摘要:

In guinea‐pig isolated vas deferens moderate cooling (within the range 16–41 °C) improved, while further cooling depressed, sympathetic neuromuscular transmission. Moderate cooling: (a) enhanced the contractile responses both to electrical nerve stimulation and (although less strongly) to exogenous noradrenaline or to the adenosine 5′‐triphosphate (ATP) analogue, α, β‐methylene ATP; (b) enhanced the overflow of [3H]noradrenaline evoked by electrical nerve stimulation at 1–8 Hz, but not that caused by direct depolarization of varicosities with 80 mM potassium; (c) reduced the depressing effect of exogenous noradrenaline, as well as the enhancing effect of the a‐adrenoceptor blocking agent phentolamine, on the secretory responses to electrical nerve stimulation; (d) while not altering the maximal secretion of tracer noradrenaline at infinitely high frequency or external calcium, lowered the frequency or calcium concentration required for half‐maximal secretion, both in the absence and in the presence of phentolamine. In conclusion: moderate cooling improves sympathetic neuromuscular transmission in guinea‐pig vas deferens, both prejunctionally, by enhancing transmitter secretion, and post‐junctionally, by increasing the responsiveness of the smooth

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07706.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The vascular system of extirpated cat legs was perfused with Tyrode's solution and insulin‐like immunoreactivity (ILI) levels were determined in the perfusate with radioimmunoassay. During unstimulated conditions perfusate levels of ILI were almost undetectable. However, in response to electrical stimulation of the sciatic or brachial nerves (within a wide range of stimuli 5–40 V, 2–20 Hz and 0.2–40 ms) 1–20 ng of ILI was recorded in the perfusate. Blockers of cholinergic and adrenergic transmissions added to the perfusate did not influence the output of the ILI induced by nerve stimulation. Furthermore, after administration of acetylcholine (ACh) (0.1 and 10 μg kg‐1)t oxytocin (0.5 and 5 IU kg‐1)i glibenclamide (25 and 100 μg kg‐1) and bombesin (100 and 500 μg kg‐1) to the cat leg preparation, ILI appeared in the perfusate in amounts similar to those induced by electrical stimulation of the nerves. When subjected to high‐performance liquid chromatography (HPLC) the insulin‐like peptide detected in the cat leg perfusate following nervous stimulation, or administration of oxytocin and glibenclamide, co‐eluted with a bovine insulin standard. We have previously shown that some peripheral nerves of the cat, such as the sciatic, brachial and vagal nerves, contain an insulin‐like peptide with HPLC characteristics similar to the bovine insulin standard. It is therefore possible that the insulin‐like peptide released from the isolated cat leg preparation by the above‐mentioned stimuli derives from this nervous pool of insulin. Alternatively, the insulin‐like peptide emanates from the striatal muscles innervated by the sciatic and brachial nerves, since also muscles have been shown

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07707.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

In the present study, a radioimmunoassay for oxytocin determinations is presented. In addition, we investigated whether the elevation of insulin, VIP and gastrin levels demonstrated to occur in response to suckling in lactating dogs may be induced by released oxytocin. Therefore, oxytocin was infused i.v. into conscious dogs in amounts calculated to give rise to plasma levels observed during physiological circumstances. Plasma levels of oxytocin, insulin, VIP (vasoactive intestinal polypeptide) and gastrin were measured by radioimmunoassay. When oxytocin was infused at a rate of 0.22 and 2.2 nmol kg‐1h‐1, plasma oxytocin levels rose to 176 ± 25 fmol ml‐1and to 1490 ± 400 fmol ml‐1, respectively, 10 min after the infusions were started. Plasma insulin levels rose in response to oxytocin administered at a rate of 0.22 and 2.2 nmol kg‐1h‐1. A peak was recorded within 5 min of oxytocin infusion, that is, before maximal oxytocin levels were recorded, and basal levels were reached within about 20 min. The VIP levels rose slightly following infusion of oxytocin at 0.22 nmol kg‐1h_I, but a clear‐cut response that lasted for 60 min was observed following infusion of oxytocin at the highest dose. In contrast, gastrin levels were not influenced by the oxytocin infusions. Suckling in dogs is followed by rapidly occurring short‐lasting elevations of oxytocin levels in plasma which amount to 50–100 fmol ml‐1. Since insulin and VIP were released by oxytocin when administered in amounts that give rise to plasma levels close to those levels, it is suggested that the secretion of insulin and VIP that occurs in response to suckling in lactating dogs may in part be caused by previously released oxytocin. If so, the role of oxytocin during lactation is not restricted to the contraction of the myoepithelial cells of the mammary glands but involves the control of neuroendocrine events associated with milk produ

