Peripherally administered desacetyl alpha-MSH and alpha-MSH both influence postnatal rat growth and associated rat hypothalamic protein expression

Desacetyl alpha-MSH predominates over alpha-MSH during development, but whether it is biologically active and has a physiological role is unclear. We compared the effects of 0.3 microg.g(-1).day(-1) desacetyl alpha-MSH with that of 0.3 microg.g(-1).day(-1) alpha-MSH on postnatal body growth by administering the peptides subcutaneously daily for postnatal days 0-14 and also used a two-dimensional gel electrophoresis gel-based proteomic approach to analyze protein changes in hypothalami, the relay center for body weight and growth regulation, after 14 days of treatment. We found that the growth rate between days 1 and 10 was significantly decreased by desacetyl alpha-MSH but not by alpha-MSH, but by day 14, a time reported for development of a mature pattern of hypothalamic innervation, both peptides had significantly increased neonatal growth compared with PBS-treated control rats. Desacetyl alpha-MSH significantly increased spleen weight, but alpha-MSH had no effect. alpha-MSH significantly decreased kidney weight, but desacetyl alpha-MSH had no effect. Both desacetyl alpha-MSH and alpha-MSH significantly decreased brain weight. By 14 days, both peptides significantly changed expression of a number of hypothalamic proteins, specifically metabolic enzymes, cytoskeleton, signaling, and stress response proteins. We show that peripherally administered desacetyl alpha-MSH is biologically active and induces responses that can differ from those for alpha-MSH. In conclusion, desacetyl alpha-MSH appears to be an important regulator of neonatal rat growth.     

Effects of Desacetyl-alpha-MSH on Lipid Mobilization in the Rainbow Trout, Oncorhynchus mykiss

Effects of melanocyte-stimulating hormone (MSH) and beta-endorphin on lipid mobilization were examined in the rainbow trout (Oncorhynchus mykiss). Plasma levels of fatty acid (FA) were measured after intra-arterial administration of alpha-MSH, desacetyl-alpha-MSH, beta-MSH, or beta-endorphin through a cannula in the dorsal aorta. Desacetyl-alpha-MSH at 1 ng/g body weight resulted in an increase in plasma FA levels 1-3 hr after the injection, whereas the other three peptides showed no significant effect at the same dose. There was no significant change in plasma levels of cortisol after administration of any of the peptides. Lipolytic enzyme activity in the liver was significantly increased in a dose-related manner 1 hr after single intra-peritoneal injection of desacetyl-alpha-MSH. The direct effect of desacetyl-alpha-MSH on lipolysis was examined in liver slices incubated in vitro. Lipase activity in the liver slice was stimulated in the medium containing desacetyl-alpha-MSH in a dose-related manner. The results indicate that desacetyl-alpha-MSH is a potent stimulator of lipid mobilization in the rainbow trout.     

Thyroid hormone effects upon Na+K+ dependent adenosine triphosphatase activity of microsomal fraction of liver, muscle and brain of toad Bufo melanostictus

Na+K(+)-ATPase activity in the liver and muscle microsomal membranes have been determined by different doses (0.1, 0.25, 0.5, 1 and 2 micrograms/gm of body weight) of L-triiodothyronine and L-thyroxine in the toad, Bufo melanostictus. The minimum effective dose of T3 was 0.5 microgram/g in case of both liver and muscle to stimulate the enzyme activity and there was dose dependent rise between T3 at the doses of 0.5 and 1 microgram/g. T3 at the doses of 1 and 2 micrograms/g produced more or less the same level of activity. T4 showed an increased activity at 1 and 2 micrograms/g without any dose dependent fashion in the two organs. The doses 0.1 and 0.25 microgram/gm body weight of T3 and 0.1, 0.25 and 0.5 microgram/gm body weight of T4 remained ineffective to elicit any response in both organs. The grain showed no significant change in the enzyme activity at any of the applied doses of T3 and T4. Cycloheximide inhibited T3 induced rise in Na+K(+)-ATPase activity of liver and muscle. Treatment with propylthiouracil caused a significant fall in Na+K(+)-ATPase activity of liver and muscle and the normal value was restored in the two organs after three consecutive injections of T4 at the dose of 1 microgram/g.     

Plasma alpha-melanocyte-stimulating hormone during the menstrual cycle in women

alpha-Melanocyte-stimulating hormone (alpha-MSH) and adrenocorticotropin (ACTH) immunoreactivity (IR) was measured in the blood of 22 healthy women with normal ovulatory process in the early and late follicular (near to ovulation) phases and in the early luteal phase of the menstrual cycle. Plasma alpha-MSH IR ranged from undetectable values to 81.3 pg/ml, the highest levels being found in the late follicular phase (15.52 +/- 4.16 pg/ml). In contrast, plasma ACTH IR was always detectable (range: 18.5-63.2 pg/ml), but its concentration did not differ significantly between the 3 phases of the menstrual cycle. High-pressure liquid chromatography fractionation of Sep pak C18-purified alpha-MSH IR revealed in all 3 phases the presence of 3 major peaks of alpha-MSH IR, coeluting with desacetyl-alpha-MSH, alpha-MSH and diacetyl-alpha-MSH, respectively. The most abundant peak always coeluted with authentic desacetyl-alpha-MSH, and the ratio between this deacetylated and the other 2 acetylated forms was similar in the 2 follicular phases (1:1.25 and 1:1.16 in the early and late phase, respectively), but significantly different in the luteal phase (1:0.48). The fluctuations in plasma concentration of the above MSH-related peptides suggest that different rates of alpha-MSH acetylation and release take place in the pituitary gland depending on the phase of the menstrual cycle.     

The influence of alpha-fluoromethylhistidine and histamine receptor antagonists on the beta-endorphin-induced corticosterone response

Involvement of a central histaminergic mechanism in the stimulating effect of beta-endorphin (beta-End) on the pituitary-adrenocortical activity, measured indirectly through corticosterone secretion, was investigated in conscious rats. The rise in serum corticosterone levels, induced by beta-End injected intraventricularly (icv) was considerably impaired by pretreatment with naltrexone, an opioid receptor antagonist. The stimulating effect of beta-End was almost totally suppressed by a prior icv administration of mepyramine, a histamine H1-receptor antagonist, and also considerably reduced by pretreatment with cimetidine, an H2-receptor antagonist. The strongest suppression, by 83%; of the beta-End-induced corticosterone response was evoked by a prior administration of alpha-fluoromethylhistidine, an inhibitor of neuronal histamine synthesis in the brain. These results indicate that both the brain neuronal histamine and central histamine H1- and H2-receptors are considerably involved in the beta-endorphin-induced stimulation of the pituitary-adrenocortical activity.     

The effects of 19-nor-aldosterone on blood pressure of adrenalectomized spontaneously hypertensive rats

The relative hypertensinogenic potencies of recently synthesized 19-nor-aldosterone and its precursor 19-OH-aldosterone were assessed in comparison to that of aldosterone (Aldo) in young (6-week-old) adrenalectomized (ADX) spontaneously hypertensive rats (SHR). Infusion of 19-nor-aldosterone for 2 weeks by Alza mini-osmotic pumps caused significant, dose-dependent increases in the systolic blood pressure (BP) of young ADX SHR; dosages of 0.1 and 0.5 microgram/day raised the BP from 127 +/- 2 mmHg to 164 +/- 9 and 180 +/- 11 mmHg, respectively. During this period, control ADX SHR receiving vehicle only remained normotensive. Similar increases in BP were seen only with infusion of slightly higher dosages of Aldo (0.5 and 1.0 micrograms/day). In contrast, 19-OH-aldosterone infused at higher dosages (10 or 25 micrograms/day) caused little change in BP of ADX SHR. Full suppression of plasma renin activity (PRA) was observed with 0.1 and 0.5 microgram/day 19-nor-aldosterone, whereas Aldo caused similar decreases in PRA only at dosages of 0.5 microgram/day and higher. Interestingly, although infusions of 19-OH-aldosterone did not cause a significant change in BP, these dosages (10 and 25 micrograms/day) significantly suppressed PRA. These studies which show that 19-nor-aldosterone is equipotent to Aldo, and perhaps slightly more active in ADX SHR, indicate that 19-nor-aldosterone is a potentially important hypertensinogenic steroid.     

