A possible role for protein kinase C in the regulatory differences between intra-abdominal and subcutaneous human adipose tissue

1. The adenosine A1-receptor agonist N6-(phenylisopropyl)adenosine inhibited lipolysis in a dose-dependent manner in human adipocytes. The effect is mediated by the inhibitory guanine-nucleotide-binding protein(s) that can be phosphorylated and thereby inactivated by protein kinase C. 2. Stimulation of protein kinase C by 12-O-tetradecanoyl-phorbol-13-acetate attenuated the inhibitory effect of the adenosine agonist. 3. Omental fat cells are less sensitive to adenosine than subcutaneous cells, although the stimulatory arm of cyclase regulation appears normal. Protein kinase C activity was measured in the soluble and particulate fractions of human omental and subcutaneous adipose tissue. Omental adipose tissue had a twofold higher membrane-bound and a threefold higher soluble protein kinase C activity. 4. It is therefore possible that the differences in regulation between the two sites are caused by different C kinase activities, causing variable phosphorylation of the inhibitory guanine-nucleotide-binding protein(s).

Role of omega-conotoxin GVIA-sensitive Ca2+ entry in angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding in bovine adrenal medullary cells

The relative contributions of Ca2+ influx and intracellular Ca2+ mobilization were examined for angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding, which reflects the level of activated protein kinase C in bovine chromaffin cells. Angiotensin II receptors activate phospholipase C in chromaffin cells, leading to a short-lived mobilization of intracellular Ca2+. Angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding was largely blocked in Ca(2+)-free buffer and by pretreatment with the Ca(2+)-channel blocker omega-conotoxin GVIA. The [3H]phorbol 12,13-dibutyrate binding response to [Sar1]angiotensin II also appeared to be voltage sensitive, as no additivity was observed with the response to the depolarizing agent 4-aminopyridine (3 mM). Threshold sensitivities of the extra- and intracellular Ca(2+)-mobilizing pathways to angiotensin II were similar, and all examined effects of angiotensin II in these cells were apparently mediated by losartan-sensitive (AT1-like) receptors. The dependence of angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding on extracellular Ca2+ entry, in contrast to stimulation by other phospholipase C-linked receptor agonists (bradykinin and methacholine), suggests that angiotensin II preferentially stimulates protein kinase C translocation to the plasma membrane, rather than to internal membranes, in bovine adrenal medullary cells.

Biphasic generation of diacylglycerol by angiotensin and phorbol ester in bovine adrenal chromaffin cells

Stimulation of angiotensin receptors in bovine adrenal medullary cells with Sar1-angiotensin II increased diacylglycerol levels in a biphasic fashion. An initial peak occurred at 3 min and an increase was observed again at 60 min and even at 18 hrs. Phorbol 12-myristate 13-acetate produced a similar pattern of increase in diacylglycerol levels. Both the angiotensin analog and the phorbol ester also increased the release of (3H)choline into the culture medium from prelabelled cells. The long-term diacylglycerol production could be derived from phosphatidylcholine rather than from the phosphoinositides. The latter may be the source of the angiotensin stimulated initial production of diacylglycerol and activation of PKC. Activated PKC then turns on the continuous production of DAG which maintains PKC in an active state for long periods of time in the presence of the peptide.

Characterization of dynorphin-containing neurons on dissociated dentate gyrus cell cultures

In the dentate gyrus, the synthesis of the opioid peptide, dynorphin, is modulated by a variety of stimuli. In order to elucidate the cellular and molecular mechanisms regulating the synthesis of dynorphin in the hippocampus, we have established a routine primary cell culture of dentate granule neurons and identified granule-like neurons by a characteristic marker, dynorphin, in these cultures. Cultures were prepared from 7-day-old rat pups and maintained in medium with 2% fetal bovine serum. These cultures contained approximately 20% neurons and survived for over 4 weeks. After 2 weeks in culture, neurons expressing dynorphin-A and its messenger RNA were detected using immunocytochemistry and in situ hybridization, respectively. In dentate cultures, enkephalin-, cholecystokinin-, neuropeptide Y- and substance P-positive cells were observed in addition to dynorphin-positive cells with immunocytochemistry. The results suggest that dentate gyrus cell cultures provide a valid in vitro model for studying molecular mechanisms regulating prodynorphin gene expression.

