Receptor binding of PDGF-AA and PDGF-BB,and the modulation of PDGF receptors by TGF-β, in human periodontal ligament cells

The growth factors PDGF-AA and PDGF-BB have previously been shown to be potent mitogens for human periodontal ligament (hPDL) cells in vitro. Additionally, the mitogenic response to PDGF-AA has been shown to be specifically inhibited by TGF-β. The purpose of the present investigation was to examine the binding of PDGF-AA and PDGF-BB, and the modulation of PDGF binding by TGF-β, in hPDL cells. Scatchard analysis identified an average of 32,000 PDGF-AA high-affinity binding sites per cell with a dissociation constant (K_d) of 0.66 nM and an average of 36,000 PDGF-BB binding sites per cell with a dissociation constant (k_d) of 0.44 nM. After treatment with TGF-β, the receptor number for PDGF-AA was found to specifically decrease by approximately 50%, with no change in binding affinity. This reduced number of binding sites was shown to correlate with both a decrease in levels of receptor tyrosine phosphorylation and a decreased number of α receptor subunits. Northern blot analysis identified the TGF-β-mediated decrease in PDGF α receptor subunit mRNA levels. PDGF-BB showed little change in the number of binding sites or in the binding affinity with TGF-β treatment, and the data were consistent with an increase in the number of β receptor subunits. These results demonstrate nearly equivalent numbers of receptors for both PDGF-AA and PDGF-BB in hPDL cells. Also, modulation of PDGF binding, by TFG-β, was shown to result in a reduced number of α receptor subunits with an increase in the number of β receptor subunits. © 1995 Wiley-Liss, Inc.     

Ablation of primary afferent terminals reduces nicotinic receptor expression and the nociceptive responses to nicotinic agonists in the spinal cord

A variety of studies indicate that spinal nicotinic acetylcholine receptors modulate the behavioral and autonomic responses elicited by afferent stimuli. To examine the location of and role played by particular subtypes of nicotinic receptors in mediating cardiovascular and nociceptive responses, we treated neonatal and adult rats with capsaicin to destroy C-fibers in primary afferent terminals. Reduction of C-fiber terminals was ascertained by the loss of isolectin B4, CGRP and vanilloid receptors as monitored by immunofluorescence. Receptor autoradiography shows a reduction in number of epibatidine binding sites following capsaicin treatment. The reduction is particularly marked in the dorsal horn and primarily affects the class of high affinity epibatidine binding sites thought to modulate nociceptive responses. Accompanying the loss of terminals and nicotinic binding sites were significant reductions in the expression of α 3, α 4, α 5, β 2 and β 4 nicotinic receptor subunits in the superficial layers of the spinal cord as determined by antibody staining and confocal microscopy. The loss of nicotinic receptors that follows capsaicin treatment results in attenuation of the nociceptive responses to both spinal cytisine and epibatidine. Capsaicin treatment also diminishes the capacity of cytisine to desensitize nicotinic receptors mediating nociception, but it shows little effect on intrathecal nicotinic agonist elicited pressor and heart rate responses. Hence, our data suggest that α 3, α 4, α 5, β 2 and β 4 subunits of nicotinic receptors are localized in the spinal cord on primary afferent terminals that mediate nociceptive input. A variety of convergent data based on functional studies and subunit expression suggest that α 3 and α 4, in combination with β 2 and α 5 subunits, form the majority of functional nicotinic receptors on C-fiber primary afferent terminals. Conversely, spinal nicotinic receptors not located on C-fibers play a primary role in the spinal pathways evoking spinally coordinated autonomic cardiovascular responses.     

Hypothyroidism-evoked shifts in hippocampal adrenergic receptors: Implications to ischemia-induced hippocampal damage

Hypothyroidism was induced in a group of male Fischer 344 rats by administration of 0.05% propylthiouracil (PTU) in the drinking water for 12 weeks. Control rats were not treated. Plasma levels of thyroid hormones indicated that PTU treatment had produced severe thyroid hormone deficiency. In PTU-treated rats compared to control rats, levels of total T₃ and total T₄ were reduced 54.5% and 53.7%; while levels of free T₃ and free T₄ were reduced 87.1% and 96.5%. Functional hypothyroidism was demonstrated by: (i) a 49.1% decrease in hepatic plasma membrane ₁-adrenergic receptor binding, and (ii) a 11.2- fold increase in hepatic -glutamyltranspeptidase activity; relative to the expression of these parameters in control rats. Membranes were isolated from hippocampi of control, PTUinduced hypothyroid and thyroxine-replaced rats and specific adrenergic receptor binding determined by radioligand binding techniques. Hypothyrodism resulted in a shift in the balance of ₁ and ₂ adrenergic receptor binding by evoking: an increase in ₁- adrenergic receptor binding to 1.57-fold of control levels; and, a decrease in ₂-adrenergic receptor binding to 64% of control levels. Thyroid hormone replacement carried out in PTU-treated hypothyroid rats at 30 g/kg s.c. per day for the last 3 days of the 12 week PTU-treatment protocol, which reversed physical and functional hypothyroidism, reversed the observed changes in hippocampal adrenergic receptor binding, indicating them to be thyroid hormone, and not PTU, -dependent. This receptor shift evoked by hypothyroidism may, in part, explain the protective effect of hypothyroidism on ischemia-induced hippocampal damage by favoring inhibitory input and limiting excitotoxic input by catecholamines.     

Prolactin stimulation of prolactin receptors in rat liver.

Hypophysectomy of the female rat results in a loss of prolactin receptors from the liver. Seventy percent of specific prolactin binding is lost within 24 hours; by 48 hours receptor levels are less than 5% of those found in livers from intact rats. A single dose of ovine prolactin to hypophysectomized rats causes a partial restoration of prolactin receptors between 12 and 18 hours after injection. As little as 0.5 mg prolactin significantly increases receptors, while doses above the 2 mg optimum are apparently less effective. These restored receptor sites are unaltered in their affinity for prolactin. Estradiol (E₂), progesterone, hydrocortisone, triiodothyronine (T₃) or E₂ plus T₃ could not mimic the prolactin effect. Neither combinations of prolactin with E₂ or T₃ nor repeated daily injections of prolactin alone increase receptors more than does a single prolactin injection. It appears that prolactin modulates the level of its own receptor in rat liver.     

Cyclical binding,processing, and functional interactions of neutrophils with leukotriene B4

Leukotrene (LT) B₄ activates human polymorphonuclear neutrophils. (PMN) by binding to plasmalemmal receptors. It stimulates PMN to raise cytosolic calcium and degranulate. Both responses end within 15–30 sec. However, in < 15 sec, LTB₄-treated PMN lose the ability to respond further to LTB₄; decrease the affinity and number of high affinity receptors available for binding LTB₄ sequester LTB₄ in plasmalemma-associated sites that are inaccessible to a releasing buffei regi i men; and begin internalizing LTB₄. Over the next 90 min, the cells increasingly internalize LTB₄ and convert it to less potent metabolites; release the metabolites; recover LTB₄ binding sites; and become fully sensitive to LTB₄. Contrastingly, during the entire 90 min incubation with LTB₄. PMN retained the capacity to bind and respond normally to a second stimulus platelet-activating factor. We therefore suggest the following model. LTB₄ receptors, when ligand-bound, initiate function but rapidly lose this capacity as they lower their ligand binding affinity and sequester, internalize, or otherwise uncouple from transducing elements. These LTB₄ receptor changes contribute to terminating PMN responses and producing a stimulus-selective state of desensitization. During the desensitization period, PMN progressively process and metabolize LTB₄. This removes LTB₄ from the environment, thereby allowing PMN to recover functional receptors for and sensitivity to the ligand.     

Enhancement of [m-methoxy3H]MDL100907 binding to 5HT2A receptors in cerebral cortex and brain stem of streptozotocin induced diabetic rats

5-Hydroxytryptamine_2A (5-HT_2A) receptor kinetics was studied in cerebral cortex and brain stem of streptozotocin (STZ) induced diabetic rats. Scatchard analysis with [³H] (±) 2,3dimethoxyphenyl-1-[2-(4-piperidine)-methanol] ([³H]MDL100907) in cerebral cortex showed no significant change in maximal binding (B_max) in diabetic rats compared to controls. Dissociation constant (K_d) of diabetic rats showed a significant decrease (p < 0.05) in cerebral cortex, which was reversed to normal by insulin treatment. Competition studies of [³H]MDL100907 binding in cerebral cortex with ketanserin showed the appearance of an additional low affinity site for 5-HT_2A receptors in diabetic state, which was reversed to control pattern by insulin treatment. In brain stem, scatchard analysis showed a significant increase (p < 0.05) in B_max accompanied by a significant increase (p < 0.05) in K_d. Competition analysis in brain stem also showed a shift in affinity towards a low affinity State for 5-HT_2A receptors. All these parameters were reversed to control level by insulin treatment. These results show that in cerebral cortex there is an increase in affinity of 5-HT_2A receptors without any change in its number and in the case of brain stem there is an increase in number of 5HT_2A receptors accompanied by a decrease in its affinity during diabetes. Thus, from the results we suggest that the increase in affinity of 5-HT_2A receptors in cerebral cortex and upregulation of 5-HT_2A receptors in brain stem may lead to altered neuronal function in diabetes.     

