Modulation of dopamine receptors by cations in 7315a, MtTW15 and estradiol-induced pituitary tumors

Modulation of dopamine (DA) receptors by cations (Na+, K+, Mg2+, Ca2+) was compared in 7315a, MtTW15, and estradiol valerate-induced (EV-T) pituitary tumors, and intact adenohypophysis. In 7315a tumors, the affinity of [3H]spiperone binding measured at 25 degrees remained unchanged in the presence of each cation individually or all these cations together (IONS) compared to the affinity obtained using a buffer without ions; the density (Bmax) was not affected by monovalent cations or Mg2+ and was decreased by Ca2+ or IONS. When binding experiments were done at 37 degrees, monovalent cations increased affinity whereas divalent cations or IONS did not modify it, and none of these cations affected Bmax values. In MtTW15 tumors, the affinity of [3H]spiperone binding measured at 25 degrees was not changed by Na+ or IONS and was decreased by K+ or divalent cations; the density was decreased by K+ and unchanged by all the other cations. When binding experiments were done at 37 degrees, Na+ increased the affinity, whereas all the other cations did not affect it: the density was unaffected by all the cations studied. In EV-T assayed at 37 degrees, the affinity was increased by monovalent cations or Mg2+ and was unchanged by Ca2+; monovalent cations did not affect the density of [3H]spiperone binding and divalent cations increased it. In binding experiments performed at 25 degrees and 37 degrees, choline chloride did not change the affinity or the density of [3H]spiperone binding to DA receptors in the three pituitary tumors investigated, suggesting that the effect of cations was specific and not due to differences in ionic strength. In the rat normal anterior pituitary, Na+ increased the affinity of [3H]spiperone for the DA receptors, whereas the affinity was unchanged by Ca2+; the density of [3H]spiperone binding was unaffected by these cations. Our results suggest that DA receptors in 7315a and MtTW15 tumors are regulated abnormally by sodium, potassium, magnesium and calcium. In contrast, DA receptors in EV-T are regulated normally by monovalent cations and abnormally by divalent cations as compared to these receptors in intact pituitary tissue.     

Beta-adrenergic responsiveness in the rat following acute administration of ethanol

Ethanol has been shown to induce a hypothermia in rats maintained in air at 26 degrees C. The objective of the present study was to assess the metabolic responsiveness of ethanol-treated rats to administration of isoproterenol, a beta-adrenoceptor agonist, and to assess whether ethanol per se, or the hypothermia accompanying its administration, contribute to changes in beta-adrenergic responsiveness. In the present study, administration of ethanol (3 g/kg, i.p.) reduced both colonic temperature (Tco) and rate of oxygen consumption (metabolic rate) of rats maintained at 26 degrees C to levels below those of saline-treated controls within 20 min after treatment. Maximal decreases in both parameters occurred within approximately 40 min. Administration of isoproterenol (50 micrograms/kg, s.c.) 10 min after treatment with either ethanol or saline was accompanied by an increase in the metabolic rates of both groups, although the magnitude of the increase in the ethanol-treated group was less than that of controls. Maximal increases in tail skin temperatures (Tsk) following treatment with isoproterenol were similar in both groups but an increase in Tsk occurred earlier in the ethanol-treated group. Tco increased after treatment with isoproterenol in the saline-treated group but decreased in the ethanol-treated group. When isoproterenol was administered 90 min after treatment with ethanol, increases in metabolic rate, Tsk, and Tco were similar in both groups, although the increase in Tsk of ethanol-treated animals was delayed until Tco reached pretreatment level. Exposure to 30 degrees C minimized ethanol-induced hypothermia. At this temperature the metabolic responses to administration of isoproterenol at 90 min after treatment with ethanol did not differ significantly between the two groups. These results suggest that the metabolic responsiveness to administration of a beta-adrenoceptor agonist is not altered by prior treatment with ethanol but is affected by the hypothermia accompanying its administration.     

Regulation of autonomic receptors in rat submandibular gland

The binding of receptor specific radioligands to autonomic receptors in the rat submandibular gland was characterized after chronic drug administration and surgical sympathetic denervation. Reserpine administration resulted in an up-regulation of both alpha 2-adrenergic receptors labeled by [3H]clonidine and beta 1-adrenergic receptors labeled by [3H]dihydroalprenolol. The increase in alpha 2-receptors was half-maximal 24 hr after a single injection of reserpine, and was about 10-fold greater than control after seven daily injections. By contrast, the beta-adrenergic receptor density was the same as control after 3 days of reserpine administration, but within 7 days was about 2-fold greater than control. Guanethidine or yohimbine administration also resulted in an up-regulation of alpha 2-adrenergic receptors. Reserpine administration or unilateral superior cervical ganglionectomy increased the density of alpha 1-adrenergic receptor binding sites 24-80%. Norepinephrine and methoxamine, but not clonidine, caused potassium to be released from submandibular gland slices. Prazosin, but not yohimbine, blocked this response to norepinephrine, indicating that the response was mediated by alpha 1-adrenergic receptors. Potassium release elicited by alpha 1-agonists was augmented in slices from animals that received reserpine. Neither drug treatment nor sympathetic denervation altered muscarinic cholinergic receptor binding. The densities of muscarinic and beta-adrenergic receptors were found to be 23-51% higher in glands from female rats than in glands from male rats.     

Assessment of tissue responsiveness after implantation of a new block copolymer into rat tissue

The report describes tissue response an implantation of new block copolymer and compares with tissue response after presently used in medicine polymer implants. Implants shaped as 15 x 3 mm cylinders were placed subcutaneously on the abdomen and into muscles of both tight of Wistar rats. After 3, 7 and 14 days was taken tissue specimens with implants and kidneys to gross and light microscope examination. During the experiment there was not toxic signs considering rat's appearance and behaviour. Microscopic examination shows no difference between tissue response to presently in medicine used implants and new polymers.     

Beta-adrenergic receptors and adenylate cyclase activity in rat reticulocytes and mature erythrocytes.

The adenylate cyclase activity in membranes from rat reticulocytes exhibits a markedly greater stimulation (relative to basal activity) by catecholamines than does the activity in membranes from mature erythrocytes; this increased responsiveness of reticulocytes to catecholamines is not observed for other hormonal adenylate cyclase activators such as prostaglandins E₁and E₂ and human growth hormone. From the order of potency ofcatecholamine-stimulated adenylate cyclase activity (isoproterenol > epinephrine > norepinephrine), and from the selective action of butoxamine compared with practolol, both in inhibiting isoproterenol-stimulated adenylate cyclase activity and in blocking the binding to membranes of ¹²⁵I-labeled hydroxybenzylpindolol, it is concluded that both reticulocytes and mature rat erythrocytes possess adrenergic receptors of the beta-2 type. Practolol acts as a partial agonist in both cell types, stimulating adenylate cyclase activity. The guanine nucleotides, GTP and 5′-guanylylimidodiphosphate (GMP-PNP), affect the adenylate cyclase activity in membranes from both cell types. GTP stimulates basal activity 2-fold, but does not affect stimulation by fluoride. In reticulocyte membranes, GTP enhances isoproterenol stimulation of adenylate cyclase to a level approximately 2-fold greater than that achieved by fluoride; in contrast, in mature erythrocyte membranes, isoproterenol stimulation of adenylate cyclase in the presence of GTP is equivalent to that of fluoride. In reticulocyte membranes, the stimulation of adenylate cyclase by GMP-PNP alone is equivalent to the stimulation in the presence of either isoproterenol or fluoride. In contrast, in membranes from mature erythrocytes the stimulation by GMP-PNP alone is equivalent to stimulation by fluoride, but is markedly lower than that obtained in the simultaneous presence of isoproterenol. It is concluded that whereas the beta-2 nature of the catecholamine receptor on rat erythrocytes remains unaltered as the reticulocyte matures, there is a pronounced change during maturation in the coupling of adrenergic-receptor occupation to adenylate cyclase activation, as indicated by the effects of guanine nucleotides.     

Beta-adrenergic responsiveness of the gastrointestinal tract in diabetic rats.

