Two cardioacceleratory peptides from the corpora cardiaca of Periplaneta americana have been purified by gel filtration and reversed-phase liquid chromatography. Based on analysis of the intact factors and their chymotryptic fragments, we have assigned the primary structure of these octapeptides as pGlu-Val-Asn-Phe-Ser-Pro-Asn-Trp-NH2, designated periplanetin CC-1, and pGlu-Leu-Thr-Phe-Thr-ProAsn-Trp-NH2, designated periplanetin CC-2. They represent new members of a family of invertebrate peptides that includes locust adipokinetic hormone and crustacean red-pigment concentrating hormone. Both peptides show adipokinetic activity in grasshoppers and hyperglycemic activity in cockroaches.One of these peptides (CC-2) has provocative sequence homology with the N112-terminal portion of glucagon.The insect corpora cardiaca (CC) are major neurohemal organs that are analogous to the vertebrate hypothalamohypophyseal system. Not only do the CC store and release products synthesized in the brain, but also they contain intrinsic glandular cells producing a variety of bioactive factors affecting developmental, metabolic, and myotropic processes (1). Many of these factors appear to be peptides; only one, adipokinetic hormone (AKH) from Locusta migratoria, has been identified (2).Corpora cardiaca of the cockroach Periplaneta americana have proven a rich and accessible source of bioactive factors. Previous studies have demonstrated that CC homogenates and partially purified fractions affect the cockroach heartbeat (3-6) and elevate the concentration of hemolymph trehalose (the main sugar in blood of most insects) (7-9). These factors appear to be peptides (3, 7), but it is difficult to assess how many are actually distinct substances or whether some of them have multiple activities (8,(10)(11)(12) In this paper we report the isolation and sequence determination of two structurally related octapeptides from the CC of P. americana that have cardioacceleratory and hyperglycemic activity in the host insect.MATERIALS AND METHODS Insects. Cockroaches (P. americana) were raised at 28°C and 50% relative humidity under a 16-hr light/8-hr dark photo regime and were fed on dry dog food. Corpora cardiaca with corpora allata attached were dissected from 0-to 6-wk-old cockroaches and collected in saline (5 mM CaCl2/1 mM MgCl2/5 mM KCI/140 mM NaCl/4 mM NaHCO3/5 mM trehalose/20 mM Hepes, pH 7.0) at 0°C prior to freezing (-20°C). A total of -4000 cockroach CC were used.Heart Bioassay. Aliquots of all fractions from purifications were assayed for bioactivity by using a semiisolated heart preparation (6). Heart rate was monitored with an impedance converter (UFI model 2991) connected to a frequency integrator and recorder. A heart was selected on the basis of frequency (-60 beats per min) and regularity and then was bathed in saline to stabilize (30 min). Test samples to be assayed were applied to the heart in a volume of 50 ,u.Carbohydrate and Lipid Bioassays. Hemolymph carbohydrate levels in P. americana and hemolymph lipid levels in th...

In contrast to adipose tissue and heart, the in vitro sensitivity of skeletal muscle to insulin is enhanced by starvation. To determine the basis for this, insulin binding and its ability to stimulate glucose metabolism were examined in the incubated rat soleus. In solei from 50-g rats, starvation for 48 h enhanced insulin binding by 50-100% at concentrations of 100 ng/ml or less. Starvation also resulted in higher basal and insulin-stimulated rates of glycogen synthesis, glycolysis, and glucose uptake. The enhanced effect of insulin only occurred at concentrations less than 50-75 ng/ml, in keeping with the increased binding of insulin in this concentration range. On the other hand, under conditions in which binding at equilibrium was the same, glucose uptake was still higher in the starved group, suggesting that some postreceptor event may have been more sensitive to insulin. These studies confirm that the in vitro sensitivity of rat skeletal muscle to insulin is enhanced by 48 h of starvation. They suggest that this is due at least partially to an increase in insulin binding at physiological concentrations.

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