Development of tolerance to the hormonal effects of morphine without changes in the aminergic functions in the brain of the rat

The effect of morphine on cold-stimulated secretion of TSH and prolactin was studied in male rats, both in acute studies and after the chronic administration of morphine for 14 days (twice a day with increasing doses). The duration of the stimulatory effect of a single dose of morphine on secretion of prolactin was shorter (less than 2 hr) than its inhibitory effect on cold-stimulated secretion of TSH (over 2 hr). In the rats pretreated with morphine, a tolerance to the depressant effect of TSH of the challenge dose of morphine was seen at 2 hr but not at 1 hr after the injection. In contrast, a tolerance to the stimulatory effect of morphine on prolactin was seen at 1 hr after the acute dose of morphine. The minor alterations of the hypothalamic amine neurotransmitters and their metabolites did not correlate with the hormonal responses or to the development of tolerance.

Effect of nitecapone and clorgyline, given intracerebro-ventricularly on L-dopa metabolism in the rat brain

A new COMT inhibitor, nitecapone (OR-462) or clorgyline, a MAO-A inhibitor, was infused into the 3rd brain ventricle (i.c.v.) of conscious male rats. None of the enzyme inhibitors given alone alter hypothalamic or striatal levels of L-dopa, dopamine or their metabolites. Most of the rats were pretreated with levodopa/carbidopa (LD/CD, 15/30 mg kg-1 intraperitoneally). Now, the action of nitecapone is localized in the hypothalamus since homovanillic acid (HVA) is decreased there, not in the striatum. The levels of 3-O-methyldopa (3-OMD) are not changed in either brain region, suggesting a lack of the peripheral leakage of nitecapone. Clorgyline (3 and 10 micrograms rat-1) elevates hypothalamic and dopamine levels. Nitecapone and clorgyline decrease prolactin (PRL) levels below those reduced by LD/CD treatment.

Long-term activation of protein kinase C by nicotine in bovine adrenal chromaffin cells

Previous results from our laboratory suggest that long-term treatment of primary cultured bovine adrenal medullary (BAM) chromaffin cells with nicotine or phorbol 12-myristate 13-acetate, either of which directly activates protein kinase C (PKC), increases the mRNA levels encoding catecholamine-synthesizing enzymes and proenkephalin. In the present study, we have examined the effects of nicotine on BAM cell PKC activity with special emphasis on long-term effects. Nicotine increased particulate PKC activity in a concentration-dependent manner when measured using in vitro enzyme assay with histone as the substrate. This effect is mediated through nicotinic cholinergic receptors, because 1,1-dimethylphenylpiperazinium, a nicotinic agonist, had a similar effect. In addition, chlorisondamine, a specific nicotine-receptor blocking drug, antagonized the effect of nicotine. Nicotine also increased specific [3H]phorbol 12,13-dibutyrate ([3H]PdBu) binding within 1 min, the effect of which was maximal between 3 and 12 min. This effect was reversed by chlorisondamine similarly after 12 min and after 18 h of nicotine treatment, indicating that continual nicotinic-receptor occupancy is required for persistent PKC activation. Compared to PKC activation, the onset of nicotine-stimulated diacylglycerol production was slow, and it was observed after 12 min of incubation with nicotine. The diacylglycerol levels, specific [3H]PdBu binding, and PKC activity remained significantly elevated for at least 18 h with continuous nicotine incubation. Furthermore, nicotine increased the PKC immunoreactivity of a particulate protein with a molecular mass of 82 kDa in the western blot. These results suggest that nicotinic-receptor activation increases PKC activity and immunoreactivity in BAM cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II receptors are coupled to omega-conotoxin-sensitive calcium influx in bovine adrenal medullary chromaffin cells

