented: the distribution of serotonin-immunoreactive fibers in the medial preoptic nucleus and of tyrosine hydroxylase-immunoreactive fibers and cells in the anteroventral periventricular nucleus. It is likely that sexual dimorphisms will be found to be characteristic of many neural and neurochemical systems. The final section of this review raises the possibility that the brain of the adult may, in response to steroid action, be morphologically plastic, and considers briefly the likelihood that the brain of the human species is also influenced during development by the hormonal environment.

ISSN:0008-4212    

DOI:10.1139/y85-098

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

This study was undertaken to determine if brown adipose tissue was involved in heat production during fever produced byS.abortus equi(1 μg) in unanesthetized rabbits aged 19–26 days. The fever (0.9–1.6 °C) occurred after a delay of 20–30 min and was frequently biphasic. Radiolabelled microspheres for measuring tissue blood flow were injected intraventricularly into three groups of animals: rabbits not given pyrogen, rabbits in which the febrile response to pyrogen was developing, and rabbits in which the febrile response had peaked. Blood flow to brown fat deposits and other organs was calculated from the fractional distribution of the microspheres and the recovery of microspheres in a reference arterial blood sample. At the fever peak, blood flow to brown fat was not significantly different (p > 0.05) from the control value (0.9 ± 0.2), but during the rising phase of the fever the flow increased significantly (p < 0.01) to 2.6 ± 0.4 mL min−1g−1. The blood flow to muscles of the forelimbs and hind limbs was also increased significantly (p < 0.05) during the rising phase of the fever. No significant change in blood flow to other organs or tissues was found during the rising phase of the fever. These results indicate that both nonshivering as well as shivering thermogenesis contribute to heat production during development of fever in the young rabbit. However, nonshivering thermogenesis was not involved in the maintenance of the elevated body temperature after the fever had peaked.

ISSN:0008-4212    

DOI:10.1139/y85-099

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Electrical stimulation of the pontine nucleus locus coeruleus (LC) caused an increase of the arterial blood pressure in anesthetized rats, and elevated plasma noradrenaline (NA) and adrenaline (A) levels. The stimulation-induced pressor response was characteristically biphasic and consisted of a sharp rise in arterial pressure at the onset of the stimulation, followed by a second elevation at the end of the stimulus. Bilateral adrenalectomy or adrenal demedullation completely blocked the secondary phase of the pressor response elicited by stimulation, but did not affect the primary phase. The latter was specifically eliminated by the destruction of the peripheral sympathetic vasomotor axons with intravenous 6-hydroxydopamine (6-QHDA). The active sites eliciting the secondary adrenomedullary pressor component appeared to be restricted to the nucleus LC, whereas the primary sympathetic vasomotor response could be elicited from sites in and around the nucleus. After brain transection at the midbrain level, stimulation of LC failed to evoke the adrenomedullary pressor response, while the sympathetic vasomotor component was not affected. Similarly, destruction of brain NA neurons by intraventricular administration of 6-OHDA did not change the sympathetic vasomotor response, but virtually abolished the adrenal response. The results demonstrate that the pressor response to stimulation of LC in the rat is due to both increased sympathetic vasomotor activity and CA released from the adrenal medulla. The study also provides evidence suggesting that the noradrenergic LC cell group play an important role in the activation of the adrenal medulla, but is not essential for the activation of the sympathetic vasoconstrictor fiber system.

ISSN:0008-4212    

DOI:10.1139/y85-100

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effects of gradually increasing doses of 1,25(QH)2D3on plasma calcium and45Ca radioactivity were studied in young dogs that had been extensively prelabelled with45Ca. The effects of orally and intravenously administered 1,25(OH)2D3were evaluated in normal and thyroparathyroidectomized dogs fed a normal diet. In normal dogs when 1,25(OH)2D3increased the plasma calcium within the normal range (2.9–3.1 mmol/L) there was no significant increase in plasma45Ca. In thyroparathyroidectomized dogs, oral or intravenous 1,25(QH)2D3increased the low blood calcium to a normal level (1.8–2.9 mmol/L) without significantly increasing plasma45Ca. In normal and thyroparathyroidectomized dogs, any 1,25(OH)2D3-induced increase in plasma calcium above the normal range was associated with a significant increase in45Ca, indicating mobilization of bone calcium. Intravenous administration of 1,25(OH)2D3in the normal or thyroparathyroidectomized dogs had a much larger effect than oral doses in mobilizing bone45Ca when inducing a similar level of hypercalcemia. The major physiological effect of 1,25(OH)2D3in the low or normal range of plasma calcium is on intestinal absorption of calcium without a significant effect on mobilizing bone calcium. The pharamacological effect of 1,25(OH)2D3in vivois to mobilize bone calcium as well as dietary calcium into blood.

ISSN:0008-4212    

DOI:10.1139/y85-101

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The utilization of triacylglycerol in slow oxidative, fast oxidative–glycolytic, and fast glycolytic skeletal muscle fiber types was examined in rats subjected to a prolonged exhaustive swim. Significant reductions of intramuscular triacylglycerol occurred following 2 h and 40 min of swimming in all muscles containing a predominance of slow oxidative and fast oxidative–glycolytic fibers, which possess a high capacity for free fatty acid oxidation. Triacylglycerol content in the soleus decreased by 48%, and reductions of 41, 29, and 27% were measured in the red vastus lateralis, red gastrocnemius, and plantaris muscles, respectively. In the white vastus lateralis and white gastrocnemius muscles (fast glycolytic fibers) triacylglycerol concentrations were unaffected. In all muscles the variability of intramuscular triacylglycerol measurements between animals was 20–50% and the within animal variance (right vs. left hindlimb) was similar. Analytical repeatability was approximately 10% in all muscles and significantly less than the between- and within-animal variances. It was concluded that a real biological variation exists in the triacylglycerol content of all rat skeletal muscles and that intramuscular triacylglycerol is an important energy source during prolonged exercise of moderate intensity.

ISSN:0008-4212    

DOI:10.1139/y85-102

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The purpose of the study was to find out how poly(C)-avid human urinary ribonuclease is handled by the kidney. Purified human urinary ribonuclease (molecular weight 33 000) was radiolabelled with125I. The enzyme was injected intravenously into dogs and monkeys with and without kidneys. The disappearance rate from the animalswithoutkidneys was markedly prolonged. In the dog and monkey with kidneys, the radiolabelled enzyme which was infused was recovered in the urine unchanged. No large molecular weight fragments were found. When125I-labelled ribonuclease was infused into rats the material recovered in the urine was primarily identical with the material infused. A very small fraction of the material recovered was found to contain some fragments which had chromatographic characteristics of monoiodotyrosine and diiodotyrosine. Two other fragments were detected but could not be identified. Autoradiographic studies of the rat kidneys also showed some reabsorption of the radiolabelled ribonuclease, particularly in the proximal tubules. With electron microscopy the radiolabelled material could be seen in the lysosomes. These observations corroborate findings discovered for other low molecular enzyme such as lysozyme (molecular weight 14 000) and suggest that the human ribonuclease is mainly excreted by the kidneys unchanged and that a minor amount may be reabsorbed by the proximal tubules and metabolized in the lysosomes.

ISSN:0008-4212    

DOI:10.1139/y85-103

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The cardiac myofibrillar component of the phosphorylcreatine shuttle mechanism enzymatically couples the functionally significant processes of energy utilization (ATPase) with substrate regeneration by creatine kinase (CK). Both components have isoenzyme forms that are transcriptionally regulated. Propylthiouracil-induced (PTU) hypothyroidism reduced rat cardiac contractile protein ATPase activity by shifting isomyosin predominance from the V1 to the V3 form. However, neither CK specific activity nor CK isoenzyme composition was altered by PTU treatment. Thus, myofibrillar components of the phosphorylcreatine shuttle, ATPase and CK, are not coordinately regulated under hypothyroid conditions.