Recently, decreased gastrointestinal beta-adrenergic responses in experimental diabetes have been demonstrated. Gastrointestinal responses to beta-adrenoceptor agonists are impaired in both insulin-dependent and non-insulin-dependent diabetic rat. Insulin treatment improves the impaired gastrointestinal beta-adrenergic responsiveness of diabetic rats. The improvement seen with insulin treatment on beta-adrenergic responsiveness is closely related to protein biosynthesis. The decreased beta-adrenergic responses in diabetic rat gastrointestinal tract seem to result from a decrease in the number of beta-adrenoceptors. It is most likely that the decreased gastrointestinal beta-adrenergic responsiveness is related to an impairment in the turnover of beta-adrenoceptors as a consequence of diabetes and that insulin has a beneficial effect on the impaired receptor turnover.     

Ontogenesis of autonomic receptors and AChE activity in the rat vas deferens

The study was undertaken to obtain some information about the development of the autonomic receptors and the AChE activity in the rat vas deferens. The results suggest that the adrenoceptors were fully developed at birth. The M1-ACh receptors were developed before the M2-ACh receptors. The AChE activity developed before the ACh muscarinic receptors of the rat vas deferens.     

Beta-adrenergic receptor responsiveness to isoprenaline in humans: concentration-effect, as compared with dose-effect evaluation and influence of autonomic reflexes.

1. Different techniques of assessing beta-adrenoceptor sensitivity in vivo, by use of i.v. infusions or bolus injections of isoprenaline (ISO), were compared in healthy volunteers. The importance of autonomic reflexes for responses to ISO was evaluated by studying the influence of 'autonomic blockade' by atropine and clonidine, which antagonize muscarinic effects and reduce sympathetic activity, respectively. Estimates of in vivo responsiveness to ISO were compared with parameters reflecting beta 2-adrenoceptor function in vitro in lymphocytes. 2. Heart rate responses to infused ISO were not significantly altered by 'autonomic blockade' when evaluated from concentration-effect curves. When related to the infused dose of ISO, however, sensitivity was artefactually increased (P less than 0.05), as the plasma concentrations of ISO were 40% higher after atropine and clonidine. Heart rate responses to bolus injections of ISO were attenuated (P less than 0.05) by 'autonomic blockade', suggesting that facilitatory reflexes contribute to these non-steady state responses. Intersubject variations in heart rate responsiveness to ISO were greater than the intrasubject variability caused by counterregulatory reflexes. 3. 'Autonomic blockade' lowered venous plasma noradrenaline at rest. The noradrenaline response to ISO infusion was attenuated and the diastolic blood pressure response enhanced, indicating that a counterregulatory vasoconstrictor reflex normally is activated by ISO-induced vasodilatation. The plasma cyclic AMP response to ISO, on the other hand, was unaffected by atropine and clonidine and reflects beta 2-adrenoceptor responsiveness in vivo. 4. In vitro data for beta-adrenoceptor binding sites (Bmax;[125I]-IHYP binding) and cyclic AMP responses to ISO in lymphocytes correlated with DBP and noradrenaline responses to infused ISO. No correlations were found between in vitro data and heart rate, plasma cyclic AMP or plasma glycerol responses to infused ISO in vivo. 5. During prolonged ISO infusions (in six other healthy subjects) physiological responses reached greater than 90% of their steady state level after 8 min, but no definite steady state level could be defined for the plasma concentration of ISO during 40 min of infusion. 6. The ISO infusion test showed a good reproducibility, especially when repeated on the same day. Evaluation of plasma concentration-effect relationships increase the precision of the ISO infusion test as confounding inter- and intra-individual variations in ISO concentrations (as caused by e.g. autonomic blockade) will be taken into account.(ABSTRACT TRUNCATED AT 400 WORDS)     