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07708.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The sympathetic nervous system is known to innervate the pancreatic islets and to have the capability to influence islet hormone release. The effects are, however, complex since the islet nerves contain catecholaminergic as well as peptidergic fibres, and the catecholamines stimulate α‐ as well as β‐adrenoceptors. The present study was undertaken to establish the possible influence of the a‐adrenoceptors on basal and stimulated insulin secretion under in vivo conditions. The α‐adrenoceptor blocker phentolamine was injected at various dose levels i.p. to mice and a dose‐dependent increase in plasma concentrations of insulin was seen. The maximal plasma insulin levels were observed 10 min after injection and were accompanied by decreased plasma glucose concentrations. Additionally, plasma glucose levels fell in response to phentolamine by an apparent insulin‐independent manner, since at the low dose of 2.6 μmol kg‐1, plasma glucose levels did decrease without any apparent increase in plasma insulin levels. After injection of a low dose of phentolamine 10 min prior to a rapid i.v. injection of one of four different insulin secretagogues, the following effects on insulin release were observed. Glucose (+ 55%) and the cholinergic agonist carbachol (+ 140%) displayed a potentiated insulin secretory response after phentolamine pretreatment, whereas the β2‐adrenoceptor agonist terbutaline (‐45%) had a blunted, though not abolished, insulin response. The absolute insulin secretory response to CCK‐8 was unaffected by phentolamine despite the fact that plasma glucose levels were lowered by phentolamine. In conclusion, phentolamine enhanced insulin secretion and depressed plasma glucose levels in mice. Further, it influenced stimulated insulin secretion by a manner dependent on the nature of the secretagogue. The results thus suggest that α‐adrenoceptors are involved in the precise regulation of basal and stimulated insulin secretion, and that a‐adrenoceptor blockade does not always result in a

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07709.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The content of vasoactive intestinal polypeptide (VIP) in rabbit oviducts was determined using a radioimmunoassay technique. Treatment with oestrogen (polyestradiolphosphate) alone for 5 days caused a significant increase in oviductal VIP content, whereas addition of progesterone during the last 3 days of an 8 day polyestradiol‐phosphate treatment resulted in a return of VIP content to control levels. The effect of VIP on oviductal smooth muscle contractility was investigated using an in vitro system. It was found that VIP caused a reduction of spontaneous contractile activity in doses as low as io‐10M and this reduction in motor activity was strictly dose dependent with an ED50value similar to that reported for the VIP activity on rabbit myometrial smooth musculat

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07710.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Experiments were performed on cats anaesthetized with chloralose and treated with adrenoceptor blocking agents. Distal colonic and rectal motility were selectively recorded by a volumetric method. The effects of muscarinic and ganglionic nicotine receptor blockade on motor responses induced by graded efferent electrical pelvic nerve stimulation (PNS) were studied. Stimulation at low current strength evoked contractions in both the colon and the rectum, which were sensitive to atropine and to hexamethonium. High intensity stimulation elicited distal colonic contractions resistant to both atropine and hexamethonium. Similar excitatory responses to high strength PNS were also observed in the rectum, though not in all experiments. Stimulation at intermediate intensities evoked distal colonic and rectal relaxations which were resistant to atropine but blocked by hexamethonium. The results indicate that PNS influences colonic and rectal motility by activation of at least three discrete non‐adrenergic nervous pathways: (1) low‐threshold excitatory fibres involving nicotinic and muscarinic transmission, (2) high‐threshold excitatory fibres with a non‐muscarinic, non‐nicotinic transmission mechanism, (3) inhibitory fibres with an intermediate stimulus intensity threshold, exerting their effect by a non‐muscarinic mechanism involving a nic

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07711.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The influence of muscle temperature (28 and 36 °C) on fatiguability and glycolytic metabolism was studied during 5 min of intermittent stimulation of motor nerves of the tibialis anterior, extensor digitorum longus (fast‐twitch) and soleus (slow‐twitch) muscles in the rat at 100 Hz (200 ms per s). The decline in isometric tension was not affected by muscle temperature either in fast‐ or in slow‐twitch muscles. In fast‐twitch muscles the utilization of glycogen during stimulation was the same at 28 and 36 °C, while in the soleus muscle it was lower at 28 °C. The concentration of glucose‐6‐phosphate immediately after stimulation was higher in the muscles at 28 °C than in those at 36 °C, whereas no difference in lactate concentration was found between the two temperature groups. These observations indicate that compared with the rate at 36 °C, the rate of glycogenosis at 28 °C is unchanged in fast‐twitch, but decreased in slow‐twitch muscle. This might imply increased economy of ATP turnover during contraction in th

