摘要:

The influence of the transepithelial voltage (Vt) on the degree of synchronization (DOS) of afferent spikes from lateral line organs to mechanical stimulation has been examined in the isolated voltage clamped skin ofXenopus laevis.With 1 mM CaCl2, 5 mM MOPS‐KOH (pH = 7.1) in the apical solution and Ringer's solution on the serosal side of the skin, changes in Vtfrom ‐60 mV to 65 mV (inside relative to outside) lead to a nonlinear reduction in DOS to a minimum value, where the afferent spikes were no longer time‐locked. Beyond this value of Vt, DOS increased until at Vt= 100–120 mV DOS was again reduced. The reduction of DOS to the minimum value was associated with a monotonic increase in the mean phase of DOS, which abruptly changed approximately 180° as the minimum was passed. Change in the apical Ca2+concentration from 0.1 mM to 10 mM increased the Vtat which the minimum value was attained, by 39 mV. The voltage dependency of DOS is in agreement with a model where the driving force for the receptor current across the apical membrane of the hair cells controls the generation of time‐locked afferent spikes to mechanical stimulation. The Vt, at which the minimum value of DOS was attained, is then equivalent to the reversal potential across the apical membrane. The influence of the apical Ca2+concentration on this V, may be caused by the change in the gradient of Ca2+or change in the ionic selectivity of the transductio

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07411.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The effects of mecamylamine on the nicotine induced changes in hypothalamic catecholamine (CA) levels and turnover in female rats ovariectomized for one month have been evaluated using a quantitative microfluorimetric approach to measure CA levels in sections of brains treated according to the Falck‐Hillarp procedure for the cellular demonstration of CA. In the same group of animals the serum prolactin, LH, FSH, TSH, GH and corticosterone levels were measured using radioimmunoassay procedures. The nicotine treatment induced a significant depletion of amine stores and an increase of amine turnover in dopamine (DA) and noradrenaline (NA) nerve terminals of the median eminence and of the peri‐and paraventricular and dorsomedial NA systems of the hypothalamus using the tyrosine hydroxylase (TH) inhibition model. Mecamylamine (2 × 1 mg/kg) partly counteracted the nicotine induced reduction of amine stores in peri‐(anterior part) and paraventricular NA nerve terminal systems as well as the nicotine induced increase of NA turnover in these systems, but not the action of nicotine on the CA systems of the median eminence. Nicotine (4 × 2 mg/kg) significantly and markedly reduced prolactin, LH, TSH, and GH secretion increased corticosterone secretin but did not influence FSH secretion. These effects were partly counteracted by mecamylamine (2 × 1 mg/kg) in the case of prolactin, LH and TSH secretion but not in the case of GH and corticosterone secretion. Taken together the results show that mecamylamine treatment (2 × 1 mg/kg) differentially counteract nicotine induced changes of amine levels and turnover in peri‐(anterior part) and paraventricular NA nerve terminal systems indicating that the cholinergic nicotine‐like receptors located in peri‐(anterior part) and paraventricular areas may be more susceptible to the blocking activity of mecamylamine than those located in the median eminence area. Furthermore, the inhibitory effects of nicotine on prolactin, LH and TSH secretion are differentially counteracted by mecamylamine. In conclusion, other inhibitory systems than the tuberoinfundibular DA neurons in the MPZ and LPZ must also be involved in mediating the inhibitory effects of nicotine on prolactin, LH and TSH secretion and different types of cholinergic nicotine‐like re

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07412.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The effect of physical training on muscle sympathetic activity (MSA) was studied by comparing resting levels of MSA in 8 well‐trained racing cyclists and in 8 age‐matched untrained subjects (mean age 22 yrs). In addition, MSA was determined for 5 untrained subjects before and after an 8‐week training program on cycle erogmeters (training group). Recordings were made from the peroneal nerve at the knee with the subject in recumbent position. The well‐trained cyclists were characterized by a clearly higher maximal oxygen uptake (VO2max) and lower heart rate at submaximal exercise (180 W) than their untrained counterparts. These variables were also significantly changed with training in the training group. In contrast, there were no training‐related effects on MSA. Thus, MSA expressed as either the number of sympathetic bursts/100 heart beats (+2%, NS) or bursts/min (‐10%, NS) did not differ between the well‐trained cyclists and the untrained controls. Furthermore, no changes in MSA occurred with training in the training group (bursts/100 heart beats: +8%, NS; bursts/min ‐2%, NS). Individual variations in MSA were large and independent of training state. It is concluded that differences in physical conditioning do not account for the large inter‐individual differences in M

