Monoamines in pancreatic islets of guinea pig, hamster, rat, and mouse determined by high performance liquid chromatography

Previous studies on the occurrence of catecholamines and serotonin in pancreatic islets using various histochemical and chemical methods have given widely different results. We therefore performed a comparative analysis of these amines in whole pancreas and islet tissue from hamster, guinea pig, rat, and mouse by the use of high performance liquid chromatography. Whole pancreas of guinea pig, hamster, and rat had a norepinephrine concentration of approximately 1.1 mumol/kg of pancreatic wet weight. The mouse pancreas had less than one-half of that concentration. Epinephrine and dopamine concentrations were on the order of 0.02 mumol/kg of pancreatic wet weight in all four species. The serotonin concentration was 2.1 mumol/kg of pancreatic wet weight in the guinea pig pancreas and approximately 0.2 mumol/kg in the other three species studied. The catecholamine concentrations were much higher in the pancreatic islets than in the exocrine pancreas. Thus, the norepinephrine concentration was approximately 35 mumol/kg of islet wet weight in hamster islets and 5-10 mumol/kg in rat, guinea pig, and mouse islets. The epinephrine concentration in islet tissue ranged between 1 and 7 mumol/kg of islet wet weight and the dopamine concentration between 0.5 and 4 mumol/kg except for guinea pig islets (12 mumol/kg). The islet tissue in the mouse, rat, and guinea pig contained disproportionately more epinephrine and dopamine relative to norepinephrine than did the exocrine pancreas. Chemical sympathectomy (6-hydroxydopamine treatment) in the mouse reduced the norepinephrine and epinephrine concentrations in islet tissue to nondetectable levels, whereas the dopamine concentration was essentially unchanged, thus suggesting an extra-neuronal source of this amine in addition to its occurrence in adrenergic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Therapy of malignant hamster insulinomas with monoamine precursors

Summary The hyperinsulinaemia and hypoglycaemia produced by malignant insulinomas pose a difficult therapeutic problem. The non-polar monoamine precursors 5-hydroxytryptophan, L-3,4-dihydroxyphenylalanine and DL-threo-dihydroxyphenylserine are readily taken up by normal hamster pancreatic islets and are converted intracellularly to serotonin, dopamine and norepinephrine. These intracellular monoamines then inhibit glucose-stimulated insulin secretion. In the present study we have determined if the monoamine oxidase inhibitor pargyline, and monoamine precursors, could modify the severe hypoglycaemia of hamsters bearing a rapidly growing transplantable insulinoma. One hour after receiving the respective precursor there was an 11, 18, and 54-fold increase in the concentration of serotonin, dopamine or norepinephrine in the insulinomas. Twenty four hours after the administration of the respective precursors there were the following increases in plasma glucose in the respective groups: 5-hydroxytryptophan, 1.9 ± 0.5 to 4.9 ± 0.3 mmol/l (mean ± SEM); L-3,4-dihydroxyphenylalanine, 1.5 ± 0.3 to 3.4 ± 0.6 mmol/l; and DL-threo-dihydroxyphenylserine, 1.5 ± 0.2 to 6.4 ± 0.7 mmol/l. The change in plasma insulin concentration was statistically significant only in the group receiving DL-threo-dihydroxyphenylserine (229 ± 59 to 81 ± 42 mU/l). To determine if this therapeutic approach could modify the rapidly fatal outcome of the tumour-bearing hamsters, they received 0.154 mol/l saline, DL-threo-dihydroxyphenylserine or pargyline plus DL-threo-dihydroxyphenylserine every two days. The survival of the groups (mean ± SEM) was: saline 8.4 ± 1.1 d; DL-threo-dihydroxyphenylserine 17.9 ± 3.5 d; and pargyline plus DL-threo-dihydroxyphenylserine 24.4 ± 5.5 d. The present study suggests that increasing the monoamine content of malignant insulinomas may favourably modify the course of these devastating tumours.     

Effect of pharmacological agents and fasting on pancreatic islet norepinephrine in the golden hamster

Summary Using a specific and sensitive radioenzymatic assay that utilizes the partially purified enzyme phenylethanolamine-N-methyltransferase, studies were done to determine if pharmacological agents and/or fasting alter the norepinephrine concentration of collagenase-isolated golden hamster pancreatic islets. The norepinephrine concentration (42.1±8.07 mol/kg net weight, mean±SEM) and the monoamine oxidase activity (5,407±530 pmol product /mg tissue/min) of hamster pancreatic islets was at least five times higher than acinar pancreas, kidney, heart, median eminence or cerebral cortex. The catechol-o-methyltransferase activity of hamster islets (7±2.3 pmol product/mg tissue/min) was one half or less than the other tissues. Islet norepinephrine was not increased by two days administration of the monoamine oxidase inhibitor tranylcypromine. Islet norepinephrine concentration was increased 2-fold by administration of the norepinephrine precursor DL-threo-dihydroxyphenylserine.This increase was enhanced by prior administration of tranylcypromine (3.5-fold) and prevented by prior administration of the decarboxylase inhibitor N¹-(DL-seryl)-N²-(2,3,4-trihydroxybenzyl) hydrazine (RO-4-4602). There was a good correlation between the islet norepinephrine concentration and the plasma glucose concentration after pharmacological agents. Reserpine administration markedly depleted the islet norepinephrine concentra tion. Fasting of 24, 48 and 72 h did not alter the norepinephrine concentration in islets and heart. It is concluded that the pancreatic islets of the hamster have an active noradrenergic system, but that islet norepinephrine does not appear to play an important role in the impaired insulin secretion of fasting hamsters.     

Effect of increased pancreatic islet norepinephrine,dopamine and serotonin concentration on insulin secretion in the Golden hamster

Summary The purpose of this study was to determine if increased concentrations of pancreatic islet norepinephrine, dopamine, or serotonin alter insulin secretion. Golden hamsters received intraperitoneal injections of the norepinephrine precursor DL-threo-dihydroxyphenylserine, the dopamine precursor L-3,4-dihydroxyphenylalanine, or the serotonin precursor 5-hydroxytryptophan with and without pretreatment of the hamsters with the monoamine oxidase inhibitor tranylcypromine. Administration of the monoamine precursors to animals pretreated with tranylcypromine resulted in a mean increase in plasma glucose of 192% and a mean decrease in plasma insulin of 58%. Using a collagenase isolation technique, islets from control and treated animals were evaluated for monoamine content and insulin secretory capacity. The monoamine concentrations in control islets, in mol/kg wet weight, were: norepinephrine 42±8; dopamine 8±2; and serotonin 26±9. Administration of the appropriate precursor to control hamsters resulted in a 1.9-fold (norepinephrine), 6-fold (dopamine), and 22-fold (serotonin) increase in monoamines. There was no alteration in the glucose (16.3 mmol/l)-stimulated in vitro insulin secretion from islets obtained from these hamsters. Administration of the precursors to hamsters pretreated with tranylcypromine resulted in a 3.5-fold (norepinephrine), 22-fold (dopamine), and 59-fold (serotonin) increase in monoamines. Glucose-stimulated in vitro insulin secretion from islets obtained from these hamsters was completely blocked. This study suggests that high concentrations of norepinephrine, dopamine, and serotonin in the pancreatic islets can decrease glucose-stimulated insulin secretion.     

Evolutionary conservation of the insulinoma gene rig and its possible function.

We have identified a gene, rig (rat insulinoma gene), that is activated in chemically induced rat insulinomas but not in normal pancreatic islets or in regenerating islets. In the present study, we have found that the insulinoma gene was activated in a BK virus-induced hamster insulinoma cell line and in a spontaneously occurring human insulinoma. From the hamster and human insulinoma cDNA libraries, rig homologues were isolated, and their nucleotide sequences were determined. In the same manner as the rat gene, both hamster and human homologues contained one open reading frame of 435 nucleotides, differing by 32- and 41-base substitutions, respectively. All the base substitutions were same-sense mutations. Accordingly, the deduced 145-amino acid sequence remained invariant in hamster, human, and rat insulinomas, suggesting that rig has evolved under extraordinarily strong selective constraints. Computerized structure analysis indicated that rig-encoded protein is a possible DNA-binding protein. The antisense oligodeoxyribonucleotide complementary to hamster rig mRNA was synthesized and injected into the hamster insulinoma cells. The antisense rig oligodeoxyribonucleotide inhibited DNA synthesis in the insulinoma cells, whereas the sense rig oligodeoxyribonucleotide or antisense insulin oligodeoxyribonucleotide had no inhibitory effect. These results strongly suggest that the activation of rig is both common and potentially significant in the oncogenic growth of pancreatic B cells of islets of Langerhans.     

Effect of L-dopa administration on islet monoamine oxidase activity and glucose-induced insulin release in the mouse

Previous studies have shown that the amine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) is rapidly converted to its corresponding amine, dopamine, in islet beta-cells. In the present investigation, we studied the effect of acute L-DOPA administration on islet monoamine oxidase (MAO) activity and on glucose-induced insulin secretory response in mice. It was observed that at 2 min after intravenous L-DOPA administration, there was a marked increase (+35%) in islet MAO activity, with serotonin as substrate. At 7 min, MAO activity towards dopamine was enhanced by 32% and that towards serotonin and phenylethylamine (PEA) was decreased by 23 and 25%, respectively. The inhibitor of L-aromatic amino acid decarboxylase, benserazide, abolished L-DOPA-induced changes of MAO activity, suggesting that the formed dopamine, and not L-DOPA itself, was responsible for the observed effects. At 60 min, no effect by L-DOPA administration on islet MAO activity was noticed. L-DOPA (125 or 250 mumol/kg), given together with glucose, induced a decrease in glucose-induced insulin response. L-DOPA (125 mumol/kg), given 7 min before glucose, totally suppressed glucose-induced insulin response. This inhibition was eliminated through pretreatment with benserazide. Enhancement of glucose-stimulated insulin response, after deposition of horseradish peroxidase (HRP) in beta-cell vacuolar system, was suppressed by L-DOPA. We conclude that acute L-DOPA-induced dopamine accumulation in pancreatic islets is accompanied by rapid changes in MAO activity, concomitant with an inhibitory effect on glucose-stimulated insulin response. Increased hydrogen peroxide production, following increased MAO activity, may possibly augment the inhibitory effect of dopamine accumulation on insulin release.     

Chronic exposure to glibenclamide impairs insulin secretion in isolated rat pancreatic islets

We investigated the effect of 24 h exposure to 100 nmol/l glibenclamide on insulin secretion in isolated rat pancreatic islets. The insulin content was similar in control islets and in islets preincubated with 100 nmol/l glibenclamide for 24 h. In islets preexposed to glibenclamide: 1) the subsequent response to a maximal glibenclamide stimulatory concentration (10 mumol/l, 1 h at 37 C) was greatly reduced in comparison to control islets (0.69 +/- 0.20% vs 2.16 +/- 0.41%; mean +/- SE; n = 14; p less than 0.001); 2) the response to 100 mumol/l tolbutamide stimulation was also reduced (0.55 +/- 0.15% vs 2.38 +/- 0.44%; n = 8; p less than 0.001); 3) the response to 16.7 mmo/l glucose, both in the presence or in the absence of 1 mmol/l IBMX, a phosphodiesterase inhibitor, was also diminished by about 50% (1.79 +/- 0.39% vs. 3.22 +/- 0.42%; n = 14, p less than 0.001). In glibenclamide pretreated islets, blunted responses to stimuli were confirmed also by dynamic studies using a perifusion system. The effect of glibenclamide preincubation was fully reversible: when islets cultured in the presence of glibenclamide were transferred to a glibenclamide-free medium for further 24 h, insulin release in response to glibenclamide stimulation returned to control values. We conclude that prolonged exposure of rat pancreatic islets to glibenclamide induces a reversible desensitization to a variety of metabolic stimuli. The inhibition by prolonged glibenclamide exposure of a common pathway in the mechanism of insulin release is one possible explanation for these results.     

Comparison of the Effects of β-Adrenergic Agents on Pineal Serotonin N-Acetyltransferase Activity and Melatonin Content in Two Species of Hamsters

The nighttime rise in pineal melatonin levels can be blocked by administration of the β-adrenergic receptor antagonist, propranolol, in both Syrian hamsters and rats. Although the administration of β-adrenergic receptor agonists such as norepinephrine or isoproterenol stimulates pineal melatonin production in the rat, these drugs are without apparent effect on indole production in the Syrian hamster. To determine whether this lack of stimulatory effect in the Syrian hamster is characteristic of this species, a comparison of the effects of norepinephrine and isoproterenol on pineal serotonin N-acetyltransferase activity and melatonin content was conducted. In contrast to their lack of effect in the Syrian hamster, norepinephrine and isoproterenol stimulated pineal serotonin N-acetyltransferase activity and melatonin content in the Djungarian hamster. Hourly injection of norepinephrine during a continuation of light into the normal dark period stimulated increases in the activity of serotonin N-acetyltransferase and melatonin content in the Djungarian hamster but was without effect on these pineal parameters in the Syrian hamster.     

Effect of diabetes mellitus and chemical sympathectomy on tissue monoamine oxidase activity and norepinephrine concentration in the golden hamster

The pancreatic islets of the golden hamster have an extremely high monoamine oxidase (MAO) activity and norepinephrine (NE) concentration. To determine the cellular component responsible for these high values, we assayed MAO activity and NE concentration in collagenase-isolated islets from normal, streptozotocin-induced diabetic, and 6-hydroxydopamine (6-OHDA) induced sympathectomized golden hamsters. There was a 53% reduction in islet MAO activity in the diabetic hamsters, with no alteration in islet MAO activity in the sympathectomized ones, suggesting that the pancreatic B cells contain a large proportion of the MAO activity. There was a 98% reduction in islet NE concentration in the sympathectomized hamsters, with no alteration in islet NE concentration in the diabetic hamsters, suggesting that the adrenergic nerve endings in the islets contain the majority of the NE. There was no alteration in the MAO activity or NE concentration in the cerebral cortex, pituitary gland, liver, kidney, acinar pancreas, or heart of diabetic hamsters. Although the MAO activity of the hypothalamus was not altered, the diabetic hamsters had a 166% increase in NE and a 199% increase in dopamine in their hypothalamus, with no change in these amines in their cerebral cortex.     

Cardiovascular responses to serotonin in experimental liver disease

Recent evidence suggests that serotonergic mechanisms within the cardiovascular system are activated and may be important in the development of the hyperkinetic circulation and the maintenance of portal hypertension in cirrhotic patients. The in vivo pressor and positive chronotropic response together with the in vitro contractile responses of aortic rings and portal veins to serotonin were studied in three different rat models of cirrhosis, portal hypertension and jaundice: the portal vein-ligated rat, the carbon tetrachloride-induced cirrhotic rat, the chronic bile duct-ligated cirrhotic rat and the 3-day noncirrhotic, nonportal hypertensive-jaundiced rat. In addition, the activity of the enzyme monoamine oxidase type A was determined in lung homogenates prepared from the four groups of sham and treated animals. In the four different groups of sham-treated or operated pithed rats, serotonin caused a dose-dependent increase in mean arterial blood pressure without any effect on the heart rate. The pressor responses to serotonin in the three models of portal hypertension were significantly attenuated from their respective sham group. In the 3-day noncirrhotic, nonportal hypertensive-jaundiced rats, the pressor response was no different than that seen in the sham-operated rats. No evidence of consistent potentiated or blunted in vitro reactivity to serotonin of arterial rings and portal veins from the four groups of rats was seen. Portal hypertension, cirrhosis and hyperbilirubinemia had no effect on the activity of monoamine oxidase type A. These data demonstrate that portal hypertension is associated with an attenuated pressor response to serotonin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extraneuronal enzymatic degradation of myocardial interstitial norepinephrine in the ischemic region

OBJECTIVE: Catechol O-methyltransferase (COMT) is believed to exert degradative action at high norepinephrine (NE) levels. Although COMT exists in cardiac tissues, the contribution of cardiac COMT activity to regional NE kinetics, particularly in ischemia-induced NE accumulation, remains unclear. We investigated the role of cardiac COMT in NE kinetics in the ischemic region. METHODS: We implanted a microdialysis probe into the left ventricular myocardium of anesthetized rabbits and induced myocardial ischemia by 60-min coronary artery occlusion. We monitored myocardial interstitial levels of NE and its metabolites in the presence and absence of a COMT inhibitor. We intraperitoneally administered entacapone (10 mg/kg) 120 min before control sampling. RESULTS: In control, entacapone increased interstitial dihydroxyphenylglycol (DHPG, intraneuronal NE metabolite by monoamine oxidase (MAO)) levels and decreased interstitial normetanephrine (NMN, extraneuronal NE metabolite by COMT) and 3-methoxy-4-hydroxyphenylglycol (MHPG, extraneuronal DHPG metabolite by COMT) levels, but did not change interstitial NE levels. Coronary occlusion increased NE levels to 165+/-48 nM at 45-60 min of occlusion. This increase was accompanied by increases in DHPG and NMN levels (11.3+/-1.1 and 9.3+/-1.3 nM at 45-60 min of occlusion). Entacapone augmented the ischemia-induced NE and DHPG responses (333+/-51 and 22.9+/-2.4 nM at 45-60 min of occlusion). In contrast, the ischemia-induced NMN response was suppressed by entacapone (2.0+/-0.4 nM at 45-60 min of occlusion). Reperfusion decreased interstitial NE levels and increased interstitial DHPG and NMN levels. Entacapone suppressed changes in NE and NMN levels, but augmented the increase in dialysate DHPG. CONCLUSION: Myocardial ischemia evoked increases in myocardial interstitial NE and NMN levels. COMT inhibition augmented the increase in NE (substrate of COMT) levels and suppressed the increase in NMN (metabolite by COMT) levels. In the ischemic heart, COMT contributes to the removal of accumulated NE in the myocardium.     

Effect of Selective Monoamine Oxidase Inhibitors on Rat Pineal Melatonin Synthesis In Vitro

Freshly cultured pineal glands respond to the monoamine oxidase A (MAO A) inhibitor clorgyline and to high concentrations of the MAO B inhibitor, deprenyl, with an increase in serotonin N-acetyltransferase activity and N-acetylated indoles and a fall in 5-hydroxylated serotonin degradation products. Glands cultured for 48 hours before challenge respond less. Response is absent in glands cultured for 72 hours and in glands from ganglionectomized animals cultured for 48 hours before challenge. These data are consistent with the hypothesis that these MAO inhibitors stimulate melatonin synthesis by protecting norepinephrine from degradation.     