Demonstration of hepatic cytosolic malic enzyme activity as a thyroid hormone sensitive physiologic parameter in a teleost, Heteropneustes fossilis bloch

Single injections of various doses (0.1, 0.25, 0.5, 5 and 20 micrograms/g) of T3 significantly increased the cytosolic malic enzyme activity (delta OD/min/mg cytosolic protein) in liver of Singi fish Heteropneustes fossilis Bloch, in a dose-dependent nature, maximum up to 5 micrograms/g dose on the 3rd day in comparison to the control. There was no difference in the enzyme activity between 5 and 20 micrograms/g of T3 doses. When the enzyme activity was expressed per mg DNA, the dose-dependent increase in the malic enzyme activity was observed upto 0.5 microgram/g of T3, whereas a fall in the enzyme activity was noticed with 5 and 20 micrograms/g of T3 doses. Lowering the dose of T3 to 0.05 microgram/g was without any effect on the malic enzyme activity (delta OD/min/mg cytosolic protein or DNA). Hepatic cytosolic protein content showed a biphasic nature of variation, significant increase with single injections of 0.05, 0.1, 0.25 and 0.5 microgram/g and a fall with 5 and 20 micrograms/g of T3 doses in comparison to the untreated control. Cycloheximide treatments of the Singi fishes counteracted both the T3-induced rise in the hepatic cytosolic malic enzyme activity (delta OD/min/mg cytosolic protein or DNA) and the hepatic cytosolic protein contents. Thiourea-treated hypothyroid fishes showed significantly decreased level of malic enzyme activity (delta OD/min/mg cytosolic protein or DNA) and cytosolic protein content in liver. A single injection of T3 at 0.25 microgram/g to the thiourea-treated fishes not only recovered but also increased the enzyme activity and cytosolic protein content above the untreated control values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of thyroid hormone in changing Na+K(+)-ATPase activity in different organs of toad, Bufo melanostictus

Single injection of T3, at the doses of 0.5 and 1 micrograms/g body weight, stimulated Na+K(+)-ATPase activity of crude liver homogenate of toad in a dose dependent fashion. Lowering the dose of T3 to 0.25 micrograms/g had no effect on the enzyme activity. T3 at the dose of 2 micrograms/g showed the same level of enzyme activity at par with that of 1 microgram/g. Na+K(+)-ATPase activity of muscle increased with T3 at the doses of 1 and 2 micrograms/g, but without any dose dependent manner while T3 at the doses of 0.25 and 0.5 micrograms/g remained unresponsive in changing the enzyme activity. T4, after 3 consecutive injections, increased the enzyme activity in liver with 1 and 2 micrograms/g and in muscle with 2 micrograms/g only while the other doses of T4 (0.25 and 0.5 micrograms/g in case of liver and 0.25, 0.5, and 1 micrograms/g in case of muscle) had no effect on the enzyme activity. Brain showed no alteration to Na+K(+)-ATPase activity with the same doses of T3 and T4. Cycloheximide counteracted the T3 induced rise in enzyme activity. The reduced level of Na+K(+)-ATPase activity in the PTU treated toad was recovered and brought to the control level after 3 consecutive injections of T4 at the dose of 1 microgram/g.     

Stimulatory effects of epidermal growth factor on deoxyribonucleic acid synthesis in the gastrointestinal tract of the suckling mouse

The effects of epidermal growth factor (EGF), cortisone and thyroxine on deoxyribonucleic acid (DNA) synthesis in the esophagus, stomach, small intestine and colon have been studied in suckling mouse. Daily administration of EGF [4 micrograms/g body weight (bw)/day] during 3 days to 8-day-old mice induced a significant increase of the incorporation of [3H]thymidine into DNA in the stomach, the small intestine, and the two halves of the colon. The DNA synthesis in the esophagus remained unaffected by the EGF treatment. The maximal increase of [3H]thymidine incorporation into DNA was observed in the colon, and represented 112%. Daily administration of cortisone acetate (25 micrograms/g bw/day) or thyroxine (1 microgram/g bw/day) during 3 days to 8-day-old mice had no significant influence of the DNA synthesis of any part of the gastrointestinal tract. These results show that EGF is able to affect the DNA synthesis in the stomach, small intestine and colon of suckling mice.     

Metabolic effects of 3,5-dimethyl-3'-isopropyl-L-thyronine and 3,5,3'-triiodo-L-thyronine in the brain and liver of hypothyroid rats. Similarities and differences

The metabolic effects of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) on subcellular activities in brain and liver, have been compared to those of T3. Thyroidectomized hypothyroid rats were treated for 10 days with DIMIT (8 micrograms/100 g/day) or T3 (0.25 microgram/100 g/day). In liver mitochondrial oxidative phosphorylation, succinate cytochrome c reductase activities and nuclear RNA polymerases I and II activities were restored to normal level by DIMIT as well as by T3 treatment. In brain T3 treatment normalized both nuclear and mitochondrial activities. On the other hand daily injection of DIMIT restored like T3 nuclear activities whereas that of brain mitochondria were unaffected. We have also examined the early effects of a single injection of T3 (2.5 micrograms/100 g) or DIMIT (80 micrograms/100 g), 20 minutes prior sacrifice. DIMIT is as active as T3 in stimulation of oxidative phosphorylation and succinate cytochrome c reductase activity in liver mitochondria. However DIMIT treatment does not affect the properties of brain mitochondria. On the basis of these observations, it is suggested that there is a tissue specificity of mitochondrial receptors to DIMIT administration as it was shown at the nuclear level.     

Mechanisms for the stimulatory effects of opioidergic and serotonergic input signals on prolactin in pregnant rats.

Dopamine (DA) neurons participate in tonic inhibition of prolactin (PRL), whereas beta-endorphin (beta-End) and serotonin (5-HT) neurons appear to be important stimulatory links for nocturnal PRL surges that occur throughout the first half of pregnancy in the rat. The purpose of this study was to determine how these neuronal components might be organized within the pathway controlling PRL release during gestation. Maximal stimulation of DA receptors with the agonist bromocriptine mesylate (Bromo) completely blocked the PRL response to beta-End (100 ng/microliters/min for 15 min) given intracerebroventricularly (i.c.v.) on day 8 of pregnancy. DA receptor blockade, produced by implanting a 25 mg pellet of haloperidol (Hal) on day 7 of pregnancy, resulted in PRL levels of 500-600 ng/ml by the following morning. beta-End i.c.v. or 250 mg/ml/kg BW of the DA synthesis inhibitor, alpha-methyl-p-tyrosine (alpha-MPT), given during the intersurge period, were equally effective in significantly increasing PRL (p less than 0.01) above pretreatment levels. beta-End and alpha-MPT evoked similar increases in rats pretreated with Hal, suggesting the stimulatory effect of beta-End on nocturnal PRL surges may primarily be due to DA inhibition. The next objective was to determine how beta-End and 5-HT might interact to stimulate the nocturnal surge. Day 8 pregnant rats were infused continuously with the opioid receptor blocker, naloxone hydrochloride (Nal), at a rate of 2.0 mg/10 min from 1000-1300 h. The PRL response to an injection of 20 mg/kg BW 5-hydroxytryptophan (5-HTP) at 1200 h was greatly attenuated, compared to controls infused with saline instead of Nal. This suggests that 5-HT stimulates PRL, at least in part, by an action at opioid receptors. Distilled H2O or 10 mg/kg BW of the selective S2 receptor blocker, ketanserin tartrate (Ket), was given intraperitoneally (i.p.) during the intersurge period on day 8 of pregnancy. All animals demonstrated an identical response to beta-End given 2 hours later, regardless of the type of pretreatment. It appears that beta-End does not stimulate PRL by way of an S2 receptor. Although beta-End induced a significant increase in PRL on day 16 of pregnancy, the response was attenuated by more than 60% compared to the response on day 8 of pregnancy. This attenuation may involve placental lactogens, shown to be secreted during this time and to inhibit PRL secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Clinical use of recombinant human hematopoietic growth factors (GM-CSF, IL-3, EPO) in patients with myelodysplastic syndrome.