Triiodothyronine nuclear receptor: Role of histones and DNA in hormone binding

The triiodothyronine (T₃) nuclear receptor was previously shown to lose rapidly its high affinity hormone-binding property after a partial purification from the nuclear extract. It was then found that histones + DNA added to the incubation medium with labeled T₃ could restore, at least in part, the high affinity T₃ binding. We now demonstrate that DNA alone increases the high affinity T₃ binding site concentration moderately, and only at low ionic strength where it can bind to the receptor. Total histones and all histone fractions studied (total core histones, F2a, H2B, H3, H4, H1) specifically increase, at low concentrations, the level of T₃ binding; but higher concentrations of some individualized histones, particularly arginine-rich histones, have an inhibitory effect. DNA, or several other polynucleotides, in the presence of histones increase the stimulating histone effect and reverse the inhibitory effect into a true activation. Histones increase the number of T₃ binding sites but decrease the affinity for T₃; addition of DNA restores the high affinity for T₃ and stabilizes the T₃-receptor complexes. Thus, some of the histone molecules could play a role in the maintenance of the T₃ binding site, but multiple interactions between histones or with DNA seem necessary to impair the negative effect exerted by other parts of the histone molecules. Whether these positive and negative effects of histones on the T₃ binding site are of biological relevance in the regulation of T₃ binding to its receptor remains to be determined.     

Chronic Antagonist Treatment Does not Alter the Mode of Interaction of Dopamine with Rat Striatal Dopamine Receptors

Abstract

Chronic treatment with the D₁ and D₂ dopamine receptor antagonists SCH 23390 (0.5 mg/kg) and haloperidol decanoate (25 mg/kg) caused an up-regulation in D₁ and D₂ receptor densities, respectively, with no change in K_D. Dopamine (20 μM) interacted with both receptor subtypes in a mixed competitive/non-competitive manner, causing a reduction in ligand binding affinity and an apparent decrease in receptor density. In the presence of dopamine, both vehicle-treated and SCH 23390-treated striatal preparations showed a significant loss in affinity for ³H-SCH 23390 binding to D₁ receptors and a decrease in D₁ receptor density of approximately 26%. Similarly, dopamine caused a substantial loss in ³H-spiperone binding affinity to D₂ receptors and a 46% decrease in B_max in both vehicle-treated and haloperidol-treated membranes. Thus, receptor up-regulation does not appear to alter the mode of interaction of dopamine with rat striatal dopamine receptors.     

Roles of alpha1- and beta-adrenergic receptors in adrenergic responsiveness of liver cells formed after partial hepatectomy

The adrenergic receptor involved in the action of epinephrine changed dramatically during the process of active proliferation which follows partial hepatectomy. In control or sham-operated animals, the stimulation of glycogenolysis, gluconeogenesis and ureogenesis by epinephrine was mediated through alpha₁-adrenergic receptors. In contrast, in hepatocytes obtained from animals partially hepatectomized 3 days before experimentation, the receptor involved in the stimulation of these metabolic pathways by epinephrine was of the beta-adrenergic type. Interestingly, the adrenergic receptor involved in the metabolic actions of epinephrine, in hepatocytes from rats partially hepatectomized 7 days before experimentation was again of the α₁-subtype. Thus, it appears that during the process of liver regeneration which follows partial hepatectomy there is a transition in the type of adrenergic receptor involved in the hepatic actions of catecholamines from β in the initial stages to later α₁. A similar transition seems to occur as the animal ages. Cyclic AMP accumulation in response to β-adrenergic stimulation was significantly enhanced in hepatocytes obtained from rats partially hepatectomized 3 days before the experiment, as compared to control hepatocytes or cells obtained from animals operated 7 days before experimentation. This enhanced β-adrenergic sensitivity is probably related to the increased number of β-adrenergic receptors observed at this stage. However, a clear dissociation between cyclic AMP levels and metabolic effects was evidenced when the different conditions were compared. The number and affinity (for epinephrine or prazosin) of α₁-adrenergic receptors did not change at any stage of the process, which indicates that the markedly diminished α₁-adrenergic sensitivity observed in hepatocytes obtained from rats partially hepatectomized 3 days before experimentation is probably due to defective generation or intracellular processing of the α₁-adrenergic signal, rather than to changes at the receptor level.     