A somatostatin analogue inhibits chondrosarcoma and insulinoma tumour growth

The in vivo effects on tumour growth of a potent somatostatin analogue, SMS 201-995 [H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-(ol)], were measured in two characterised transplantable tumours: a) the Swarm rat chondrosarcoma, known to be insulin-, growth hormone (GH)-, somatomedin- and corticosteroid-dependent, b) a hamster insulinoma, bearing specific high affinity somatostatin receptors. SMS 201-995 (1.25 mg/kg/day) given for 25 days to rats bearing freshly transplanted chondrosarcomas inhibited tumour volume by 48%. A significant tumour growth inhibition was measured also in well developed tumours treated with high doses of SMS 201-995 (1.25mg/kg/day) for 7 days. In the treated animals, GH was significantly inhibited. In hamsters bearing a freshly transplanted insulinoma, the daily application of SMS 201-995 (200 micrograms/kg/day, sc) for 33 days could significantly inhibit the growth (as measured by tumour volume) of the tumour. A moderate inhibitory effect of SMS 201-995 on the growth of well grown insulinomas could also be observed. This study shows that SMS 201-995 under the present experimental conditions has a moderate but significant growth inhibitory effect in two different transplantable tumour models. In the rat chondrosarcoma, the effect of SMS 201-995 is probably indirect, due to inhibition of GH, somatomedin and insulin. In the hamster insulinoma, the effect is possibly due to a more direct action of SMS 201-995 on specific somatostatin receptors present in this tumour.     

Effect of various doses of medroxyprogesterone acetate on intestinal functions in rats

The dose relationship between medroxyprogesterone acetate (MPA), a long acting contraceptive, and rat intestinal digestive and absorptive functions has been investigated. The study revealed that the activities of brush border sucrase, lactase and leucine aminopeptidase were stimulated only at high doses, viz 70 mg/kg (180 mumol/kg) body weight and above, whereas the activity of alkaline phosphate was depressed at comparatively low dose (17.5 mg/kg; 45 mumol/kg body weight). This decrease was found to be significant (p less than 0.001) at all the doses tested. The inhibition in the intestinal uptake of calcium paralleled the decrease in alkaline phosphatase activity. Relatively high amount of MPA (140 mg/kg; 360 mumol/kg) was required to augment the uptake of glucose and amino acid. The results obtained do not indicate a close relationship between the dose of the drug and the extent of alteration in the rat intestinal digestive and absorptive functions. The study appears to confirm the association between brush border enzymes activities and uptake of nutrients in rat intestine.     

Abnormal hepatic uptake of low doses of sulfobromophthalein in Gilbert's syndrome: the role of reduced affinity of the plasma membrane carrier of organic anions

The plasma disappearance rate of sulfobromophthalein (VBSP; mumol/kg/min) was measured in 15 Gilbert's syndrome patients and 12 control subjects after intravenous injection of two different doses (0.59 and 5.90 mumol/kg) of the dye. Plasma disappearance rate was significantly reduced in Gilbert's syndrome patients after administration of 0.59 mumol sulfobromophthalein/kg (0.119 +/- 0.016 vs. 0.146 +/- 0.018 mumol/kg/min; mean +/- S.D.; p less than 0.001), whereas no difference was found with the higher dose (0.754 +/- 0.040 vs. 0.767 +/- 0.072 mumol/kg/min). Significant reduction was also found after administration to four Gilbert's syndrome patients and four control subjects of 0.29 and 2.95 mumol sulfobromophthalein (0.060 +/- 0.005 mumol/kg/min vs. 0.077 +/- 0.07 mumol/kg/min and 0.480 +/- 0.012 mumol/kg/min vs. 0.591 +/- 0.015 mumol/kg/min, respectively; p less than 0.01). Competition studies with combined administration of sulfobromophthalein (0.59 mumol/kg) and different doses of rifamycin SV (0.59, 1.47 and 2.95 mumol/kg) showed a significant (p less than 0.001) reduction in plasma disappearance rate in Gilbert's syndrome patients but not in controls. The rifamycin SV dose at which a 50% inhibition in plasma disappearance rate was observed was 0.8 mumol/kg. The apparent affinity (Km) of the hepatic transport was higher in Gilbert's syndrome patients than in control subjects (3.61 +/- 0.37 mumol sulfobromophthalein/kg vs. 2.76 +/- 0.29 mumol sulfobromophthalein/kg, mean +/- S.D.; p less than 0.01), whereas no difference was found in Vmax (0.95 +/- 0.11 mumol sulfobromophthalein/kg vs. 0.93 +/- 0.10 mumol sulfobromophthalein/kg/min, mean +/- S.D.; N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Rat thyroid monoamine oxidase (MAO) is regulated by thyrotrophin: evidence that the main form of the enzyme (MAO-A) is not directly involved in iodide organification.

The characteristics and regulation of monoamine oxidase (MAO) were studied in rat thyroid tissue. A measured Michaelis constant (Km) value of 102 mumol/l was similar to the Km values found in other tissues. Maximal velocity (Vmax) was 1.028 nmol/mg protein per min. It is known that MAO is present as two isoenzymes, A and B, which are sensitive to clorgyline and deprenyl respectively. The in-vitro effect of graded concentrations of these selective MAO inhibitors was used to estimate the relative proportion of A and B isoenzymes. Clorgyline strongly decreased thyroid MAO activity at concentrations as low as 1 pmol/l while the effect of deprenyl was observed only at concentrations higher than 10 mumol/l. These results indicated that MAO-A is the main form of the enzyme in the rat thyroid. In-vivo administration of L-thyroxine (5.6-224 nmol/kg) significantly reduced thyroid MAO activity at doses equal to or greater than those which have been reported to inhibit iodine output from the thyroid. Increased TSH levels, induced either by exogenous TSH or methimazole administration, resulted in a significant increase in thyroid MAO activity. Theophylline, a phosphodiesterase inhibitor and dibutyryl cyclic AMP were also able to stimulate MAO activity when administered in vivo. Iodide organification (protein-bound 131I) in vivo as well as the relative proportion of the different thyroid iodo-compounds were not affected in animals with reduced or increased thyroid MAO activity induced by clorgyline or theophylline respectively. It was concluded that rat thyroid MAO activity is under the influence of TSH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serotonin coexists with epinephrine in rat adrenal medullary cells

Immunoreactive serotonin is demonstrated to be present in 75% of rat adrenal medullary cells using an antibody to serotonin and peroxidase-antiperoxidase immunocytochemical method. The concentration of serotonin in rat adrenals was found to be 7.7 +/- 0.1 X 10(-6) mol/kg wet weight by high-performance liquid chromatography with electrochemical detection. Drugs that block serotonin synthesis (p-chlorophenylalanine) or deplete biogenic amines (reserpine) diminish immunostaining. The serotonin precursor L-tryptophan and pargyline, a monoamine oxidase inhibitor, augment staining in reserpine-depleted adrenals. Serotonin is localized in those medullary cells which contain phenylethanolamine-N-methyltransferase, an enzyme which is necessary for the synthesis of epinephrine. We conclude, therefore, that serotonin coexists with epinephrine in rat adrenal medullary chromaffin cells. These results suggest that the adrenal medulla may play a major role in the metabolism of serotonin.     

Inhibitory effect of streptozotocin on tumor development in transgenic mice bearing an elastase I-SV40 T-antigen fusion gene.

Transgenic mice, bearing a fusion gene of rat elastase I promoter and SV40 T-antigen, developed acinar cell tumors of the pancreas, as predicted by the model. In addition, they developed insulinomas and somatostatin (delta)-cell hyperplasia of the pancreatic islets. The insulinomas and the delta-cell hyperplasia appeared to be functional, as evidenced by changes in plasma glucose, insulin, and somatostatin. Streptozotocin, which has been shown to inhibit pancreatic carcinogenesis in the hamster model, significantly reduced the numbers of insulinomas and delta-cell hyperplasias. Streptozotocin did not cause a statistically significant reduction in exocrine tumors.     

Effect of DOV 102,677 on the volitional consumption of ethanol by Myers' high ethanol-preferring rat

BACKGROUND: Inhibitors of monoamine neurotransmitter transporters are well established as antidepressants. However, the evidence that single (serotonin) or dual (serotonin-norepinephrine) neurotransmitter uptake inhibitors can treat ethanol abuse, either as a comorbidity with depression or as a separate entity, is inconsistent. Drugs that have, in addition, the ability to inhibit dopamine uptake may have an advantage in the treatment of alcohol abuse. Therefore, the inhibitor of norepinephrine, serotonin and dopamine uptake, DOV 102,677, was tested for its effects on the volitional consumption of ethanol by an ethanol-preferring rat strain. METHODS: Myers' high ethanol-preferring rats were screened by a 10-day, 3 to 30% step-up test and then given free access to the preferred concentration of ethanol in a 3-bottle choice task. Consumption of ethanol (g/kg), water, food, and body weight were measured daily during a 3-day predrug treatment period, a 3-day treatment period, and a 3-day posttreatment period. Additional Sprague-Dawley rats were observed for 24 hours for the behavioral effects of 2.0 mg/kg s.c. reserpine after a 30-minute pretreatment with different doses of DOV 102,677. RESULTS: The triple monoamine uptake inhibitor DOV 102,677 dose-dependently decreased the volitional consumption of ethanol by as much as 71.2% (20 mg/kg i.p., b.i.d.) over 3 days of administration. This effect carried over into the posttreatment period. Similarly, the proportion of ethanol to total fluids consumed declined by 66.2% (20 mg/kg s.c., b.i.d.), while food consumption and body weight were unaltered. In contrast, amperozide (2 mg/kg i.p., b.i.d.) suppressed the amount of ethanol consumed by 56%, while naltrexone (5 mg/kg i.p., b.i.d.) was without effect. DOV 102,677 (40 mg/kg s.c.) inhibited reserpine-induced akinesia and ptosis, but not hypothermia in Sprague-Dawley rats, consistent with its transient inhibition of serotonin transport, and more long-lived inhibition of norepinephrine and dopamine uptake. CONCLUSIONS: DOV 102,677 significantly decreased the volitional consumption of ethanol with minimal alterations in the intake of food or on body weight in an ethanol-preferring rat strain, suggesting that triple reuptake inhibitors may find utility in treating alcohol abuse.     

Lactate transport in insulin-secreting beta-cells: contrast between rat islets and HIT-T15 insulinoma cells.

The transport of L- and D-lactate into rat pancreatic islets and HIT-T15 insulinoma cells was studied by measuring uptake of 14C-labelled substrate at room temperature and by following changes in intracellular pH (pHi) in islets and HIT-T15 cells loaded with 2',7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF). Uptake of L-lactate into HIT-T15 cells was rapid, reaching equilibrium after 5 min with an apparent Km value of 4.8 mM. Transport was markedly inhibited by alpha-cyano-4-hydroxycinnamate, alpha-fluorocinnamate, quercetin and p-chloromercuribenzenesulphonate (pCMBS), and was enhanced in citrate medium. Uptake of D-lactate was less rapid, apparent equilibrium not being reached within 10 min. In contrast to HIT-T15 cells, rat pancreatic islets showed greatly reduced rates of transport of L- and D-lactate together with a correspondingly lower degree of inhibition by alpha-cyano-4-hydroxycinnamate. The addition of L- or D-lactate to HIT-T15 cells, but not dispersed islet cells, resulted in a marked and rapid intracellular acidification followed by a gradual recovery. In both HIT-T15 cells and isolated islets, the rates of transport of both L- and D-lactate in the presence of alpha-cyano-4-hydroxycinnamate were significantly greater in a depolarising K+ medium compared to the normal Na+ medium. These observations suggest that native rat islet cells have considerably reduced activity of the lactate-/H+ transport system compared to HIT-T15 insulinoma cells. There is evidence in both cell types of an additional electrogenic pathway for lactate which might play a role in coupling lactate efflux to beta-cell depolarisation.