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Biomedical subjects

L I Gilbert

Publications and source records attributed to L I Gilbert.

At least 127 records · Page 7Linked to original sources
PubMed1974

The Secretion of alpha-Ecdysone by the Prothoracic Glands of Manduca sexta In Vitro.

Prothoracic glands of tobacco hornworm larvae cultured in vitro secrete into the culture medium a substance which was active in ecdysone bioassays and determined to be ecdysone-like by radioimmunoassay. The prothoracic glands appear to be the sole source of this substance. The material was identified as alpha-ecdysone by thin-layer, gas-liquid, and high-resolution liquid chromatography and mass spectrometry. No other active moulting principles were present in the medium. It appears that the prothoracic gland secretes a prohormone, alpha-ecdysone, which is subsequently converted into the active moulting hormone, beta-ecdysone, in other insect tissues.

Journal Article↗
PubMed1974

Transport of lipids in insects.

Many insect species are almost completely dependent on lipids for their metabolic needs, although this is usually a function of developmental stage. The primary storage organ is the fat body, which can constitute 50% of the fresh weight of the insect and also acts as the major metabolic center (analogous to the vertebrate adipose tissue and liver). Bathing the fat body (and all other tissues and organs) is the hemolymph, the main functions of which are to transport nutrient substrates to utilization sites and to deliver metabolic wastes to the excretory system. Although neutral lipids are stored as triglycerides, in times of need they appear to be endergonically released into the hemolymph as diglycerides in the majority of insects thus far studied (particularly silkmoths and locusts). Indeed, diglycerides constitute the largest neutral lipid fraction in the hemolymph of silkmoths, locusts, cockroaches, bugs, etc. In the hemolymph the diglyceride is found as a constituent of specific lipoproteins, and one specific lipoprotein class (lipoprotein I; high density lipoprotein) appears to be necessary for the transport of diglyceride from the fat body cell into the hemolymph. This particular lipoprotein is also involved in the transport of cholesterol from the gut into the hemolymph. Thus, lipoprotein I appears to be the major neutral lipid and sterol transport agent in the insects studied and, in addition, plays a regulatory role in the release of both diglycerides and sterols. Hemolymph lipoprotein II (very high density lipoprotein) may be important in providing protein and lipid to the insect ovary during oogenesis. Ecdysone, the polyhydroxy steroidal insect molting hormone, is probably carried "free" in the hemolymph, although reports exist of specific hemolymph-binding proteins in some species. The other major insect growth hormone, juvenile hormone, is transported by hemolymph lipoproteins in silkmoths and locusts and by a lower molecular weight hemolymph protein in the tobacco hornworm.

Adipose Tissue↗
PubMed1972

Binding proteins for an ecdysone metabolite in the crustacean hepatopancreas.

When crustacean hepatopancreas is incubated in the presence of alpha-(3)H]ecdysone of high specific activity and is then homogenized and centrifuged, a peak of protein-radioactivity is recovered after gel filtration of the 105,000 x g supernatant. Analysis of this peak by sucrose gradient centrifugation revealed the presence of two complexes of protein and labeled material ( approximately 11.5 S and 6.35 S). The same results were obtained in vivo. On standing at low ionic strength, the lighter component disappeared, suggesting that the heavier component is an aggregate of the lighter one. Chemical analysis of radioactive material in the complex revealed that it is not alpha- or beta-ecdysone nor any previously described metabolite of the ecdysones. This new metabolite of alpha-ecdysone is found mainly in the incubated hepatopancreas. Partial structures consistent with the analytical data are inferred for this metabolite. It is suggested that the metabolite may be active in the action of molting hormone.

Animals↗
PubMed1972

Juvenile hormone induction of esterases: a mechanism for the regulation of juvenile hormone titer.

Within a few hours after injection of juvenile hormone into Hyalophora gloveri pupae, several fast-migrating carboxylesterases (EC 3.1.1.1) that are sensitive to diisopropylfluorophosphate appear in the hemolymph. Treatment of the pupae with puromycin or actinomycin D prevents the appearance of these hemolymph enzymes, suggesting de novo synthesis of the carboxylesterases. Of the several other compounds investigated, only a potent mimic of the juvenile hormone is able to induce these enzymes. When the induced enzymes are incubated in vitro with (14)C-labeled juvenile hormone, the hormone is rapidly and efficiently degraded. It is suggested that these induced carboxylesterases play an important role in the regulation of juvenile hormone titer.

Animals↗
PubMed1971

Aspects of research on insect growth hormones.

Current research on insect growth hormones includes studies on the binding of hormones to receptor molecules, probably proteins. Evidence has been obtained that this process does in fact occur and may be the means whereby the hormones "recognize" target tissues. Other studies on the possibility of a feedback effect when growth hormones are used for insect control suggest that there is a positive feedback relationship between the hormone titre and the activity of prothoracic glands and corpora allata, but the details are not yet clear. Cyclic adenosine 3',5'-monophosphate has an important role as "second messenger" in vertebrate endocrinology and may also be important in insects. Studies have shown that adenyl cyclase is present in pupal epidermis and the preliminary results have shown that it can be stimulated by a steroid hormone.

Adenylyl Cyclases↗