The contribution of an omega-conotoxin GVIA (omega Cgtx)-sensitive Ca2+ influx pathway to the effects of angiotensin II (AII) receptor activation was examined in bovine adrenal medullary (BAM) cells. Pretreatment of BAM cells with 10(-6) M omega Cgtx blocked stimulation of exocytosis by the degradation-resistant analogue, sarcosine1-angiotensin II (S1-AII). In contrast, omega Cgtx had no effect on basal secretion, nor did it inhibit [3H]norepinephrine and [32P]ATP release in response to bradykinin, another phospholipase C-linked receptor agonist. Similarly, omega Cgtx pretreatment inhibited the stimulation of 45Ca2+ uptake by S1-AII, but did not affect the response to bradykinin. This selective inhibition did not appear to be due to blockade of AII receptors by omega Cgtx, as the accumulation of 3H-labeled inositol phosphates in response to S1-AII was not inhibited. The peak S1-AII-stimulated increase in the intracellular free Ca2+ concentration (Cai) in fura 2-loaded BAM cells also was not significantly reduced by omega Cgtx (or by stimulating in nominally Ca(2+)-free buffer), indicating that this response is dependent on intracellular Ca2+ pools. However, a small omega Cgtx-sensitive Cai response was detected after depletion of intracellular Ca2+ pools with ionomycin. This study shows that AII receptors, but not bradykinin receptors, are linked to an omega Cgtx-sensitive Ca2+ influx pathway in BAM cells.

Different in vivo properties of three new inhibitors of catechol O-methyltransferase in the rat

1. We compared three new catechol O-methyltransferase (COMT) inhibitors (OR-611, Ro 40-7592 and CGP 28014; 10 and 30 mg kg-1, i.p.) in male rats given levodopa (L-DOPA, 50 mg kg-1, i.p.) and carbidopa ((-)-L-alpha-methyl dopa, 50 mg kg-1, i.p.). In some studies pretreatment with pargyline (80 mg kg-1, i.p.) was used to block the function of monoamine oxidase (MAO). 2. Decreases of hypothalamic and striatal 3-O-methyl-dopa (3-OMD) levels were used as measures of the inhibition of peripheral COMT. The inhibition of brain COMT activity was estimated by decreases of hypothalamic and striatal homovanillic acid (HVA) and 3-methoxytyramine (3-MT; after pargyline) levels. 3. The three COMT inhibitors studied had different individual characteristics. OR-611 was primarily a peripherally acting COMT inhibitor, decreasing 3-OMD levels in the striatum (to 31-52%) and in the hypothalamus (to 16-27%) both in the control and pargyline-treated animals at 1 and 3 h. It did not have any effect on brain HVA and 3-MT. 3. Ro 40-7592 was a broad spectrum COMT inhibitor decreasing striatal and hypothalamic 3-OMD (always to less than 30%), HVA (to less than 50%) and 3-MT levels (to less than 23%) significantly both at 1 and 3 h. It was more potent than OR-611. 4. CGP 28014 functioned as a weak COMT inhibitor in the periphery inhibiting 3-OMD formation only at 3 h. In contrast, it was fairly potent in decreasing the brain HVA and 3-MT levels at 1 h (to 37-22% and 42-35% in the striatum, and to 57-33% and 64-35% in the hypothalamus, respectively) but not at 3 h. Since CGP 28014, unlike OR-611 and Ro 40-7592, did not generally increase the brain DOPA, dopamine or DOPAC levels, it was not a typical COMT inhibitor.

Anterolateral hypothalamic deafferentation inhibits histamine-induced prolactin secretion and potentiates TRH-induced thyrotropin secretion in male rats

We studied the effect of histamine on serum prolactin and thyrotropin (TSH) levels in male rats with anterolateral hypothalamic deafferentation of hypothalamic connections or anterolateral cut (ALC). The success of ALC was confirmed by immunohistochemistry of somatostatin (SRIF) in the medial basal hypothalamus. ALC did not affect basal prolactin or TSH levels. Thyrotropin-releasing hormone (TRH, 200 ng/rat, i.p.) did not affect prolactin secretion either in sham-operated or ALC rats. In sham-operated rats intracerebroventricularly administered histamine increased significantly prolactin levels. Hypothalamic deafferentation abolished the effect of histamine on prolactin levels. TRH increased significantly serum TSH levels both in sham-operated controls and ALC rats. In the latter, however, the TSH-secretory response to TRH was significantly (p less than 0.05) larger compared to the controls. Intracerebroventricularly infused histamine (2 micrograms/rat) did not change the TRH-induced TSH secretion in either group of rats. These results show that (1) the effect of histamine on prolactin secretion is mediated through nerve tracts which are destroyed by ALC, and (2) cutting of afferent TRH (through sensitization) and SRIF fibers (through lacking inhibition) entering medial basal hypothalamus may both contribute to the enhanced TSH response to exogenous TRH.

