Selective inhibition of cardiac cyclic nucleotide phosphodiesterases by doxorubicin and daunorubicin

Doxorubicin and daunorubicin, the anthracycline antitumor agents, were evaluated for their in vitro and in vivo effect on phosphodiesterase (PDE) activity in mouse tissues. Doxorubicin at a concentration of 10(-4)M inhibited cardiac c-AMP (adenosine 3',5', monophosphate) PDE activity 50% of the control whereas in lungs and spleen, the activity was inhibited only 20%. On the contrary no effect was seen in kidney and liver. In addition, cardiac c-GMP (guanosine 3',5' monophosphate) PDE appeared less sensitive to doxorubicin than c-AMP PDE though inhibition in heart was more pronounced than in any other tissue. It appears that daunorubicin inhibits c-AMP PDE activity in heart markedly less than doxorubicin. Kinetic studies indicate that both inhibitions of c-AMP and c-GMP PDE by doxorubicin were non-competitive with substrate. Intravenous administration of 20 and 30 mg/kg of free doxorubicin to CDF1 mice resulted in 33 and 39% decreases in cardiac c-AMP PDE activity respectively by 72 hrs. In contrast, similar intravenous injections of same doses of doxorubicin entrapped in cardiolipin liposomes had no effect on c-AMP PDE activity in any tissues. These studies demonstrate the relative selectivity of the cardiac cyclic nucleotide PDE inhibitory effect of doxorubicin suggesting that this inhibition might be one aspect of the mechanism of anthracycline-induced cardiotoxicity.     

Isoproterenol-stimulated renin secretion in the rat: second messenger roles of Ca and cyclic AMP

These experiments were designed to elucidate which of two second messengers (cyclic 3',5' adenosine monophosphate [c-AMP]; intracellular calcium [Cai]) was more closely related to the renin secretory process. The rat renal cortical slice preparation was used. Agents which previously were shown to inhibit basal renin secretion by increasing Cai (ouabain, vanadate, angiotensin II, antidiuretic hormone, and 60 mM K) antagonized and/or blocked isoproterenol-stimulated secretion, which is thought to be mediated by adenylate cyclase activation and increased levels of c-AMP. The stimulatory effect of dibutyryl c-AMP was antagonized and/or blocked by the same agents which antagonized and/or blocked isoproterenol-stimulated secretion. Thus, the inhibitory effects of these agents on isoproterenol-stimulated secretion cannot be explained by a Ca-induced decrease in c-AMP production. Secretory rate was stimulated by a potent phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine). A combination of this and dibutyryl c-AMP produced even greater stimulation. Ouabain blocked the stimulatory effect of this combination. These results are not consistent with an invariant direct relationship between c-AMP and renin secretory rate, but are consistent with an inverse relationship between Ca; and renin secretion. Further, they are consistent with the hypothesis that in isoproterenol-stimulated renin secretion. c-AMP is the second and Cai the third or the final messenger.     

LH- and FSH response to long-term application of LH-RH analogue in normal males.

The effect of luteinizing hormone-releasing hormone (LHRH) analogue after subcutaneous application over a 12-day period was evaluated in 15 normal males to determine whether gonadotropin secretion is influenced by longterm application. After 1.25 mcg/day, LH increases were measurable 3 hours after daily receipt of the analogue. After 2.5 mcg/day, the release of LH secretion was even greater, although this stimulation was markedly reduced in the 2nd week. After 5 mcg in 2-day intervals, a clearly induced LH increase was observed on the day of administration and was maintained for 10 hours. Similar results were noted for follicle-stimulating hormone (FSH). There was a response of FSH after 1.25 mcg and 2.5 mcg, but this response decreased in the 2nd week. After application of 5 mcg every other day, there was a consistent FSH increase that subsided on the treatment-free day and continued into the 2nd week of treatment. These findings suggest that LHRH analogues should be administered in low doses subcutaneously or intranasally at daily intervals to enable a longterm effect on gonadotropin release.     

