Purification of Somatostatin from Frog Brain: Coisolation with Retinal Somatostatin-Like Immunoreactivity

Somatostatin-like immunoreactivity (SLI) was purified from frog brain and retina, and the structure of the brain peptide was determined. Frog brain (101 g) and retinal (45 g) tissues were extracted with 3% acetic acid, yielding 9.6 and 0.44 nmol of SLI, respectively. SLI was further purified by chromatography on a somatostatin immunoaffinity column followed by sequential application to reverse-phase C-18 HPLC columns. The brain and retinal peptides, purified roughly 100,000-fold with net yields of 7.5 and 2.3%, respectively, appeared identical in the final steps of purification. The amino acid sequence of brain SLI, as determined by a gas-phase automated Edman degradation technique, was as follows: Ala-Gly-(Cys)-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-(Cys). Our data indicate that despite structural variations in somatostatins of other lower vertebrates, the amino acid sequence of frog brain and, by deduction, retinal SLI is identical to that of somatostatin tetradecapeptide. These findings support the physiological relevance of studies directed at elucidating the neurotransmitter function of somatostatin using the well-established models of frog brain and retina.     

Predation and bark beetle dynamics

Bark beetle populations may undergo dramatic fluctuations and are often important pests in coniferous forests. Their dynamics are thought to be primarily driven by factors affecting the resistance of the host tree to attack, i.e., bottom-up forces, while natural enemies are usually assigned a minor role in these systems. I present behavioral experiments that suggest that the clerid beetle Thanasimus dubius may be an important source of mortality for the bark beetle Dendroctonus frontalis during attack of the host tree, and determine the nature of the functional response of T. dubius under conditions close to natural. I also examine the numerical response of T. dubius to large-scale fluctuations in D. frontalis density, and the relationship between bark beetle population trends and predator density, and find that beetle populations tend to decline when predator densities are high. Combined with the effects of clerid larvae on bark beetle broods, these results suggest that top-down forces generated by natural enemies could also be an important component of bark beetle dynamics. The implications of these results for bark beetle dynamics are discussed in relation to the prolonged life-cycle of clerid beetles. Received: 23 January 1997 / Accepted: 5 April 1997     

Metabolism of H-Gibberellin A(1) and H-Gibberellin A(4) by Phaseolus coccineus Seedlings

[³H]-Gibberellin A₁ (GA₁) and ³H-GA₄ were applied separately to Phaseolus coccineus seedlings grown under red light. ³H-GA₁ was converted to a compound with gas-liquid radiochromatography retention times identical to those of GA₈. ³H-GA₄ underwent conversion to at least three metabolites, none of which corresponded to GA_1-38. The rate of metabolism of ³H-GA₄ was significantly higher than that of ³H-GA₁.     

HISTOLOGICAL AND HISTOCHEMICAL CHANGES IN DEVELOPING AND RIPENING PEACHES. II. THE CELL WALLS AND PECTINS

Reeve , R. M. (U.S.D.A., Albany, California.) Histological and histochemical changes in developing and ripening peaches. II. The cell walls and pectins. Amer. Jour. Bot. 46(4): 241–247. Illus. 1959.—Histological and histochemical observations on developing and ripening clingstone and freestone peaches have revealed that, after cell divisions have ceased in the mesocarp, cell wall thickening and cell enlargement in the mesocarp parenchyma increase until the fruit is nearly full cell size. The cell walls then decrease in thickness as the fruit ripens and softens. Degree of methyl esterification of the pectic substances, as estimated histochemically, remains at about 75–80% in immature fruits during their cell-enlargement phase of growth. Percent of methyl esterification apparently is much lower, or amounts of esterified pectates are very low during the meristematic phases of fruit growth. Just prior to ripening, degree of esterification increases and approaches 100% in hard, ripe fruit at about the same time that the parenchyma cell walls exhibit their greatest thickness or degree of hydration. The degree of esterification of the pectic substances then rapidly decreases and the cell walls become appreciably thinner as the ripening fruit softens. Further relation of these changes in wall thickness, in degree of esterification of the pectins, and in other cell wall carbohydrates to the textural qualities of ripening fruits is discussed. Interpretations concerning cell wall plasticity, cell growth and relation between auxin and changes in pectins also are presented.     

Identification of serotonin from rabbit upper stomach as a stimulant of in vitro gallbladder contraction

Using an in vitro rabbit gallbladder bioassay, the distribution and identification of bioactive substances in rabbit gastrointestinal tract were investigated. Comparison of the bioactivities of tissue extracts before and after cholecystokinin was removed by affinity chromatography demonstrated that the distributions of cholecystokinin and non-cholecystokinin substances were different. While cholecystokinin bioactivity per g of tissue was highest in the duodenum, non-cholecystokinin bioactivity was greatest in the upper stomach. The biochemical properties of the non-cholecystokinin substance in the upper stomach could not be distinguished from those of serotonin. These included molecular weights of 176, identical ultraviolet spectra, similar nuclear magnetic resonance spectra, and co-chromatography in HPLC. By weight, serotonin had 1/6th of the bioactivity of cholecystokinin octapeptide. We conclude that the principal gallbladder-contracting substance in rabbit upper stomach is serotonin.     

Private Governance, Public Purpose? Assessing Transparency and Accountability in Self-Regulation of Food Advertising to Children

Reducing non-core food advertising to children is an important priority in strategies to address childhood obesity. Public health researchers argue for government intervention on the basis that food industry self-regulation is ineffective; however, the industry contends that the existing voluntary scheme adequately addresses community concerns. This paper examines the operation of two self-regulatory initiatives governing food advertising to children in Australia, in order to determine whether these regulatory processes foster transparent and accountable self-regulation. The paper concludes that while both codes appear to establish transparency and accountability mechanisms, they do not provide for meaningful stakeholder participation in the self-regulatory scheme. Accordingly, food industry self-regulation is unlikely to reflect public health concerns or to be perceived as a legitimate form of governance by external stakeholders. If industry regulation is to remain a feasible alternative to statutory regulation, there is a strong argument for strengthening government oversight and implementing a co-regulatory scheme.