Beta-adrenergic receptors and catecholamines in acute myocardial infarction

Lymphocyte beta-adrenergic receptor density and plasma catecholamine concentrations were determined in 28 patients with acute myocardial infarction and compared with those in patients with angina pectoris and healthy persons. In patients with acute myocardial infarction beta-adrenergic receptor density was significantly lower (p less than 0.001) and plasma catecholamine levels significantly higher (p less than 0.001) as compared with corresponding values in patients with angina pectoris or healthy persons. beta-adrenergic receptor density in patients with angina pectoris were not significantly different from those in controls. A significant negative correlation between beta-adrenergic receptor density and plasma norepinephrine levels was observed in patients with acute myocardial infarction (r = -0.593; p less than 0.001; r = -0.615; p less than 0.001 respectively). It is suggested that decreased beta-adrenergic receptor density is a consequence of elevated plasma catecholamine levels in patients with acute myocardial infarction. It has been well documented that acute myocardial infarction is associated with enhanced activity of the sympathetic nervous system. Several studies have already been done showing that urinary excretion of catecholamines and plasma catecholamine concentrations are raised in the acute phase of myocardial infarction. Particularly high levels of plasma catecholamines appeared to be related to the severity of clinical course of myocardial infarction and were found in patients with cardiogenic shock, heart failure and arrhythmias. It is of interest that the peak elevation of plasma catecholamines correlated with the extent of myocardial damage as reflected by peak plasma CK activity and also correlated with acute and long-term mortality.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beta-adrenergic receptors and reflex tachycardia after single and repeated felodipine administration in essential hypertension.

To verify the possible contribution of beta-adrenergic receptor down-regulation to the reversal of reflex tachycardia during chronic treatment with a dihydropyridine calcium antagonist, 11 hypertensive patients were studied with noninvasive blood pressure (BP) and heart rate (HR) monitoring after a placebo period, and on the first and seventh day of felodipine administration, 5 mg twice daily. Plasma catecholamines and neutrophil beta-adrenergic receptors were measured on the first and seventh day of treatment, immediately before and 2 h after drug administration. The first administration of felodipine was followed by a significant drop in BP (peak reduction in mean BP 24 +/- 7 mm Hg), lasting 6 h and mirrored by reflex tachycardia (peak increase in HR 14 +/- 9 beats/min). On the morning of the seventh day, 12 h after the previous felodipine administration, mean BP (MBP) was 16 mm Hg lower than on the last placebo day, while HR was unchanged. The next administration of felodipine was followed by a smaller drop in BP (MBP - 15 +/- 7 mm Hg; NS vs. placebo), while reflex tachycardia was the same as after acute felodipine (HR 13 +/- 8 beats/min; p less than 0.05 vs. placebo, NS vs. acute administration). Plasma noradrenaline concentration increased after both acute and chronic administration (p less than 0.0001), and preadministration values were highest on day 7 (p less than 0.05). Neutrophil beta-adrenergic receptor density and affinity did not change either acutely or chronically. This study gives both indirect and direct evidence that beta-adrenoceptor down-regulation does not occur during repeated felodipine administration in hypertension. Reflex tachycardia is not abolished, but is reset to lower BP levels.     

Effects of hypoxia on atrial muscarinic cholinergic receptors and cardiac parasympathetic responsiveness

Chronic exposure of rats to hypoxia resulted in a lower resting heart rate and a supranormal increase in heart rate in response to parasympathetic blockade by atropine. The density of muscarinic cholinergic receptors labeled by the antagonist [³H]quinuclidinyl benzilate was elevated significantly in the atria of animals kept hypoxic for 2–4 weeks. Chronic hypoxia did not change the affinity of the receptor for [³H]quinuclidinyl benzilate, the weight of the atria, or the amount of protein per atrial pair. Thus, the decrease in resting heart rate may be explained by the increase in the density of atrial muscarinic cholinergic receptors.     

小儿垂体增生误诊垂体腺瘤

目的观察小儿垂体增生的临床特点和药物治疗后垂体影像学检查的变化。方法分析8例影像学检查显示"垂体增大,不能除外垂体腺瘤"的内分泌紊乱儿童的临床、MRI特点及激素替代治疗效果。结果 8例均存在明显的内分泌功能紊乱所致的临床症状和体征,以性早熟和甲状腺功能低下为主,无明显的颅内占位或侵袭症状。内分泌检查与临床吻合。颅脑MRI均提示垂体增大,部分病例平扫或增强信号不均匀,疑诊"垂体腺瘤"。予相应激素替代治疗后3个月,复查垂体明显缩小或正常,间隔3个月再随诊垂体未见异常改变。结论提示小儿垂体增生易与垂体腺瘤误诊,应重视临床特点和内分泌检查,必要时应用相应激素治疗后复查,避免不必要的手术治疗。     

Characterization of autonomic receptors in the rat sublingual gland by biochemical and radioligand assays