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07712.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The role of the prejunctional α2‐receptors for the response to vaso‐constrictor nerve stimulation has been examined before and after inhibition of neuronal transmitter reuptake in mesenteric resistance vessels from the rat. Small arteries (diameter about 200 μm) feeding the jejunum were mounted in a myograph for recording of their isometric wall tension during transmural field stimulation of the intramural nerves. Blockade of prejunctional α2‐receptors with 0.01 μm idazoxan (RX 781094) caused a marginal potentiation of the neurogenic response when neuronal reuptake was left intact. Also, inhibition of reuptake alone with 3 μm cocaine had little effect on the response. However, when both α2‐receptors and reuptake had been inhibited, a strong enhancement of the neurogenic vasoconstriction was observed. Similar findings were made when yohimbine and LU 3–010 instead were used for α2‐blockade and reuptake inhibition, respectively. The results thus indicate that in these resistance arteries the effector response is normally influenced by the combined activity of α2‐receptors and uptake, and that failure of one mechanism increases the activity of the other, so as to maintain a largely const

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07713.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Neuropeptide Y (NPY) immunoreactivity (‐IR) was found to be present in perivascular nerves in the cat dental pulp and oral mucosa. Many ganglion cells in the superior cervical ganglion also contained NPY‐IR. Ligation of the inferior alveolar or lingual nerves produced an accumulation of NPY‐IR in axons proximal to the site of ligation, suggesting an anterograde axonal transport of the peptide. After unilateral sympathectomy the NPY‐IR disappeared in the dental pulp and oral mucosa on the ipsilateral side. Reversed phase high performance liquid chromatography showed that the main peak of NPY‐like immunoreactivity found in the superior cervical ganglion co‐chromatographed with synthetic porcine NPY. Changes in blood flow in dental pulp or oral mucosa were measured indirectly by recording local clearance of125I during electrical stimulation of the sympathetic nerve or during close intra‐arterial infusion of noradrenaline or NPY. All three procedures resulted in a pronounced decrease in local blood flow of a similar magnitude in both tissues. After a‐adrenoceptor blockade with phentolamine, the vasoconstrictor effect of noradrenaline was abolished. However, the effect of sympathetic stimulation after phentolamine was only partially reduced (23–54%) and the response to NPY was almost unaffected by the a‐receptor blockade. The remaining effect of sympathetic stimulation after phentolamine was abolished by guanethidine. However, the response to NPY was not changed by the latter drug. In conclusion, the vasoconstrictor response in the dental pulp and oral mucosa caused by activation of sympathetic nerves is more resistant to phentolamine than the response induced by infusion of exogenous noradrenaline. Since NPY is probably co‐localized with noradrenaline in the sympathetic perivascular nerves and NPY reduces local blood flow,it is proposed that this peptide is involved in sympathetic vascular co

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07714.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The purposes of the present investigation were: (1) to evalute a possible use of changes in the mean spectral frequency (MSF) of the EMG power spectra as a measure of reflex cardiovascular responses originating from the muscles durig static exercise; and (2) to study the relation between muscle fibre composition, EMG, and the cardiovascular response. Heart rate (HR), artirial blood pressure (BP), myoelectric signal (EMG), and intramuscular temperature (Tm) were measured during prolonged static contractions in feive healthy male subjects (25–44 yrs). Two studies were performed. In study 1 constant EMG contraction muscle force in the first 5 s of the knee‐extensor contraction was set to 20% MVC, (maximal voluntary contraction), and in the rest of the 5 min contraction the myoelectric signal was kept constant by visual feedback from an oscilloscope. In study II, (constant force contraction) two 1 h 7% MVC isometric contractions of the elbow‐flexors and extensors were performed on two separate days. During the 5 min constant EMG contranson, the force fell from 20 to 11% MVC, mean BP (MAP) increased from 97±5 to 120±4 mmHg (P<0.01), and the EMS MSF decreased from 87±16 to 66±9 Hz (P<0.01). The decrease in MSF was strongly correlated to the increase in MAP (r = 0.96, P<0.01). The intramuscular temperature showed a small increse from 34.3 °C (P<0.01). During the 1 h constant force contraction involving m. triceps, MAP increased from 104±10 to 120±12 mmHg, with a simultaneous decrease in the EMG MSF from 96±11 to 70±19 Hz and an increase in the EMG anplitude (247% of the initial value). In the contractions involving m. biceps, however, both MAP and EMG MSF remained almost unchanged, but EMG amplitude increased (197% of the initial value). Very modest changes in HR were observed: 63±6 to 66±6 beats min‐1and 61±5 to 59±7 beats min‐1in the contractions involving m. triceps and m. biceps, respectively. The intramuscular temperature increased simultaneously, 1.3 °C and 0.7 °C in m. triceps and m. biceps, respectively. The results from the constant EMG contractions indicate the existence of a common ‘trigger’ for both the increase in BP and the decrease in EMG MSF; and the extracellular [K] is put forward as a candidate. In study II, the demonstrated link between muscle fibre composition and cardiovascular responses during light, static work is explained from differences in metabolic characteristics and in the maintenance of homeostasis in slow and fast twitch muscles, respectively. Finally, the relative importance of central and peripheral control mechanisms in regulation of the circulation during static work is discussed on the basis of the demonstrated changes in EMG MSF and amplitude. It is concluded that peripheral control mechanisms seem to dominate in low level muscle c

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1985.tb07715.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY