α1-Adrenergic Receptor-Mediated Downregulation of Angiotensin II Receptors in Neuronal Cultures

Previous evidence has suggested that brain catecholamine levels are important in the regulation of central angiotensin II receptors. In the present study, the effects of norepinephrine and 3,4-dihydroxyphenylethylamine (dopamine) on angiotensin II receptor regulation in neuronal cultures from rat hypothalamus and brainstem have been examined. Both catecholamines elicit significant decreases in [125I]angiotensin II-specific binding to neuronal cultures prepared from normotensive rats, effects that are dose dependent and that are maximal within 4-8 h of preincubation. Saturation and Scatchard analyses revealed that the norepinephrine-induced decrease in the binding is due to a decrease in the number of angiotensin II receptors in neuronal cultures, with little effect on the receptor affinity. Norepinephrine has no significant actions on [125I]angiotensin II binding in cultures prepared from spontaneously hypertensive rats. The downregulation of angiotensin II receptors by norepinephrine or dopamine is blocked by alpha 1-adrenergic and not by other adrenergic antagonists, a result suggesting that this effect is initiated at the cell surface involving alpha 1-adrenergic receptors. This is further supported by our data indicating a parallel downregulation of specific alpha 1-adrenergic receptors elicited by norepinephrine. In summary, these results show that norepinephrine and dopamine are able to alter the regulation of neuronal angiotensin II receptors by acting at alpha 1-adrenergic receptors, which is a novel finding.     

Studies of the interaction between glucagon and alpha-adrenergic agonists in the control of hepatic glucose output

alpha-Adrenergic stimulation of hepatocytes prevented, in a dose-dependent manner, the stimulation of [U-14C]lactate conversion to [14C]glucose by glucagon and exogenously added cAMP and Bt2cAMP. The inhibition was referable to an interaction with adrenergic receptors which resulted in a small decrease in hepatic cAMP levels. Low concentrations of epinephrine (10 nM) were able to inhibit phosphorylase activation and glucose output elicited by low doses of glucagon (5 X 10(-11) M to 2 X 10(-10) M). The ability of epinephrine (acting via alpha 1-adrenergic receptors), vasopressin, and angiotensin II to elicit calcium efflux was inhibited by glucagon, suggesting that intracellular redistributions of Ca2+ are importantly involved in the gluconeogenic process. It is proposed that vasopressin, angiotensin II, and catecholamines, acting primarily via alpha 1-adrenergic receptors, are responsible for inhibition of glucagon mediated stimulation of gluconeogenesis by altering subcellular calcium redistribution and decreasing cAMP levels.     

Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats

Earlier studies from our laboratory have indicated insulin sensitizing action of chromium picolinate as the mechanism of its anti-diabetic activity in experimental models of type I and type II diabetes. In the present investigation, we have evaluated the effects of chronic administration of chromium picolinate on the functional and histological alterations of streptozotocin (STZ)-induced diabetes in rats. Type I diabetes was induced by intravenous injection of STZ (40 mg/kg) in adult rats, whereas, type II diabetes was induced by intraperitoneal injection of STZ (90 mg/kg) in 2-day old rat pups which in adulthood develop abnormalities resembling type II diabetes. Chromium picolinate was administered at 8 μg/ml in drinking water for 6 weeks and was found to improve glucose tolerance and increase insulin sensitivity of STZ-diabetic rats. This treatment decrease elevated serum creatinine and urea levels as well as elevated serum levels of hepatic enzymes of both groups of diabetic rats. Histopathological studies of kidney and liver show decrease in the intensity and incidence of vacuolations, cellular infiltration and hypertrophy of STZ and nSTZ (neonatal STZ) diabetic rats. Chronic treatment with chromium picolinate however, did not alter the normal function or morphology of control rats. Chronic chromium picolinate at the therapeutic doses that improved glucose tolerance, was observed to have no hepatotoxic or nephrotoxic potential. It was rather found to improve renal and hepatic function and to reduce abnormalities associated with STZ-diabetes. Chromium picolinate could play an important role in the long term management of diabetes mellitus.     

Des(1–3)IGF-1 Treatment Normalizes Type 1 IGF Receptor and Phospho-Akt (Thr 308) Immunoreactivity in Predegenerative Retina of Diabetic Rats

Little is known about interventions that may prevent predegenerative changes in the diabetic retina. This study tested the hypothesis that immediate, systemic treatment with an insulin-like growth factor (IGF)-1 analog can prevent abnormal accumulations of type 1 IGF receptor, and phospho-Akt (Thr 308) immunoreactivity in predegenerative retinas of streptozotocin (STZ) diabetic rats. Type 1 IGF receptor immunoreactivity increased approximately 3-fold in both inner nuclear layer (INL) and ganglion cell layer (GCL) in retinas from STZ rats versus nondiabetic controls. Phospho-Akt (Thr 308) immunoreactivity increased 5-fold in GCL and 8-fold in INL of STZ rat retinas. In all cases, immunoreactive cells were significantly reduced in STZ des(1–3)IGF-1–treated versus STZ rats. Preliminary results suggested that vascular endothelial growth factor (VEGF) levels may also be reduced. Hyperglycemia/ failure of weight gain in diabetic rats continued despite systemic des(1–3)IGF-1. These data show that an IGF-1 analog can prevent early retinal biochemical abnormalities implicated in the progression of diabetic retinopathy, despite ongoing hyperglycemia.     

Modulation by thyroid status of cyclic AMP-dependent and Ca2+-dependent mechanisms of hormone action in rat liver cells. Possible involvement of two different transduction mechanisms in alpha 1-adrenergic action

The actions of hormones which are associated to cAMP-dependent and calcium-dependent mechanisms of signal transduction were studied in hepatocytes obtained from rats with different thyroid states. In cells from euthyroid and hyperthyroid rats, the metabolic actions of epinephrine were mediated mainly through alpha 1-adrenoceptors; beta-adrenoceptors seem to be functionally unimportant. In contrast, both alpha 1- and beta-adrenoceptors mediate the actions of epinephrine in hepatocytes from hypothyroid animals. Phosphatidylinositol labeling was strongly stimulated by epinephrine, vasopressin and angiotensin II in cells from eu-, hyper- or hypothyroid rats. However, metabolic responsiveness to vasopressin and angiotensin II was markedly impaired in the hypothyroid state. The glycogenolytic response to the calcium ionophore A-23187 was also impaired, suggesting that hepatocytes from hypothyroid rats are less sensitive to calcium signalling. The persistence of alpha 1-adrenergic responsiveness in the hypothyroid state suggests that the mechanism of signal transduction for alpha 1-adrenergic amines is not identical to that of the vasopressor peptides. alpha 1-Adrenergic stimulation of cyclic AMP accumulation was not detected in cells from hypothyroid rats. These data suggest that factors besides calcium and besides cAMP are probably involved in alpha 1-adrenergic actions. Metabolic responses to glucagon and to the cAMP analogue dibutyryl cAMP were not markedly changed during hypothyroidism, although cAMP accumulation produced by glucagon and beta-adrenergic agonists was enhanced. In hyperthyroidism, cell responsiveness to epinephrine, vasopressin, angiotensin II and glucagon was decreased, but sensitivity to cAMP was not markedly altered. The factors involved in this hyposensitivity to hormones during hyperthyroidism are unclear.     

Roles of alpha 1- 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 alpha 1-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 alpha 1-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 beta in the initial stages to later alpha 1. A similar transition seems to occur as the animal ages. Cyclic AMP accumulation in response to beta-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 beta-adrenergic sensitivity is probably related to the increased number of beta-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 alpha 1-adrenergic receptors did not change at any stage of the process, which indicates that the markedly diminished alpha 1-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 alpha 1-adrenergic signal, rather than to changes at the receptor level.     

Alterations in vascular endothelial function in the aorta and mesenteric artery in type II diabetic rats

We used the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create an experimental diabetic syndrome in adult rats that appears closer to type II diabetes mellitus than other available animal models. The dosage of 230 mg/kg of nicotinamide given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded animals with hyperglycemia (187.8 +/- 17.8 vs. 103.8 +/- 2.8 mg/dL in controls; P < 0.001) and preservation of plasma insulin levels. This study assessed the relationship between endothelial dysfunction and agonist-induced contractile responses in such rats. In the thoracic aorta, the acetylcholine (ACh) induced relaxation was significantly reduced and the noradrenaline (NA) induced contractile response was significantly increased in diabetic rats compared with age-matched control rats. In the superior mesenteric artery, the ACh-induced relaxation was similar in magnitude between diabetic and age-matched control rats; however, the ACh-induced endothelium-derived hyperpolarizing factor (EDHF) type relaxation was significantly weaker in diabetic rats than in the controls. The phenylephrine (PE) induced contractile response was not different between the two groups. The plasma concentration of NOx (NO2- + NO3-) was significantly lower in diabetic rats than in control rats. We conclude that vasomotor activities in conduit arteries are impaired in this type II diabetes model.     

Characterization of sarcolemma and sarcoplasmic reticulum isolated from skeletal muscle of the freeze tolerant wood frog, Rana sylvatica: the beta(2)-adrenergic receptor and calcium transport systems in control, frozen and thawed states

In freeze tolerant wood frog Rana sylvatica, the freeze-induced liberation of glucose plays a critical role in survival in response to sub-zero temperature exposure. We have shown that the glycaemic response is linked to selective changes in the expression of hepatic adrenergic receptors through which catecholamines act to produce their hepatic glycogenolytic effects. The purpose of the present study was to determine if skeletal muscle, another catecholamine-sensitive tissue with glycogenolytic potential, displayed similar or different changes. In order to achieve these objectives, skeletal muscle derived from Rana sylvatica was studied in control, frozen and thawed states. In isolated sarcolemmal fractions, freezing effected an 88% decrease in beta(2)-adrenergic receptor expression but was without effect on the calcium pump; while thawing resulted in a recovery of the beta(2)-adrenergic receptor to 60% of control levels and a 2.4-fold increase in calcium transport. In isolated sarcoplasmic reticular fractions, freezing effected a 52% decrease in calcium binding and a 92% decrease in oxalate-stimulated calcium uptake; while thawing elicited partial normalization to control levels to 70% with respect to calcium binding and to 47% with respect to calcium uptake. Freezing and thawing were associated with increases and decreases, receptively, in blood glucose levels but were without effect on skeletal muscle glycogen content. Thus these muscle changes in Rana sylvatica in freezing and thawing are not linked to glycogen breakdown, are different from those previously seen in liver, and may provide a role in recovery of muscle function during thawing by protecting glycogen stores for contraction and maximizing extracellular calcium for excitation-contraction coupling in the frozen state. The involvement of thyroid hormone in triggering these muscle changes is discussed.     

Compromised Wound Healing in Ischemic Type 2 Diabetic Rats

Ischemia is one of the main epidemic factors and characteristics of diabetic chronic wounds, and exerts a profound effect on wound healing. To explore the mechanism of and the cure for diabetic impaired wound healing, we established a type 2 diabetic rat model. We used an 8weeks high fat diet (HFD) feeding regimen followed by multiple injections of streptozotocin (STZ) at a dose of 10mg/kg to induce Wister rat to develop type 2 diabetes. Metabolic characteristics were assessed at the 5th week after the STZ injections to confirm the establishment of diabetes mellitus on the rodent model. A bipedicle flap, with length to width ratio 1.5, was performed on the back of the rat to make the flap area ischemic. Closure of excisional wounds on this bipedicle flap and related physiological and pathological changes were studied using histological, immunohistochemical, real time PCR and protein immunoblot approaches. Our results demonstrated that a combination of HFD feeding and a low dose of STZ is capable of inducing the rats to develop type 2 diabetes with noticeable insulin resistance, persistent hyperglycemia, moderate degree of insulinemia, as well as high serum cholesterol and high triglyceride levels. The excision wounds on the ischemic double pedicle flap showed deteriorative healing features comparing with non-ischemic diabetic wounds, including: delayed healing, exorbitant wound inflammatory response, excessive and prolonged ROS production and excessive production of MMPs. Our study suggested that HFD feeding combined with STZ injection could induce type 2 diabetes in rat. Our ischemic diabetic wound model is suitable for the investigation of human diabetic related wound repair; especically for diabetic chronic wounds.     

Involvement of AT(1) angiotensin receptors in the vasomodulatory effect of des-aspartate-angiotensin I in the rat renal vasculature

Angiotensin II is known to act primarily on the angiotensin AT(1) receptors to mediate its physiological and pathological actions. Des-aspartate-angiotensin I (DAA-I) is a bioactive angiotensin peptide and have been shown to have contrasting vascular actions to angiotensin II. Previous work in this laboratory has demonstrated an overwhelming vasodepressor modulation on angiotensin II-induced vasoconstriction by DAA-I. The present study investigated the involvement of the AT(1) receptor in the actions of DAA-I on angiotensin II-induced vascular actions in the renal vasculature of normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and streptozotocin (STZ)-induced diabetic rats. The findings revealed that the angiotensin receptor in rat kidney homogenate was mainly of the AT(1) subtype. The AT(1) receptor density was significantly higher in the kidney of the SHR. The increase in AT(1) receptor density was also confirmed by RT-PCR and Western blot analysis. In contrast, AT(1) receptor density was significantly reduced in the kidney of the streptozotocin-induced diabetic rat. Perfusion with 10(-9)M DAA-I reduced the AT(1) receptor density in the kidneys of WKY and SHR rats suggesting that the previously observed vasodepressor modulation of the nonapeptide could be due to down-regulation or internalization of AT(1) receptors. RT-PCR and Western blot analysis showed no significant changes in the content of AT(1) receptor mRNA and protein. This supports the suggestion that DAA-I causes internalization of AT(1) receptors. In the streptozotocin-induced diabetic rat, no significant changes in renal AT(1) receptor density and expression were seen when its kidneys were similarly perfused with DAA-I.     

Possible interaction of alpha 1-adrenergic receptor with pertussis-toxin-sensitive guanine-nucleotide-binding regulatory proteins (G proteins) responsible for phospholipase C activation in rat liver plasma membranes

Islet-activating protein (IAP; pertussis toxin) was employed to test the hypothesis that IAP-sensitive GTP-binding regulatory proteins (G proteins) are coupled with alpha 1-adrenergic receptor in rat liver plasma membranes. The high-affinity state of the binding of alpha 2-adrenergic agonist, which is known to be coupled with IAP-sensitive G protein, was abolished in IAP-treated plasma membranes. IAP treatment of plasma membranes could also diminish the high-affinity state of the alpha 1-adrenergic receptor for the agonist. Restoration of the high-affinity state of the alpha 1-adrenergic receptor for the agonist occurred on reconstitution of the bovine brain IAP-sensitive G proteins. The alpha 1-adrenergic receptor agonist stimulated inositol triphosphate (InsP3) production from [3H]inositol-labeled liver plasma membranes in a concentration-dependent manner. IAP treatment also decreased alpha 1-adrenergic-agonist-induced InsP3 production but not completely. From these results, we concluded that there is a possibility that both IAP-sensitive and IAP-insensitive G proteins were involved in alpha 1-adrenergic-receptor-stimulated phospholipase C activation in rat liver plasma membranes.     

Hepatic adrenergic receptors in the genetically diabetic C57 BL/KsJ (db/db) mouse

1. At 30 weeks of age, homozygote diabetic C57 BL KsJ (db/db) mice were grossly obese, lethargic and displayed moderate hair loss relative to heterozygote control C 57 BL KsJ (db/+) mice. 2. In diabetic mice, compared to control, the total body weights, liver weight: body weight ratios, and blood glucose levels were increased 2.3 fold, 20% and 3.1 fold, respectively. 3. Analysis of plasma membranes isolated from control and diabetic mouse liver established that comparable purity levels were achieved since relative specific activities of the plasma membrane markers 5'-nucleotidase and gamma-glutamyltranspeptidase were similar: 10.2 and 11.4 fold with respect to 5'-nucleotidase in control and diabetic states respectively; and 8.0 and 8.3 fold with respect to gamma-glutamyltranspeptidase in control and diabetic states respectively. 4. A select effect of diabetes on gamma-glutamyltranspepetidase, however, was observed. The activity of this enzyme was found to be reduced 16% in diabetic liver compared to control liver. 5. Assessment of [3H]prazosin and [3H]dihydrolalprenolol binding to mouse liver plasma membranes indicated that although there was no difference in beta-adrenergic receptor binding in control and diabetic states, alpha 1-adrenergic receptor binding was found to be reduced 43% in diabetic mouse liver plasma membranes. 6. Scatchard analyses of kinetic studies indicate that the reduction is a reflection of decreases in alpha 1-adrenergic receptor numbers with no change in alpha 1 receptor affinity in the diabetic state: since for diabetic and control liver plasma membranes, Kd values were 3.41 +/- 0.02 nM and 3.40 +/- 0.01 nM respectively; and Bmax were 650.12 +/- 16.44 fmol mg-1 and 380.76 +/- 12.92 fmol mg-1, respectively.     

Homologous and heterologous desensitization of one of the pathways of the alpha 1-adrenergic action. Effects of epinephrine, vasopressin, angiotensin II and phorbol 12-myristate 13-acetate

Activation of protein kinase C blocks the alpha 1-adrenergic action in hepatocytes. Preincubation of hepatocytes (in buffer with or without calcium) with vasopressin, angiotensin II, phorbol myristate acetate (PMA) or epinephrine + propranolol markedly diminished the alpha 1-adrenergic responsiveness of the cells (stimulation of ureagenesis) assayed in buffer without calcium. On the contrary, when the alpha 1-adrenergic responsiveness was assayed in buffer containing calcium no effect of the preincubation with vasopressin, angiotensin II or PMA was observed. Preincubation with epinephrine diminished the alpha 1-adrenergic responsiveness of the cells. In hepatocytes from hypothyroid rats the preincubation with the activators of protein kinase C (vasopressin, angiotensin II, phorbol 12-myristate 13-acetate and epinephrine) reduced markedly the alpha 1-adrenergic responsiveness of the cells, whereas in identical experiments using cells from adrenalectomized rats only the preincubation with epinephrine diminished the responsiveness. It is concluded that activation of protein kinase C induces desensitization of the alpha 1-adrenergic action in hepatocytes and that the calcium-independent pathway of the alpha 1-adrenergic action (predominant in cells from hypothyroid animals) resensitizes more slowly than the calcium-dependent pathway (predominant in cells from adrenalectomized rats). Epinephrine in addition to inducing this type of desensitization (through protein kinase C) leads to a further refractoriness of the cells towards alpha 1-adrenergic agonists.     

Alpha2 adrenergic and high affinity serotonergic receptor changes in the brain stem of streptozotocin-induced diabetic rats.

The brain stems (BS) of streptozotocin (STZ)-diabetic rats were studied to see the changes in neurotransmitter content and their receptor regulation. The norepinephrine (NE) content determined in the diabetic brain stems did not show an increase, while epinephrine (EPI) content increased significantly compared with control. The NE to EPI turnover showed a significant increase. The alpha2 adrenergic receptor kinetics revealed that the receptor affinity was significantly reduced during diabetes. In insulin treated rats the NE content decreased while EPI content remained increased as in the diabetic state. Insulin treatment increased the Bmax for alpha2 adrenergic receptors significantly while the increase in Kd reversed to normal. Unlabelled clonidine inhibited [3H]NE binding in BS of control diabetic and insulin treated diabetic rats showed that alpha2 adrenergic receptors consisted of two populations of binding sites with Hill slopes significantly away from unity. In diabetic animals the ligand bound weaker to the low affinity site than in controls. Insulin treatment reversed this alteration to control levels. The displacement analysis using (-)-epinephrine against [3H]yohimbine in control and diabetic animals revealed two populations of receptor affinity states. In control animals, when GTP analogue added with epinephrine, the curve fitted for a single affinity model; but in the diabetic BS this effect was not observed. In both the diabetic and control BS the effects of monovalent cations on affinity alterations were intact. Our data thus show that alpha2 adrenergic receptors have a reduced affinity due to an altered post receptor affinity regulation The serotonin (5-HT) content in the brain stem increased. Its precursor (5-hydroxy) tryptophan (5-HTP) showed an increase and its breakdown metabolite (5-hydroxy) indoleacetic acid (5-HIAA) showed a significant decrease. This showed that in serotonergic nerves there is a disturbance in both synthetic and breakdown pathways which lead to an increased 5-HT. The high affinity serotonin receptor numbers remained unaltered with a decrease in the receptor affinity. The insulin treatment reversed these altered serotonergic receptor kinetic parameters to control level. Thus our study shows a decreased serotonergic receptor function. These changes in adrenergic and serotonergic receptor function were suggested to be important in insulin function during STZ diabetes.     

Pharmacological characterization of alpha1- and beta-adrenergic synergism of 5'DII activity in rat brown adipocytes

The role of adrenoceptor subtypes was studied in rat brown adipose tissue (BAT). The type II 5'-deiodinase (5'DII) was activated in response to simultaneous stimulation by beta3- and alpha1-adrenergic agonists, BRL 37344 or CGP 12177, and cirazoline, in brown adipocytes. Inhibition of the alpha1- and beta-adrenergic phenylephrine-stimulated 5'DII activity was obtained by the alpha1-adrenergic antagonists in the order of prazosin >/= wb 4101 > 5-methylurapidil. In comparison, the binding of [3H]prazosin to rat BAT plasma membranes was inhibited by alpha1-adrenergic antagonists in the order of prazosin > WB 4101 = benoxathian > 5-methylurapidil. Although the order of the alpha1-adrenergic competition seemed to be rather typical for the alpha1B-adrenergic receptors, a molecular analysis on adrenoceptor mRNAs should be made to confirm the exact alpha1-adrenergic subtypes at the level of brown adipocytes, since the possibility of a mixture of different receptor subtypes in brown fat cells and/or tissue may interact with the pharmacological characterization. Thus, specific alpha1- and beta-adrenoceptor subtypes participate in the regulation of 5'DII activity in the rat brown adipocytes, and therefore, an impaired alpha1- and beta-adrenergic co-work may be involved in a defective BAT function, e.g., in obese Zucker rats, too. An interesting possibility is that the decreased number of alpha1-adrenoceptors in the BAT of obese Zucker rats is due to the decrease in the alpha1B-adrenoceptor subtype which would further be involved especially in the regulation of BAT 5'DII activity.     

Reciprocal expressions of alpha 1- and beta-adrenergic receptors, but constant expression of glucagon receptor by rat hepatocytes during development and primary culture

The stimulations of cyclic AMP formation and adenylate cyclase activity by glucagon and isoproterenol were both found to be highest in neonatal rat hepatocytes and to decrease during development. Adult hepatocytes still showed a considerable response to glucagon, but a negligible response to isoproterenol. The decrease in cyclic AMP formation during development can be explained in the case of the response to beta-adrenergic agonist as due to decrease of its receptor number, judging from binding of [125I]iodocyanopindolol to purified plasma membranes. But in the case of the glucagon response, the decrease in the response may be due to change of post-receptor components of the adenylate cyclase system, because the receptor number tended to increase during development, as shown by binding of [125I]iodoglucagon. Similarly, alpha 1-adrenergic receptors increased in number during development, but their IC50 value did not change, as measured by binding of [3H]prazosin to plasma membranes. Previous studies on primary cultures of adult rat hepatocytes showed that the beta-adrenergic response and its receptor number increased markedly during short-term culture (Nakamura, T., Tomomura, A., Noda, C., Shimoji, M., & Ichihara, A. (1983) J. Biol. Chem. 258, 9283-9289). However, in this work the amount of alpha 1-adrenergic receptor of adult rat hepatocytes was found to decrease by one third during 1-2 days culture. Therefore, changes of alpha 1- and beta-adrenergic receptors during development of rat liver and during primary culture of adult rat hepatocytes were reciprocal, although the directions of change in the two conditions were opposite. The additions of various hormones to primary cultures of adult rat hepatocytes did not affect the reciprocal changes of adrenergic receptors, suggesting that these hormones did not regulate the changes of the receptors.     

Role of catecholamines in the inhibitory effect of immobilization stress on testosterone secretion in rats

Immobilization stress applied for 6 h induced, in adult male rats, a rise of epinephrine (E) and norepinephrine (NE) plasma levels and a decrease of baseline plasma testosterone (T) values and of human chorionic gonadotropin (hCG)-induced T response. Treatment of the animals for 5 weeks with guanethidine (G), a sympathetic neuron toxic agent, significantly decreased E and NE responses to stress and partly antagonized the inhibitory effects exerted by immobilization on T biosynthesis. Adrenalectomy totally suppressed circulating E and reduced the stress-induced NE increase while partly antagonizing the inhibitory effects exerted on T biosynthesis. Combined G and adrenalectomy treatments totally suppressed plasma E and NE, and completely blocked the effects of immobilization on T levels. Treatment of the animals with the alpha 1-adrenergic blocker, prazosin, and the beta 1-adrenergic blocker, metoprolol, did not modify the effects of stress on T biosynthesis. Treatment with propranolol or with butoxamine, a nonspecific beta- and a specific beta 2-adrenergic receptor blocker, respectively, antagonized the testicular hyposensitivity to hCG induced by stress. Stress- or treatment-induced changes of plasma luteinizing hormone (LH) and hCG levels were not consistently correlated with plasma T modifications. These findings suggest that at least part of the inhibitory effects of immobilization stress on T biosynthesis is exerted by catecholamines through a beta 2-adrenergic receptor.     

Acute hyperglycemia induced by ketamine/xylazine anesthesia in rats: mechanisms and implications for preclinical models

The effects of anesthetic agents, commonly used in animal models, on blood glucose levels in fed and fasted rats were investigated. In fed Sprague-Dawley rats, ketamine (100 mg/kg)/xylazine (10 mg/kg) (KX) produced acute hyperglycemia (blood glucose 178.4 +/- 8.0 mg/dl) within 20 min. The baseline blood glucose levels (104.8 +/- 5.7 mg/dl) reached maximum levels (291.7 +/- 23.8 mg/dl) at 120 min. Ketamine alone did not elevate glucose levels in fed rats. Isoflurane also produced acute hyperglycemia similar to KX. Administration of pentobarbital sodium did not produce hyperglycemia in fed rats. In contrast, none of these anesthetic agents produced hyperglycemia in fasted rats. The acute hyperglycemic effect of KX in fed rats was associated with decreased plasma levels of insulin, adrenocorticotropic hormone (ACTH), and corticosterone and increased levels of glucagon and growth hormone (GH). The acute hyperglycemic response to KX was dose-dependently inhibited by the specific alpha2-adrenergic receptor antagonist yohimbine (1-4 mg/kg). KX-induced changes of glucoregulatory hormone levels such as insulin, GH, ACTH, and corticosterone were significantly altered by yohimbine, whereas the glucagon levels remained unaffected. In conclusion, the present study indicates that both KX and isoflurane produce acute hyperglycemia in fed rats. The effect of KX is mediated by modulation of the glucoregulatory hormones through stimulation of alpha2-adrenergic receptors. Pentobarbital sodium did not produce hyperglycemia in either fed or fasted rats. Based on these findings, it is suggested that caution needs to be taken when selecting anesthetic agents, and fed or fasted state of animals in studies of diabetic disease or other models where glucose and/or glucoregulatory hormone levels may influence outcome and thus interpretation. However, fed animals are of value when exploring the hyperglycemic response to anesthetic agents.     

Curcuminoids modulates oxidative damage and mitochondrial dysfunction in diabetic rat brain

Diabetes exacerbates neuronal injury induced by hyperglycemia mediated oxidative damage and mitochondrial dysfunction. The aim of the present study is to investigate the effects of curcuminoids, polyphenols of Curcuma longa (L.) on oxidative stress and mitochondrial impairment in the brain of streptozotocin (STZ)-induced diabetic rats. A marked increase in lipid peroxidation and nitrite levels with simultaneous decrease in endogenous antioxidant marker enzymes was observed in the diabetic rat brain, which was restored to normal levels on curcuminoids treatment. Down-regulation of mitochondrial complex I and IV activity caused by STZ induction was also up-regulated on oral administration of curcuminoids. Moreover, curcuminoids administration profoundly elevated the ATP level, which was earlier reduced in the diabetic brain. These results suggest that curcuminoids exhibit a protective effect by accelerating antioxidant defense mechanisms and attenuating mitochondrial dysfunction in the brain of diabetic rats. Curcuminoids thus may be used as a promising therapeutic agent in preventing and/or delaying the progression of diabetic complications in the brain.