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07413.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Enzyme activities were determined in pools of type I (slow twitch) and IIA and II B (fast twitch) fibres of the thigh muscle from individuals engaged to a high degree in physical training of an endurance character and from non‐endurance‐trained controls. The endurance‐trained (ET) group had significantly higher activity levels of the mitochondrial enzymes citrate synthase, malate dehydrogenase, and 3‐OH‐acylCoA dehydrogenase both in type I (2.1×, 1.7×, 1.4×) and in type IIA (2.3×, 1.8×, 1.4×) and IIB fibres (2.0×, 1.5 ×, 1.5×) than the non‐endurance‐trained (NET) group. Of the glycolytic enzymes, phosphofructokinase (PFK) in type I fibres was significantly higher (I.8×) in the ET than in the NET group whereas glyceraldehydephosphate dehydrogenase (GAPDH) in type I fibres was similar in the two groups. In type II fibres both PFK and GAPDH levels tended to be higher in the ET group. Lactate dehydrogenase (LDH) of both fibre types were not different in the two groups. Type 1 fibres differed significantly from type II fibres for all the six enzymes measured in both groups. However, no significant difference between fibres of types IIA and IIB was found. The results indicate that fibres of types I, IIA and IIB in human skeletal muscle all possess great adaptability with regard to their oxidative capacity. Furthermore, the data suggest that extensive endurance training may enhance the glycolytic capacity in both type I and type II fibres although the glycolytic capacity of the muscle as a whole generally is low in endurance trained subjects owing to a predominance of type I fibres. It is concluded that further studies are needed to determine whether there is a metabolic distinction between fibr

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07414.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Somatostatin and gastrin‐like immunoreactivity was measured in peripheral venous plasma at 22, 24, 02, 04 and 06 hours in 10 experiments performed on 6 healthy volunteers. In five of the experiments the subjects had been pretreated with propranolol 20–40 mg three times daily for one week. At 22 h gastrin and somatostatin levels averaged 153 and 143 pg/ml without treatment with β‐blockers and 93 and 74 with such treatment. Gastrin and somatostatin levels fell during the course of the night to ˜ 10 and 60% of the 22 h value, respectively. Somatostatin levels reached their lowest value at 02 h (50%) of the 22 h value. Treatment with β‐blockers tended to decrease gastrin as well as somatostatin levels over the whole experimental period, but did not influence the gradual decline of gastrin and somatostatin levels occurring during the night or the 02 h dip in somatostatin levels. It is suggested that the nocturnal dip in somatostatin secretion is vagally mediated and that the peak in acid output occurring at this hour is due to the decreased output of gastric somatostatin. The fact that the nightly dip in somatostatin secretion coincides with the peak output of the pituitary hormones prolactin and growth hormone is

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07415.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The interaction of two coexisting transmitters in the cat submandibular gland has been elucidated by studying effects of VIP and carbachol on cyclic AMP accumulation in isolated acini from the gland. Carbachol was found to potentiate the cyclic AMP increase induced by VIP by an atropine sensitive mechanism. The effect of carbachol on cyclic AMP accumulation was abolished by including EGTA in the incubation medium as was the carbachol mediated potentiation of VIP responses. The calmodulin inhibitor trifluoperazine had a similar, but less marked effect. The effect of carbachol was mimicked by phenylephrine (30 μM) and by the calcium inophore A 23187 (3 μM), and also by ethanol in a concentration reported to enhance membrane fluidity. The phospholipase A2inhibitor, mepacrine, tended to decrease carbachol actions.Our results show that the poteniation of VIP responses in feline submandibular gland is calcium‐dependent. The mechanism could involve a calcium‐calmodulin‐induced stimulation of adenylate cyclase or calcium‐induced change in membrane phospholipid m