Receptor Interactions of Abbott-81988, A Highly Potent,Non-Peptide Angiotensin-II Antagonist Selective for Type-1 Receptors

Abstract

Abbott-81988 (A-81988) was selected from a series of related compounds as a highly potent and selective antagonist of angiotensin receptors. In the rabbit aorta, A-81988 exhibited a _pA₂ of 10.12 (± 0.08) vs. angiotensin-II, for type 1 receptors (AT₁), and the antagonism appeared competitive. These results agreed with radioligand assays in which A-81988 inhibited the binding of [¹²⁵l]-Sar¹ –lle⁸—Angiotensin-II to rat liver membranes with a _pK_I of 9.12 (± 0.63). A-81988 was selective for AT₁ receptors based on its lack of activity at other sites, such as aortic α 1 receptors. Moreover, A-81988 lacked affinity for AT₂ receptors of bovine cerebellar membranes or for α or β adrenergic receptors in binding assays. A-81988 lowered blood pressure significantly in vivo in renal artery-ligated rats at doses of 0.3 mg/kg administered either i.v. or p.o. The compound was rapidly and almost completely absorbed from the duodenum of anesthetized rats and demonstrated very low first-pass metabolism in the rat liver. These properties of selectivity toward and potency for antagonizing AT₁ receptors, activity in lowering blood pressure in experimental animals, and favorable pharmacokinetic properties indicate that A-81988 should be a useful antihypertensive agent in man.     

Correlation between myocardial malate/aspartate shuttle activity and EAAT1 protein expression in hyper- and hypothyroidism

In the heart, elevated thyroid hormone leads to upregulation of metabolic pathways associated with energy production and development of hypertrophy. The malate/aspartate shuttle, which transfers cytosolic-reducing equivalents into the cardiac mitochondria, is increased 33% in hyperthyroid rats. Within the shuttle, the aspartate-glutamate carrier is rate limiting. The excitatory amino acid transporter type 1 (EAAT1) functions as a glutamate carrier in the malate/aspartate shuttle. In this study, we hypothesize that EAAT1 is regulated by thyroid hormone. Adult rats were injected with triiodothyronine (T3) or saline over a period of 8-9 days or provided with propylthiouracil (PTU) in their drinking water for 2 mo. Steady-state mRNA levels of EAAT1 and aralar1 and citrin (both cardiac mitochondrial aspartate-glutamate transporters) were determined by Northern blot analysis and normalized to 18S rRNA. A spectrophotometric assay of maximal malate/aspartate shuttle activity was performed on isolated cardiac mitochondria from PTU-treated and control animals. Protein lysates from mitochondria were separated by SDS-PAGE and probed with a human anti-EAAT1 IgG. Compared with control, EAAT1 mRNA levels (arbitrary units) were increased nearly threefold in T3-treated (3.1 +/- 0.5 vs. 1.1 +/- 0.2; P < 0.05) and decreased in PTU-treated (2.0 +/- 0. 3 vs. 5.2 +/- 1; P < 0.05) rats. Aralar1 mRNA levels were unchanged in T3-treated and somewhat decreased in PTU-treated (7.1 +/- 1.0 vs. 9.3 +/- 0.1, P < 0.05) rats. Citrin mRNA levels were decreased in T3-treated and unchanged in PTU-treated rats. EAAT1 protein levels (arbitrary units) in T3-treated cardiac mitochondria were increased compared with controls (8.9 +/- 0.4 vs. 5.9 +/- 0.6; P < 0.005) and unchanged in PTU-treated mitochondria. No difference in malate/aspartate shuttle capacity was found between PTU-treated and control cardiac mitochondria. Hyperthyroidism in rats is related to an increase in cardiac expression of EAAT1 mRNA and protein. The 49% increase in EAAT1 mitochondrial protein level shows that malate/aspartate shuttle activity increased in hyperthyroid rat cardiac mitochondria. Although hypothyroidism resulted in a decrease in EAAT1 mRNA, neither the EAAT1 protein level nor shuttle activity was affected. EAAT1 regulation by thyroid hormone may facilitate increased metabolic demands of the cardiomyocyte during hyperthyroidism and impact cardiac function in hyperthyroidism.     

