Uptake and turnover of cholesterol- 14C in Y-organs of the crab Hemigrapsus as a function of the molt cycle

Abstract

The uptake of cholesterol- 14C and incorporation into cholesterol pools and derivatives in vivo were studied in Y-organs, hemolymph, and whole bodies of male crabs. Tissues and serum, removed 24 hr after injection of 1–4 μCi per crab, were extracted for total lipid and analyzed by chromatography (thin-layer, gas-liquid), autoradiography, and scintillation counting. Y-organs of late intermolt crabs took up 650 times more labeled cholesterol per unit weight of tissue than the general body mass of the same stage, and the order of 100 times more than Y-organs of premolt or postmolt animals. Uptake of label occurred against a 70:1 Y-organ:serum concentration gradient of total cholesterol. Since Y-organ total cholesterol did not change markedly with stage, the increased uptake at intermolt reflected rapid turnover of cholesterol pools. Labeled derivatives of cholesterol, cochromatographing through three solvent systems with α- and β-ecdysone standards, were found in all tissues and sera. Absolute amounts of the labeled products in Y-organs were too low for additional physicochemical analyses and their identity as ecdysones is provisional. Concentrations (cpm/unit weight tissue), however, were distinctly higher in Y-organs than in carcasses. Among Y-organs, the largest concentrations were found in premolt which contained 60 and 260 times more labeled “β-ecdysone” than intermolt or postmolt glands, respectively. The occurrence of accelerated cholesterol uptake and turnover in Y-organs of summer intermolt, followed by accumulation in premolt of newly synthesized ecdysone-like metabolites, supports physiological evidence that these organs are involved in the molting process. The data suggest that they function as sources of a form of sterol molting hormone.