We have conducted several phase I/II clinical studies in a total of 65 MDS patients utilizing recombinant human hematopoietic growth factors including GM-CSF, IL-3, and EPO. Twenty-seven patients with MDS were treated with either continuous i.v. infusion or single daily s.c. injection of rhGM-CSF at dosages from 15 micrograms/m2 to 1000 micrograms/m2. All of them exhibited white cell responses during the treatment cycles, but no sustained rise in reticulocytes or platelets was recorded. In four of the patients, all with > or = 15% blast cells in the bone marrow, the percentage of circulating blast cells increased during treatment with rhGM-CSF (at dosages of 500 micrograms/m2 and 1000 micrograms/m2, respectively), although no leukemic conversion occurred. Of 9 patients treated so far with rhIL-3 at single daily s.c. dosages of 60 micrograms/m2, all exhibited white cell responses; 8 exhibited significant improved platelet and reticulocyte counts. Nineteen further patients received rhEPO for a period of 14 weeks by s.c. (10,000 U five times weekly) or i.v. bolus administration (150-450 U/kg). None of these patients experienced an increase in white cell and platelet counts. A significant increase of the reticulocyte count was recorded in 3 patients only. Another strategy involves the recruitment of leukemic cells into the cell cycle by hematopoietic growth factors followed by treatment with cycle-specific cytostatic agents. Therefore in 10 patients administration of rhGM-CSF (250 g/m2/day x 14, s.c.) was combined with Ara-C treatment (20 mg/m2/day x 14; s.c.). Initial results of this pilot study available in 5 patients indicated that this approach may control leukemic cell proliferation and may increase number of mature myeloid cells in both bone marrow and peripheral blood. A similar approach utilizing rhIL-3 in conjunction with Ara-C is on-going.     

Effects of MSH on food intake, body weight and coat color of the yellow obese mouse

Viable yellow obese mice (Avy/a) were treated for 10 days with 5, 15, 50 or 150 micrograms/d of either alpha-MSH or desacetyl-MSH. The half-maximal effect on weight gain occurred with a dose of 5 micrograms/d for desacetyl-MSH and at a 30 fold higher level of 150 micrograms/d for alpha-MSH. In contrast, the half-maximal stimulation of eumelanin production by alpha-MSH occurred at 15 micrograms/d and with desacetyl-MSH at 150 micrograms/d, a 10-fold increase. Desacetyl-MSH produced a dose-related increase in the weight of muscle, as well as white and brown adipose tissue. Desacetyl-MSH and alpha-MSH both increased plasma corticosterone concentrations, but desacetyl-MSH was more potent. In a 2 x 2 factorial designed study, body weight was significantly increased in viable yellow mice only by treatment with desacetyl-MSH but in the lean animals, both alpha-MSH and desacetyl-MSH increased body weight. Food intake was significantly different between genotypes, and was stimulated by desacetyl-MSH. These studies demonstrate potent differences in biological actions on food intake, body weight, and a variety of organ weights between acetylated and desacetylated forms of MSH.     

Naltrexone modulates body and brain development in rats: a role for endogenous opioid systems in growth

Preweaning rats receiving daily injections of 20, 50, or 100 mg/kg naltrexone, a potent opiate antagonist, had body and brain weights that were increased 16-22% and 6-13%, respectively, from control levels on day 21 (weaning). All of these dosages of naltrexone blocked the opiate receptor for 24 hr/day as measured in opiate challenge experiments. Dosages of 0.1, 1, and 10 mg/kg naltrexone, which blocked the opiate receptor for less than 12 hr/day, inhibited growth. Repetitive administration of low dosages (3 mg/kg naltrexone, 3 times daily), which blocked the receptor 24 hr/day, increased body and brain development by 31% and 10%, respectively, whereas a cumulative dosage of 9 mg/kg naltrexone given once daily retarded growth. These results show that developmental events are dictated by the duration of opiate receptor blockade and provide compelling evidence that endogenous opioid systems play a crucial role in growth.     