Structure activity relationships for central and peripheral alpha adrenergic activities of imidazoline derivatives.

The α adrenergic agonistic activity of a number of imidazolines was measured on the α adrenergic receptors of the isolated rabbit intestine. A number of imidazolines were full agonists having an intrinsic activity constant equal to 1 in relation to noradrenaline as a standard. Some other derivatives had only partial agonist activity. The affinities of the imidazolines for these adrenergic receptors was assessed using pD₂ values. The pD₂ values were correlated with a number of physicochemical parameters of the drugs, i.e. pK_a, the molar volume and the apparent and true partition coefficients (APC and TPC respectively) by stepwise regression analysis.Results indicate that pD₂ was correlated with pK_a primarily, whereas molar volume also was a factor determining agonistic activity at the peripheral α adrenergic receptor.Central α adrenergic receptor stimulating properties of the imidazolines were determined by measuring bradycardia induced by these agents after intrahypothalamic injection into rats. Although it was not possible to correlate central α adrenergic activity with any of the physicochemical parameters due to the lack of action of a number of imidazolines, results show that structural requirements for central α adrenergic activity clearly differ from those for peripheral α adrenergic activity.These data are discussed in view of the mechanism of action of the antihypertensive imidazoline clonidine.     

Regulation of expression of antioxidant enzymes by vitamin E and curcumin in <Emphasis Type="SmallCaps">l</Emphasis>-thyroxine-induced oxidative stress in rat renal cortex

The present study investigates the antioxidative effects of vitamin E and curcumin against l-thyroxine (T₄)-induced oxidative stress in renal cortex of adult male rats. Rats were made hyperthyroid by administration of l-thyroxine (0.0012%) in their drinking water for 30 days. Vitamin E (200 mg/kg body weight/day) and curcumin (30 mg/kg body weight/day) were supplemented singly or in combination orally for 30 days along with l-thyroxine treatment. The elevated level of oxidative stress parameters (lipid peroxidation and protein carbonylation) and decline level of small antioxidant molecules (reduced glutathione and ascorbic acid) in renal cortex of T₄-treated rats were restored back by supplementation of vitamin E or/and curcumin. Increased superoxide dismutase and catalase activities in kidney cortex of T₄-treated rats were ameliorated in response to vitamin E or/and curcumin treatment. The elevated translated product of Cu/Zn-SOD, Mn-SOD and catalase in T₄-treated rats were differentially reduced by the administration of vitamin E and curcumin independently or in combination. Cu/Zn-SOD expression was ameliorated by both vitamin E and curcumin independently or in combination, whereas Mn-SOD expression was ameliorated by the supplementation of vitamin E or curcumin independently. However, the expression of catalase was alleviated by only supplementation of vitamin E to T₄-treated rats. The results suggest that both vitamin E and curcumin may play an important role in protecting T₄-induced oxidative stress in rat renal cortex by differentially modulating the activities of antioxidant enzymes and oxidative stress parameters.     

Modulation of cardiac A1-adenosine receptors in rats following treatment with agents affecting heart rate

Effects of chronic treatment affecting heart rate on A₁ adenosine receptor levels and their functions were studied. Treatment of rats with isoproterenol for 10 days accelerated heart rate and increased the level of adenosine receptors, in both the atria and ventricles. Negative dromotropic response of isolated heart to adenosine was enhanced in isoproterenol-treated rats. Similar results were obtained following treatment with atropine sulfate, or swimming training but not after treatment with thyroxine. On the other hand, treatment with amiodarone, which normally causes a decrease in heart rate, also increased the level of adenosine receptors in both atria and ventricles. The sensitivity of the isolated heart to the negative dromotropic and chronotropic effects of adenosine was not enhanced in the amiodarone treated rats. Similar results were obtained following treatment with propranolol, while treatment with PTU (6-n-propyl-2-thiouracil) increased adenosine sensitivity in the isolated heart. It was concluded that the levels of A₁ adenosine receptors in the heart correspond to heart rate, and to cardiac efficiency. While an increase in heart rate was followed by up-regulation of A₁ adenosine receptors, a decrease in heart rate caused a moderate elevation of these receptors.     