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07416.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Responses to intravenous injections of an endotoxin (E. coli‐lipopolysaccharide, 1 μg/kg b.wt.) and endogenous pyrogen were studied in euhydrated and hyperhydrated goats. The biphasic febrile response to theendotoxinwas associated with a pronounced increase in the renal excretion of measured prostaglandin (PG) metabolites (11‐ketotetranor PGF metabolites). This increase was time‐correlated with the elevation of the rectal temperature, and (in hyperhydrated animals) with an inhibition of the water diuresis and an increase in renal excretion of arginine vasopressin (AVP). Other effects of the endotoxin were an immediate depression of renal Na and K excretion followed by the development of pronounced natriuresis, and a reduction of plasma Fe and Zn concentrations. The appearance of the febrile reactions (peripheral vasoconstriction and shivering) was accompanied by miosis. The maximum elevation of the rectal temperature was significantly greater during euhydration than during hyperhydration. Alsoendogenous pyrogenelicited miosis concomitant with febrile reactions, and an elevation of the renal excretion of PG metabolites which was closely correlated in time with the monophasic febrile response, and (during hyperhydration) with temporary inhibition of the water diuresis and an increase in the renal AVP excretion. However, the responses were much weaker than the corresponding endotoxin effects. No appreciable changes in renal excretion of Na and K were observed in response to the endogenous pyrogen. It is concluded that the observed effects on renal cation excretion were manifestations of direct endotoxin influences on kidney function. The possibilities are discussed that the observed stimulation of the AVP release might have been secondary to increased PG liberation, and that the miosis was the manifestation of direct pyrogen stimulation of cerebral pupillomotor neurons. The close temporal correlation between the PG response and the elevation of the rectal temperature could be regarded as further indirect support of the idea that some component of the PG system acts as CNS mediator in the fever mec

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07417.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The effects of the tertiary amine atropine and its structural analogues homatropine and scopolamine, as well as the quarternary amine emeprone, were evaluated on noradrenaline (NA)‐induced contractions of isolated female rabbit urethral ring preparations. In addition, the abilities of these antimuscarinics to inhibit3H—dihydro—alpha—ergocryptine (3H—DHE) binding to alpha—adrenoceptors were studied on a crude membrane preparation from the female rabbit bladder base and urethra. Atropine and homatropine depressed the NA‐ induced contractions in a concentration‐dependent way, whereas this was not seen with scopolamine. Emeprone 10‐510‐4M augmented the contractions, an effect possibly attributable to a NA‐uptake blocking effect. All antimuscarinics displaced specific3H— DHE binding, the order of potency being atropine>homatropine>emeprone>scopolamine. In general a good correlation was seen between the binding and mechanical activity studies for atropine, homatropine and scopolamine, while this was not found for emeprone. It is concluded that alpha‐adrenoceptor blockade by atropine can be observed at concentrations exceeding 10‐7M. Scopolamine, showing alpha‐adrenoceptor blocking properties only in high concentrations, may be used as an alternative for blockade

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07418.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Reduced concentrating and diluting capacity of the kidney in acute and chronic hypercalcemia may partly be due to inhibition of transcellular sodium reabsorption (RNa) in the thick ascending limb of Henle's loop. To examine this hypothesis, local heat production and RNawere measured during normo‐and hypercalcemia at comparable glomerular filtration rate (GFR) in volume expanded, anesthetized dogs. Changes in proximal RNawhich might occur during CaCl2infusion, were minimized by infusing acetazolamide (75 mg/kg body wt iv). When ultrafiltrable calcium was increased from 1.12±0.09 to 2.95±0.10 mmol/1, cortical heat production was unchanged, whereas outer medullary heat production fell by 32±4%. RNawas reduced by 32±6%. Bicarbonate reabsorption did not change but calcium reabsorption and potassium excretion increased significantly. The potassium content of cortex and outer medulla increased during hypercalcemia, whereas ouabain, an inhibitor of Na+K+‐ATPase reduces the potassium content. We conclude that hypercalcemia does not inhibit transcellular RNain the diluting segment by a direct effect on the Na+K+‐ATPase or the mitochondria, but by interfering with the coupled NaCI transport across the luminal cell

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07419.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Adenine nucleotide levels were measured in extracts of murine calvaria after different periods of culture with or without parathyroid hormone (PTH; 10‐8M) or PGE2(10‐7M). In control calvaria the energy charge, (ATP+1/2 ADP)/(ATP+ADP+AMP), remained at close to 0.7 over a 24 hour culture period. However, bones cultured with PTH or PGE2showed a transient fall in the energy charge down to 0.5. This was not associated with a fall in total adenine nucleotides. The rate of adenosine metabolism in cultured bone in vitro was studied by determining the contents of adenosine, inosine, 2‐deoxyadenosine, 2‐ deoxyinosine and hypoxanthine in the culture medium. There was a continuous increase in adenosine, inosine and hypoxanthine as well as a disappearance of medium 2‐deoxyadenosine that was accounted for by appearance of 2‐deoxyinosine. The deaminating activity could only partly be accounted for by activity in the medium and thus probably mainly resides in the bone cells. PTH (10‐8M) did not alter the rate of disappearance of 2‐ deoxyadenosine or adenosine deaminase activity determined in bone extracts. The results demonstrate that two substances that increase calcium mobilization from bone alter ATP utilization and/or synthesis without significantly influencing adenosine productio

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1984.tb07420.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY