Inhibition of hepatic alpha 1-adrenergic effects and binding by phorbol myristate acetate

Treatment of isolated hepatocytes with the tumor-promoting agent, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) produced a time- and dose-dependent, non-competitive inhibition of alpha 1-adrenergic responses, including the activation of phosphorylase, increase in Ca2+ efflux, increase in free cytosolic Ca2+, and release of myo-inositol-1,4,5-P3. The actions of [8-arginine] vasopressin (AVP) on liver cells were also inhibited by PMA, but the inhibition could be overcome by high AVP concentrations. No significant inhibition of beta-adrenergic and glucagon-mediated activation of phosphorylase was induced by PMA and no inhibitory or synergistic effects of PMA were observed on the dose-dependent activation of phosphorylase by the Ca2+ ionophore A23187. In radioligand binding studies, PMA did not directly interfere with [3H]prazosin specific binding, the displacement of [3H]prazosin by (-)-norepinephrine nor with [3H]AVP specific binding to purified liver plasma membranes. Plasma membranes prepared from livers perfused with PMA exhibited a 30-44% reduction in [3H]prazosin binding capacity. Under identical conditions [3H]AVP binding was unchanged. The alpha 1-receptors remaining in membranes from PMA-treated livers had equivalent affinities for [3H]prazosin and (-)-norepinephrine, and were unaffected in terms of coupling to guanine nucleotide-regulating proteins as indicated by the ability of guanosine 5'-(beta, gamma-imido)triphosphate to promote the conversion of the remaining alpha 1-receptors into a low affinity state. These data indicate that tumor promoters are potent antagonists of alpha 1-adrenergic and vasopressin (low dose) responses in liver. It is proposed that PMA acting via protein kinase C (which presumably mediates the action of PMA) exerts its inhibitory action on alpha 1-adrenergic responses at the alpha 1-adrenergic receptor itself and also at a site close to or before myo-inositol-1,4,5-P3 release.     

Effect of vasopressin administration and deficiency upon 3H-AVP binding sites in the CNS and periphery during development.

Arginine8-vasopressin (AVP, 40 micrograms/100 g b.wt., SC) was administered to male Long-Evans (LE) pups from day 1 to 7 of life and the pups were sacrificed on day 8 or 60. 3H-AVP binding was performed on membranes prepared from the liver, kidney, and septum. No significant changes were observed in the kidney or septum of animals 8 or 60 days old. However, the chronic AVP treatment did result in a significant increase in the density of 3H-AVP binding sites in the liver when compared to control day 8 pups (control 44 +/- 2 vs. AVP 56 +/- 3 fmol/mg protein), with no change in affinity. This effect was maintained into adulthood, as the day 60 AVP-treated LE rats also showed a significant increase in liver 3H-AVP binding sites compared to control (control 186 +/- 9 vs. AVP 239 +/- 14 fmol/mg protein), with no change in affinity. A comparison of 3H-AVP binding sites in 8-day-old LE, heterozygous Brattleboro (HET-BB), and homozygous Brattleboro rats (HOM-BB) was performed to assess the effect of complete (HOM-BB) and partial (HET-BB) VP deficiency on binding sites in the CNS and periphery. The liver again was the only tissue in which a change in 3H-AVP binding characteristics was noted. The HOM-BB rat (Bmax 144 +/- 6 fmol/mg protein) displayed a significant increase in AVP binding sites from the LE rat (Bmax 100 +/- 7 fmol/mg protein), while the 3H-AVP binding sites in the HET-BB rat liver (Bmax 69.8 +/- 9 fmol/mg protein) were significantly lower than LE rats. Thus hepatic AVP receptors appear most sensitive to the presence or absence of vasopressin during the early postnatal period.     

Age-related changes in the control of hepatic cyclic AMP levels by alpha 1- and beta 2-adrenergic receptors in male rats

Hepatocytes from juvenile male rats (80-110 g) showed a 12-fold elevation of cAMP in response to epinephrine, which was mediated by beta 2-adrenergic receptors. In these cells, either alpha 1- or beta 2-adrenergic stimulation alone activated phosphorylase and glucose release although the alpha 1-phosphorylase response was 10-fold more sensitive to epinephrine and resulted in more rapid (by 10-20 s) activation of the enzyme. This suggests that the beta 2-adrenergic response is functionally unimportant for glycogenolysis, even in juvenile rats. beta 2-Adrenergic stimulation did, however, produce an increase in the rate of gluconeogenesis from [U-14C] lactate in these cells. Aging in the male rat was associated with attenuation of the beta 2-adrenergic cAMP response coupled with the emergence of an alpha 1-receptor-mediated accumulation of cAMP. The order of potency displayed by the alpha 1-adrenergic/cAMP system to adrenergic agonists and antagonists was identical with that of the alpha 1-adrenergic/Ca2+ system. These data suggest that, in maturity, hepatic alpha 1-receptors become linked to 2 separate transduction mechanisms, namely Ca2+ mobilization and cAMP generation. Calcium depletion of hepatocytes from adult, but not juvenile, male rats increased the alpha 1-component of the cAMP response to epinephrine, but under these conditions, alpha 1-activation of phosphorylase occurred more slowly than in calcium-replete cells. Blockade of alpha 2-adrenergic receptors did not significantly modify catecholamine effects on hepatocyte cAMP or phosphorylase a levels in male rats at any age studied, suggesting a lack of functional significance for these receptors in the regulation of glycogenolysis.     

Studies on the hepatic alpha 1-adrenergic receptor. Modulation of guanine nucleotide effects by calcium, temperature, and age

The effects of guanine nucleotides on the hepatic alpha 1-adrenergic receptor were studied using norepinephrine (NE) displacement of [3H]prazosin binding to rat liver plasma membranes. Nonhydrolyzable GTP analogues caused large rightward shifts of norepinephrine displacement curves of [3H]prazosin binding in EGTA-treated membranes, but only small shifts in membranes prepared with Ca2+. The effect of a brief Ca2+ exposure on NE displacement curves was not reversed by adding excess EGTA prior to binding experiments. Analysis of the curves showed that the EGTA membranes had an increased number of high affinity agonist sites (Kd, 42 nM) and that guanyl-5'-yl imidodiphosphate (GppNHp) converted these to low affinity sites (Kd, 1039 nM). When binding was carried out at 2 degrees C, the norepinephrine displacement curves were shifted to the left, and GppNHp was without effect. Neither EGTA, Ca2+, nor 2 degrees C treatment altered [3H]prazosin binding per se. Attempts were made to differentiate the potency order of GTP analogues which alter glucagon receptor binding (presumably mediated by the stimulatory GTP-binding protein, Na, of the adenylate cyclase system) from the potency order of GTP analogues which alter alpha 1-receptor agonist binding (presumably mediated by a yet uncharacterized GTP-binding protein which some have speculated may be distinct from Ns). However, the potency series of GTP analogues to alter norepinephrine binding was GTP gamma S greater than GppNHp greater than or equal to GTP greater than or equal to GDP greater than or equal to GppCHp greater than GMP (where GTP gamma S represents guanosine 5'-O-(thiotriphosphate) and GppCHp represents guanyl-5'-yl (beta, gamma-methylene)diphosphonate) and was identical to that for inhibition of [125I]iodoglucagon binding. The ability of GppNHp to alter norepinephrine displacement of [3H]prazosin binding increased with the age of the rat from which membranes were prepared. This was due to the fact that juvenile rats (50-75 g) had few alpha 1-receptors in the high affinity state, whereas in old rats (430-490 g) more of the receptors were in this form. Age has previously been shown to increase alpha 1-adrenergic stimulation of cAMP in isolated hepatocytes (Morgan, N.G., Blackmore, P. F., and Exton, J. H. (1983) J. Biol. Chem. 258, 5103-5109) but did not affect the dose-response curves for norepinephrine-induced Ca2+ mobilization and phosphorylase activation in these cells. These data suggest that alpha 1-adrenergic receptors can become coupled to a guanine nucleotide-responsive moiety in hepatic plasma membranes and that this may be similar to Ns.(ABSTRACT TRUNCATED AT 400 WORDS)     

Binding kinetics and sequencing of hepatic alpha1-adrenergic receptors in two marine teleosts, mackerel (Scomber scombrus) and anchovy (Engraulis encrasicolus)

Liver alpha(1)-adrenoceptors (ARs) are demonstrated, or at least hypothesized, in freshwater and brackish-water teleosts, whereas no data are available for marine teleosts. This study evaluates the presence of alpha(1)-ARs in the liver of two marine teleosts, the anchovy Engraulis encrasicolus and the mackerel Scomber scombrus, and examines on a broad scale the possibility that habitats posing different challenges also influence phenotypic trait selection. Binding assays were performed also on liver membranes from the carp Cyprinus carpio as a direct comparison with a freshwater species. Scatchard analysis of [(3)H]prazosin binding to purified liver membranes from anchovy, mackerel and carp resulted in K(d) values of 1.51+/-0.085, 1.26+/-0.098, and 2.61+/-0.22 nM, and B(max) values of 87.4+/-9.12, 77+/-8.29, and 115.22+/-3.31 fmol/mg protein, respectively. Thus, alpha(1)-ARs of the two marine teleosts showed higher [(3)H]prazosin affinity compared with those of the freshwater/brackish-water fish studied thus far, whereas the number of liver binding sites did not differ significantly from that of carp, eel or trout. A preliminary phylogeny based on amino acid sequence analysis indicated the presence of at least an alpha(1A)-AR in mackerel and an alpha(1D)-AR in both anchovy and mackerel. This is the first indication of alpha(1)-AR subtypes in any marine species, but further studies are needed to ascertain the physiological role of these alpha(1)-ARs in these two marine species.     

Prolactin receptors in the hypoprolactinemic male rat (IPL nude rat): measurement in testis and induction in liver

In order to evaluate the importance of PRL in the regulation of its own receptors, characteristics of specific binding for PRL were studied in membrane preparations from liver and testis of a new hypoprolactinemic male rat, the IPL nude male rat, and this was compared to those found for normal male rats. Under basal conditions, hepatic specific binding of PRL in IPL nude rats, as in normal rats was not detectable. Following castration, it became detectable in both groups, and was 6.99 +/- 0.78% and 6.34 +/- 0.87% for IPL nude and normal rats respectively. Under such conditions, the apparent affinity constant (Ka) and the binding capacity (Nmax) obtained were also similar for both groups (Ka) = 1.36 +/- 0.14.10(9) M-1, Nmax = 102 +/- 14 fmol/mg protein in IPL and Ka = 1.34 +/- 0.28.10(9) M-1, Nmax = 97 +/- 11 fmol/mg protein in normal rats) although a decrease in serum levels of PRL was observed in both groups. This decrease was greater for IPL nude rats. As already reported, estradiol injection following castration was able to further increase the percentage of PRL hepatic specific binding (4 times). Furthermore, our results demonstrated that the affinity constant was significantly increased by estradiol injection in both groups. On the other hand, for testicular PRL binding characteristics, a statistically significant difference was found between IPL nude and normal rats. The PRL specific binding percentage was 7.01 +/- 0.85% for the IPL nude rat and 10.07 +/- 0.64% for the normal rat. By Scatchard analysis, the Ka of testicular membranes for labelled oPRL was similar in both groups, while the capacity differed (Nmax = 9.82 +/- 1.25 fmol/mg protein for IPL nude rat and Nmax = 26.06 +/- 4.39 fmol/mg protein for normal rats). These data established the fact that IPL nude male rats presented characteristics of hepatic PRL receptors similar to those of normal rats, while their testicular oPRL binding significantly differed. These findings therefore suggest that in genetic hypoprolactinemic rats (IPL nude rats), PRL might be more involved in the regulation of testicular PRL receptors than in that of hepatic receptors.     

Decreased activity and impaired hormonal control of protein phosphatases in rat livers with a deficiency of phosphorylase kinase.

1. Livers from gsd/gsd rats, which do not express phosphorylase kinase activity, also contain much less particulate type-1 protein phosphatases. In comparison with normal Wistar rats, the glycogen/microsomal fraction contained 75% less glycogen-synthase phosphatase and 60% less phosphorylase phosphatase activity. This was largely due to a lower amount of the type-1 catalytic subunit in the particulate fraction. In the cytosol, the synthase phosphatase activity was also 50% lower, but the phosphorylase phosphatase activity was equal. 2. Both Wistar rats and gsd/gsd rats responded to an intravenous injection of insulin plus glucose with an acute increase (by 30-40%) in the phosphorylase phosphatase activity in the liver cytosol. In contrast, administration of glucagon or vasopressin provoked a rapid fall (by about 25%) in the cytosolic phosphorylase phosphatase activity in Wistar rats, but no change occurred in gsd/gsd rats. 3. Phosphorylase kinase was partially purified from liver and subsequently activated. Addition of a physiological amount of the activated enzyme to a liver cytosol from Wistar rats decreased the V of the phosphorylase phosphatase reaction by half, whereas the non-activated kinase had no effect. The kinase preparations did not change the activity of glycogen-synthase phosphatase, which does not respond to glucagon or vasopressin. Furthermore, the phosphorylase phosphatase activity was not affected by addition of physiological concentrations of homogeneous phosphorylase kinase from skeletal muscle (activated or non-activated). 4. It appears therefore that phosphorylase kinase plays an essential role in the transduction of the effect of glucagon and vasopressin to phosphorylase phosphatase. However, this inhibitory effect either is specific for the hepatic phosphorylase kinase, or is mediated by an unidentified protein that is a specific substrate of phosphorylase kinase.     

Distribution and subtype determination ofβ-receptors in the spinal cord of the adult rat

1. We determined the number of beta-receptors in the whole spinal cord of the adult rat and in the cervical, thoracal, and lumbal/sacral parts. 2. The undivided spinal cord contains 47 +/- 10 fmol/mg beta-receptors (KD = 2066 +/- 982 pmol/liter), and the cervical part of the spinal cord contains 53 +/- 8 fmol/mg protein (KD = 3224 +/- 1775 pmol/liter). The thoracal part shows 40 +/- 1 fmol/mg protein (KD = 3229 +/- 104 pmol/liter), and the lumbal/sacral spinal cord contains 48 +/- 8 fmol/mg protein (KD = 3610 +/- 1610 pmol/liter). 3. Competitive inhibition studies with l-practolol, dl-atenolol, and ICI 118,551 were performed and we calculated by a computer program in the whole spinal cord the following ratio of beta-receptor subtypes: 80 +/- 5% Beta 1-receptors and 20 +/- 5% beta 2-receptors. 4. The basal and (-)-isoproterenol- and NaF-stimulated activity of adenylate cyclase was highest in the cervical part of the spinal cord and equally distributed between the thoracal and the lumbal/sacral parts. 5. The whole synaptosomal protein of the cervical part of the spinal cord contained 132 +/- 20 fmol, the thoracal part 117 +/- 3 fmol, and the lumbal/sacral part 133 +/- 22 fmol.     

Regulation of hepatic glycogen phosphorylase and glycogen synthase by calcium and diacylglycerol

Incubation of rat hepatocytes with angiotensin II (1 nM) produced a time-dependent accumulation of 1, 2-diacylglycerol and inactivation of glycogen synthase with maximum effects at 10 min. The level of diacylglycerol then gradually declined and the activity of glycogen synthase I returned to control values at 30 min. In contrast, angiotensin II caused an increase in cytosolic Ca2+ and an activation of glycogen phosphorylase which were rapid and transient, reaching maximum values in less than 2 min and then returning to control levels at 15 min. There were excellent correlations between the changes in glycogen synthase I and diacylglycerol levels and between the changes in phosphorylase alpha and cytosolic Ca2+ in these time-course studies. However, there was no correlation between the changes in diacylglycerol and phosphorylase alpha or between the changes in cytosolic Ca2+ and glycogen synthase I. Norepinephrine also caused a slow increase in diacylglycerol and inactivation of glycogen synthase, and a rapid increase in cytosolic free Ca2+ and activation of glycogen phosphorylase. Addition of an alpha1-adrenergic blocker (prazosin or phentolamine) caused rapid decreases in cytosolic free Ca2+ and phosphorylase alpha, but only slowly reversed the inactivation of synthase and accumulation of diacylglycerol. The dose-response curves for norepinephrine and prazosin on glycogen synthase were well correlated with those on diacylglycerol. It is proposed that in liver cells, Ca2+-mobilizing hormones regulate phosphorylase a through a Ca2+-dependent mechanism and inactivate glycogen synthase through the generation of diacylglycerol, at least in part. The data provide additional support for the view that protein kinase C may be important in the regulation of glycogen synthase in liver.     

Adrenergic receptor properties of hepatocytes from male and female rats

alpha 1- and beta-adrenergic receptor properties of intact hepatocytes from adult male and female rats were evaluated in ligand binding studies using [3H]prazosin and [3H]CGP-12177 (4-(t-butylamino-2-hydroxypropoxy)-[5,7-3H]benzimidazole-2-one-HCl), a hydrophilic beta antagonist. Prior work had suggested that the response of hepatocytes from males to alpha 1-adrenergic stimulation was greater than that of cells from females. However, little sexual difference in prazosin affinity, number of binding sites or kinetics of association/dissociation with the cells was found. Epinephrine, [3H]prazosin competition for binding sites on intact cells was performed at 2 degrees C and 80-90% of agonist sites remained in a high affinity state with an epinephrine Kd comparable to that previously found in glucose release and phosphorylase alpha activation studies. Agonist Kd inferred from these competition experiments also showed no sexual dimorphism. These data suggest that the greater rise in the concentration of cytosolic free calcium and release of 45Ca from cells of males in response to epinephrine stimulation is not due to male/female alpha 1-receptor differences but, rather, may be a function of the previously observed sexual difference in cell calcium metabolism. [3H]CGP binding to hepatocytes from females was stereospecific, saturable and identified a single, high affinity site. Comparable sites were not found on cells from males, however, [3H]CGP binding to crude membrane preparations from both sexes was identical. This suggests that the loss of hepatic beta-receptor function in the adult male is due to an inaccessibility of beta-receptors at the external surface of the plasma membrane of the intact cell. Further studies with other beta-receptor ligands are being carried out to confirm these initial findings.     

应激大鼠肾胞液[^3H]醛固酮结合活性的变化及调节机制的初步研究

为探讨烫伤引起病理性应激时大鼠肾胞液醛固酮结合活性的变化及可能的调节机制,以[～3H]-醛固酮为配体,用放射性配基-受体结合分析法测定了正常对照组、轻度烫伤组和重度烫伤组大鼠肾胞液醛固酮结合活性的结合容量(Rt)和表观解离常数(Kd);采用体内注射TNF-α、IL-1β中和抗体和α-促黑色素细胞刺激激素(α-melanocyte-stimulatinghormone,α-MSH)和合成肽KPV(Ac-D-Lys-L-Pro-D-Val)等措施调节其改变.结果发现,肾胞液存在两种不同结合容量、不同亲和力的醛固酮结合活性受体.与正常对照组的Rt(Rt141.6±7.2fmol/mgpro;Rt2317.6±70.0fmol/mgpro)相比,轻烫组的Rt(Rt141.4±5.0fmol/mgpro;Rt2314.8±45.7fmol/mgpro)无显著差异(P>0.05;P>0.05);重烫组的Rt(Rt122.4±5.4fmol/mgpro;Rt2196.3±32.5fmol/mgpro)则显著下降(P<0.01;P<0.01).体内注射TNF-α与IL-1β中和抗体、α-MSH及KPV均能明显提高重烫组Rt值.结果提示,重度烫伤大鼠肾胞浆醛固酮结合活性降低,TNF-α、IL-1β中和抗体、α-MSH及KPV均可防止重度烫伤引起病理性应激时醛固酮结合活性降低.     

Alpha 1-Adrenergic stimulation of Ca2+ mobilization without phosphorylase activation in hepatocytes from phosphorylase b kinase-deficient gsd/gsd rats.

Phenylephrine, vasopressin and the bivalent cation ionophore A23187 mobilized Ca2+ normally, but failed to activate phosphorylase, in hepatocytes from gsd/gsd rats with a deficiency of liver phosphorylase b kinase. These data provide strong evidence that phosphorylase b kinase is the site of action of the Ca2+ mobilized intracellularly during alpha 1-adrenergic activation of phosphorylase in liver cells.     

Hepatic lipids of intact or thyroidectomized rats after administration of tetracycline or ethanol]

The purpose of this work was to study the quantitative modifications of the hepatic lipids in adult thyroidectomized rats after administration of tetracycline or ethanol (acute dose or prolonged ingestion). 1. - Thyroidectomy did not inhibit the accumulation of fat in the liver of fed euthyroid or hypothyroid rats after intraperitoneal infusion of tetracycline (320 mg/body weight in 2 injections at an interval of 16 h, the diet containing 6% of lipids). 2. - Sixteen hours after the oral administration of a single large dose of ethanol (5 g/kg body weight), there were only found some small modifications of the lipid composition of the liver in fasting euthyroid or thyroidectomized rats, receiving a diet with 6% of lipids before the experiment; on the contrary, when the diet contained 19% of lipids, a fatty liver occurred in the intact rat, but not in the thyroidectomized rat. 3. - The prolonged ethanol intake (in a 20% solution in water) for 5 months with a diet containing 19% of lipids did not induce a fatty liver in intact rats but produced a decrease of hepatic non-phosphorus lipid and an increase of the cholesterol amounts. After the administration of L-thyroxin (10 mug/100 g body weight per day) to these alcoholic thyroidectomized rats during 2 weeks, it was found an increase of the hepatic non phosphorus lipids till an higher amount than in the euthyroid rats. 4. - The hepatic phospholipid amounts were relatively constant in the different experiments. These results accounting for this differential effects were discussed.     

Characteristics and metabolism of alpha 1 adrenergic receptors in a nonfusing muscle cell line

The BC3H1 nonfusing muscle cell line possesses binding sites for [3H]prazosin. These binding sites are typically alpha 1 adrenergic receptors as shown by their greater affinity (3700-fold) for prazosin than for yohimbine. Both kinetic and equilibrium analyses indicated that [3H]prazosin interacted with only one category of independent binding sites with the following characteristics. KD = 0.13 +/- 0.01 nM. Bmax = 97 +/- 5 fmol/mg of protein corresponding to 25,000 sites/cell (n = 17). Biosynthesis of the alpha 1 adrenergic receptor was investigated at cell confluency (when the number of cells and their total protein content were constant). Phenoxybenzamine (10(-9) M) irreversibly blocked 50% of the alpha 1 receptors in intact cells. More than 95% blockade of receptors was obtained with 10(-7) M phenoxybenzamine. After this blockade, new alpha 1 adrenergic receptors reappeared in the cells with monoexponential kinetics. These new receptors corresponded to synthesized receptors since their appearance was blocked by cycloheximide (1 micrograms/ml). The cycloheximide action was reversible. If one makes the simple and probable hypotheses that the receptor production is constant and that degradation is a monoexponential process, the analysis of the kinetics of reappearance allows the determination of the rate constant for receptor degradation (k = 0.03 h-1) and the rate of receptor production (r = 3.2 fmol/mg/h) corresponding to the synthesis of about 760 receptors/cell/h. The half-life of the receptor was 23 h.     

HPLC-purified 2-[125I]iodomelatonin labels multiple binding sites in hamster brain

Binding of 2-[125I]iodomelatonin in hamster brain synaptosomal membranes at 0 degrees C is rapid, saturable, reversible and sensitive to heat and trypsin treatment. Computer resolution of curvilinear Scatchard plots yielded high- and low-affinity components as follows: Kd1 = 0.32 +/- 0.14 nM, Bmax1 = 5.6 +/- 1.7 fmol/mg protein and Kd2 = 10.5 +/- 3.2 nM, Bmax2 = 123 +/- 33 fmol/mg protein (n = 3). Competition experiments indicated that 2-iodomelatonin and prazosin are the most potent inhibitors of high-affinity binding. Unlike prazosin, several alpha-adrenergic agents and various neurotransmitters were ineffective. These findings suggest that prazosin may be a potent antagonist at a unique, non-alpha-adrenergic, high-affinity binding site for melatonin.     

Reappearance of cyclicity of vaginal smears in androgen-sterilized rats following thyroidectomy

During studies on the mechanism of hypersensitivity to gonadotropins of thyroidectomized rat ovary, results were obtained which suggest an increase in the endogenous luteinizing hormone (LH) release after thyroidectomy in androgen-sterilized rats. Female rats were injected subcutaneously with 1 mg of testosterone propionate dissolved in .05 ml of olive oil on Day 5 after birth. At the age of 10-12 weeks, those animals which showed persistent vaginal cornification were thyroidectomized. Within 1-2 days after thyroidectomy, the thyroidectomized rats exhibited leukocytic and epithelial vaginal smears for 2-6 days. Irregular cyclicity with the pattern of 2-6 days diestrus and 3-10 days estrus persisted for 1 month. Histological examination revealed that the corpora lutea were intermingled with a number of cystic follicles in the ovaries of the androgen-sterilized and throidectomized rats while the ovaries of androgen-sterilized controls had vesicular follicles but were devoid of corpora lutea. The results indicate a rapid enhancement in the LH release in androgen-sterilized rats following thyroidectomy.     

alpha-adrenergic receptor in rat heart. Effects of thyroidectomy.