Penetration of erythromycin into periapical lesions after repeated doses of erythromycin acistrate and erythromycin stearate: a pilot study

In 26 patients who had undergone apicectomy and extirpation of granulomas (n = 9) or radicular cysts (n = 17), concentrations of erythromycin, 2'-acetyl erythromycin, and their anhydro forms were determined with a novel chemical method in plasma and periapical lesions after at least 2 days of treatment with erythromycin acistrate (EA) (400 mg three times daily, n = 11) or erythromycin stearate (ES) (500 mg three times daily, n = 15). Oral surgery was performed 2 1/2 to 3 hours after the last dose. Blood samples were collected at the time of operation, and immediately before antibiotic treatment, and 1, 2, and 6 hours after treatment. At all time points EA produced at least twice the total antibiotic (2'-acetyl erythromycin plus erythromycin) concentrations in plasma as ES. Erythromycin levels in plasma were at least as high after EA treatment as after ES. In periapical lesions erythromycin concentration after EA was three times higher (1.34 +/- 0.28 micrograms/gm) than after ES treatment (0.40 +/- 0.17 micrograms/gm). Although the total drug concentration in periapical lesions was about the same after EA (2.64 micrograms/ml) and ES (3.41 micrograms/ml), most of the drug recovered after ES was antimicrobially inactive anhydroerythromycin (3.01 micrograms/gm). The concentration of anhydroerythromycin in plasma was approximately the same as that of erythromycin after ES throughout the dose interval. After EA treatment both plasma and the periapical lesion samples contained hardly detectable amounts of anhydroerythromycin. Hence EA has a good bioavailability essential for treatment and prophylaxis of bacterial infections in dentistry.

Long-term activation of protein kinase C by angiotensin II in cultured bovine adrenal medullary cells

Previous studies from our laboratory suggest that protein kinase C (PKC) is involved in the angiotensin II (AII)-induced increase in the expression of genes encoding proenkephalin and catecholamine biosynthesizing enzymes in primary cultured bovine adrenal medullary (BAM) cells. The purpose of this study was to examine the effects of [Sar1]-AII (S1-AII), an AII agonist, on PKC activity in BAM cells. Thirty-minute incubation with S1-AII produced a dose-dependent activation of PKC. The particulate PKC activity was significantly increased by 2 nM S1-AII after both 30 min and 12 h of incubation. A high concentration of S1-AII (200 nM) caused an increase in particulate PKC activity after 30 min of incubation and this increase was still observed after 18 h of continuous incubation. [Sar1, Thr8]-angiotensin II (S1, T8-AII) (100 microM), an AII antagonist, inhibited the effect of S1-AII (20 nM) on PKC activity, suggesting a specific AII receptor-mediated effect. An increase in BAM cell particulate PKC immunoreactivity after 18 h of S1-AII treatment was observed in Western blot analysis of PKC-immunoreactive protein (82 kDa). The persistent activation of PKC seen in this study is consistent with our hypothesis that PKC may mediate the S1-AII-induced increase in the expression of genes encoding proenkephalin and catecholamine synthesizing enzymes in BAM cells.