Lymphosarcoma-induced alterations in hepatic adrenergic receptors: Implications to the hypoglycemia of cancer cachexia

A highly malignant transplantable rat lymphosarcoma was studied to determine the involvement of hepatic adrenergic receptors in the development of the hypoglycemia of cancer cachexia. Following inoculation of Fischer 344 rats with lymphosarcoma cells, rats were examined at 2 and 4 weeks, at the pre-cachexic stage; 6 weeks, at the transitional stage; and 7 weeks, at the cachexic hypoglycemic stage of lymphosarcoma progression. Death occurred by the 8th week. Blood glucose levels in lymphosarcoma-bearing rats relative to control rats were: unaffected at week 2; significantly reduced 8% at weeks 4 and 6; and reduced 24% at week 7. ₁ adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 114, 89, 67 and 30% of control at weeks 2, 4, 6, and 7, respectively. Kinetic analysis indicated that the lymphosarcoma-induced decrease at week 7 was due to a decrease in numbers of receptors with no change in affinity: Bmax_control: 1411.1 fmol/mg; Kd_control: 0.44 nm; Bmax_lympho: 345.5 fmol/mg; Kd_lympho: 0.50 nm. ₂ adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 130, 137, 243 and 212% of control at weeks 2, 4, 6, and 7, respectively. The pattern of changes in hepatic ₁, ₂ and adrenergic receptors at week 6 was comparable to that of 17 day fetal liver: a decrease in ₁ and and an increase in ₂. Hepatic adrenergic receptor changes occurred in the absence of liver damage and were not due to contamination of the liver plasma membrane fractions with lymphosarcoma cells. Plasma insulin levels displayed modest (10–15%), but not statistically significant, increases post-inoculation after week 4. Plasma glucagon levels fluctuated post-inoculation until week 7 where they were significantly increased: 202% of control. Plasma T₃ and T₄ levels displayed an early and steady decline after lymphosarcoma inoculation: T₃: unchanged at week 2 and significantly decreased 14, 44 and 50% at weeks 4, 6 and 7, respectively. T₄ increased 20% at week 1; decreased 9% at week 4 and significantly decreased thereafter: 55 and 49% at weeks 6 and 7, respectively. We propose that the development of the hypoglycemia of cancer cachexia in this lymphosarcoma model is due primarily to an early and progressive thyroid hormone dependent decrease in the number of hepatic ₁ adrenergic receptors, compounded by an increase and decrease, respectively, in the hepatic and ₂ adrenergic receptors.     

Changes in adrenergic receptors during the development of heart failure

Moderate and severe stages of congestive heart failure due to the loss of myocardium upon coronary occlusion in rats was associated with an increase in alpha-adrenergic receptors and a decrease in beta-adrenergic receptors in the viable left ventricle. However, at early stages of heart failure the number of beta-adrenergic receptors was decreased without any changes in the number of alpha-adrenergic receptors. The affinities of these receptors to alpha receptor antagonist (³H-prazosin) and beta receptor antagonist (³H-dihydroalprenolol) were not altered in the failing hearts. On the other hand, the pattern of changes in both alpha- and beta-adrenergic receptors in heart membranes treated with oxygen free radical generating system was different from that seen in the failing hearts. In particular, the affinities for these receptors were decreased whereas the number of beta-receptors was increased and the number of alpha-receptors was decreased or unchanged. These results indicate that alterations in the adrenergic receptors in heart failure are not due to the formation of oxygen free radicals.     

The Effects of Triiodothyronine on Rat Testis: A Morphometric and Immunohistochemical Study

The aim of present study was to investigate the effects of 3,3′,5-triiodothyronine (T₃) on rat testis both morphometrically and immunohistochemically with determining of insulin-like growth factor I (IGF-I) expression. Adult male Wistar-albino rats used in the study were divided into two groups; control and T₃-treated groups. After T₃ treatment there was observed to be a decrease in testicular weights, diameters of seminiferous tubules and the number of sertoli cells, and an increase in the number of leydig cells (P<0.05). Some of the seminiferous tubule lumens of T₃ administrated rats had cellular debris. IGF-I was localized in sertoli cells, late spermatids and leydig cells of all groups. IGF-I immunoreactivity in T₃ treated rats was higher than in controls in all stages of the cycle of rat seminiferous epithelium, but the staining intensity of leydig cells were similar in both groups. In conclusion, the present results suggest that T₃ may modulate the testicular function by affecting IGF-I activity at the gonadal level.     