Regulation of the cardiac calcium channel by protein phosphatases

The calcium current (ICa) through the L-type channel in cardiac ventricular cells is enhanced by phosphorylation of a channel protein [Kameyama, M., Hofmann, F. & Trautwein, W. (1985) Pflügers Arch. Eur. J. Physiol. 405, 285-293]. We investigated the possible contribution of the 'catalytic subunits' of protein phosphatase 1 and 2A in the down-regulation of the cardiac calcium channel. Single guinea-pig ventricular myocytes were voltage clamped and the following results were obtained. (1) Intracellular perfusion of the myocyte with the catalytic subunits of protein phosphatase 1 (2 microM) as well as 2A (2.3 microM) completely abolished the increase of ICa induced by isoprenaline (0.05 microM) but did not decrease the basal level of ICa. Alkaline and acid phosphatases were without detectable effect. (2) Cell dialysis with the modulator of protein phosphatase 1 (inhibitor-2) under control conditions (without addition of isoprenaline) caused a slow significant increase of ICa. (3) The time course for the wash-out of the isoprenaline effect was considerably prolonged in the presence of high concentrations of inhibitor-2. (4) Perfusion of the myocyte under basal conditions with adenosine 5'-[gamma-thio]triphosphate led to a slow increase of ICa. Additional superfusion of the cell with a threshold concentration of isoprenaline (0.01 microM) resulted in a rapid increase of ICa which could not be washed out during at least 10 min. From these results we make the following conclusions. (1) The calcium channel from guinea-pig myocytes is regulated by phosphorylation-dephosphorylation. (2) The catalytic subunits of the protein phosphatases 1 as well as 2A, purified from rabbit skeletal muscle, catalyse the down-regulation of the channel. (3) Indirect evidence suggests that endogenous protein phosphatase 1 contributes only partially to the dephosphorylation of the calcium channel in the intact myocyte.     

Effect of ACTH, dexamethasone, and adrenalectomy on the secretion of testosterone in the rat

The effect of ACTH (100 micrograms/animal/day, i.p.), dexamethasone (75 micrograms/animal/day, s.c.), both for three consecutive days, and adrenalectomy, with or without dexamethasone, maintained according to the group, one, two or three days, on the plasmatic testosterone and corticosterone levels, has been studied in adult male Wistar rats. ACTH and adrenalectomy produced a high decrease in testosterone levels (p less than 0.001 for the three days studied). Dexamethasone produced lower testosterone levels in the first day followed by partial recuperation between the second and the third days of its administration. Dexamethasone produced the effects mentioned for intact animals. The changes in corticosterone levels were according to an adequate response of the hypothalamus-pituitary-adrenal system under these experimental circumstances. ACTH exerts an inhibitory effect on testosterone secretion in the rat, so that such an effect from the data obtained after adrenalectomy and simultaneous dexamethasone injections, does not seems to be mediated either by the presence of adrenals or high corticosterone levels.     

Effect of nitric oxide donors on isoprenaline-induced lipolysis in rat epididymal adipose tissue: studies in isolated adipose tissues and immobilized perfused adipocytes

The present investigation was directed to study the effect of in vitro or ex vivo NO donors, sodium nitroprusside and molsidomine, using isolated sliced adipose tissue or in the form of immobilized and perfused adipocytes on the basal and isoprenaline-stimulated lipolysis. The results demonstrated that 1) in vitro application of sodium nitroprusside to perfused adipocytes or molsidomine to sliced adipose tissues affects isoprenaline-induced lipolysis in two ways, an increase in lipolysis at low isoprenaline concentrations (which means the sensitization of adipose tissues to adrenergic effect by NO) and decreased adrenergic agonist-stimulated lipolysis at higher concentration of isoprenaline (a decrease in the maximum lipolytic effect of isoprenaline), 2) low concentrations of molsidomine alone induced lipolysis from adipose tissue which attained more than 60% of that by isoprenaline (pD2 value for molsidomine = 11.2, while pD2 for isoprenaline = 8.17) while sodium nitroprusside did not affect the basal lipolysis significantly, 3) in vivo administration of molsidomine for 2 days reduced the maximum lipolytic effect of isoprenaline and (only non-significantly) increased the sensitivity to low doses of isoprenaline. In conclusion the present data demonstrate that NO plays an important role in adrenergic lipolysis in adipose tissues and further investigations are needed to unravel the exact role of NO in lipolysis.     