Summary The autonomic receptors of the rat sublingual gland were characterized by radioligand binding and by specific functional responses involving the release of K⁺ and the generation of cyclic AMP in vitro. Both muscarinic cholinergic and alpha₂-adrenergic receptors were present in moderately high density in the sublingual gland, as judged by the binding of the specific radioligands ³H-QNB and ³H-clonidine (B _max in pmol/g tissue=18.4±2.4 and 9.9±1.3, respectively). By contrast, although alpha₁ and beta-adrenergic receptors were detected, they were not present in large numbers. The B _max (pmol/g tissue) for the binding of ³H-prazosin and ³H-DHA were, respectively, 3.2±0.6 and 3.6±0.4. Stimulation of muscarinic cholinergic receptors with carbamylcholine (2×10^–5 M) caused a net release of K⁺ from sublingual slices incubated in an enriched, oxygenated Krebs Ringer bicarbonate medium of 35±7% after 10 min of incubation. Norepinephrine, phenylephrine, clonidine and isoproterenol did not induced K⁺ release from the slice preparation, but actually reduced the basal or unstimulated release of K⁺. As in the submandibular and parotid glands, the release of K⁺ from sublingual slices had two components, a passive efflux and an active uptake which depended on the activation of an ouabain-sensitive Na⁺, K⁺ ATPase. The release of K⁺ was also dependent on the presence of Ca²⁺ (2.7 mM) in the incubation medium. Stimulation of beta-adrenergic receptors with isoproterenol (10^–5 M) caused a 9-fold increase in the content of glandular cyclic AMP (from 4.0±0.6 to 36.0±2 pmol/mg/10 min). A similar increase was observed with norepinephrine (10^–4 M) in the presence of phentolamine (10^–4 M). Clonidine at concentrations of 10^–5 and 10^–4 M reduced the cyclic AMP content to below basal levels. The rat sublingual gland has functional cholinergic receptors and can release K⁺ in vitro in the presence of cholinergic agents. In contrast to the other major salivary glands, it has a low density of alpha₁-adrenergic receptors and fails to release K⁺ upon stimulation with alpha₁-agonists. The functional significance of a low density of beta-adrenergic receptors is still unclear, although there is a definite glandular cyclic AMP response upon stimulation with isoproterenol. Abundant alpha₂-adrenergic receptors in the sublingual gland are apparently negatively coupled to adenylate cyclase.     

Effects of prenalterol on beta adrenergic responsiveness and receptors in the cerebral cortex of the rat

The activity of the beta-adrenoceptor agonist, prenalterol, at beta adrenoceptors in the cerebral cortex of the rat and the effect of chronic intraperitoneal infusion of prenalterol on the biochemical responsiveness and density of cerebral cortical beta adrenoceptors was studied. Whereas isoproterenol caused a four-fold rise in the content of cyclic AMP in slices of cerebral cortex, prenalterol did not produce a significant increase in cyclic AMP. However, prenalterol inhibited the isoproterenol-stimulated increase in cyclic AMP in cortical slices in a concentration-dependent manner. Using an in vivo binding technique, prenalterol (3.8 mg/kg/hr) infused intraperitoneally through osmotic minipumps, penetrated the brain and significantly inhibited the binding of the beta adrenoceptor antagonist, [125I]iodopindolol (125I-IPIN), to cortical beta adrenoceptors. Infusion of prenalterol (3.8 mg/kg/hr) for 7 days resulted in a small (20%), but significant, reduction in the ability of isoproterenol to stimulate maximally the accumulation of cyclic AMP in slices of cerebral cortex. No alteration in the Bmax or KD of the binding of [125I]iodopindolol was observed in homogenates of cortex obtained from prenalterol-treated rats. Furthermore, no change was observed in the binding of the hydrophilic ligand [3H]CGP-12177 in homogenates of cortex. In this study, then, prenalterol exhibited properties in vitro of a beta adrenoceptor antagonist, but did cause modest desensitization of beta adrenoceptor responsiveness when administered continuously in vivo.     

