Intracellular transduction of trehalose synthesis by hypertrehalosemic hormone in the fat body of the tropical cockroach blaberus discoidalis

Abstract

Fat body of adult male Blaberus discoidalis cockroaches exposed to B. discoidalis hypertrehalosemic hormone (HTH) in vitro showed a decline in tissue glycogen as carbohydrate increased in the medium In vivo HTH injections increased hemolymph carbohydrate and fat body glycogen phosphorylase activity >2-fold compared to controls. In vivo trehalose synthesis was unaffected by agents that enhance intracellular levels of cyclic nucleotides including: dibutyryl cAMP, dibutyryl cGMP, forskolin (adenylyl cyclase activator) and isobutyl methylxanthine (IBMX) or theophylline (cAMP phosphodiesterase inhibitors). DbcAMP + IBMX stimulated trehalose biosynthesis of fat body in vitro and had additive effects with a minimally stimulatory HTH concentration. However, adenyl cyclase activity was unaffected by HTH either with isolated fat body or fat body membrane preparations. We conclude that cAMP is not a second messenger for HTH, but cAMP can stimulate trehalose production independent of HTH through actions on common regulatory events related to trehalose biosynthesis. Dibutyryl cGMP and phorbol esters and diacyglycerol (activators of protein kinase C) also failed to stimulate trehalose biosynthesis in vitro. Extracellular Ca 2+ enhanced HTH-dependent phosphorylase activity, glycogenolysis and hypertrehalosemia and maintained basal levels of phosphorylase a at twice those observed in the absence of Ca 2+ However, Ca 2+ entry by Ca 2+ ionophore (A23187) did not mimic HTH effects. Results of these studies demonstrated that extracellular Ca 2+ is important for HTH-dependent trehalose biosynthesis but cAMP and cGMP are not involved.