Compactin inhibits insect HMG-CoA reductase and juvenile hormone biosynthesis

The activity of 3-hydroxy-3-methylglutaryl CoA reductase in homogenates of the corpora allata of the tobacco hornworm, $\text{Manduca sexta}$, was competitively inhibited by compactin. The K_I for the sodium salt form of compactin was 0.9 nM for the reductase from both male and female corpora allata. In intact female corpora allata juvenile hormone biosynthesis was also inhibited by approximately 50 percent at 10 nM compactin. Following injection with compactin, darkening of the cuticle, an indication of juvenile hormone deficiency, was observed in larvae after ecdysis from third to fourth instar. Hence, compactin shows potential as an inhibitor of insect growth and development.     

Problems in the measurement of zinc using heparin as an anticoagulant

Although several reports imply that anticoagulants and preservatives contain zinc, the quantity of zinc in heparin, if any, has not been documented. Zinc concentration was determined by flame atomic absorption spectroscopy in varying dilutions of multiple commercially obtained samples of purified sodium heparin N = 15 (microgram Zn/1000 Units heparin). Rubber stoppers of sterile heparin vials and of blood evacuation tubes were incubated in pre-analyzed water or saline on a mechanical shaker with fluid aliquots obtained up to 27 hours and analyzed for zinc content (microgram Zn/0.1 ml). Heparin, with contact or without contact with rubber stoppers, recorded identical zinc concentrations. Zinc concentrations varied from 0.222 +/- 0.01 (mean +/- SE) to 3.49 +/- 0.005 microgram Zn/1000 Units heparin. Leaching of zinc from rubber stoppers of vacutainer tubes (N = 9) was noted only with those containing known chelators of zinc. These results indicate that zinc is present in certain lots of sodium heparin and that caution must be exercised when reporting zinc concentrations of blood samples that contain sodium heparin as the anticoagulant.     

The effect of phencyclidine on dopamine metabolism in the mouse brain

The administration of phencyclidine (PCP) to mice resulted in no change in brain levels of tyrosine, dopamine (DA), norepinephrine (NE), or homovanillic acid (HVA). Although PCP reduced plasma tyrosine levels, no effect of PCP on the utilization of DA of NE after blockade of synthesis with α-methyl-p-tyrosine (AMPT) was observed. In addition, PCP did not affect the probenecid-induced accumulation of HVA. However, PCP was observed to potentiate the haloperidol-induced increase in HVA concentration, and the haloperidol-induced decline in DA levels after AMPT. The former effect was blocked by baclofen, suggesting that PCP mobilizes DA for impulse-dependent release. This effect could not be attributed to an antagonism of presynaptic DA receptors. These effects are similar to those of the “non-amphetamine” stimulant class of drugs.     

Review of the Eustrophinae (Coleoptera, Tetratomidae) of America north of Mexico

The Nearctic fauna (north of Mexico) of Eustrophinae is reviewed, and consists of the following five genera and 12 species: Pseudoholostrophus (Pseudoholostrophus) impressicollis (LeConte), Pseudoholostrophus (Holostrophinus) discolor (Horn), Holostrophus bifasciatus (Say), Eustrophus tomentosus Say, Eustrophopsis confinis (LeConte), Eustrophopsis bicolor (Fabricius), Eustrophopsis brunneimarginatus (Dury), Eustrophopsis indistinctus (LeConte), Eustrophopsis arizonensis (Horn), Eustrophopsis ornatus (Van Dyke), Eustrophopsis crowdyisp. n., and Synstrophus repandus (Horn). A lectotype is designated for Eustrophus brunneimarginatus Dury. A key is given to separate genera and species, supplemented with illustrations of relevant features, including aedeagi of all Nearctic species of Eustrophopsis. Detailed distribution (including Mexican records) and natural history data are provided.     

Variation in age and height of onset of reproduction in the saguaro cactus (<Emphasis Type="Italic">Carnegiea gigantea</Emphasis>) in the Sonoran Desert