The role of melanocortins and their receptors in inflammatory processes,nerve regeneration and nociception

The melanocortins are a family of bioactive peptides derived from proopiomelanocortin. Those peptides, included among hormones and comprising ACTH, alpha-MSH, beta-MSH and gamma-MSH, are best known mainly for their physiological effects, such as the control of skin pigmentation by alpha-MSH, and ACTH effects on pigmentation and steroidogenesis. Melanocortins are released in various sites in the central nervous system and in peripheral tissues, and participate in the regulation of multiple physiological functions. They are involved in grooming behavior, food intake and thermoregulation processes, and can also modulate the response of the immune system in inflammatory states. Research of the past decade provided evidence that melanocortins could elicit their diverse biological effects by binding to a distinct family of G protein-coupled receptors with seven transmembrane domains. To date, five melanocortin receptor genes have been cloned and characterized. Those receptors differ in their tissue distribution and in their ability to recognize various melanocortins. These advances have opened up new horizons for exploring the significance of melanocortins, their ligands and their receptors for a variety of important physiological functions. We reviewed the origin of MSH peptides, the function and distribution of melanocortin receptors and their endogenous and exogenous ligands and the role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception. Moreover, we analyzed their interaction with opioid peptides and finally, we discussed the postulated role of the melanocortin system in pain transmission at the spinal cord level.     

Effect of treatment with submaximal and excessive doses of caerulein on pancreatic growth in newborn rats

Different groups of CFY female newborn rats were treated with saline, or 1 microgram/kg or 100 micrograms/kg doses of caerulein given s. c. 3 x/day. Application of 100 micrograms/kg dose of caerulein for 3 days stimulated pancreatic growth inducing pancreatic hyperplasia; both (1 and 100 micrograms/kg) doses evoked increase in trypsin/DNA ratio inducing pancreatic hypertrophy in 4-days-old rats. Using the indices as before application of 1 microgram/kg caerulein for 10 days stimulated pancreatic growth and both (1 and 100 micrograms/kg) doses elicited glandular hypertrophy in 11-days-old rats. In 24-old-rats the 1 microgram/kg doses of caerulein given for 3 days stimulated pancreatic growth and induced pancreatic hypertrophy, the 100 micrograms/kg doses of the peptide given for 3 days, however, evoked pancreatic aplasia and atrophy.     

Dose dependent inhibition of B-16 melanoma growth in vivo by a synthetic analogue of PGE2

Daily intratumor administration of 16,16-dimethyl-PGE2-methyl ester in two different dosages inhibited tumor growth in C57Bl/6J mice bearing subcutaneous B-16 melanomas. The larger dose (20 microgram/day/mouse) produced a 68% decrease in tumor volume, a 69% decrease in tumor weight and a 60% decrease in the number of cells in mitotic phase. The smaller dose (10microgram/day/mouse) was one fifth less effective than the 20microgram dose but produced similar changes. Histological examination of tumors revealed no significant differences either in the inflammatory cell population or the amount of necrosis in the control and di-M-PGE2-treated tumors.     

Blood alcohol concentration and microencephaly: a dose-response study in the neonatal rat