Pharmacology of the Adenosine A3 Receptor in the Vasculature and Essential Hypertension

Background

Essential hypertension is considered to be a multifactorial disorder and its aetiology has yet to be clearly identified. As the adenosine receptors have a significant role in mediating vasodilation, alterations in their structures or signalling pathways may be involved in the development of hypertension. This study aimed to measure the expression of adenosine A₃ receptors in a range of cardiovascular tissues and determine whether they could be altered with essential hypertension, and to functionally test responses to adenosine A₃ receptor agonists in coronary blood vessels using the isolated perfused heart preparation.

Methods

mRNA samples from cardiovascular tissues and a range of blood vessels were collected from 10 week old male spontaneously hypertensive rats and age-gender matched Wistar rats (n = 8). The Langendorff heart perfusion preparation was used to characterise adenosine A₃ receptor mediated coronary vasodilation in the rat heart.

Results

Adenosine A₃ receptor agonists induced coronary vasodilation. The expression of adenosine A₃ receptors in cardiovascular tissues was altered in a tissue-specific pattern. Specifically, down-regulation of adenosine A₃ receptor expression occurred in hypertensive hearts, which might be associated with attenuated vasodilator responses observed in coronary vessels to adenosine A₃ receptor agonists.

Conclusions

This study demonstrated alterations in the expression of adenosine A₃ receptors occurred in a tissue specific mode, and reduced adenosine A₃ receptor mediated coronary vasodilation in hearts from spontaneously hypertensive rats. Our findings with regard to changes in the adenosine A₃ receptor in hypertensive hearts suggest that adenosine A₃ receptor might play a role in the physiopathology of essential hypertension and potentially open the way to pharmacologic manipulation of vasomotor activity by the use of adenosine A₃ receptor agonists.     

Differential supersensitivity of beta-receptor subtypes in rat cortex and cerebellum after central noradrenergic denervation

Inhibition of ³H-dihydroalprenolol binding to rat cortex and cerebellum β-receptors by the selective β₁-antagonist practolol, and the selective β₂-agonist salbutamol, was shallow and biphasic, with log-logit slopes less than 1.0. The relative affinities of these inhibitors suggested that the predominant β-adrenergic receptor population in cortex and cerebellum was β₁ and β₂ respectively. specific lesion of the ascending dorsal norepinephrine bundle, in addition to increasing β-receptor number in the cortex, significantly increased the affinity of practolol, but did not change the affinity of salbutamol, at cortex β receptor sites. Similar lesions decreased cerebellar β-receptor binding and reduced the affinity of salbutamol but not of practolol for those same sites. Iterative computer analysis of the inhibition data showed mixed populations of β₁- and β₂- receptors in both cortex and cerebellum. Dorsal NE bundle lesion doubled the number of cortical β₁-receptors, but did not alter the number of β₂-receptors. In contrast, these lesions induced a selective decrease in cerebellar β₂-receptors. It is concluded that the relevant neuronal β-receptors which are postsynaptic to central NE nerve terminals are β₁ in the cerebral cortex and β₂ in the cerebellum.     

Hormonal modulation of atrial natriuretic factor receptors and effects on adrenal glomerulosa cells of female rats

This study was done to determine if a decrease in the aldosterone-suppressant effect of atrial natriuretic factor (ANF) by progesterone and an increase by estrogen was caused by modulation of adrenal zona glomerulosa ANF receptors. Freshly dispersed glomerulosa cells from virgin, 13–15 day pregnant, ovariectomized (OVX) estradiol-17β-treated and OVX progesterone-treated rats were used. Competitive displacement of specifically bound [¹²⁵I]ANF_1–8 with unlabelled ANF_1–28 yielded concentrations of guanylate cyclase-linked ANF-R1 plus ANF-R2 (clearance) receptors and the displacement with unlabelled ANF_4–23 yielded ANF-R2 receptors; the difference between the two was treated as the concentration of ANF-R1 receptors. Pregnancy and progesterone decreased and estrogen increased the number of glomerulosa ANF-R1 receptors. ANF produced a significantly greater suppression of potassium-induced aldosterone secretion in cells from OVX estradiol-treated rats than in cells from OVX progesterone-treated animals. These data suggest that the inhibition of the aldosterone-suppressant activity of ANF by progesterone is the result of a downregulation of ANF-R1 receptors.