The objective of this study is to determine the height and age at which reproduction begins (i.e., production of flowers and fruits; the transition to adulthood) in the giant saguaro cactus (Carnegiea gigantea) in four geographically and environmentally distinct populations, and to relate observed variability to environmental differences. The onset of reproduction has been estimated at a height of 2.2 m in near optimal conditions. This value has been widely accepted and applied to populations in less optimal conditions, although variations under less ideal conditions have not been investigated. In addition, previous research has demonstrated that Carnegiea growth rates are highly variable over their range. Thus, even if 2.2 m is a consistent transition height to adulthood over their range, the age of individuals in different populations would be different. I investigate the age and height at which this transition occurs. The author sampled the heights of the shortest reproductive individuals and the tallest non-reproductive individuals to estimate the mean height of the onset of flowering in each of four locales in the northern Sonoran Desert. Using a previously published age-height-growth model, the mean age of the start of reproduction was also computed for the four sites. ANOVA and t-tests were used to compare the average transition to adulthood across sites by both age and height. Statistical results are robust and significant variations in the onset of reproduction are observed by both age and height across the four sites. Saguaro National Park and Organ Pipe Cactus National Monument individuals are transitioning to adulthood, on average, at younger ages and shorter heights than the other two locales. At the arid and marginal Kofa site, individuals that established during the regeneration peak of the late 1800s-early 1900s are only now becoming reproductive (individuals that established around 1899), while at Saguaro National Park, on average, individuals that established in the 1950s are already transitioning to adulthood. These results have implications for regeneration, particularly in marginal locales where regeneration is already limited.     

Branch direction in Carnegiea gigantea (Cactaceae): Regional patterns and the effect of nurse plants

Abstract. Branch direction in Carnegiea gigantea (saguaro) cacti affects PAR interception and CO₂ uptake, and may influence reception of photomorphogenic cues. Branch direction data were collected in 29 saguaro populations over Arizona to determine if the southerly bias observed in previous studies at two locales can be generalized to the American range of the saguaro, and to determine the effect of shading by nurse plants on branch direction. Locally observed S bias from previous studies can be extended and generalized to include the American saguaro range. Branches were statistically uniform across environmental variability regarding temperature and precipitation. The S bias was not found in saguaros shaded by large nurse plants, supporting the assertion that branch direction occurs, in part, to maximize receipt of insolation.     

A unique regulatory profile and regional distribution of [3H]pirenzepine binding in the rat provide evidence for distinct M1 and M2 muscarinic receptor subtypes

We recently demonstrated that the non-classical muscarinic receptor antagonist [³H]pirenzepine ([³H]PZ) identifies a high affinity population of muscarinic sites in the rat cerebral cortex. We now report that cortical muscarinic sites to which [³H]PZ binds with high affinity are modulated by ions but not guanine nucleotides. We also have examined equilibrium [³H]PZ binding in homogenates of various rat tissues using a new rapid filtration assay. All regional saturation isotherms yielded a similar high affinity dissociation constant (K_d = 2 ? 8 nM) in 10 mM sodium-potassium phosphate buffer. Receptor density (B_max in fmol/mg tissue) varied as follows: corpus striatum = 154.5, cerebral cortex = 94.6, hippocampus = 94.3, ileum = 1.3, cerebellum = 1.0, and heart = 0.45. The cerebral cortex and hippocampus possess 61 percent of striatal binding sites, while the ileum, cerebellum and heart contain only 0.84 percent, 0.65 percent and 0.29 percent of striatal sites respectively. The [³H]PZ sites in heart, ileum, and cerebellum represent 3.1 percent, 9.6 percent, and 10.4 percent of the sites obtained by using [³H](?)quinuclidinyl benzilate. Thus, [³H]PZ labels high affinity muscarinic receptor binding sites with a tissue distribution compatible with the concept of distinct M₁ and M₂ receptor subtypes. Accordingly, regions such as heart, cerebellum, and ileum would be termed M₂, though each have an extremely small population of the M₁ high affinity [³H]PZ site. [³H]PZ therefore appears to be a useful ligand for M₁ receptor identification. Furthermore, the inability to demonstrate a significant effect of guanine nucleotides upon high affinity [³H]PZ binding to putative M₁ receptors suggests that M₁ sites may be independent of a guanine regulatory protein.     

The measurement of free nitrendipine in human serum by an equilibrium dialysis - radioreceptor assay

A radioreceptor assay using [³H]nitrendipine and rat cerebral cortical membranes, in conjunction with equilibrium dialysis, measures the unbound (free) level of nitrendipine in human sera. The sensitivity of the assay is 0.1–0.2 picomoles/ml and is linear from 4 × 10^?11 to 4 × 10^?9 M nitrendipine. Other dihydropyridine calcium channel antagonists may be measured using this assay if these compounds are used to generate the standard curve. Blank serum interferes with specific [³H]nitrendipine binding (24 percent inhibition per 20 μ1 serum) whereas serum dialysates do not. Total serum nitrendipine levels may be measured, but the sensitivity of the assay is decreased due to interference by serum. Nitrendipine is highly protein bound in serum (93 – 99 percent). This protein binding is essentially unchanged over a serum concentration from 1 to 100 ng/ml. This assay is suitable for pharmacokinetic and pharmacodynamic studies.