Short and long term regulation of catecholamine biosynthetic enzymes by angiotensin in cultured adrenal medullary cells. Molecular mechanisms and nature of second messenger systems

The purpose of this study was to examine the effects of angiotensin on the enzyme activities and gene expression of two catecholamine synthesizing enzymes, tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT), in bovine adrenal medullary (AM) cells. Short term (15 min) incubation of cultured AM cells with 2 nM [Sar1]angiotensin II (s1-AII) did not increase basal secretion of catecholamines; however, longer incubations (3, 24, or 72 h) produced 4-10-fold increases. To determine whether angiotensin affects synthesis of catecholamines, the activities of TH and PNMT were examined. Incubation with s1-AII (15-30 min) decreased the Km of TH for its biopterine cofactor [6R)-5,6,7,8-tetrahydro-1-biopterin dihydrochloride (BH4] without affecting the Vmax, suggesting activation of TH. After long term incubation (72 h) the Km value was identical to that of control, while increases in the apparent Vmax were observed. PNMT activity was unaffected during a 30-min treatment with s1-AII; however, 2-fold increases occurred after a 48-72-h incubation. s1-AII (24 h) increased the relative abundance of TH and PNMT mRNAs, suggesting that the long term increase in enzyme activities reflected increased expression of TH and PNMT genes. Maximal increases were observed at 2 nM s1-AII and the changes were antagonized by saralasin. Induction of TH mRNA by s1-AII was additive to the effects of veratridine or forskolin indicating that effects of angiotensin were not due to membrane depolarization or increased cyclic AMP levels. Incubation with Ca2+ ionophore A23187 increased TH and PNMT mRNA levels in AM cells raising the possibility that the increase in cellular [Ca2+] could mediate effects of angiotensin. Angiotensin-induced increases in TH and PNMT mRNA were inhibited by nifedipine indicating involvement of voltage-dependent Ca2+ channels. In addition, the increases in TH, but not PNMT mRNA, were antagonized by dantrolene, which inhibits mobilization of Ca2+ from intracellular stores. Calmodulin involvement was suggested by the inhibition of s1-AII induced changes in mRNA with 1 microM calmidazolium.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of adrenal medullary cells in vivo and in vitro induces expression of c-fos proto-oncogene

The nuclear proto-oncogene, c-fos, has been implicated in the coordinated regulation of gene expression during cell proliferation and differentiation. In this study, we have demonstrated the induction of the c-fos gene products in differentiated cells of the adrenal medulla by non-mitogenic signals. Activation of adrenal medullary cells in vivo by insulin-induced hypoglycemia, and in vitro by nicotine or angiotensin resulted in the rapid and transient elevation of c-fos mRNA levels. Induction of the c-fos mRNA by angiotensin and nicotine were accompanied by the appearance of the c-fos protein. The increase in c-fos protein occurred initially in the cytoplasm and, later, in the nucleus, and it was co-localized with tyrosine hydroxylase. Nuclear expression of the c-fos protein was also induced by veratridine, forskolin and the calcium ionophore A231287. The role of calcium in the regulation of the c-fos gene by angiotensin with nifedipine and inhibition of the effects of angiotensin with nifedipine and sphingosine, a protein kinase C inhibitor. Activation of the c-fos gene may play a role in the coordinated induction of genes involved in the long-term adaptation of adrenal medullary cells to increased functional demands.

Comparison of the effects of intraventricular taurine, GABA and homotaurine on serum prolactin levels in male rats

The effects of taurine (2-aminoethanesulphonic acid), gamma-aminobutyric acid (GABA) and homotaurine (3-aminopropanesulphonic acid), a structural analogue of both taurine and GABA, on serum prolactin (PRL) levels were compared in conscious, unrestrained male rats. Taurine, injected into the lateral brain ventricles at doses of 6 and 10 mumol per rat, elevated serum PRL level by 52% (P less than 0.01) and 90% (P less than 0.001), respectively. GABA elevated serum PRL level (41%, P less than 0.05) only at the lowest dose (1 mumol) tested. Homotaurine was the most effective compound, eliciting increases of 353% and 449% (P less than 0.001) at 6 and 10 mumol per rat, respectively. The rank order of the three amino acids in elevating serum PRL level bears some similarity to their known rank order of potency in altering cerebral dopamine metabolism.