Mannose, glucosamine and inositol monophosphate inhibit the effects of insulin on lipogenesis. Further evidence for a role for inositol phosphate-oligosaccharides in insulin action.

The mechanism of insulin signalling is not yet understood in detail. Recently, a role for inositol phosphate (IP)-oligosaccharides as second messengers transmitting the insulin signal at the post-kinase level was proposed. To evaluate this hypothesis further, we studied whether IP-oligosaccharides isolated from 'haemodialysate' have insulin-like activity. We found that these compounds mimic, in a dose-dependent fashion, the following effects of insulin in adipocytes. (1) Lipogenesis. Incorporation of [3H]glucose into lipids (expressed in nmol/min per 10(6) cells): basal, 0.74 +/- 0.05; insulin (1 mu unit/ml), 4.43 +/- 0.21; IP-oligosaccharide (2 micrograms/ml), 4.07 +/- 0.19. (2) Inhibition of isoprenaline (isoproterenol) (1 microM)-stimulated cyclic AMP levels and lipolysis. Cyclic AMP (pmol/10(5) cells): basal 0.84 +/- 0.05; isoprenaline, 4.03 +/- 0.19; isoprenaline + insulin (200 mu units/ml), 2.06 +/- 0.7; isoprenaline + IP-oligosaccharides (2 micrograms/ml), 2.4 +/- 0.29. Inhibition of lipolysis (mumol of glycerol/mg of protein): isoprenaline (1 microM), 166 +/- 11; isoprenaline+insulin (150 mu units/ml), 53 +/- 3.5; isoprenaline+IP-oligosaccharides (2 micrograms/ml), 58 +/- 5. (3) Stimulation of 3-O-methylglucose transport; basal, 9 +/- 3%; insulin (1 mu unit/ml), 67 +/- 4%, IP-oligosaccharides (2 micrograms/ml), 54 +/- 2%. To identify the active molecules of the IP-oligosaccharide fraction, competition experiments were performed. IP-oligosaccharide effects on lipogenesis were blocked by inositol monophosphate, glucosamine and mannose. In contrast, these compounds did not inhibit IP-oligosaccharide effects on membrane-mediated functions (3-O-methylglucose transport, cyclic AMP levels, lipolysis). We also found that the effect of insulin on lipogenesis was blocked by mannose, glucosamine and inositol monophosphate, whereas the insulin effects on 3-O-methylglucose, cyclic AMP and lipolysis were unaffected. The following conclusions were reached. (1) IP-oligosaccharides mimic the major metabolic effects of insulin in adipocytes. This is consistent with the proposed role of IP-oligosaccharides as second messengers of certain insulin effects. (2) Mannose and glucosamine are functionally important sugar residues for the effect of IP-oligosaccharide on lipogenesis. (3) The observation that mannose, inositol monophosphate and glucosamine block the action of insulin of on lipogenesis supports a role of mannose- and glucosamine-containing IP-oligosaccharides as second messengers for this insulin effect.     

The effects of adrenalectomy and of hydrocortisone administration on adenylate cyclase activity in rabbit adipose cells (author's transl)]

Adenylate cyclase activity in rabbit adipocyte plasma membranes was studied with special reference to the effects of adrenalectomy and administration of cortisol in vivo. Adrenalectomy was accompanied by an increase in adenylate cyclase activity during basal conditions; cortisol (5 mg/kg body wt., intramuscularly) partly prevents this effect of adrenalectomy. The response of adenylate cyclase to corticotropin, epinephrine and norepinephrine stimulation was higher in the adrenalectomized rabbit than in the sham operated animal. Our in vitro results were in agreement with the striking fat mobilization observed in rabbit plasma after adrenalectomy and with the hypolipemic effects of cortisol we had previously observed in both normal and adrenalectomized rabbit.     

Plasma Insulin in Response to Enterostatin and Effect of Adrenalectomy in Rats

Enterostatin has previously been reported to alter serum insulin and corticosterone levels after central administration of the peptide. The purpose of the present study was to investigate the effect of peripheral administration of enterostatin on insulin and corticosterone levels as well as the response of plasma insulin to enterostatin administration in adrena-lectomized rats. Female Sprague-Dawley rats were given a bolus injection intravenously with enterostatin alone or together with glucose. Enterostatin increased basal plasma levels of insulin, but significantly inhibited the increase in plasma insulin stimulated by glucose. Plasma corticosterone levels were not altered after a single intravenous injection of enterostatin. In rats infused chronically with enterostatin, plasma insulin levels were significantly reduced and plasma corticosterone levels were increased. The daily food intake was lower in these rats, but there was no effect on body weight. After adrenalectomy, the responsiveness of plasma insulin to enterostatin infusion was completely abolished. Furthermore, adrenalectomy itself reduced basal plasma levels of insulin and increased plasma levels of endogenous enterostatin. These results suggest that peripheral enterostatin administration produces a similar effect as central infusion of the peptide, and that the glucocorticoid hormones are involved in the regulation of plasma insulin by enterostatin.     

Cardioprotective effect of magnesium chloride in experimental acute myocardial infarction

Cardioprotective role of intravenous administration of magnesium chloride was evaluated in rabbits by biochemical and histopathological parameters. Myocardial damage was induced by injecting (i.v.) isoprenaline 1, 2.5, 5 and 7.5 mg/kg body weight of animal. There was a dose dependent increase in the activity of cardiac enzyme creatinine kinase CK (C Max). Maximal elevation of CK (C Max) was observed with 2.5 mg isoprenaline. The mean T-max (mean of the time duration in hr at which maximum creatinine kinase activity of individual rabbit was observed in a group) shifted early, significantly with 2.5, 5 and 7.5 mg isoprenaline compared to control group. Histopathologically, myocardial damage was quite significant in 2.5 mg isoprenaline subgroup of animals. A mortality of 29% was observed in animals injected with 5 and 7.5 mg isoprenaline, whereas all animals subjected with 1 and 2.5 mg isoprenaline were alive for 72 hr. Considering the data on serial determination of cardiac enzyme CK and histopathological changes, 2.5 mg isoprenaline was chosen as standard dose to study efficacy of cardioprotection by gold standard verapamil and magnesium chloride. Verapamil (5 microM) injected prior to 2.5 mg isoprenaline administration revealed significant reduction of CK (C Max) activity (P < 0.05) compared to animals infused with isoprenaline alone. T-max value did not show any alteration in both the groups. Histopathological findings showed no areas of necrosis and cellular infiltrates in animals primed with 2.5 mg isoprenaline following verapamil. Highly significant reduction in CK (C-max) activity was observed in animals administered with 40 mg magnesium chloride prior to isoprenaline compared to animals treated with isoprenaline alone (P < 0.001). In addition to this, significant delay in T-max of CK activity was observed in group treated with 40 mg magnesium chloride and isoprenaline compared to group treated with only isoprenaline (P < 0.01). The study clearly highlighted and confirmed the valuable role of magnesium chloride as cardioprotective agent.     

Adrenalectomy-Induced Increase of Brain Protein Synthesis Is Antagonized by Corticosterone Replacements in Free-Moving Rats

Abstract: The autoradiographic method with l [³⁵S]-methionine was used to determine whether changes in glucocorticoid circulating levels were associated with changes in local rates of protein synthesis in rat brain. Chronic bilateral adrenalectomy induced an increase of me-thionine incorporation rates into proteins in 60 of the 62 brain regions examined (mean effect, +50%). This effect was confirmed biochemically and quantified by correcting for the relative contribution of methionine derived from protein degradation to the precursor pool for protein synthesis in the whole brain. Acute or chronic administration of corticosterone, at doses that normalize basal levels of adrenocorticotrophic hormone, reversed or prevented the adrenalectomy-induced increase of protein synthesis in most regions. However, in nearly all the regions studied (59 of 62), acute corticosterone administration to sham-operated rats did not change the apparent rate of protein synthesis. These results demonstrate that glucocorticoids exert a generalized inhibitory action on brain protein synthesis, because the stimulatory and persistent effect of adrenalectomy on protein synthesis was antagonized by corticosterone replacements at physiological doses. Thus, the regulation of overall brain protein synthesis by glucocorticoids emphasizes the role of neuroendocrine events on long-term neurochemical processes.     

3,5-diiodo-L-thyronine increases resting metabolic rate and reduces body weight without undesirable side effects

Recently, it was demonstrated that 3,5-diiodo-L-thyronine (T2) stimulates the resting metabolic rate (RMR), and reduces body-weight gain of rats receiving a high-fat diet. The aim of this study is to examine the effects of chronic T2 administration on basal metabolic rate and body weight in humans. Two euthyroid subjects volunteered to undergo T2 administration. Body weight, body mass index, blood pressure, heart rate, electrocardiogram, thyroid and liver ultrasonography, glycemia, total cholesterol, triglycerides, free T3 (FT3), free T4 (FT4), T2, thyroid stimulating hormone (TSH) and RMR were evaluated at baseline and at the end of treatment. RMR increased significantly in each subject. After continuing the T2 treatment for a further 3 weeks (at 300 mcg/day), body weight was reduced significantly (p<0.05) (about 4 percent), while the serum levels of FT3, FT4 and TSH, were unchanged. No side effects were observed at the cardiac level in either subject. No significant change was observed in the same subjects taking placebo.     

The effect of pyridoxal-5-phosphate on the inhibition of platelet aggregation and adenosine-3'-5'-cyclic monophosphate accumulation in human platelets

Platelet adenosine-3'-5'-cyclic monophosphate (c-AMP) was determined in platelet rich plasma and washed platelets by a modification of the c-AMP protein binding assay. Studies were performed in the presence and absence of platelet aggregation inducers (adenosine diphosphate and thrombin) and inhibitors (pyridoxal-5-phosphate (PALP), prostaglandin E1 (PGE1), theophylline and papaverine). At 70% inhibitory concentration of platelet aggregation (PA) induced by papaverine or theophylline, a small but significant increase in platelet c-AMP level was found. With PALP however the inhibition of PA was not associated with a significant increase in the c-AMP level. PALP or theophylline potentiated greatly both the inhibition of PA and c-AMP accumulation induced by PGE1. Yet PALP potentiated the inhibition of PA induced by theophylline without increasing platelet c-AMP level. Our results indicate that the inhibition of PA by PALP is not mediated by c-AMP accumulation. However in the presence of PGE1, the increment in PA inhibition, is mediated by further indirect activation of the adenyl-cyclase.     

Opioid peptide effects on insulin release and c-AMP in islets of Langerhans

The time course and specificity of the effect of opioid peptides on c-AMP production in the islets of Langerhans was examined. An enkephalin analogue, d-Ala2Me Phe4 Met(O)-ol enkephalin (DAMME, Sandoz) produced a significant stimulation of basal c-AMP levels, with a peak of stimulation at 5 minutes and a decline thereafter. These changes in intracellular c-AMP levels were of the same order of magnitude as those induced by other secretagogues, but did not coincide in time with the more rapid peak of enkephalin-induced insulin release. The rise in islet c-AMP and insulin secretion induced by DAMME and alpha-endorphin but not leu enkephalin was antagonised by naloxone. The effects of high and low concentrations of a variety of opioid peptides and naloxone on insulin release and islet c-AMP levels were determined, alpha-endorphin, dynorphin, leu enkephalin and met enkephalin all stimulated insulin secretion significantly, though not to the same extent. Higher concentrations of alpha-endorphin, dynorphin and met enkephalin inhibited insulin release relative to effects at low opiate concentrations. However, higher concentrations of leu enkephalin stimulated insulin release further. We conclude from these results that the mode of action of opioid peptides in stimulating insulin release is not via increased islet c-AMP exclusively. Furthermore, the results obtained with different classes of opioid suggest the presence of distinctive types of opiate receptor in islets of Langerhans.     