ISSN:0008-4212    

DOI:10.1139/y85-104

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The inotropic selectivity of dobutamine was examined in pentobarbital-anesthetized, vagotomized dogs pretreated with a ganglion blocker. The purpose was to determine if, in the presence of hexamethonium and vagotomy, the inotropic selectivity of dobutamine could be attributed to an action of dobutamine on alpha-adrenoreceptors. Dose–response curves were determined for either isoproterenol or dobutamine 30 min after treatment with hexamethonium (20 mg/kg). Analysis of heart rate versus right ventricular contractile force showed that dobutamine produced less tachycardia for a given increase in contractile force than isoproterenol; this was statistically significant when contractile force was increased by either 50 or 100%. In a separate series of experiments, dobutamine (8 μg∙kg−1∙min−1) was administered 20 min after propranolol (3 mg/kg). Under these conditions there was a slight increase in contractile force which represented 12% of the dobutamine response prior to propranolol administration. This increase in contractile force in the presence of propranolol was completely prevented by the addition of phentolamine (1 mg/kg). Consequently, in another series of experiments, dose–response curves for dobutamine were performed in the presence of hexamethonium before and 30 min after phentolamine alone (1 mg/kg) or vehicle. Phentolamine did not influence the effect of dobutamine on heart rate or contractile force, but prevented the increase in diastolic blood pressure caused by dobutamine. In addition, analysis of heart rate versus contractile force indicated that there were no statistically significant effects of phentolamine on the inotropic selectivity of dobutamine. Thus, it appears that dobutamine may exert an effect on myocardial contractility through activation of alpha-adrenoreceptors; however, this effect is so minimal that in the presence of hexamethonium and vagotomy, activation of alpha-adrenoreceptors does not appear to influence the inotropic selectivity of dobutam

ISSN:0008-4212    

DOI:10.1139/y85-105

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

To investigate the involvement of vagal afferents in renal nerve release of catecholamines, we compared norepinephrine, dopamine, and epinephrine excretion from innervated and chronically denervated kidneys in the same rat. The difference between innervated and denervated kidney excretion rates was taken as a measure of neurotransmitter release from renal nerves. During saline expansion, norepinephrine excretion from the innervated kidney was not statistically greater than from denervated kidneys. Vagotomy increased norepinephrine release from renal nerves. Thus vagal afferents participated in the suppression of renal sympathetic nerve activity during saline expansion. No significant vagal control of dopamine release by renal nerves was detected under these conditions. Bilateral carotid ligation stimulated renal nerve release of both norepinephrine and dopamine in saline-expanded rats. The effects of carotid ligation and vagotomy were not additive with respect to norepinephrine release by renal nerves. However, the baroreflex-stimulated renal nerve release of dopamine was abolished by vagotomy. Electrical stimulation of the left cervical vagus with a square wave electrical pulse (0.5 ms duration, 10 V, 2 Hz) increased dopamine excretion exclusively from the innervated kidney of hydropenic rats. No significant change in norepinephrine excretion was observed during vagal stimulation. Increased dopamine excretion during vagal stimulation was associated with a larger natriuretic response from the innervated kidney than from its denervated mate (p < 0.05). We conclude that under appropriate conditions vagal afferents stimulate renal release of dopamine and produce a neurogenically mediated natriuresis.

ISSN:0008-4212    

DOI:10.1139/y85-106

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The roles of thyroid and growth hormone, and food restriction in maintenance of heart mass and in carbon monoxide-stimulated cardiac growth were examined. First, thyroidectomized and normal adult male rats inhaled up to 500 ppm CO in air for 42 days. Combined ventricular weights of thyroidectomized rats inhaling CO and air were 12 and 23% smaller than predicted, respectively, while the combined ventricular weight of normal rats inhaling CO was 29% larger than predicted. Thyroidectomy increased the mass of the left ventricle relative to the right ventricle; this was reversed by CO treatment. While the hematocrit increased in thyroidectomized–CO rats, it was lower than in normal–CO rats: likewise the hematocrit of thyroidectomized–AIR rats was lower than that of normal rats in air. Body weights of the thyroidectomized rats were 57% that of normals. As additional controls, two groups of normal rats (one AIR, one CO) were maintained at the same body weight as the thyroidectomized rats, by adjusting food intake. Combined ventricular weight was less than predicted in AIR rats and failed to increase in CO animals, while hematocrits were the same as normals in air and in CO. Serum thyroxine (T4) and growth hormone levels assayed in thyroidectomized rats were less than 15 and 25% of normal rats, respectively. Growth hormone levels were not altered by CO inhalation in thyroidectomized and in normal rats. Levels of both hormones were normal in food-restricted rats. While thyroidectomy produced cardiac atrophy, cardiac growth was stimulated by CO inhalation, although heart mass then only approached that of normals in air. Food restriction also produced cardiac atrophy, but CO inhalation failed to stimulate heart growth.

ISSN:0008-4212    

DOI:10.1139/y85-107

出版商:NRC Research Press    

年代:1985

数据来源: NRC