Effects of hypochlorite and hydrogen peroxide on cardiac autonomic receptors and vascular endothelial function

1. Reactive oxygen species (ROS) are known to be involved in the progression of various cardiovascular diseases. One source of ROS is activated neutrophils, which can release superoxide anion radicals and hydrogen peroxide by membrane-bound NAD(P)H oxidases. These ROS not only destroy bacteria, but may also affect mammalian tissue. In addition, hydrogen peroxide serves as a substrate for myeloperoxidase, an enzyme that is released by activated neutrophils during inflammatory processes, as seen, for instance, in reperfusion injury and atherosclerosis. Myeloperoxidase catalyses the oxidation of chloride by hydrogen peroxide, yielding hypochlorite, an extremely potent oxidant. 2. The purpose of the present study was to evaluate the effects of hypochlorite on a variety of receptor-dependent processes in rat isolated left atria and rat thoracic aorta and to compare these results with the phenomena observed after incubation with hydrogen peroxide. 3. In the presence of hypochlorite (300 micro mol/L), the positive inotropic response of alpha1-adrenoceptor stimulation by methoxamine (300 micro mol/L) was converted into a negative inotropic response. In contrast, the positive inotropic effects of the beta1/beta2-adrenoceptor agonist isoprenaline (3 micro mol/L) and endothelin (ET)-1 (100 nmol/L) remained largely unaffected. 4. The inversion of alpha1-adrenoceptor-mediated inotropy was not obtained in the presence of hydrogen peroxide (500 micro mol/L). Hydrogen peroxide did not affect the positive inotropic response of isoprenaline, but it completely abolished the inotropic effect of ET-1. 5. The effect of cardiac M2-receptor stimulation was studied in the presence of hypochlorite and hydrogen peroxide. The negative inotropic response to acetylcholine (ACh) was significantly enhanced after hypochlorite incubation compared with control. 6. In the rat thoracic aorta, endothelial function, evaluated by means of ACh-induced vasodilation, was completely abolished in the presence of hypochlorite (100 micro mol/L), but remained unaffected by treatment with the same concentration of hydrogen peroxide. 7. From these data, we conclude that hypochlorite exerts more toxic properties than its precursor hydrogen peroxide, leading to substantial physiological alterations in cardiac and vascular tissue.     

Increased acetylcholine and quisqualate responsiveness after blockade of GABAB receptors.

The aim of this study was to gain further insight into the function of cortical GABAB receptors. In chloral hydrate-anaesthetized rats, microiontophoretic administration of the GABAB receptor blocker CGP 35348 induced a moderate increase in firing of spontaneously active neurons in the rostral and caudal sensorimotor cortex. This increase in cell firing was accompanied by a reduction in the baclofen-induced inhibition of cell activity. In contrast to the GABAA receptor antagonist bicuculline methiodide, CGP 35348 did not induce any paroxysmal discharges. The excitatory responses of rostral cortical neurons elicited by iontophoretically applied acetylcholine and quisqualate were potentiated in most neurons after both microiontophoretic and intravenous administration of CGP 35348. The potentiation was observed in the absence of any change in the spontaneous firing rate. These effects were dose-dependent for both routes of administration. The potentiation of the quisqualate response was reversed by intravenously applied baclofen. In conclusion, these findings suggest that cortical GABAB receptors are involved in the control of cortical neuronal excitability.     

垂体促甲状腺素腺瘤的诊断和处理

目的探讨垂体促甲状腺素(TSH)腺瘤的临床特点及治疗方法。方法垂体TSH腺瘤患者4例,男1例,女3例,年龄25-47岁,中位病程7.5年,延误诊断4.2年。4例患者均有不同程度的甲状腺增大和甲亢症状,血浆FT3、FT4、T3、T4增高,3例患者TSH增高。1例对促甲状腺激素释放激素(TRH)激发试验有反应。头部鞍区MRI检查显示3例为大腺瘤,1例为微腺瘤。确诊后4例患者行经鼻-蝶窦入路垂体瘤切除术,其中1例术后辅以放疗。结果术后病理均证实为垂体腺瘤。随访至今(术后约5-7年),鞍区MRI检查未见肿瘤复发,甲状腺激素水平基本控制在正常范围。结论垂体TSH腺瘤发病率极低,甲亢患者血清TSH水平不被抑制时应警惕垂体TSH腺瘤的存在;鞍区影像学检查有助于垂体TSH腺瘤的早期诊断和治疗。