Synergistic activation of salmon cardiac function by endothelin and beta-adrenergic stimulation

The aim was to find out the effects of endothelin-1 (ET-1) in salmon (Salmo salar) cardiac contractile and endocrine function and its possible interaction with beta-adrenergic regulation. We found that ET-1 has a positive inotropic effect in salmon heart. ET-1 (30 nM) increased the contraction amplitude 17+/-4.7% compared with the basal level. beta-Adrenergic activation (isoprenaline, 100 nM) increased contraction amplitude 30+/-13.1%, but it did not affect the contractile response to ET-1. ET-1 (10 nM) stimulated the secretion of salmon cardiac natriuretic peptide (sCP) from isolated salmon ventricle (3.3+/-0.14-fold compared with control) but did not have any effect on ventricular sCP mRNA. Isoprenaline alone (0.1-1,000 nM) did not stimulate sCP release, but ET-1 (10 nM) together with isoprenaline (0.1 nM) caused a significantly greater increase of sCP release than ET-1 alone (5.4+/-0.07 vs. 3.3+/-0.14 times increase compared with control). The effects on the contractile and secretory function could be inhibited by a selective ETA-receptor antagonist BQ-610 (1 microM), whereas ETB-receptor blockage (by 100 nM BQ-788) enhanced the secretory response. Thus ET-1 is a phylogenetically conserved regulator of cardiac function, which has synergistic action with beta-adrenergic stimulation. The modulatory effects of ET-1 may therefore be especially important in situations with high beta-adrenergic tone.     

Mineralocorticoid-induced increase in beta-adrenergic receptors of cultured rat arterial smooth muscle cells

We have investigated the effect of mineralocorticoids on beta-adrenergic receptors in cultured arterial smooth muscle cells. Mineralocorticoid (aldosterone) treatment resulted in a significant increase in beta-adrenergic receptors measured by [3H]dihydroalprenolol (DHA) binding. This effect required at least 20 hours of incubation with aldosterone and was completely blocked by cycloheximide (10 micrograms/ml), indicating protein synthesis was required for this response. Aldosterone at the concentration range of 10(-8)-10(-6) M increased [3H]DHA binding, but was ineffective at 10(-9) M. Scatchard analysis of [3H]DHA binding revealed that the observed significant increase in binding was due to an increased number of binding sites (P less than 0.05), and that the affinity was unchanged. The aldosterone (1 x 10(-8) M) effect was completely blocked by the combination of RU 38486 (10(-6) M) and spironolactone (10(-7) M), but not by the glucocorticoid antagonist RU 38486 alone. While basal c-AMP levels were not changed by aldosterone (10(-6) M) treatment, the isoproterenol (10(-6) M) stimulated level of c-AMP was significantly higher in cells treated with aldosterone (P less than 0.05). We conclude that aldosterone, acting through the mineralocorticoid receptor, has a direct effect on arterial smooth muscle cells mediated through modulation of beta-adrenergic receptors of these cells.     