The relationships among microencephaly, peak blood alcohol concentration (BAC), and dose of alcohol were examined in a rat model of third-trimester fetal alcohol effects. Ethyl alcohol was administered to neonatal rats from postnatal day 4 to day 10 during the brain growth spurt via an artificial rearing technique. Groups of rats received one of nine doses of alcohol (0.0, 2.5, 3.3, 4.0, 4.5, 5.3, 6.6, 7.5, or 8.5 g/kg body weight) administered in 8 hours each day. BACs were determined on postnatal days 6 and 7 at times corresponding to peak and trough BACs, respectively. On postnatal day 10, brains were removed, and total brain weights, cerebellar weights and brainstem weights were measured. Pups receiving 4.0 g/kg/day or less had mean peak BACs below 150 mg/dl and did not exhibit significant microencephaly when compared with controls. Higher dosages further increased the peak BAC and produced significant microencephaly. While a dose of 4.5 g/kg/day was sufficient to decrease significantly both total brain weight and cerebellar weight, a minimum dose of 6.6 g/kg/day was required for significant restriction of brainstem weight. The dose of 7.5 g/kg/day yielded a mean peak BAC of 420 mg/dl and reduced total brain weight, cerebellar weight, and brainstem weight by 33%, 52%, and 22%, respectively, relative to controls. Exposure to 8.5 g/kg/day was uniformly lethal. Peak BAC and total brain weight were highly correlated (r = -.916). As peak BAC increased, total brain weight decreased linearly. Comparisons with previous studies indicate that condensing the daily dose of alcohol effectively reduced the threshold doses for microencephaly and lethality.     

Angiotensin in the brain suppresses epinephrine-induced cardiac arrhythmias through CNS opioid mechanisms.

To test the hypothesis that angiotensin II (Ang II) in the central nervous system modulates catecholamine-induced cardiac arrhythmias and to determine whether endogenous opioids are operative in this action, arrhythmias were produced in male Wistar rats, by continuous infusion of epinephrine at incremental doses until the development of fatal arrhythmias that were usually ventricular fibrillation. Rats were instrumented with catheters in the lateral cerebral ventricle, femoral vein and femoral artery. Ang II, 0.5 microgram, in the lateral cerebral ventricle (ICV) markedly and significantly (p less than 0.05) increased the epinephrine dose, at the occurrence of ventricular premature beats compared to the control group 228 +/- 11 (SEM) vs 116 +/- 7 micrograms epinephrine/kg and at the onset of fatal arrhythmias 225 +/- 13 vs 185 +/- 9 micrograms epinephrine/kg. Ang II, 0.5 microgram i.v., did not affect arrhythmia threshold. The angiotensin converting enzyme inhibitor captopril, 1 mg/kg, decreased arrhythmia threshold as ventricular arrhythmias were first noted at 106 +/- 4 and fatal arrhythmias occurred at 118 +/- 4 micrograms epinephrine/kg. The Ang II receptor antagonist saralasin 150 micrograms/kg ICV, blunted and 300 micrograms/kg ICV reversed the effect of Ang II. The mu opioids antagonist naloxone and the kappa opioid antagonist MR 2266, 50 micrograms/kg ICV, prevented the effect of Ang II on fatal arrhythmias. The action Ang II on arrhythmias could not be explained by the effects of Ang II on blood pressure or heart rate. These data indicate a role for Ang II within the CNS to modulate cardiac arrhythmias and that this is mediated in part, by endogenous opioids.     

Effect of oestradiol dipropionate and testosterone propionate on protein, RNA and DNA contents and RNase and DNase activity in the liver of the toad (Bufo melanosticus)

A single injection of oestradiol dipropionate increased the HSI and protein, RNA and DNA contents and decreased the RNase and DNase activities of the liver of male and female toads. The minimum effective dose of oestrogen required to induce most of these changes was found to be 1 microgram/g (single injection), but the liver RNA content increased at the dose of 0.5 microgram/g. Oestrogen in a dose of 0.1 microgram/g did not cause any of these changes in male and female toads. Testosterone propionate (0.1, 0.5, 1 or 2 micrograms/g, single injection) was mostly ineffective in these respects, while in male toads higher doses of testosterone (1 and 2 micrograms/g) enhanced the liver RNA content only. The oestrogenic responses occurred earlier in female toads than in males. The liver protein and DNA contents increased from the 3rd day in female and on the 5th day in male toads. The liver RNA reached the higher level from the 2nd day in female and from the 3rd day in male. The RNase and DNase activities were reduced from the 2nd and 3rd day, respectively, in female and on the 5th day in male toads.