Cholinergic regulation of thyrotropin secretion in male rats

The cold-stimulated thyrotropin (TSH) secretion in male rats was suppressed by muscarinic agonists, i.e. Oxa-22, McN-A-343 (an M1 agonist), oxotremorine (an M2 agonist) and methacholine (a quaternary compound). The inhibitory effect of Oxa-22 was antagonized by atropine, butylscopolamine and glycopyrrolate as well as by pirenzepine, an M1 antagonist and AF-DX 116, a new M2 antagonist. Various muscarinic antagonists were not active when given alone. Cytisine, a peripheral nicotinic agonist, was not active but nicotine significantly suppressed the cold-stimulated TSH secretion. Its effect was counteracted by mecamylamine but not by hexamethonium. The thyrotropin releasing hormone (TRH)-induced TSH secretion was not inhibited by Oxa-22, nicotine or methacholine. These results show that irrespective of the receptor subtype (muscarinic1 or muscarinic2, nicotinic), cholinergic activation inhibits the cold-stimulated TSH secretion. The results also suggest that this inhibitory effect is at the hypothalamic rather than the anterior pituitary level. The muscarinic action seems to occur outside the blood-brain barrier but the nicotinic action occurs inside this barrier.

Further studies of serotonergic activity in the regulation of the cold stimulated thyrotropin secretion in male rats

Serotonergic agonists and antagonists were used to study the role of 5-HT in the regulation of thyrotropin (TSH) secretion in male rats. When given peripherally, the agonists like 5-HT, quipazine and m-chlorophenylpiperazine (mCPP) decreased dose-dependently the cold-stimulated TSH-secretion. The action of 5-HT was antagonized by metergoline but not by ketanserin. The effect of quipazine was counteracted by both antagonists. Small intraperitoneal doses of ketanserin seemed to be stimulatory on the TSH secretion while high doses of both ketanserin and metergoline clearly decreased the cold-stimulated TSH levels. Infusion of quipazine into the 3rd ventricle inhibited significantly the TSH cold-response whereas 5-HT and mCPP did not. The action of quipazine was only partially antagonized by ketanserin pretreatment. 5,7-dihydroxytryptamine (5,7-DHT) was used to make serotonergic lesions into different regions of the brain. The TSH lowering effects of intraperitoneal quipazine and mCPP were potentiated in the rats lesioned in the 3rd ventricle or bilaterally into the posterior hypothalamus but not in the rats lesioned bilaterally into the anterior hypothalamus. Hence serotonergic activity in the vicinity of the posterior part of the 3rd ventricle seems to decrease the cold-stimulated TSH secretion. Both 5-HT1 and 5-HT2 receptors appear to participate in this regulation.

Effect of chronic morphine treatment on thyrotropin and prolactin levels and acute hormone responses in the rat

The effects of three chronic morphine regimens on basal and cold-stimulated thyrotropin (TSH) and on prolactin levels were studied in male rats with and without acute morphine challenge. All the chronic regimens decreased basal and cold-stimulated TSH levels, but only one regimen (10 mg/kg b.i.d.) significantly enhanced the prolactin levels. The altered cold-stimulated TSH and prolactin levels were recovered within about 96 and 48 hr, respectively, after the last morphine injection on the 7-day pretreatment period. After the chronic administration (14 days), acute morphine challenges were performed either when cold-stimulated TSH secretion was suppressed (12- and 24-hr lag time) or when the response to cold was normalized (96-hr lag time). When the TSH levels were still low, the small challenge doses of morphine (10 and 15 mg/kg) no longer suppressed the TSH secretion. This was due neither to the real tolerance nor to the persistent effect of chronic morphine but to the withdrawal stress, which was also reflected as elevated corticosterone levels. However, after a 96-hr lag time, the challenge doses of morphine decreased TSH secretion after each morphine regimen as effectively as in the naive rats. Thus, the regimens did not induce the development of tolerance to the effect of morphine on cold-stimulated TSH secretion. Most regimens seemed to cause some tolerance to the stimulatory effect of morphine on prolactin secretion irrespective of the duration of the lag time. Even after the mildest regimen (10 mg/kg once a day), a tolerance developed to the antinociceptive effect of morphine, and it lasted well up to 96 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption of erythromycin acistrate and erythromycin base in the fasting and non-fasting state

