Effects of horsefly (Tabanidae) salivary gland extracts on isolated perfused rat heart.

The speed with which horseflies (Diptera: Tabanidae) obtain a bloodmeal suggests they have potent vasodilators. We used isolated perfused rat heart to examine the vasoactivity of salivary gland extracts (SGEs) of three horsefly species, Hybomitra bimaculata Macquart, Tabanus bromius Linnaeus and Tabanus glaucopis Meigen. Administration of horsefly SGEs to the heart produced biphasic coronary responses: a decrease and subsequent increase in coronary flow (CF), characterized by initial vasoconstriction followed by prolonged vasodilation of coronary vessels. However, although SGEs of H. bimaculata induced a significant decrease in left ventricular pressure (LVP), the effect on changes in CF was not significant except at the highest dose tested. The ability to reduce LVP without significantly lowering CF, or affecting heart rate and rhythm, represents a unique set of properties that have considerable therapeutic potential if they can be reproduced by a single molecule.

Complex steroid-peptide-receptor cascade controls insect ecdysis.

Insect ecdysis sequence is composed of pre-ecdysis, ecdysis and post-ecdysis behaviors controlled by a complex cascade of peptide hormones from endocrine Inka cells and neuropeptides in the central nervous system (CNS). Inka cells produce pre-ecdysis and ecdysis triggering hormones (ETH) which activate the ecdysis sequence through receptor-mediated actions on specific neurons in the CNS. Multiple experimental approaches have been used to determine mechanisms of ETH expression and release from Inka cells and its action on the CNS of moths and flies. During the preparatory phase 1-2 days prior to ecdysis, high ecdysteroid levels induce expression of ETH receptors in the CNS and increased ETH production in Inka cells, which coincides with expression of nuclear ecdysone receptor (EcR) and transcription factor cryptocephal (CRC). However, high ecdysteroid levels prevent ETH release from Inka cells. Acquisition of Inka cell competence to release ETH requires decline of ecdysteroid levels and beta-FTZ-F1 expression few hours prior to ecdysis. The behavioral phase is initiated by ETH secretion into the hemolymph, which is controlled by two brain neuropeptides-corazonin and eclosion hormone (EH). Corazonin acts on its receptor in Inka cells to elicit low level ETH secretion and initiation of pre-ecdysis, while EH induces cGMP-mediated ETH depletion and consequent activation of ecdysis. The activation of both behaviors is accomplished by ETH action on central neurons expressing ETH receptors A and B (ETHR-A and B). These neurons produce numerous excitatory or inhibitory neuropeptides which initiate or terminate different phases of the ecdysis sequence. Our data indicate that insect ecdysis is a very complex process characterized by two principal steps: (1) ecdysteroid-induced expression of receptors and transcription factors in the CNS and Inka cells. (2) Release and interaction of Inka cell peptide hormones and multiple central neuropeptides to control consecutive phases of the ecdysis sequence.

Vasodilatory activity in horsefly and deerfly salivary glands.

Salivary gland extract (SGE) of four horsefly species (Hybomitra bimaculata Macquart, Hybomitra ciureai Séguy, Tabanus bromius L., Tabanus glaucopis Meigen) and one deerfly species (Chrysops relictus Meigen) (Diptera: Tabanidae) were shown to contain vasodilatory activity. Aliquots equivalent to 1, 5 and 10 pairs of salivary glands (SG) relaxed rat femoral artery (with intact endothelium) pre-constricted with phenylephrine. Vasodilatory activity was dose-dependent. SGE of one horsefly species (Haematopota pluvialis L.) did not induce relaxation. The kinetics of vasodilation induced by SGE of four horsefly species differed from the deerfly. These results indicate that tabanid species may produce more than one type of vasodilator to aid blood feeding.

Corazonin reduces the spinning rate in the silkworm, Bombyx mori.

The insect neuropeptide, [Arg(7)]-corazonin was injected into larvae of the silkworm, Bombyx mori to investigate its influence on development and behavior. A single injection of 50 pmol of corazonin into the fourth and fifth instar larvae induced prolongation of the spinning period in all experimental groups except for those injected on day 10 of the fifth instar. The injection also caused a prolongation of the pupal period in some experimental groups, while it had no effect on the timing of larval ecdysis and the length of feeding period of the fifth instar. The spinning period was significantly prolonged even at a low dose of 1 pmol. Both the spinning rate and the rate of increase in hemolymph ecdysteroid level during the spinning stage were reduced by injection of corazonin. However, corazonin injection during days 5-7 of the fifth instar reduced the spinning rate without influencing the ecdysteroid level until the end of day 8, thereafter the rate of increase in hemolymph ecdysteroid level was slower in the corazonin-injected larvae than in the control larvae. Therefore, the suppressed ecdysteroid level observed in the corazonin-injected larvae appears to be a result rather than a cause of the reduced spinning rate. This study is the first published report for the corazonin effect on the behavior in insects.

Prolonged release of morphine alkaloid from a lipophilic suppository base in vitro and in vivo.

The in vitro release characteristics of four suppository formulations of morphine (15 mg) were investigated using the USP rotating basket dissolution apparatus. Morphine hydrochloride in polyethylene glycol (PEG), a hydrophilic suppository base, morphine alkaloid in PEG and morphine hydrochloride in Novata BBC (a lipophilic suppository base) completely released the drug within 25 min whereas, morphine alkaloid in Novata BBC (MAN) released the drug over 10 h. The absorption of the morphine hydrochloride/PEG (MHP) suppository was compared with that of a 15 mg oral solution in eight patients with malignant disease in a crossover design. Time of peak plasma morphine concentration (tmax) was similar for both preparations (1.8 +/- 1.6 h and 1.2 +/- 0.5 h, respectively; p > 0.05), showing that the MHP suppository was rapidly absorbed. The MAN and MHP suppositories were then compared in a further nine patients in a crossover design. Prolonged release of morphine from the MAN suppository was also evident in vivo as tmax (2.5 +/- 1.4 h) was significantly greater than that for the morphine hydrochloride/PEG suppository (0.7 +/- 0.3 h; p < 0.002). There was no significant difference in AUC (0-7 h) (34.5 +/- 19.2 versus 38.9 +/- 16.1 ng.h/ml, respectively; p > 0.05) indicating a similar amount of morphine absorbed. Plasma morphine concentrations were more sustained for 7 h after dosage with the MAN suppository, with lower peak (8.3 +/- 4.9 and 12.3 +/- 6.6 ng/ml, respectively) and higher 6 h plasma morphine concentrations (5.81 +/- 4.85 and 3.30 +/- 1.0 ng/ml, respectively; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cingulotomy in the rat fails to block opiate withdrawal effects but elevates stress-induced plasma beta-endorphin.

1. Male, albino, Sprague Dawley rats underwent surgical cingulotomy or sham operation and were then implanted with subcutaneous morphine pellets or exposed to forced running. 2. The conditions of cingulotomy or forced running alone did not cause a significant increase in plasma i.r. Beta endorphin concentrations. 3. The combined treatment of cingulotomy plus forced running caused a significant elevation of plasma beta-endorphin concentrations. 4. The cingulum is involved in the elicitation of stress hormone responses in the rat.