The effects of thyroid status on alpha-adrenergic receptors in the rat myocardium were investigated. The potent antagonist [3H]dihydroergokryptine was used to identify alpha-adrenergic receptors in rat heart particulate and sarcolemmal fractions. Administration of triiodothyronine to thyroidectomized rats decreased specific binding to alpha-adrenergic receptors in heart particulate and sarcolemmal fractions by 41% and 45%, respectively. Scatchard analysis revealed that the cardiac sarcolemmal fraction from thyroidectomized rats contained 29.3 fmol/mg of protein, as compared with 17.0 fmol/mg of protein found in the heart preparation of thyroidectomized rats treated with triiodothyronine. The equilibrium dissociation constants for the interaction of receptors with dihydroergokryptine were similar (about 1.5 nM) in the heart sarcolemmal fractions derived from these two groups of rats. The results of this study demonstrate that thyroid hormone can regulate the number of cardiac alpha-adrenergic receptors. In addition, there appears to be a reciprocal relationship between alpha-adrenergic and beta-adrenergic receptors in the rat myocardium.     

Effects of fasting on the distribution of cytoplasmic and nuclear oestrogen receptors in rat liver, uterus, pituitary and hypothalamus before and after exogenous oestrogen administration

The accumulation of oestrogen receptors in the liver cell nuclei of intact female rats 45 min after administration of 100 micrograms 17 alpha-ethynyloestradiol-17 beta i.p., decreased progressively during a 72-h fast from 2550 +/- 860 to 257 +/- 67 fmol/mg DNA, a level not significantly different from that in uninjected animals. Cytoplasmic oestrogen receptor concentrations also decreased, but only to about 60% of the original level (from 84.1 +/- 27.5 to 50.3 +/- 2.09 fmol/mg protein during the fast). Similar differences were found when these parameters were examined in normally fed and 72-h-fasted ovariectomized rats. On the other hand these parameters were unaffected in uterus, pituitary and hypothalamus. Uterine cytoplasmic receptor concentrations remained at about 500 fmol/mg protein during the fasting period, those in the pituitary and hypothalamus at about 230 and 30 fmol/mg protein, respectively. Nor was in vivo translocation in these organs affected by fasting. Regardless of nutritional status, the nuclear oestrogen receptor concentrations in uterus rose from about 500 to 2000 fmol/mg DNA after ethynyloestradiol administration, those in the pituitary and hypothalamus from approximately 250 to 2000 and from 250 to 500 fmol/mg DNA respectively.     

Iminodipropionitrile-Induced Dyskinesia in Mice: Striatal Calcium Channel Changes and Sensitivity to Calcium Channel Antagonists

Administration of 3,3'-iminodipropionitrile (IDPN) (1 g/kg, i.p. for 3 days) in mice leads to the development of a characteristic syndrome consisting of lateral and vertical head and neck movements, hyperactivity, random circling, increased locomotor activity, and increased startle response. Nifedipine, verapamil, and diltiazem (10 mg/kg) inhibited significantly the symptoms of IDPN-induced dyskinesia. However, there was no change in the affinity (KD) or the density of PN 200-110 binding sites (Bmax) in whole brains of IDPN-treated mice. Similarly, the K(+)-depolarization-dependent Ca2+ uptake in synaptosomes from whole brain, cortex, or striatum was not altered following IDPN treatment. However, IDPN caused a significant increase in the Bmax value (from 157 +/- 7 fmol/mg to 237 +/- 31 fmol/mg in control and treated groups, respectively) of PN 200-110 binding to the striatum without change of KD value (38 +/- 4.7 pM versus 33 +/- 1.6 pM). IDPN also caused a slight but significant decrease in the KD value (from 68 +/- 10.1 pM to 45 +/- 4.5 pM in control and treated groups, respectively), without significant change of Bmax value (563 +/- 51 fmol/mg versus 485 +/- 41 fmol/mg) of PN 200-110 binding to the cortex. IDPN did not alter omega-conotoxin binding in whole brain, striatum, or cortex. The behavioral effects of chronic IDPN treatment as inhibited by L-type calcium channel antagonists and this may be associated with the observed increase in striatal L-type calcium channels.