Differences in c-AMP levels in epithelial cells from pelvic and pectoral regions of the toad skin

Arginine vasopressin (AVP) stimulated active Na+ transport (JNa+) and osmotic water flow (JH2O) across the pelvic skin but only JNa+ across the pectoral skin of the toad, Bufo woodhouseii. Isolated epithelial cells from the pelvic skin had a maximal c-AMP level of 11.16 pmoles/mg protein after 5 min of AVP treatment while that of pectoral skin was 3.64 pmoles/mg protein. The c-AMP level of both skin areas fell to unstimulated values after 20 min of AVP treatment; however, JH2O (pelvic skin) and JNa+ (pelvic and pectoral skin) remained elevated during 3 hr of treatment. Dibutyryl c-AMP and theophylline stimulated JH2O across the pelvic but not the pectoral skin. Maintaining toads in water for 12-24 hr resulted in a substantial lowering of JH2O across the pectoral skin which was not reversible by treatment with c-AMP and theophylline.     

Decrease of homovanillic, dihydroxyphenylacetic acid and cyclic-adenosine-3',5'-monophosphate content in the rat caudate nucleus induced by the acute administration of an aminoacid mixture lacking tyrosine and phenylalanine.

The oral administration of an aminoacid mixture lacking tyrosine and phenylalanine induces, in rats, a profound depletion of tyrosine in serum and in brain. Brain tyrosine is maximally depleted by 73%, 2 h after treatment, when there is a concomitant decrease in the levels of HVA (by 50%), DOPAC (by 30%) and c-AMP (by 28%) in the basal ganglia. However, 4 to 8 h after treatment, when brain tyrosine is still depleted by 47 and 28%, respectively, DA metabolites and c-AMP levels have returned to normal. Our findings indicate that striatal tyrosine hydroxylase is fully saturated in v i m by the concentrations of tyrosine normally present in the basal ganglia. The results also suggest indirectly that decreased DA turnover results in decreased nerve activity, as judged by the decreased cyclic AMP levels.     

Regulatory effects of steroids on the pituitary response to LH-RH.

The effects of continuous intravenous administration of luteinizing hormone-release hormone in conjunction with physiological or pharmacolog ical doses of estradiol (E2), progesterone (P), 17alphaOH-progesterone (17-P), 20alphaOH-progesterone (20-P), chlormadinone acetate (CA), testosterone (T) and 5alpha-dihydrotestosterone (5-DHT) on pituitary response was evaluated in normal and postmenopausal women, normal men, and 1 patient with Klinefelter's syndrome. An all subjects, except the Klinefelter's syndrome patient, 132 mcg/hour/6 hours of E2 blocked the pituitary response to LH-RH, although a dose of 6.6 mcg/hour/6 hours was not markedly effective. None of the progestational steroids blocked the pituitary response to LH-RH. However, the dual administration of CA with E2 antagonized the pituitary response in normal and postmenopausal women. 600 mcg/hour/6 hours of T partially inhibited the pituitary resp onse in men, but had little effect on postmenopausal women and the Klinefelter's syndrome patient. The pituitary response to LH-RH was not inhibited by 5-DHT. The results indicate that sex steroids can modulate the hypothalamic-pituitary axis, though estradiol by itself does not appear to increase the pituitary response to LH-RH since it is not solely responsible for the pituitary responsiveness to LH-RH at the mid-luteal phase.     

Maintenance of neonatal endocrine cells of the rat. I. Effects of 2-deoxyglucose and 2-deoxy-2-fluoroglucose

Pancreatic endocrine cells of the neonatal rat cultured in medium with 5.5 mM glucose for 7 days showed no response to glucose. By contrast, the supplementation of the medium with 1.0 mM 2-deoxyglucose or with 0.1-5.0 mM 2-deoxy-2-fluoroglucose maintained the capacity of glucose-induced insulin release and biosynthesis, and the recovery of insulin in cells at day 7 at levels significantly higher than in basal medium; the highest responses were recorded for 1.0 mM deoxysugars. Moreover, the addition of 1.0 mM deoxysugars caused a selective deletion of fibroblasts and yielded monolayers mostly consisted of endocrine cells at the end of the culture study period. In these monolayer cells, the stimulating level of c-AMP release was significantly higher than the basal. On the other hand, the in vitro function of A cells in culture was also better preserved in media with 1.0 mM deoxysugars.