Absorption of erythromycin acistrate (EA) and two erythromycin base (EB) preparations (enterotablet A and B) taken after an overnight fast or immediately before a standard breakfast was studied in 29 healthy volunteers in three separate studies, in a cross-over, randomized design. In Study I, the absorption of a single dose (400 mg) of EA was similar in the fasting and non-fasting state. There was, however, more interindividual variation and in two subjects absorption was markedly impaired in the presence of food. Cimetidine given at two doses (400 + 800 mg) had no effect on the pharmacokinetics of erythromycin acistrate. In Study II, the effect of food on the bioavailability of the two EB preparations was studied after a single dose of 500 mg (2 x 250 mg enterocoated tablets) and after multiple dosing (2 x 250 mg tid). When given with a standard breakfast, erythromycin base was significantly better absorbed from enterotablet A than from enterotablet B, whether given as a single dose or in repeated doses. Study III followed the same design as Study II except that the tablet size of both enterotablets A and B was now 500 mg. Even in this study the absorption of enterotablet A was significantly better than that of enterotablet B. EA is adequately absorbed when taken before a meal. Cimetidine does not interfere with its elimination. Concomitant food intake produced considerably dissimilar absorption of two commercially available enterocoated EB preparations. Although at steady-state this was less prominent than after a single dose, it may have some clinical significance.

Antibiotic concentration in suction skin blister fluid and saliva after repeated dosage of erythromycin acistrate and erythromycin base

The drug concentration in plasma, suction skin blister fluid (SBF), urine and saliva after repeated dosage of either erythromycin acistrate (EA) or enterocoated pellets of erythromycin base (EB) was studied in young healthy volunteers with a cross-over design in two separate studies. In Study I, the total drug concentration (erythromycin + 2'-acetyl erythromycin) after EA (400 mg tid) was slightly higher than the erythromycin concentration after EB (500 mg tid). The concentration of erythromycin after EA was about half of that after EB. In SBF the total antibiotic concentration after EA and erythromycin concentration after EB were 49 and 46% of the corresponding plasma concentrations, respectively. The degree of hydrolysis of 2'-acetyl erythromycin was higher in SBF (44%) than in plasma (39%). An equal proportion (7.3-7.5%) of the dose was excreted in urine after administration of both drugs. The degree of hydrolysis of 2'-acetyl erythromycin in urine was 58%. In Study II, the plasma/saliva concentration ratio ranged from 0.11 to 0.17 after EA 400 mg tid, 0.12 to 0.20 after EA 500 mg tid and 0.17 to 0.22 after EB 500 mg tid. The degree of hydrolysis of 2'-acetyl erythromycin was considerably higher in saliva (61-78%) than in plasma (27-41%). In plasma, the percentage of hydrolysis of 2'-acetyl erythromycin was inversely correlated with the concentration of acid-alpha 1-glycoprotein. The penetration of 2'-acetyl erythromycin and erythromycin into the extravascular space as evaluated from SBF and saliva levels was equal, and adequate concentrations of erythromycin were obtained for the treatment of bacterial infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Tonsillar penetration of erythromycin and its 2'-acetyl ester in patients with chronic tonsillitis

Concentrations of erythromycin and 2'-acetyl erythromycin were analysed in serum or plasma and tonsil tissue after repeated dosage of erythromycin acistrate (EA), a new erythromycin prodrug, in two separate studies in 61 young patients. The reference preparations were: (1) enterocoated tablets of erythromycin base (EB enterotablets, (2) erythromycin base as enterocoated pellets (EB enterocapsules) and (3) erythromycin stearate (ES). All drugs were given 500 mg tid for three days before scheduled tonsillectomy. Tonsils were removed about 3 h after intake of the last dose. Blood samples were collected at 0, 2 and 6 h and at the time of tonsillectomy. At all time points EA produced several-fold higher total drug (erythromycin + 2'-acetyl erythromycin) concentrations in serum or plasma than any of the reference preparations. Similarly, after EA the mean total antibiotic levels in tonsil tissue exceeded the erythromycin levels after the reference preparations by at least a factor of 3. Tonsil/serum or plasma ratios of the total antibiotic were quite similar with all preparations (means 38-50%). Peak erythromycin levels in circulation did not differ significantly from each other in spite of two nonabsorbers after EB enterotablets. The same was true of tonsil tissue. There were, however, 15 tonsils with undetectable erythromycin: 4/25 (16%) with EA, 5/12 (42%) with EB enterotablets, 2/12 (17%) with EB enterocapsules and 4/12 (33%) with ES. The degree of hydrolysis of 2'-acetyl erythromycin to erythromycin was 23-43% higher in tonsil tissue than in circulation.

Opiate receptor subtypes in the regulation of thyrotropin and prolactin secretion in the rat

In the present study both MR 2034 (kappa-agonist) and DAMME (mu-agonist) decreased thyrotropin (TSH) secretion stimulated by cold in the rat when infused into the 3rd ventricle. After infusion into the posterior hypothalamus (PH), a small dose of MR 2034 increased the TSH response to cold whereas other doses did not. The stimulatory (at PH) but not the inhibitory (at 3rd ventricle) effect of MR 2034 was antagonized by naloxone. DAMME had no statistically significant effect at this location. Both the mu- and kappa-agonist stimulated prolactin secretion when infused into the 3rd ventricle, but DAMME was more effective than MR 2034. Furthermore, the stimulatory effect of DAMME, but not that of MR 2034, on prolactin secretion was antagonized by naloxone.

Opioid peptides in the regulation of TSH and prolactin secretion in the rat

The effect of beta-endorphin, met-enkephalin and leu-enkephalin on cold-stimulated TSH and prolactin secretion after infusion of the drugs into the 3rd ventricle or into the posterior hypothalamus (PH) was investigated in male rats. beta-endorphin (0.25 microgram/rat, but not 0.05, 0.5 and 1 microgram/rat) increased and met-enkephalin (20 and 100 micrograms/rat) decreased TSH secretion when infused into the 3rd ventricle. After bilateral infusion into the PH, beta-endorphin (0.25 microgram/side, but not 0.05 and 1 microgram/side) increased TSH secretion, but met-enkephalin (1 and 10 micrograms/side) induced no changes. beta-endorphin (0.05-1 microgram/rat) and met-enkephalin (100 micrograms/rat) both increased prolactin secretion when infused into the 3rd ventricle, but only a high dose of beta-endorphin (1 microgram/side) was effective after infusion into the PH. Leu-enkephalin had no effect on TSH or prolactin secretion at the hypothalamic level. These results favour the hypothesis that mu-receptors mediate the inhibitory effect and other types (possible epsilon-receptors) of opiate receptors mediate the stimulatory effect of opioid peptides on TSH secretion at periventricular sites. However, only stimulatory mu-receptors affect prolactin secretion at these sites. After infusion into the PH, the effect of a high dose of beta-endorphin on prolactin secretion may also be mediated through periventricular sites, but its effect on TSH secretion is evidently mediated through opiate receptors in the PH.

Adrenalectomy modifies the effect of intracerebral histamine on the cold-stimulated TSH secretion in male rats

Cold-stimulated TSH secretion remained normal after adrenalectomy in conscious male Sprague-Dawley rats, but the inhibitory effect of a small dose of histamine (1.0 micrograms/rat into the 3rd ventricle, i.c.v.) on the TSH secretion was abolished. Adrenaline (0.01-1.0 mg/kg s.c.) inhibited dose-dependently the cold-stimulated TSH secretion. However, although adrenalectomy causes a prominent decrease in releasable adrenaline, a larger dose of histamine (2.5 micrograms/rat i.c.v.) decreased the TSH secretion. The effect of histamine was not modified after pretreatment with either corticosterone or dexamethasone, irrespective of whether intact or adrenalectomized rats were studied. Corticosterone decreased and dexamethasone increased the cold-stimulated TSH secretion when given intraperitoneally. Chlorisondamine (10 mg/kg i.p.), a peripheral ganglionic blocking drug, suppressed the TSH cold-response in intact rats. Histamine (1.0 microgram/rat i.c.v.) had no additional inhibitory effect after chlorisondamine. The results suggest that the effect of intracerebral histamine on cold-stimulated TSH secretion is caused neither by stimulation of the hypothalamus-pituitary-adrenocortical axis nor by increased adrenomedullary catecholamine release. Further, the effect of intracerebral histamine is obviously not due to enhanced neurosympathetic activity. The effect of histamine is modified by adrenalectomy, but the adrenal glands are not essential for it.